(SANITIZED)UNCLASSIFIED STUDIES OF FERROCENE IN THE USSR(SANITIZED)

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• Document Number (FOIA) /ESDN (CREST): CIA-RDP80T00246A008000080002-3
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• Document Creation Date: December 21, 2016
• Document Release Date: March 26, 2009
• Sequence Number: 2
• Publication Date: October 16, 1959
• Content Type: REPORT

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STUDIES OF FERROCENE IN THE USSR
? Ferrocene or dicyclopentadienyliron (C5H5Fe(:6H5) was dis-
covered in' 1951 by Kealy and Pauson (1).
The unusual chemical and physical properties of this compound
at once attracted the attention of chemists in many countries.
These properties prompted Woodward and co-workers in 1952 (2)
to ascribe to it a three-dimensional structure of a pentagonal anti-
prism or the so-called sandwich structure (I) with an atom of iron
placed between two parallel five-membered rings.
All studies (both chemical and physical) of ferro-
cene and of its analogues with other transitional
metals confirmed configuration I.
The nature of the linkage between the cyclopen-
tadienyl rings and the iron atom is not clear as yet.
Fe Several hypotheses have been advanced on this
score, more or less substantiated by quantum
mechanical calculations.
In any case the chemical and physical properties
of ferrocene.favour the assumption that the linkage
between the organic part of the molecule and the
iron atom is effected by means of the a-electrons of the cyclopen-
tadienyl rings and the d-electrons of the atom of the transitional
metal.
Ferrocene is an orange-coloured, crystalline substance with a
melting point of 174?C. It is diamagnetic, its dipole moment being
zero. Ferrocene is readily soluble in most organic solvents, it is in-
soluble in water, and can be distilled with water vapours; its sublima-
tion temperature is about 100?C.
The most characteristic properties of ferrocene are: a) exception-
al thermal stability (it is not destroyed up to 450?C); b) the stability
of the linkage between the cyclopentadienyl radicals and iron (it
withstands boiling with concentrated HCI, and is resistant to alkalis);
c) exceptional sensitivity to the action of oxidizing agents (sulphuric
and nitric acids, halogens, silver sulfate, quinone, peroxides) which
transform ferrocene into the unstable ferrocinium cation
[(C5H5)2 Fe+] and eventually completely destroy it; d) total absence
of reactions to double bonds of cyclopentadienyl rings; e) a tendency
to enter into substitution reactions in the cyclopentadienyl rings
All these properties characterize ferrocene, on the one M
an organometallic compound of a new type with an unu%M
between the organic radicals and metal, and as a wrv owrwWu
system on the other.
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In the USSR, studies of ferrocene were begun in 1953 in the
laboratory of Academician A. Nesmeyanov. The subject of these
studies was the reactivity of the organic part of the ferrocene mole-
cule. It is these studies that yielded most of the data confirming the
aromatic nature of the new organometallic compound.
The results of the researches carried out so far are represented at
the exhibition in the form of a diagram, accompanied by samples of
the substances obtained.
As studies of ferrocene were undertaken simultanedusly and
independently in several countries, there has been an inevitable
overlapping in the directions of research. Such instances are referred
to in the prospectus.
In 1954 A. Nesmeyanov, E.. Perevalova, R. Golovnya and
0. Nesmeyanova (3) effected mercuriation, metallation with butyl
lithium and arylation of ferrocene.
These early experiments demonstrated that in substitution
reactions ferrocene behaves like benzene or rather like such su-
peraromatic systems as furan or thiophene. This is borne out by
mercuriation with mercuric acetate under mild conditions which
resulted in a mixture of di- and monomercuriated ferrocenes. No
mercuriation of benzene is possible under such conditions. The same
applies to metallation with butyl lithium, which cannot be accom-
plished with benzene, while in the case of ferrocene it produces a
mixture of di- and monolithium derivatives of ferrocenes.
Arylation of ferrocene with aromatic diazonium salts was carried
out under the conditions of Homberg's reaction.
Somewhat later metallation with butyl lithium (4) and arylation
of ferrocene (5, 6) were reported by British and American authors.
Three reactions described in the first report proved to be highly
fruitful from the viewpoint of synthesis. Further studies in the
arylation of ferrocene with diazonium salts (7, 8) resulted in the
synthesis of a whole series of mono- and diarylferrocenes. Some of
these were obtained not by direct arylation but by secondary trans-
formations (aminophenylferrocenes from nitrophenylferrocenes,
and p-terrocenylanizol from p-ferrocenylphenol).
A study of the properties of arylferrocenes revealed the nature of
ferrocenvl as ,i substituent in the benzene ring. A measurement of
dissociation ronstant% off ferrocenylanilines, ferrocenylphenols,
fr.rr-ceiivlbenzoic wets and ferrocenylamine and a comparison
tI. rr?-! u rth the diswK?iation c.-nstants of the respective biphenyl
-,r?aled that terruK?envl is a strong electron-donor sub-
fit `t
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A.Nesmeyanov, E.PerrNnl-,~.l ;1ncl O.Nesmeyanova used mercuric
derivatives of ferrocene posse--.mg the usual properties of organo-
mercury compounds (symmetrical 01 reaction. splillint )il' of
mercury by boiling in concentrated I II.1. 141 .vnthe%ize wnie I t rr orene
derivatives which could not he obtained otherwi.e.
Thus, by action of bromine and iodine on iuereurialed ferrocenes
iodo-, bromo-, diiodo- and dibromoferrocenes were obtained (10).
Action of free rhodan produced rhodanide, which, however, was
reduced to diferrocenyl disulphide in the process of separation (11).
Action of chlormercuriferrocene on triphenylchloromethane resulted
in the synthesis of triphenyIferroceniImethane (11). The latter reac-
tion demonstrates the mobility of mercury in the ferrocene nucleus.
A study of the properties of halogenoferrocenes revealed that
the halogen in the ferrocene nucleus is even more inert than an
aromatic halogen.
Lithium and later obtained sodium derivatives (12) of ferrocene
made it possible to synthesize ferrocene mono- and dicarboxylic
acids and, what is of special interest, ferrocenylamine (9). The latter
was obtained by the method of K. Kocheshkov by reaction of
ferrocenyllithium with the benzyl ester of hydroxylamine.
Almost simultaneously ferrocenylamine was synthesized by
Arimoto and Haven (13) from the azide of ferrocenecarboxylic acid.
Despite the preliminary data obtained hy.some authors (14), in
1956 A. Nesmeyanov and N. Kochetkova (15) effected alkylation
of ferrocene with alkyl halides in the presence of aluminum chloride.
It was demonstrated that alkylation of ferrocene, like that of ben-
zene, results in mixtures of mono-, di-, and poly-substituted products.
Separate alkyl ferrocenes were obtained by A. Nesmeyanov
and N. Volkenau (16) by reduction of acylferrocenes using
Clemensen's method. Dimethylferrocene was synthesized by reduc-
tion of dimethyl ester of ferrocenedicarhoxylic acid with lithium
aluminum hydride (12). Esters and ketons of the ferrocene series are
in general easily reduced by lithium aluminum hydride producing
hydroxyderivatives and then alkyl derivatives of ferrocene (12).
A detailed study of acylation (the first substitution reaction
carried out for ferrocene) was also made by Soviet chemists.
Thus, it was demonstrated (3) that acylation of ferrocene takes
place not only in the presence of aluminum chloride, but unlike that
of benzene, also in the presence of stannic tetrachloride, under
milder conditions. By using various modifications of the Friedel-
Crafts method a considerable number of ketones and ketoacids of
the ferrocene series were synthesized (16, 17, 18).
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Highly interesting is intramolecular acylation achieved within
the ferrocene series. In 1956 A. Nesmeyanov, N. Volkenau and
V. Vilehevskaya (18) carried out cyclization of di-((')-carboxy-
twi-p%li ferrocene by means of polyphosphoric acid. As a result, di-
JL#4.4t4rahydroindenyl)-iron was obtained and its structure ascer-'
t'rtned by reducing it to di-(tetrahydroindenyl)-iron, obtained earlier
... Fischer (19). The synthesis and the establishment of the structure
(20) of ketotetrahydroindenyl-(cyclopentadienyl)-iron from w-
carboxyprop yl-ferrocene and of a ferrocene analogue of antraqui-
none (I1) from o-carboxybenzoyl-ferrocene confirmed that cyclization
proceeds into the same cyclopentadienyl ring which already has
the substituent in it.
In 1956 A. Nesmeyanov and 1. Kritskaya
demonstrated the condensation of ferrocene with
lfuric acid (21)
f
h
.
su
e presence o
aldehydes in t
Interaction between ferrocene and formaldehyde,
henzaldehyde and p-dimethylaminohenzaldehyde
yielded the following products:
C; H5 Fe C; H3 (CHR)., C5 H3 FeC5 H5 [R = H CG H5,
(CH3)5NCGH4] and CSH5FeC5H4(CHR)[CH(OH)R]
- CSH3FeC5H5 [R = CAH,. (CH3).,NCGH4].
By means of infrared spectra and by destruc-
tive bromination it was shown that the compounds thus produced
contained unsubstituted cyclopentadienyl rings, i. e., that conden-
sation takes place twice into the same cyclopentadienyl ring.
Interaction between ferrocene and formaldehyde and benzal-
dehyde had been achieved somewhat earlier by Weinmayr (22) in
the presence of anhydrous HF, and later by Riemschneider and
Helm (14).
The instability of ferrocene to the action of oxidizing agents
makes it impossible to involve it in the most characteristic reactions
of electrophilic substitution, such as nitration and halogenation.
In 1955 A. Nesmeyanov, E. Perevalova and S. Churanov
(23) succeeded in sulfonation of ferrocene with pyridine sulfo-
trioxide, obtaining di- and monosulfonic acids of ferrocene. Esters
and chlorides of these sulfonic acids were also synthesized. Chloride
of ferrocene monosulfonic acid was reduced to diferrocenyldisulfide
(23).
Sulfonic acids of ferrocene were synthesized independently by
Weinmayr (22) who had used concentrated sulfuric acid in acetic
anhydride as a sulfonating agent. C
Soviet chemists are conducting researches aimed at establishing
the effects of substituents on the reactivity of cyclopentadienyl rings
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REFERENCES
? 1. T. J. Kealy, P. L. Pauson - Nature, 168, 1039 (1951).
2. C. Wilkinson, M. Rosenblum, M. C. Whiting, R. B. Woodward - J. Am.
Chem. Soc., 74, 2125 (1952).
3. A. N. Nesmeyanov, E. G. Perevalova, R. V. Golovnya, 0. A. Nesmeyanava -
Doklady Akad. Nauk SSSR, 97, 459 (1954).
4. R A. Benkeser, D. Goggin, G. Schroll - J. Am. Chem. Soc., 74 4025 (1954).
5. G. D. Broadhead, P. L. Pauson - J. Chem. Soc., 367 (1955).
:6. V. Weinmayr - J. Am. Chem. Soc., 77, 3012 (1955).
7. A. N. Nesmeyanov, E. G. Perevalova, R. V. Golovnya Doidady Akad?
Nauk SSSR, 99, 539 (1954).
8. A. N. Nesmeyanov, E. G. Perevalova, R. V. Golovnya - Do&1 7.Akad?
Nauk SSSR, 103, 81 (1955)
.9. .^ N. Nesmeyanov, E. G. Perevalova, R. V. Golovnya, L. S. ShIl0VtfeVa --
poklady Akad. Nauk SSSR, 102, 535 (1955)
10. A. N. Nesmeyanov, E. G. Perevalova, O. A. Nesmeyanova - Dok3ady
Akad. Nauk SSSR, 100, 1099 (1955)
11. A. N. Nesmeyanov, E. G. Perevalova, O. A. Nesmeya>aova - Doitt'
Akad. Nauk SSSR (in press).
12. A. N. Nesmeyanov, E. G. Perevalova, Z. A. Beinoravichute -- Doklady
Akad. Nauk SSSR, 112, 439 (1957)
13. F. S. Arimoto, A. C. Haven, Jr. - J. Am. Chem, Soc., 77. 1265 (1965)
14. R. Riemschneider, D. Helm ~-- Chem. Ber., 89, 155 (1956).
15. A. N. Nesmeyanov, N. S. Kochetkova - Doklady Akad. Nauk SSSR
109, 543 (1956).
16. A. N. Nesmeyanov, N. A. Volkenau - Doklady Akad. Nauk SS8R,167, 167,202
(1956)
17. A. N. Nesmeyanov, N. A. Volkenau - Doklady Akad. Nauk SSSR, 111,
.605 (1956).
18. A. N. Nesmeyanov, N. A. Volkenau, V. D. Vilchevskaya - Doklady Akad.
Nauk SSSR, 111, 362 (1956).
19. E.O. Fischer, D. Seus - Z. Naturforsch., 9b, 386 (1954).
20. A. N. Nesmeyanov, N. A. Volkenau, V. D. Vilchevskaya - Doklady Akad.
Nauk SSSR (in press).
21. A. N. Nesmeyanov, I. I. Kritskaya - Bull. Acad. Sci. USSR, Classe sci.
chim., 253 (1956).
22. '.'. Weinmayr - J. Am. Chem. Soc., 77, 3009 (1955).
23. A. N. Nesmeyanov, E. G. Perevalova, S. S. Churanov r- Doklady Akad.
Nauk SSSR, 114. 335 (1957).
4 A. N. Nesmeyanov, E. G. Perevalova, R. V. Golovnya, T. V. Nikitina,
V A Simukova - Bull. Acad. Sci. USSR, Classe sci. ch'm., 739 (1956).
23 % Y N meyannv, Jr., 0. A. Reutov - Doklady Akad. Nauk SSSR (in
pr.?SO1
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in ferrocene. In this connection A. l'vsmeyanoy and E. - Perevalova
with a group of co-workers (24) developed two methods for ascer-
taining the structure of ferrocene compounds: a) destructive bromi-
nation and h) destructive hydrogenation. The first method involving
the action of excess bromine on the compound investigated, makes it
possible to establish the presence of an unsubstituted cvclupenta-
dienyl ring in the molecule by the formation of pentabromocyclo-
pentane. The second method-hydrogenation under rigid conditions
over Raney nickel - reduces the compound investigated to known
cvclopentane derivatives.
By now, some information has been collected indicating that
alkyl substituents have a certain activating effect. and acyl substi-
tuents, a certain deactivating effect on ferrocene in electrophilic
substitution reactions (17).
There are also some preliminary indications that the effect of
substituent is transmitted from one cyclopentadienyl ring to another
through the iron atom (25).
Thus, the integrated researches, the results of which are repre-
sented at the exhibition in a nutshell, were directed at investigating
ferrocene as a new aromatic system.
The information obtained clearly illustrates this aspect of the
new compound. According to this information, ferrocene behaves as
a superaromatic compound in many typical substitution reactions.
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A. N. Nesmeyanov and E. G. Perevalova, Uspekhi Khimii
27: 3 (1958).
CYCLOPENTADIENYL COMPOUNDS OF METALS AND
RELATED COMPOUNDS
In spite of many attempts, it has not been possible up to
the present time to obtain alkyl and aryl organometallic compounds
for the majority of the transition metals. he few representa-
tives of this class of compounds described in the literature are
distinguished by great instability)"2.
Thus all attempts to isolate ferro-organic compounds were
unsuccessful3T7. The assertion of Afanasyev and Tsyganov8 that
they obtained a mixture of diethyl and monoethyl iron bromides
as a result of the reaction of metallic iron with ethyl bromide
is completely without basis.
Allyl (and benzyl) organometallic compounds are usually much
less stable than alkyl and aryl compounds. Jaffe and Doak9
believe that the difficulty in obtaining organic compounds of
transition elements is explained by the slight stability of pure
covalent bonds between metal and carbon; at the same time these
bonds can not be very ionic because of the insufficiently great
difference in electronegativities between transition elements
and carbon.
Therefore the discovery in 1951-1952 of the class of organo-
metallic compounds, unique in both properties and structure,
namely the dicyclopentadienyl derivatives of transition metals,
was completely unexpected.
The first representative of this new class of compounds was
dicyclopentadienyliron--an iron-organic compound obtained first
in 1951 by Kealy and Pauson1O, and then independently in 1952
by Miller, Tebboth, and Tremainll((
Kealy and Pa.uson'O in the attempt to synthesize dicyclopenta-
dienyl, C5H5-CH5 by the reaction of ferric chloride with
cyclopentadienylmagnesium bromide, obtained instead of the
expected hydrocarbon a crystalline, extraordinarily stable,
orange-colored compound which contained carbon, hydrogen, and iron
and corresponded in elemental analysis to dicyclopentadienyliron.
This compound, which later according to the suggestion of
Woodward and coworkers12 came to be called ferrocene, immediately
attracted the attention of chemists of a number of countries (the
Soviet Union, the United States, Germany, and others). The study
of the properties of ferrocene provided the start of the investi-
gation of a new field of organometallic compounds--the chemistry
of dicyclopentadienyl derivatives of transition metals.
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Investigations in this field began to develop in two directions:
(1) the obtaining of dicyclopentadienyl derivatives of
various metals and the establishment of their
structures and
(2) multilateral study of the reactions of ferrocene.
Soon after the discovery of ferrocene, dicyclopentadienyl
derivatives of practically all transition elements were synthesized,
and there were also obtained diindenyl compounds, cyclopentadienyl-
carbonyls, and cyclopentadienylnitrosyls of some metals, and also
compounds of metals with benzene (dibenzenechromium and others).
Up to the present time, more than 200 works have been devoted to
ferrocene and compounds similar to it. This interest was aroused
by the great singularity of the structure and properties of this
type of compound.
Ferrocene and some other dicyclopentadienyl derivatives of
transition elements are unusually stable for organometallic com-
pounds. In spite of the great formal unsaturation, addition
reactions are unknown for these compounds. For ferrocene itself,
a wide circle of reactions of electrophilic substitution, typical
of aromatic systems, has been found.
Earlier investigations in the field of the chemistry of
organometallic compounds played a great role in the formulation
of a theory of valence, and in connection with the study of
dicyclopentadienyl derivatives of transition metals, the question
again arises as to the limits of applicability of the classical
postulate of valence.
Several reviews13-16 of dicyclopentadienyl derivatives of
metals were published in 1955, but at the present time. they are
already far from including all the literature on this question.
I. METHODS OF OBTAINING DICYCLOPENTADIENYL COMPOUNDS OF METALS
Dicyclopentadienyl derivatives of transition metals are
obtained by the action of salts or acetylacetonates of these
metals on cyclopentadienylmagnesium bromide, on cyclopentadienyl-
lithium or sodium, or also by the immediate reaction of cyclo-
pentadiene with the salt or carbonyl of the corresponding metal.
Each of these methods is briefly characterized below.
In table 1 there are listed all the dicyclopentadienyl
derivatives of metals synthesized as of the present time, with
indication of the formal valence of the metal in them, the means
of obtaining the compound, the yield (when indicated in the
article), and the literature references. The means of synthesis
are indicated by corresponding letters A, BT C, etc.; the nature
of the method is set forth in the text.
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117
A. The reaction of cyclopentadienylmagnesium bromide with
the halide of the metal is a convenient method of obtaining
dicyclopent,dienyl derivatives of metals. The reaction is carried
out in ethet or ether-benzene solution. Thus, in the reaction of
ferric chloride with cyclopentadienylmagnesium bromide in ether
solution Kealy and Pausonl first obtained ferrocene (yield 34%o),
later Riemschneida and Helm17 raised the yield to 52% by carrying
out the reaction in.ether-benzene medium. Probably the ferric
chloride first is reduced by the organomagnesium compound to
ferrous, which then reacts with another molecule of cyclopentadienyl-
magnesium bromide:
2C5HSMgBr + 2 FeC13 -~ 2 FeC12 + C5H5-CSH5 + MgBr2 + MgC12
2 C5H5MgBr + FeC12 -~ (C5H5)2Fe + MgBr2 + MgC12
Such a reaction mechanism has in no way been proved; therefore the
possibility is not excluded that the first step is formation of
dicyclopentadienylferric chloride, which then is reduced by an
excess of the Grignard reagent:
2 C5H5MgBr + FeC13 + (C5H5)2 FeCl + MgBr2 + MgC12
2(C5H5)2FeC1 + 2 C5H5MgBr -' 2(C5H5)2Fe + C5H5-C5H5 + MgBr2 +
MgCl2
By this method there have been obtained dicyclopentadienyl
compounds of cobalt,1.8 titanium,19 zir.conium,l9 vanadium,l9'2O and
others (see table 1).
B. The reaction of cyclopentadienylmagnesium bromide with
the acetylacetonates of metals has been used with success in the
case of metals whose halides are difficultl;~t soluble in ether.19
Thus, dicyclopentadienyl compounds of iron, 1 nickel,19 cobalt,22
ruthenium,23 rhodium,24 and iridium44 have been obtained.
C. The reaction of cyclopentadienylsodium (or lithium) with
halides25 allowed one to obtain in good yields dicyclopentadienyl
compounds of iron,2? titanium,20 vanadium,20 molybdenum,27 tungsten .27
tantalum2O and manganese:25
2(C5H5)Na + McXn -- (C5H5)2MeXn-2 + 2NaX
By this same method tricyclopentadienyl compounds of scandium,
yttrium, and the lanthanides were obtained2 '2e:
3 C5H5Na + MeX3 - (C5H5)3Me + 3NaX
Tetrahydrofuran or ethylene glycol dimethyl ether served as
solvent.20'26,27
Pauson3O used a method analogous to this for the synthesis of
diphenyl-, polyphenyl- and dibenzhydrylferrocene. He obtained the
lithium derivative of the substituted cyclopentadiene and brought
it into reaction with ferric chloride in ether solution:
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6 C6H5G5H4Li + 2 FeCl3 2 (C6H5C5H4 )2 Fe
+ C6H5C5H4 _ C5H4 C6}i5 + 6 LiCl
D. Dicyclopentadienyl compounds are obtained in high yields,
except in the case of chromium and molybdenum, by the reaction of
cyclopentadienyllithium, sodium, or potassium with the thiocya-
natoammines of metals and subsequent thermal dissociation of the
dicyclopentadienylmetal ammine 31-33).
Q
Co(SN)2N'tI31,4 L1
+ 2 CFFiSK 2KSC;~ + Co(C5H5 ) 2 (Nh3 )4
3
Co(CicHc,)2(NH3)4 Co(C,HCi)2 + 4NH3
E.- Cyclopentadiene reacts with carbonyls of transition metals
at 250_3500, yielding dicyclopentadienyl compounds, it is true, in
low yields (10_30%)121,3411. The reaction for-
or some metals is
reversible(35):
Cr(CO)6 + 2 C5H6 - Cr(C~H5)2 + 6 CO + Ha
Intermediate products are mixed cyclopentadienyl carbo yls of
the metals, which are usually obtained by this method'36137
(See the section "Cyclopentadienylcarbonyls and cyclopentadienyl-
nitrosyls of metals.")
2 Fe(CO)5 + 2 CFH6 --* C5H5 Fe(CO)4FeC5H5 + H2 + 6 CO
C5H5ie(CO)4FeC5H5 20-~-> Fe(C5H5)2
Hallam and Pauson38 suggested the carbonyl method for the
synthesis of substituted ferrocenes. By the reaction of benzyl-
cyclopentadiene with iron pentacarbonyl, they obtained l,l'dibenzyl-
ferrocene; during this process there is first formed bis (benzyl-
cyclopentadienyliron)-tetracarbonyl:
2 C6H5CH2C5H5 + 2 Fe(CC)5--y C6H5CH2C5H4Fe(CO)4FeC5H4CH2C6H5
-* (C6H5CH2C5H4 )2Fe
By the same method, 1,3,1',3'-tetraphenylferrocene was synth-
esized from 1,3-diphenylcyclopentadiene, however in this case it
was not possible to isolate the carbonyl compound.
Bis (cyclopentadienyliorn)-tetrac~irbanyl, 'CS~iSFe(CC)4FeC5H5
was used by Hallam and Pauson38 for the obtaining of derivatives of
ferrocene with substituents in one oyolopentadlenyl ring. By the
reaction of benzylcyclop(-tadiene and i.,3 diphenylcyclopentadiene
with bis (cyclopentadienyliron) tetracarbonyl, they prepared
benzylferrocene and 1,3-diphenylferrocene, respectively.
F. In the presence of orgE-nic bases cyclopentadiene reacts
with halides 26,39:
2 C5H6 + FeC12 (C?HG)aNH (CSH-)2Fe + HC1
r ,nY,MTT~U ED
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-5-
By this method ferrocene is obtained in a yield of 94-98%26.
G. Ferrocene was obtained as well by the reaction of cyclo-
pertadiene with reduced iron in the presence of oxides of various
metals".
Dicyclopentadienylmercury reacts with powdered iron yielding
ferr?ocene4 ? in 24-30% yield.
As of the present time dicyclopentadienyl compounds of almost
all the transition metals, and also of some elements of non-
transition groups, have been synthesized (see Table I). The latter
are organometallic compounds of the usual type ar';.th a very reactive
C-metal bond.
II.- PROPERTIES OF FERROCE 3E
Physical Properties and Structure of Ferrocene
The first investigations of the properties of ferrocene
showed that the structure (II), which was at . first suggested,' tquite
naturally, by Pauson, does not agree at all with the Physical and
chemical properties. Ferrocene is stable 4r. air, does not decom-
pose upon being heated to 470 , sublimes at 100?, is steam distill-
able, melts without decomposition at 173-174p10, dissolves in organic
solvents, and withstands heating with concentrated hydrochloric acid
and with alkali.
Ferrocene is diamagnetic. The infrared spectrum21'41 indi-
cates the presence of C_H bonds of only one type. The dipole
moment is virtually zero,41'59
In 19952 Wilkinson and coworkers 42 suggested for ferrocene the
structure of a pentagonal antiprism, the "sandwich"-structure (II).
The iron is located in the center of symmetry of the molecule, which
has only one type of C_H bond.
C OMT TNU ED
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Further investigations of the chemical and, above all, of the
physical rroperties of ferrocene showed l be correcness of the
"sandwich" structure (II).
?Waptum mechanical calculations by the method of molecul.:r
orbita:?ls16.A76.4,1 also shows that there do not exist great hindrances
to the free rotation of the cyclopentadienyl rir:s around the axis
of symmetry inasmuch as the energy of interaction does not depend
on the mutual rotation of the rings. bteric inter:_ction of the
carbon atoms of different rings favors tha antiparallel centrally
symmetrical configuration which is found in the ferrocene crystal.
Lxperimental investig,,l..tions show, th_ t In the crystalline state the
cyclopentadienyl rings undergo oscillations around an axis of the
fifth order, but the ayeerage conf ig:uration with time proves to be
centrally symmetrical 1160-65.) Free reciprocal rotation'
otation of the rings
in the vapor phase at 4OC" has been proven by electronogra)hic
investig;,-tion 6..6 of ferrocene. in solutions, rotation is somewhat
hindered 67,
:ome chemical arguments in support of free rotation of the
rims will be presented in examinin,>: the acylLLtion of ferrocene.
Investigation of the magnetic properties. of ferrocene showed
that the ferrocene molecule is diamagnetic, 41, 68, 69 _. and conse-
quently does not have unpaired electrons. Ferricinium salts are
paramagnetic. The paramagnetic moment of the picrate ("~ = 2.26
Bohr magnetons) indicates the presence of one unpaired electron,
as in the ferroeyanide ion. = 2.33 Bohr magnetons) 4 1.. For "fer
rocene the nuclear magnetic resonance spectrum has also been taken 76
The results of x-ray diffraction studies of ferrocene crystals
6.o!, 6.5y- 71?:73 support the "sandwich" structure. The presence of
a center of symmetry in the ferrocene molecule definitively deter-
mines the antiprismatic structure (II).
Data on electron diffraction studies of ferrocene66 also
supports the "sandwich" structure. Bond lengths found by this
method agree well with those obtained on the basis of x-ray dif-
fraction analysis.
The C-C bond distances in ferrocene (1.43 .) and in benzene
(1.39 ti) are very close. The distance between the rings (3.25
)
is very close to the distance between the layers in graphite
(3.35 ). Consequently, there is very little direct bonding be-
tween the rings 66
spectroscopic investigations. It has already been mentioned
above, that in the infrared spectrum only one frequency has been
detected for the C_ti bon:+, which allows one to assert 21,41 that
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in ferrocene there.is.only one. type of C_H bond,.?in'.agreement
with structure (II). The basic lines in the infrared spectrum,
characteristic for ferrocene, are maintained, although with changes
in intensity, in the spectra of ferricinium saltso and monosub-
stituted ferrocenes (see below), This permits one to detect the
presence of the unsubstitutued ring in derivatives of ferrocene
13.,30,74 In the Haman spectrum 67 there is _lso only one C_H
bond frequency.
absorption spectra of ferrocene and ferricinium salts differ
markedly 131.75 The absorption spectra have been investigated for
ferrocene in the crystalline state 76,77. The infrared spectrum
has been taken for a monocrystal 26
Kauer 78 and Hoke 79)80. Investigated the x-ray absorption
spectra of ferrocene and of other cyclopentadienyl derivatives.
These works are considered in detail In the review by Dyatkina 81,
Investigation of mass spectra, carried out by Friedman, Irsa,
and Wilkinson S2 shows that they differ sharply from spectra of
ionic as well as covalent organometallic compounds.
Thermochemical investigations. Cotton and ilkinson 83 deter-
mined the heatcf combustion of ferroene from the elements ( L Hf?
2 980 = 33.8 ? 1.3 kG -1/mole) . The heat of formation of ferrocene
gas from- aseont`metal anc C'.g ~"5 radical equals A H298 = - 147
kcal/moleZl The heat of sublimation 5.s 16.9 kcal/mole 75
The bond enerp,.y bet-_een the metal and the C55 radical in
ferrocene and nickelocene is 286 and 211 keel/mole, respectively 61.
j-olarogra.phic investigations 20,41,84 The oxidation-re-
duction potential Of 'the sysitebi:
(C~HFe =+
5) 2 (C5H5) :e in 90/, aloohb1 equals + 0.30 V. The
system is reversible. 'in aqueous solution of ferricinium per-
chlorate hs a half wave potential of + 0.16 V t:ith reference to
the normal calomel electrode. The shift of the half-r--gave potential
in groin;; from an alcoholic to an aqueous solution confirms the
chemical findings that ferricinium in neutral aqueous medium par-
tially decomposes forming ferrocene. The determination of the a-
mount of electricity required for electrolysis shows that the
oxidation of ferrocene to ferricinium is a mor_oelectronie process.
The polarographic data shot,: th,. t ferrocene and other cyclo-
pentadienyl com?:ounds are distinct in their behavior from corres-
pondin:g ions of the metal and related complex ions with the same
degree of oxidation 13,2o.:
The electronic structure of dicyclopentadienyl derivatives of
transition metals presents t great interest, or the one hand from the
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point of view of explainir, the valence state of the metal in these
compoun:_;.s, and ai the other for en understanding of the reasons
behind the phenomenon of aromatic -:.rcperties.
yhe ques jon of the srecial'nature of he electronic structure
of ferrocene and similar compounds is thoroughly discussed in the
review d' Lyatkir 91, therefore, -'e limit ourselves to a mention
of the two directions existing for the solution of the problem.
"isoher and coworkers ?6: 71, 85-88, look upon ferrocene
and similar comootind.s s comrdexes in which all the Ti - electrons
of the c--clo;,ertadienyl ring,-1 take part in the formation of the
bend. with iron. ~=ueh 89, 90 offers a theoretical basis for this
point of vicv=. In the opinion of Tischer and co?-,orkers, 18, 71
721 85-87 ferrocene Is a complex analogous to the hexacyanoferr=~te
ions, with a central divalent iron. X11 6 TI - electrons of each
cycloe: entadienyl rind; (in the form of the anion C5E5) form
approximately octahedrally directed coordinate covalent bonds with
the free d?sp3 orbit.- is of the metl ion i,;e++31 Around the
central metal atom there is formed the stable 36.-electron confi v-'ur-
ation of the noble krypton, which ,ives the compound its
great stability. uch a hypothesis regarding bonding is applied
by rischer to all-cyelopentaaienyl,ahd benzene derivatives of`tran-
sition metals.' 6, 1'_, 3 , 86, 97
Jaffe 63, Lunitz and Orgel r5o p 61, 91-93 i~'Ioffitt 62, '94 and
a number cf other authors 64, 915-98 -;.pproacn the electronic struc-
ture of ferroeene on the basis oi* the method of molecular orbitals
and believe that in the formation of the bond with iron only a part
of the 'II_electrons of the cyclorentadienyl rings participate.
The indicated atathors con.- ider the possible combinations of orbi-
tals of the metal with molecular orbitals of each cyclopentadienyl
radical as a whole, and not with separate carbon atoms.
C:E : i IC:_L i G ' J Tlis::; Ci~ t gRi CC. Ni;
=s has already been noted, ferrocene possess a thermal stabi-
lity surprising for an organometalllc compound, but still more
unusual are the various chemical transformations of ferrocene, and
above all its distinctly expressed tendency toward reactions ir.-
volvina:' substitution of the hydrogens of the cyclooentadier:yl rings,
and the absence of properties characteristic for unsaturated com-
pounds.
The reactions of ferrocene can be divided into three groups:
1) oxidation; 2) reactions invclvin,- cleava.'e of iron-carbon bonds;
3) subs::titution of hydrogens ir- the cyclo .entadiene rings (so-
called reactions of "arom;.tic" substitution).
1. Oxidation
In ferrocene the iron is formally divalent but in air ferrocene
is completely stable and does not oxidize either in the crystalline
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stE.te or in solution. The oxidation of ferrocene takes place
easily upon electrolysis (anode Trocess) and also by means of such
oxidants as holol ens 7.1, 17 ferric chloride, curio sulfate, silver
sulfate or p-quinone In or--anlc solvents in the presence of
acid 41,88 ferrocene is also oxidized by sulfer dioxide in
anhydrous hydrogen fluoride at 10C0 and " pressure of 7 atm. 99
and by N_bromosuccinimide in acetic acid 1:3{
In acid solutions ferrocene is oxidized by the"oxymt-n..of the
ai'r; Upon' sdluti,on Of ferrocene in sulfuric lo, loo or nitric
acid 10, 41oxidation also takes place.
ferrocene reduces the triFhenylmethyl cation to triphenyl_
methyl radical and is oxidized thereby to the ferricinium cation
(C5H5)2 Fe +(~GH5)3d' (C5~5)2 Fe +("'6~15)3Lo
The reaction ~:: as c.. rried out :-. ith solution of tri c henylm ethyl
chloride in nitromethane, in which tripheniylmethyl chloride is
ionized 102.
l'Es r75) 3 v;e. Z_ (1+6 '75) 3 C + G. ?
In benzene, the oxidation of ferrocene by (C6 H_9)3 C Cl. takes
place only in the r.:resence of small quantities of phenol, which
probably facilitates the ionization of triphenylmethyl chlorideiQ?.
Upon oxidation, ferrocene is converted into the blue, water-
soluble ferricinium cation, (v5 H5)2 ie+, which is easily reduced
by LnC12 sodium sulfite or thiosulfate, ascorbic acid 99,10o
Tie (c4)3 1113 and other reciuctants. Upon addition c-.f alkali,
aqueous solutions of the cation evolve ferrocene 71.
Salts of the f errieinium cation with
such N03-, S04--, C, . 04 _, are water soluble: thecationocanabeCpreciBpi'
tated in the form of the tetrachlorogallate, (C5H5)2 Fe Ga C%,
and the picrate, as well as the silicotungstate, reineckeate, tet-
raphenylborate, (C5H5)2 Fe B(C6H 1,71
s)44 and others18'88
Salts of the ferricinium cation are
magnetic
paramagnetic. moment of the picratel"Ae= 2.26 Bohr The para-
the presence of one unpairedelection4~etons which
The ease of converson of ferrocene into a much less stable
cation 12 , 41j s perhaps one of the reasons why no one has succeeded
in nitrating or halogenating ferrocene 12 Besides, the presence
of a positve charge on the ferricinium cation can hinder electro-
philic attack. Bunitz and Orgel 61 believe that in cations of
dicycloi)entadienyl compouni.s the.: d-orbit..a~.is of the central atoms
are much more stable than the"YT-orbitals of the rings, and hence
in the ferricinium cation the bonds are shifted to a greater degree
toward the ionic st.a_te. These discussions are in complete agree-
ment faith the observed decrease in stability of the ferricinium
cation (particularly toward hydrolysis) in comparison with ferro-
CV.I'J1Ii U. D
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cene, and allow one to suggest that the cation will be inert in
reactions of.electrpphiaic substitution.
2. Reactions Involving Cleavage of the Bonds
Betwwen iron and the Cyclopentadiene j~ings
ferrocene, as has already bI s at 'r C? 4 1, 75.
The COn t, decompositf.on of fe:crocene into iron oxide and
unidentified urodu o:ts takes place upon heating an aqueo:~us suspeii-
s1.on of It in a closed system at 350?; in 3b1 hydrofluoric acid
ferrocene W=1r.11mposes at 1000 99.
The properties characteristic for compounds with conjugated
double bends are not evinced by ferrocene. =hus, it does not
react with maleic anhyd.r.?ide, is not hydrogenated in the presence
of platinum 12, 86-and also is not hydrogenated in the presence
of Haney nickel at 1400 and 150 atm. pressure 16, 86
i-iowever, Nesmeyanov, Perevalova, Golovnya, Nikitina and
imykova 104 hydrogenated fe rocene under very sever conditions -
in the presence of janey nickel at 280 atm. and 300-340?; under
these conditions the bonds between the cyclopentadiene rings and
iron are ruptured and cvclopentane is formed In 67% yield:
(('5 h5)2 Fe +5H2 Z 2 C5Hio + Fe
In contrast to the severe conditions for catalytic hydrogena-
tion, the cleavage of the ferrocene nucleus by means of solutions
of alkali metals in liquid ammonia or amines takes place very
readily; the reaction goes best with lithium in diethylamine. In
this reaction iron and cyclo :entadiene are formed, the latter being
isolated in good yield in the form of its adduct !-~ith maleic
anhydride 105:
11 _
(C5 H5)2 Fe ii )2 Fe +2 i .
The iron-carbon bonds in ferrocene are easily broken by the
action of bromine 104. rerrocene forms a complex compound witui
bromine 17j 104S .06 which upon brief heatiihg in C CK.4 with excess
bromine decomposes with the formation of pertabromocyclotentane
(yield 70..40%)
2(C5 H5) 2 Fe+13 Br2 - L- CS H5 13rs + 21,'e Bra
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Chlorir.e (in C (; F. -3 --> -->
(IV)
CO C6Hg
For dibenzoylferrocene (VI) it has also been rigorously shown
that the benzoyi groups are located in different rings: upon re-
duction of the carbinol (VII) which is formed by reaction of
dibenzoylferrocene ^-ith phenylmagnesium bromide, dibenzhydrylferro-
cene is obtained (VIII), Identical =ith that synthesized from
benzhydrylcycloper_tadiene 13, 30.
Fe
FeC,r a
L!\ J/
Li CH(C6H5
-C-(C6H5 )z
C61r i5iL.gBr ., ~ T C
Fe
(V (
1'611512--v" \
OH
H(CGH5)2
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X-ray crystallographic studies, carried out by "=truehkov73,
19q, showed that in crystals of dibenzoylferrocene the berzoyl
groups occupy the positions 1, 2'.
The interatomic distances in dibenzoylferrocen agree with those
found for ferrocene. Liacetyl-and dibutryrlferrocene probably
have the 1,2i_configuration as 1, -el173, 1?9,.
In solutions, probably, free rotation of the substituted cyclo-
pentadiene rings is possible, which is in accord with the fact that
only one isomer is obtained in independent syntheses of ferrocene
derivatives disubstituted in different rings.. Richmond and
Freiser 110 believe that the existence of free rotation. is indica-
ted by the presencecf a dipole moment in diacetylferrocene.*
The reactions of intramolecular acylation of ferrocene have
been accomplished by Nesmeyanov, Volkenau, and Vilchevskaya 112 ,
113.. In the reaction of ferrocene with succinic anhydride, they
obtained 1,1'-di-(L,*-carboxypropionyl)-ferrocene (XI) (yield 19%),
which was reduced by the Clemrnens.en method to yield di-(w-carbox-
ypropyl) ferrocene (-,) in 77% yield, which v ,,,as as then cyclized by
heating :ith rolyphosphoric acid with the formation of di-(ketote-
trahydroindenyl) Ir cm (41) (yield, 46?,) :
Fe >->-* ->
HGCu G_ HGCC (Ci2) 3---
(CH2 y _j f
CO(CH2)2 CCOH
CH2) 3 CCOH
* .nor a discussion of the work of iichmond and Freiser 110, see the
review of Lyatkina 81. E-'-lso see the work of Semenov and Loberts
iii on the dipole moment of di-(p-chlorophenyl)-ferrocene.
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The structure of di-(detotetrahydrolndenyl)-iron(XI) was proved
by converting; it by Olemmensen reduction to di-(tetrahydroindenyl)-
iron identical with the compound obtained by Fischer .nd eus
114 via hydrogenation of diindenyliron (see the section "Ciindenyl
compounds of metald').
By analogous methods Nesmey:nov, , Jolkenau, and Vilchevshaya
113 obtained cyclopentadienylketD tetrahydroindenyl Iron (./.III)
and the ferrocene analog of anthroquincne (AIv').
1
f 1
/ -I._ ,~-~-~
(:,IV )
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It must be noted that it is not possible to cyclize w-carboxy-
propionylferrocene while o-cerboxybenzoylferrocene is easily cycl-
ized giving compound XIv 113 Thus a complete analogy to benzene
derivativesis observed. It is known that benzoylpropionic acid
does not cyclize while o-benzoylbenzoic acid readily forms anthra-
quinone upon heating.
Somewhat later the intramolecular acylation of ferrocene was
carried out as well by fiinehart and coworkers 115, 116 sub-
stances obtained by them arc listed in table 2.
Ferrocenerropionie acid, in contrast to its higher homologues,
cyclizes with the formation of a bridge between the two cyclopen-
tadiene rings 115 The structure of 1,1' - 2 -(ketotrimethylene,
ferrocene) (XV) was proved spectroscopically.
`~ - _ CH2Ci2COH
Fe
X--Ch2
N. Z
Fe ~;H2
(xV )
Fauson 13 showed that ferrocene is acylated in the presence of
AQC.3 more rapidly than anisole: upon competitive acetylation, by
means of the complex CH3 CO A03, of a mixture of ferrocene
and anisole taken in the ratio 1:10, acetylferrocene is formed,
not methoxyacetophenone.
The ease of substitution of the hydrogens in ferrocene is evi-
dent in the fact that in contrast to benzene, ferrocene is acyla-
ted not only in the rresence of but also In the presence of
Sn Cf4? in which case monoa.cetylferrocepe ~g obtained 117
(~5r 5 )4 Fe + 0:1.13000)4 14.C5H5 Fe C5H4 COCI-3
i~.onoacetylferrocene is formed in good yield in the acylation
of ferrocene with acetic anhydride in the presence of BF3 118 or
of phosphoric acid 119. ~onopropionyl 11# and monobenzoylferrccene
1?.Q t 12 a have been described.
Formylation 119, 122, 123 of ferrocene is accomplished by the
action of N-methylformanilide and FOC93 on ferrocene; in this case
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ferrocenylaldehyde is formed in 70% yield; the d.ialdehyde was not
detected. cH3 N (:;EC) C6145
C5H5) e ->-, >--> >>-> C5H5 Fe C5H4. CHO
FO 03
The mild conditions required for formylation amain indicate
the increased reactivity of ferrocene in comparions to benzene.
b)Alkylation
Alkylferrocenes we e first obtained by ~~esmeyanov and Volkenau
X9,3 by "~'ierntrensen reduction of acylferrocenes. By this means,
ethyl-, 1,1.' -diethyl-, 1,Y - dipropyl-, 1,1` -dibutyl-, and 1,11 _
dibenzylferrocene (yields 0_7O%) were synthesized. i.ethyl-.124 and
1,1'_dimethylferrocene 12 were obtained by lithium aluminum hyd-
ride reduction of the corresponding fcrroceneca.rboxylic acids.
Nethylferrocene 12' 46 v.*,as also prepared by sodium amol am reducation
of the methiodide of 1,N-dlmethylaminomethylferrocene (see the
section ' eaotions.of condensation and. other reactions"),
In one of the patents, the catalytic reducation of'ferroeenyl
ketones 12.6 , CS1ist'e05h4 0O'0nH2n+1 (where iv = 1 to 15) . to alkyl-
ferrocenes is described.
Attempts by Eiemschneider and helm 1 to alkyl>a.te ferrocene
by the Friedel-grafts method were unseocessful.
Direct alkylation of ferrocene in the presence of aluminum ch-
'
loride was described by Nesmeyanov and Kochetkova in 1956 127- . 130
i,s alkylating agents alkyl halides were used (methyl bromide and
iodide, ethyl bromide, isopropyl, t-butyl, and t-amyl chlorides),
and also benzyl chloride, dichioroethane, ana olefins (ethylene,
propylene, and isobutylene), The reaction was carried out in an
excess of alkyl halide, in n-heptane, or in petroleum ether.
In the alkylation?of ferrocere, a m'.xture of mono-, di-, and
polyalk_ylferrocenes is obtained.
By means of infrared spectra (in individual cases by brorrlina-
tion) it was established that the dialkylferrocenes formed by direct
alkylation (even di-tert_butylferrocere and di12ert_amylferrocene)
contain an unsubstituted cyclopenta..diene rint,
Thus, the introduction of an alkyl group into the ferrocene
nucleus facilitates subsequent alkylation, just as is the case in
the benzene series, in which process a mixture of dialkylferrocenes
is obtained with suUa:tituents in a single cyclopentadiene ring,
6uch dialkylferrocenes we shall subsequently refer to is homoan-
nular.
Homoaranular isomeric dialkylferrocenes were separated chroma..
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tographically on alumina. It was found that a characteristics dif-
ference exists in the infrared spectra of isomeric dialkyl=
ferrocenes 74
2S.
;'~lkylation of ferrocene by isobutylene at 50-60? leads chief-
ly to mono- and tob:zomoannular di-t-butylferrocene. Lt higher tem-
pertures (10G-150 ) a crystalline tri-t-butylferrocene and a
liquid tetra-t-butylferrocene are formed. In the infrared spectra
of these substances there ar no characteristic frequencies in
the region 1003 and 1107 cm'.. ant consequently the t-butyl groups
are situated in different cyclopentadiene rings 13?.
In the reaction of ferrocene with dichloroethane in the
presence of anhydrous aluminum chloride, along with diferrocenyle-
thane and other products, under specific conditions 127 a powdery
high polymer can be obtained.
in possesses the characteristics of an on exchange resin.
the capacity upon oxidation with a u.IN solution of potassium di-
chromate in sulfuric acid under static condtions is 2.8 - 3.5 milli-
equivalents per gram of air-dried resin.
c) Sulfonation
i~ttempts to sulfonate ferrocene by means of concentrated sul-
furic acid did not yield positive results: upon solution of ferro-
cene in concentrated sulfuric aci3., it is converted into the ferri-
cirium cation 190 and the obtaining of ferrocenesulfonic acid is
unseccessful99
''esmeyanov, r erevalova, and ::burar_ov 131' 132 showed that
ferrocene is sulfonated by pyrldinesulfur trioxide in a manner
analogous to that of five-membered heterocycles Upon heating
ferrocene for four hours with pyridire-sulfur trioxide in dichloro-
ethane, ferrocenemonosulfonic acil is obtained in 80`i, yield, cal-
culatir_: from the forrocene w h'ch reacted. Upon more Prolonged
heating of ferrocene with an excess-of pyridine-sulfur trioxide,
ferrocene disulfonic'f-1d-i's obtained in a 41% yield. The mono-
disulfonic acids were isolated in th?s case in the form of their
barium or lead salts.
Weinmayr9.9 sulfon:ted ferrocene with a mixture of sulfuric
acid and acetic anhydride**? and obtained ferrocenemor_o- and diful-
fonic acids w=hich were isolated the ammonium salts. Oxidation
of ferrocene to the cation does n::t t:.ke ,lace under the conditions
of the reaction.
The monosulfonic acid of ferrocene in the form of its crystal-
line dihydrate was obtained. by ~,esmeyanov, Perev:~lov?a, and Chura-
nov 132 in quantitative yield upon tret!ent of its lead salt with
*The sulfonaating agent in this case is probably acetyl sulfate.
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hydrogen sulfide, and also upon sulfonation of ferrocene with di-
oxane:ulfotrioxide in equim:olecular amount at room temperature
(yield 52'i based on reacted ferrocene):
S C3di .ane C05Fe%5 -i4 : C3H,211~0
2 = e- -.!
5 21.S03dioxaae Fe 5 1-14 C3
If dioxanesulfotrioX:ide is taken with ferrocene in the ratio of
3.1, then the disulfonic acid is obtained in good yield (in the form
of comr.lex 132 with d4.ox ne) virtually without admixture of-the
mono-acid.
i?otentiometric titration of the ferrocened5_sulforte acid thus
obtained gives a curve typical of a monobasl.c acid, which indicates
the clc mess of the first and second inr_iz~ +.ton constants, and
h .~ce the s 1::Pht of the sulfoni e acid groups cn each
other. This is -n; evidence fcr the location of the sulfonic
acid groups in cyclopentadienyl rinf s 132 , which is also
confirmed spectroscopically 133.
For both sulfonic acids, S-benzylthiouronium salts and salts
with several amines have been obtained132,
By the action of diazomethane, the methyl esters of the ferro-
cenesulfonic acids have been synthesized. The acid chloride of the
monosulfonic acid is easily formed in good yield upon unprolonged
heating of the acid or its lead salt with an excess of PC.f(313.2
C5H5Fe C5p4 03H PC 3 C5t 5 Fe C5H4S02 C
Upon red.uctior of the acid chloride with lithium aluminum hy-
dride, ferroeenyldisulfide isobtained, identical with that obtained
from diferrocenylmercury 13:3.
2 05H5 Fe ~5h4
((;5H5 Fe C
.;4 ) arig
H4
C5H5FeC5H4 -S-5-C5H4 -1'e-
(C1"S)2
4 Hy
x'a2 '"2 03
The diacid chloride of the disulfonic acid is obtained upon
heatinS the disulfonic acid with 1'oC. 3; by .,the action of an excess
of PV3, the half acid chlorid is obtained '13S
POC9 3
~~--~>--> Fe(C5H4 G2 0X )2
Fe (C5114 C3n)2-------
FC.Q3
C2 C5H4 Fe C5H4 :$03 H
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d) Metallation
Ferrocene metallates extraor.idnar4ly easily under conditions
under uhich benzene does not react. the mercuration of ferrocene
by mercuric acetate 117 and the obtaining of the lithium and sodium
derivatives by means of'n-butyllithium : and rhenylsodium
respectively, was described by NeSmeyandv axed ,;cb=:tk=erksrs in 1}54#
The metallation of ferrocene by ~~-butyllithium was also published
somewhat later. by : enkeser, (oggir, and Schroll 135.. The metal-
lated ferrocenes thus formed can be used for a whole series of.syn-
theses.
-Mercury Derivatives of Ferrocene
Haloferrocenes
The mercuration of ferrocene, in contrast to benzene, is easily
accomplished by means of mercuric acetate at room temperature in
ether-alcohol or' benzene-alcohol solution. In this process there
Is i rmed a mixture of acetates of mono-and di.-mercurated ferrocene
which is converted into the chlorides by potassium chloride
(overall yield 657) 117:
Hg (C00 ;t-3) 2 n
2(C5H5)2re --a>>>>-a C5H5Fe ?5H4H.gC.k, +
KCAL.
H4 n
Fe (C5HgCk)2
Ferrocenylmercuric chloride readily symmetrizes in the pre-
sence of a saturated aqueous solution of thiosulfate, giving
diferrocenylmercury:_11.7
C5H51i'e C5H4 HgC 9?
tia2 203
-~ --> -~ -3 Fi r e C `i2 ) Hg
5 5 5' 2
By means of the mercury derivatives of ferrocene, Nesmeyanov,
rerevalova, and N~esmeyanova 106 obtained halogen derivatives of
ferrocene, which cannot be obtained by direct halogenation..
By the action of an excess of iodine on ferrocenylmercuric
chloride, there first forms a complex v:ith iodine; upon further re-
action with iodine, a replacement of mercury by iodine takes place
and.iodoferrocene is formed in the form of a complex .;ith iodine,
which then is decomposed by me=ans of thiosulfate; yield of iodo-
ferrocene, 64%.
2.12
C5ri5Fe C5H4 Hg C. -~~--- C5H. Fe C5H41;212
C5H5Fe C5`34 Hg CR2I2 Iz
Na2S2C'3 C5H5F`e CH4 I
In 1957, nausch, 'ogel and -Kosenberg repeated this work.
C C Y I NU 2L
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Iodine in iodoferrocene is inert to nucleoprilic substitution
and in this respect surpasses the.iodine of icdobenzene. Thus, it
does not react with solutions of potassium acetate and potassium
hydroxide in methatof upon heating to 10C?. Attempts to use ccrper
as a catalyst dild not yield _positive results. i-ertocenylmagr.esium
iodide could not be obtained by heating iodoferrocene with magne-
sium in ether.
33romoferro::ene is obtained by the action of bromine on diferro-
cenylmercury. Diiodoferrocene and dibromoferrocene were synthe-
sized analogously-by the action of the corresponding halogens on
f~a:rrocere dimercuric chloride 106.
12
Fe (C5H4 HgC `) 2 -----------
Brz
Fe(C5H4I)2
Fe(C5H4Br)2
With tiocyanogen, diferrocenylmercury also reacts and forms
a complex in which mercury is probably replaced by__SCi" upon further
reaction with thiocyanogen, but thiocyaratoferrocene cannot be
isolaleted because upon subsequent treatment of the reaction mix-
ture with sodium thiosulfate, (to remove excess thiocyanogen) it is
converted into ferrocenyl disulfide, identical with that obtained
by reduction of ferrocenesulfonyl chloride 133, 136.
(SCN)2
3
-->--~-~>~,-->
(C5H5FeC5h4 )2Hg -->>-* CC5H5Fe C5H4 'C``"
C ham: e C, h _~:_? h i I'` ~S1i
S 5 4 5 e 1.5~iS ~.~._.....+ C5215Fe 5
So2CX
The synthetic ,ossibilities of mercurated ferrocene are not
limited to usin;~v, it. for obtaining halogen derivatives and ferrocenyl-
disulfide. It was found that ferrocenylmercuric chloride and
especially diferrocenylmercury are extraordinarily reactive in re-
actions of electrophilic substitution as is ferrocene itself. Thus,
diferrocenylmercury reacts with triphenylmethyl chloride yielding
tri;.henylmethylferrocene; with acetyl chloride it forms acetyl-
ferrocene, and upon reaction with benzene--ard ferrocenesulfonyl
chlorides there is .obt iced r.henylferrocenylsulfone and diferro-
cenyl sulfone respectively 136:
(C~;H5i0C5i--,4. )2Hg
s . ~C C C5H5 Fe C05H4 `DC2 Chi 5
3 ~;?,A> C5H5 Fe C5"14 C(C+6H5)3
( ; 5 H - CSH4 CGCH3
5H5 Fe C514 ) 2 C'2
Upon reaction of `-e Br., with diferrocenylmercury, selenium is
reduced and diferrocenylselenium is formed136. .
Na3 520
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LITHIUM AND SODIUM DERIVATIVES OF FERROCENE
Ferrocenylamine
Ferrocene is metalated by n-butyllithium in ether solution:17113E
Upon heating for 12 hours with an excess of butyllithium, an equi-
molecular mixture of ferrocenylrnono- and dilithium is formed which.
yields a mixture of ferrocenecarboxylic and ferrocenedicarboxylic
acids117 upon carbonation with an average yield of 30%5:
(C5H5)2Fe
n-C4H9Li, CSH5FeC5H4Li + Fe(C5H4Li)2 ----~
CO2
C02 C5H5FeC5H4COOH + Fe(C5H4000H)2
The ferrocenedicarboxylic acid obtained in this way is identical
with the acid obtained by Woodward and coworkers12 by oxidation of
1,11-diacetylferrocene (see the section "Properties of acylferrocenes")
The lithium derivatives of ferrocene have been used to obtain
mono- and di(triphenylsilyl)-ferrocene135, and also mono- and di -
(trimethylsilyl)-ferrocene' 4.
The use of ferrocenyllithium to obtain aminoferrocene'37 by the
method described by Sheverdina and Kocheshkov138 affords great
interest. Thus, Nesmeyanov, Perevalova, and Shilovtseva 37, by the
action of.0-benzylhydroxylamine on ferrocenyllithium, obtained
ferrocenylamine characterized by its acetyl and benzoyl derivatives,
picrate, and Schiff's base131s137:
H2O
C5H5FeC5H4Li + C6H5CH2ONH2 ---? C5HSFeC5H4NH2 + (C5H5)2 Fe +
C6H5CH2OH
Ferrocenylamine is rapidly oxidized in air; under the action of
nitrous acid under usual diazotization conditions it undergoes
drastic changes, and the formation of a diazonium salt could not be
detected. The basicity constant of ferrocenylamine in 80% alcohol
is 1.55 x 10 9 and surpasses by 20-fold the constant for aniline
under the same conditions, which indicates the more powerful electron-
donating properties of ferrocenyl radical as compared with pheny1139.
Later Arimoto and Haven'40 synthesized ferrocenylamine from the
azide of ferrocenecarboxylic acid by means of the Curtius rearrange-
ment:
C5H5FeC5H4COOH PC15 [C5H5FeC5H4COC1] N---N3 C5H5FeC5H4CON3
CSH5FeC$H4NH2
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The acid chloride was not isolated. It was not possible to obtain
ferrocenylamine from the oxime of acetylferrocene or from the amide
of ferrocenecarboxylic acid14o.
By the action of phenylsodium125 on ferrocene, the disodium
derivative is formed which upon reaction with C02 is converted into
ferrocenedicarboxylic acid (yield k2%) identical with that obtained
by other methods. The carboxyl groups in the ferrocenedicarboxylic
acid thus obtained are located in different cyclopentadiene rings
which is rigorously proved by the isolation. upon hydrogenation of
cyclopentanecarboxylic acid104:
C5H5Na C02
(C5H5) 2Fe -----~ Fe (C5H4Na) 2 --~ Fe (C5H4COONa) 2
Hz/Ni
--~---- 2C5H9COONa - 2C5H9COOH
e) Arylation
The conditions under which the above observed reactions of
substitution of the hydrogens of ferrocene take place allow one to
compare this organo-iron compound in reactivity with such benzene
derivatives as phenol and aniline. Therefore one might expect that
ferrocene would undergo the azo coupling reaction. However, it was
found that the reaction proceeds in a different direction.
In 1954 Nesmeyanov, Perevalova, and Golovnya'17'114 first
showed that upon reaction of ferrocene with diazo compounds nitrogen
is evolved.and arylferrocenes are formed. Thus, the reaction of
arylation of ferrocene proceeds similarly to the reaction of obtaining
the unsymmetrical biaryls142:
ArN2X
(C5H5)2Fe -----) C5H5FeC5H4Ar + N2
The arylation of ferrocene is carried out in water-ether
medium at 20-35?;; under these conditions monoarylferrocenes are
preferentially formed (yields k0-6k%i, in some cases along with a
small quantity of diarylferrocenes14 . Thus p-tolyl-, p-nitrophenyl-,
p-hydroxyphenyl-, p-anisylferrooene, and others were obtained (see
table 6). In the case of benzenediazonium salts, polyphenylferrocenes
are obtained.
The reaction mechanism is probably free radical.
Later (1955) Broadhead and Pauson1O3 accomplished the arylation
of ferrocene by means of diazonium salts in acetic acid solution;
yields in this process are usually lower than in carrying out the
reaction in ether. They also showed that phenylation of ferrocene
can be carried out by means of benzenediazonium sulfate or the double
salt of benzenediazonium chloride with -ZnCl2 as well as with N-nitro-
soacetanilide, which confirms the free radical nature of the reaction
mechanism. The reaction with N-nitrosoacetanilide and with the
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double diazonium salt was carried out in cyclohexane and in acetic
acid; the yield and ratio of phenyl- and diphenylferrocene are close
in both cases. Ferrocene cannot be arylated by phenyl radicals
which are formed in the decomposition of phenylazotriphenylmethane or
benzoyl peroxide, or by the reaction of phenylmagnesium bromide with
bromobenzene in the presence of COC12103.
Broadhead and Pausonlo3 suggest that ferrocene forms an inter-
mediate complex with the diazonium salt which rearranges wth the
formation of the arylferrocene or arylferricinium salt.
Weinmayr10? showed that ferrocene can be arylated as well in
the form of the ferricinium cation in strongly acidic medium, the
yields being of the same order as are obtained when carrying out the
reaction with ferrocene itself in ether or acetic acid medium, but
the quantity of di- and polyarylferrocenes is usually greater.
It must be noted that in both cases (with ferrocene and with
the ferricinium salt) the reaction products contain ferrocene and the
arylferrocenes formed both in the free state as well as in the form
of the ferricinium salts, which indicates that the arylation of
ferrocene is accompanied by oxidation-reduction processes.
Pauson'3 suggests that the mechanism of arylation of the
ferricinium cation differs from the mechanism of arylation of free
ferrocene.
Further arylation of arylferrocenes always takes place in a
different cyclopentadiene ring, which indicates the deactivating
Influence of the aryl group on ferrocene. Only in the reaction of
p-methoxybenzenediazonium salts did Broadhead and Pausonlo3 isolate
in small amount (0.7%) a homoannular dianisylferrocene in which the
presence of an unsubstituted cyclopentadiene ring was proved by them
by means of infrared spectra; the relative positions of the
anisyl groups was not established.
The position of the aryl groups in 1,1'-diphenylferrocene was
proved by an independent synthesis from phenylcyclopentadiene3O, and
in 1,11-di-(p-nitrophenyl)-ferrocene by hydrogenation under pressure
in the presence of nickel sponge (cyclopentylcyclohexane was
obtained)104.
The reaction of diazonium compounds with ferrocene is a
convenient method for the synthesis of arylferrocenes. This method
allows one to obtain arylferrocenes having various substituents in
the benzene rings, and is more widely applicable and much less beset
with difficulties than the obtaining of arylferrocenes by means of
arylcyclopentadienes3O. However, the]atter means is used with
success for the synthesis of polyphenylatedferrocenes with known
relative positions of the phenyl groups30,100 (see table 6).
The great reactivity of ferrocene in reactions of homolytic
substitution is indicated as well by the reaction with trichloromethyl
radical, formed in the thermal decomposition of trichloracetic acid
in the presence of cupric chloride; after the hydrolysis of tri-
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chloromethylferrocene, ferrocenecarboxylic acid is isolated (yield
5.7%)143. In this way, from the data presented it is quite apparent
that ferrocene is very active both in reactions of electrophilic and
free radical substitution. The substitution reactions proceed with
ferrocene much more easily than with benzene.
f) Condensation Reactions and Other Reactions
Ferrocene, like aromatic hydrocarbons condenses with form-
aldehyde and benzaldehydel7'99'121'144. Nesmeyanov and Kritskaya'44
showed that the reaction proceeds in the presence of concentrated
sulfuric acid upon unprolonged heating. With formaldehyde there
forms first a derivative of the ferricinium cation, which after
reduction in acid medium yields a substance which probably has
structure (XVI); the presence in this compound of an unsubstituted
cyclopentadiene ring was proved spectroscopically and by the isolation
of pentabromocyclopentane upon bromination 4:
Fe Fe
CsH5
-,CH--_
CH -1 i
t~ ~~ I
\. ; C6Hs
With benzaldehyde, ferrocene forms two substances17'99'141'145,
one of which has, apparently, structure (XVII)74, analogous to that
offered for the product of the reaction of ferrocene with form-
aldehyde. The substance obtained upon condensation of ferrocene
with dimethylaminobenzaldehyde contains the hydroxyl group74.
In liquid hydrogen fluoride at 30-1000, ferrocene undergoes
a unique transformation to cyclopentenylferrocene (XVIII) in which
process a part of the ferrocene decomposes .
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liquid
HF
XVIII
The presence of the double bond in the compound obtained (XVIII)
was proved by hydrogenation In the presence of platinum oxide.
C-,,clopenteny7_"errecene, in site of the presence of the double bond,
is stable in hydrogen fluoride at 100? and does not undergo polymer-
ization or react with benzene".
The condensation with olefins (propylene or diisobutylene) in
liquid hydrogen fluoride, which proceeds easily in the benzene series,
does not proceed with ferrocene9 . The great nucleophilic activity
of ferrocene is manifest in the reaction with formaldehyde and
dimethylamine'46.
CH2O + (CH3)2NH
(C5H5)2Fe ; C5H5FeCSH4CH2N(CH3)2
The N,N-dimethylaminomethylferrocene (XIX) thus formed yields a
methiodide with methyl iodide (XX) which is used to obtain a series
of other ferrocene derivatives (the yields in most cases are
good)124)147-1490 Thus, by the action of aqueous alkali, the
.
methiodide'(XX) is transformed into ferrocenylcarbinol 147, while
upon reduction of of methy1ferroceneareandformeda
quantity of the simple
formed124:
...- CH2N (CH3) 3 . I
k
1~aOn
Na Hg C5H5FeC5H4CH3
C5H5FeC5H4CH2)20
XXI
~,,ZO , C5H5FeCsH4CH2OH
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Upon treatment of the methiodide (XX) with potassium amide in
liquid ammonia N,N-dimethylaminoethylferrocene (XXII) was obtained,
the methiodide of which was then converted into vinylferrocene147..
KNH2
C5H5FeCSH4CH2N(CH3)3 I 7 C5H5FeC5H4CH2CH2N(CH3)2
? 9 KNH2
CSH5FeC5H4CH2CH2N(CH3)3 I ; C5H5FeCSH4CH=CH2
CH3I
Upon reaction of the methiodide (XX) with aqueous sodium
cyanide, 1-cyano--2--methylferrocene (XXII1 is formed, from which the
methiodide of 1-methvl-2--dimethylaminoferrocene (XXIV) is synthesized
by reduction and mcthyl2tion. Hydroly is of the nitrile (XXIII)
yields 2-methylferrOU?a-,~~-c7a?-'rho.xylic actc?. which is reduced to
1?- hydrexymethyl cen..e (XX,iy ~ h~c~z u;;,on NLnO2 oxidation
yi ids 7.-formy 1- 2. -:n~~ tYr; l e r ro ene XXVII .
ID ) Na.CN
CH2N(CH3 )3 I -
FeC5H5
XXII
Ie
CH2N(CH3)3
CH2NH2
CHO
.- CH3 ~ CH3 ! :_.CH3 CH3
CN ... ~_..__~/
~r/i CH3
FeC5H5
FeC5H5
XXIII
CH2OH
FeC5H5
FeC5H5 FeC5H5 FeC5H5
XXIV XXV XXVI XXVII
Kursanov and Parness150,151 found. that the hydrogens of
ferrocene do not exchange with D20 in the -pY;esence of an alkaline
catalyst (N,N-dimethylpyridonimine).
The absence of exchange indicates the covalent character of the
bonds between iron and the cyclopentadiene rings since the cyclo-
pentadienyl anion under these conditions would enter into the reaction
of hydrogen exchange.
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26
REACTIONS OF FERROCENES SUBSTITUTED IN THE NUCLEUS
The introduction of substituents into the cyclopentadienyl
rings exerts a profound influence on the reactivity of the ferrocene
nucleus. This influence manifests itself not only in the ease of
further substitution of the cyclopentadienly hydrogens and the
stability of the bonds between the iron and the cyclopentadiene rings,
but also in the lability to oxidation to derivatives of ferricinium
cation and the stability of the latter. The character of the
influence depends on the degree of electrophilicity of the substituent
Particular interest is engendered by the investigation begun
recently of the orientative influence of the substituent already
present in further substitution within the same cyclopentadiene ring.
The properties of the ferrocenes substituted in the nucleus
which have been most thoroughly studied - acyl-, aryl-, alkyl-, and
carboxy-ferrocenes - are discussed below.
PROPERTIES OF ACYLFERROCENES
For acylferrocenes, two types of reactions are of primary
interest - the substitution of the hydrogens of the cyclopentadiene
rings, which affords great interest from the point of view of
influence of the acyl group on the reactivity of the ferrocene
nucleus, and reactions of the keto-group which do not involve the
ferrocene nucleus.
It has been found that the introduction of an acetyl group
sharply lowers the lability toward further substitution within the
same cyclopentadiene ring and noticeably lowers the tendency toward
substitution in the second cyclopentadiene ring. Thus, further
acylation of acetylferrocene goes preferentially, as has already
been indicated, in the second cyclopentadiene ring, and furthermore
forms only a very small quantity of 1,2-diacetylferrocene; hence
the second acetyl group goes to the carbon neighboring-the one which
already bears an acetyl group108.
Triacetylferrocene can not be obtained152. The two acetyl
groups in 1,1'-diacetylferrocene greatly deactivate both rings (each
deactivates its own as well as the other ring).
.1,11-Diacetylferrocene does not react with mercuric acetate,
either at room temperature sunder conditions for mercurating
ferrocene) or upon heating1 2.
The deactivating influence of an acetyl group on the second
cyclopentadiene ring is evident.in the fact that in the presence
of SnC14 - a catalyst whose action is milder than that of AiC13a
only monoacetylferrocene is formed'17,.
In ferrocenemonoaldehyde, a second formyl group can not be
introduced by the action of N-methylformanilide in the presence of
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POC13, which also indicates the deactivation of both cyclopentadiene
rings by the aldehyde group119'123.
Acetyl-, 1,1'-diacetyl- and 1,11-dipropionylferrocene dissolve
in concentrated hydrochloric acid to produce a deep violet-red
color12'1o7. Upon dilution of the hydrochloric acid solutions with
water right after solution, the ketones are isolated without change
and in this way can be purified of ferrocene. Upon standing for
several hours in hydrochloric acid solution, the acylferrocenes
decompose with formation of ferrous ionsl7, which indicates the
sharp decrease in stability to hydrolysis of the bonds between iron
and the substituted cyclopentadiene rings as compared with the
corresponding bonds in f, -rrocene itself.
Upon reaction with diazonium salts, 1,11-diacetylferrocene
behaves quite differently from ferrocene. Upon carrying out the
reaction under co ?c?ition3 are a7.ogous to the co nn:ditions for arylation
1oa=:`.17' =1 fl
of errocene .1 y fe^xocene nucleus is cleaved and
:.
products are formed which do not contain iron and corresponding in
elemental analysis to arylazoacetocyclopentadiene, but their
structures are not as yet proved's2:
Fe(C5H4COCH3)2 + ArN2X '
CH3-CO-C5H4N2Ar + FeX2
The reaction was carried out with p-nitrobenzene-, p-toluene-,
and benzenedi-azonium saltsZJ2.
It must be noted that acetylferrocenes upon oxidation are not
transformed into derivatives of ferricinium cation, but yield
fer:nocenecarboxylic acids; hence in acylferroceness the iron is not
zed to the trivalent state. Thus, Weinmayr'91 153 , by hypoiodite
o,~.: Jation of acetylierrocene obtained ferrocenecarboxyl.ic acid which
vas, earlier synthesized by A. N. Nesmeyanov and coworkers117 by
means of ferrocenyllithium
NaOI
CSH5FeC5H4COCH3 ; C5H5FeCSH4CO0H
Upon oxidation with hypochlorite or hypoiodite of 1,1'- and
-djace tyl error ne, 1,1' - and 1, 2-ferrocenedicarboxylic acid
were obtained
NaOC1
Fe
-~~~.COOH
COOH
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Thus, the acetyl group in acetylferrocene sharply lowers the
tendency toward further substitution in the same ring, and more
weakly, but nevertheless noticeably lowers the reactivity toward
substitution in the second ring; on the other hand - in acetyl-
ferrocene (and especially in diacetylferrocene) the stability of the
iron toward oxidation increases, and the stability of the bonds of
the cyclopentadiene rings with iron decreases.
The carbonyl group in acylferrocenes gives reactions
characteristic of ketones 117-119' 121' 154' among which it reacts
with organomagnesium compounds with the formation of the corresponding
tertiary alcohols containing the ferrocenyl group17'125.
Riemschneider and Helm17, by the reaction of 1,1'-diacetyl-
ferrocene with ethylmagnesium bromide, obtained 1,1'-bis(a-hydroxy-
sec.-butyl)-ferrocene (XXVIII) having two asymmetric carbon atoms:
(CH3COC5H4)2Fe + 2C2H5MgBr (2)H20
/CH3
C
OH C2H5
and isolated two stereoisomers, probably the meso form and racemate.
Upon dehydration of these carbinols by KHSO4, Riemschneider and
Helm'7 obtained a mixture of isomeric l,l'-bis-(a,p-dimethylvinyl)-
ferrocenes (XXIX).
KHSO4
XxvIII -----~
CH3
~-- C=CH-CH3
Fe
CH3CH=C
CH3 XXIX
Upon dehydration of 1,1'-bis-(a-hydroxyisopropyl)-ferrocene,
only polymer forms.- (C1sH18O1sFe)il?.
(sic)
Clemmensen reduction of acylferrocenes, as has already been
mentioned, is a method of obtaining individual alkylferroceneslo7.
1,1'-Diacetylferrocene is readily reduced catalytically in the
presence of Raney nickel107.
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By reduction of acetylferrocene with lithium aluminum hydride,
Arimoto and Haven140 obtained methylferrocenylcarbinol, upon dehydra-
tion of which, and also upon pyrolysis of its acetate, vinylferrocene
was isolated. They prepared polymers of vinylferrocene and also its
copolymers with methyl methacrylate, styrene, and chioroprene.
Upon reduction of 1,11-dibenzoylferrocene with aluminum iso-
propoxide, 1,1'-bis-(phenylisopropoxymethyl)-ferrocene is obtained
(XXX)17 and upon reduction with LiAlH4, 1,1'-dibenzylferrocene125 is
formed in almost quantitative yield.
(C6H5COCSH4)2Fe
Al(OC3H7-i
0),3 C6H5
---~ C6H5CHCSH4FeC5H4CH
OC3H7 OC3H7
(XXX)
(C6H50005H4)2Fe
LiAlH4
(CSH5CH2CSH4)2Fe
Very recently, various other transformations of the carbonyl
group have been accomplished with acetyl-118'119, benzoyl-120'12 ,
and formylferrocenes119,147 , and for acetylferrocene, condensations
involving the a-hydrogen atom have also been carried out1161118,119,
leading to various ferrocenyl-substituted alcohols, acids, unsaturated
ketones and other derivatives which are presented in the correspond-
ing tables.
Formylferrocene enters into virtually all the reactions typical
of the aldehyde group. However, oxidation to the acid was not
successful119. . Ferrocenecarboxylic acid is obtained from the
aldehyde only by means of the Cannizzaro reaction147.
It must be noted that in the infrared spectrum of formylferrocenE
taken above 45?, bands characteristic of the hydroxyl group were
unexpectedly found'19.
PROPERTIES OF ARYL- AND ALKYLFERROCENES
In the study of the properties of arylferrocenes, interest is
afforded by the elucidation of the mutual influence of the aryl and
ferrocenyl groups. On the basis of the extant experimental data,
one may say that arylferrocenes show a somewhat decreased reactivity,
in comparison with ferrocene, toward further substitution of the
hydrogens of the cyclopentadiene rings. Thus, in the further
phenylation of pphenylferrocene, the unsubstituted ring is attacked
preferentially) 3, and in arylation of ferrocene with an excess of
arenediazonium salt, 1,1'-diarylferrocenes are obtained. Only in 3
the case of p-methoxybenzenediazonium salts did Broadhead and Pausonl0.
isolate a small quantity of homoannular di-(p-anisyl)-ferrocene with
the relative positions of the p-anisyl groups undetermined.
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A sharp decrease in reactivity. toward electrophilic substitution
is observed with p-nitrophenyl- and especially with 1,l'-di(p-nitro-
phenyl)-ferrocene 52. Neither of these compounds is acylated or
sulfonated under those conditions under which these reactions
proceed for ferrocene. 1,1..'--Di(p-nitrophenyi)ferrocene is not
mercurated, while mono-p-nitrophenylferrocene yields di-(chloro-
mercury)-p-nitrophenylferrocene, only in 15% yield while 72% of the
original R-nitrophenylferrocene is recovered unchangedls2.
By the reduction of p- and m-nitrophenylferrocene, p- and m-
ferrocenylaniline are obtained and a series of their derivatives T37
(acetyl, benzoyh, and others). The basicity constants of these
amines, and also the dissociation constants of p-ferrocenylphenol'39,
p- and o-ferrocenylbenzoic acids131, and for comparison some aromatic
derivatives are presented in table 10.
The basicity constant of p-ferrocenylaniline is three times as
great than the constant of aniline and 17 times as great as the
constant of p-aminobiphenyl. Similar comparisons are observed for
phenols: p-ferrocenylphenol is significantly less acidic that phenol
and p-hydroxybiphenyl. From comparison of the data given, it
follows that ferrocenyl is a considerably more powerful electron-
donating group than phenyl, and when introduced into the benzene ring
behaves as a sharply defined orth-para director.
Thus, with respect to ferrocenyl, the aryl group is an electron
acceptor. Indeed as has already been mentioned, not only p-nitro-
phenyl, but also the unsubstituted phenyl group somewhat lowers the
reactivity of the ferrocene nucleus.
As has already been said above, alkyl groups, in contrast to
aryl, increase the tendency toward further substitution of the
hydrogens of the ferrocene nucleus. Thus, Nesmeyanov and Volkenauls4
did not succeed in obtaining monoacetylethylferrocene from ethyl-
ferrocene in the presence of AiC13 under the conditions for obtaining
monoacetylferrocene. Monoacetylethylferrocene was synthesized by
them by the action of acetyl silicate on ethylferrocene in the
presence of SnC14. The products isolated were homoannular ethyl-
acetylferrocene (XXXI), 1,1'-ethylacetylferrocene (XXXII), and ethyl-
diacetylferrocene (XXXIII) in the ratio 3.5 : 1 :.1.
CH3CO
__C5H3FeCSHs
C2H5
CH3COC5H4FeC5H4C2H5
XXXI XXXII
CH3CO
C5H3FeC5H4COCH3
C2H5
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Upon reduction, (XXXI) yields homoannular diethylferrocene (the
relative positions of the ethyl groups is not established; the
presence of an unsubstituted ring was proved by bromination);
(XXXII) is transformed into l,l'-diethylferrocene, and (XxXIII) forms
triethylferrocene, the structure of which is not established..
Thus the ethyl group orients the acetyl group in subsequent
substitution chiefly in the same cyclopentadiene ring and
principally in one specific position (it is not established in which).
Upon acylation with acetic anhydride in the presence of A1C13
of 1,1'-dimethy1ferrocene, 1,11-dimethyl-3-acetyiferrocene (XXXIV)
and 1,1'-dimethyl-2-acetylferrocene (XX~.'V)155, are formed in the
ratio of 7 : 3. The ratio. of the corresponding isomers obtained
upon acylation of 1,1'-diisopropylferrocene155 is equal to 9 : 2.
Thus in this case as well, the formation of one of the isomers in
greater quantity is observed.
CH3 COCH3
Fe
CH3
1 ~`?
XXXIV xxXv
Acetyldialkylferrocenes are oxidized to the corresponding
dialkylferrocenecarboxylic acids and reduced to trialkylferrocenes.
The relative positions of the groups within one ring is established
spectroscopically155.
Nesmeyanov and coworkers156 showed-that in acylation of
1,1'-dimethylferrocene with acetyl chloride in the presence of A1C13s
triacetyldimethylferrocene is formed along with diacylated products.
This fact indicates that the methyl groups which are present in the
ferrocene nucleus significantly facilitate subsequent acylation..
As has already been mentioned, attempts to obtain triacetylferrocene
by means of the Friedel-Crafts reaction are not successful.
Rinehart and Motz157isolated stereoisomers for 1,1'-dimethyl-
2,2'-diacetylferrocene, XXXVI and XXXVIi, and for 1,1'-dimethyl-3,3'-
diacetylferrocene, XXXVIII and XXXIX, and reduced them to the
corresponding dimethyldiethyiferrocenes.
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CH3CO
CH3
CH3
CH3
CH3CO
COCr3
CH3
".~,._._-COCH3
'y --- COCH3
1 i
CH3
XXXVII
CH3
("_COCK,
CH3 CH3
XXXVIII
XXXIX
As has already been noted in the section "Alkylation", in the
alkylation of ferrocene homoannular dialkylferrocenes are formed.'
This indicates the activating influence of the alkyl group especially
on that cyclopentadiene ring to which it is attached.
Aryl- and alkylferrocenes are easily oxidized to derivatives
of the ferricinium cation107'141. Upon standing, liquid alkyl-
ferrocenes gradually decompose with formation of a precipitate107.
Piper and Wilkinson70 took the nuclear magnetic resonance
spectrum of 1,1'-dimethylferrocene.
PROPERTIES OF FERROCENECARBOXYLIC ACIDS
Ferrocenecarboxylic acids (monoferrocenecarboxy'_?ic acid and two
diacids - 1,1'- and 1,2-ferrocenedicarboxylic acids have been
obtained*) are quite stable substances, yielding water-soluble salts
with alkalies and forming methyl esters under ordinary
corditions1291os'i17'lss. The nitrite of ferrocenecarboxylic acid
has been synthesized via the oxime of formylferrocene122 and from
the amide143. Derivatives of 1,2-ferrocenedicarboxylic acid have
already been described in the section "Acylation and alkylation of
ferrocene".
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`The method of obtaining them is described in the sections "Metalation"
and "Properties of Acylferrocenes".
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The monoamide and mononitrile of 1,l'-ferrocenedicarboxylic
acid have been obtained by Nesmeyanov and Reutov143,
By the reduction of the dimethyl esters of ferrocenecarboxylic
acids, Nesmeyanov, Perevalova and Beinoravichute125 obtained
ferrocenylcarbinol and 1,1'-di(hydroxymethyl)-ferrocene in good yeild.
C5H5FeC5H4000CH3
LiAlH4
C5H5FeC5H4CH2OH
Fe(C5H4COOCH3)2
LiAlH4
3 Fe(CSH4CH2OH)2
The dimethyl ester of ferrocenedlcarboxylic acid also is
easily reduced by lithium aluminum hydride to 1,1'-dimethylferrocene
(yield 89%) 125s
Fe(C5H4000CH3)2
LiAlH4
------~) Fe (C5H4CH3) 2
In the work of Wilkinson, Cotton and Birmingham26 the synthesis
of 1,1'-dimethylferrocene by means of methylcyclopentadienylsodium
is mentioned (reference to unpublished data).
The carboxylic acid group exerts a deactivating influence on
further substitution of the hydrogens of the ferrocene nucleus.
Thus, Nesmeyanov and Reutov158 showed that in the reaction of
dioxanesulfotrioxide.with a mixture of ferrocene and ferrocene-
carboxylic acid (competitive sulfonation) ferrocene is sulfonated
while the acid is unchanged. Acylation of the methyl ester of
ferrocenecarboxylic acid proceeds in the unsubstituted cyclopenta-
diene ring. In the reaction of this ester in the presence of
aluminum chloride with the acid chlorides of acetic and butyric
acids, acetyl- and butyrylferrocenecarboxylic acids are obtained
after subsequent saponification. The location of the substituents
in different cyclopentadiene rings was.established spectroscopically
and also by oxidation of acetylferrocenecarboxylic acid to the known
1,1'-ferrocene.dicarboxylic acid158. Ethyl- and butylferrocene-
carboxylic acids were obtained by reduction of these keto acids.
An interesting study of the influence of substituents on the
dissociation constants of ferrocenecarboxylic acids was carried
out by these same authors158. They found that the alkyl or acetyl
group located in one cyclopentadiene ring influences the dissociation
constant of a carboxyl group located in the other ring. Alkyl groups
lower, while acyl groups augment the dissociation constant of the
corresponding acid.
The order of influence was compared with the influence of the
same substituents on the dissociation constant in p-substituted
benzoic acids.
Ferrocene and compounds similar to it constitute the first
example of a conjugated system (see 159) which includes a metal atom.
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Generalizing the properties of ferrocene discussed above, one
can note the following particulars:
1. Unusual stability for an organometallic compound.
2. Complete absence of the addition reactions characteristic of
unsaturated compounds.
3. Ease of electrophilic substitution reactions which take place
under milder conditions than are necessary for benzene.
4. Ease of oxidation of the iron to the trivalent (formal) state
and at the same time complete stability to oxidation of the
internal bonds of the cyclopentadiene rings.
Strong influence of substituents on the reactivity of the
ferrocene riiieletts, especially evident within one cyclopenta-
diene ring, bW very sigizificantly transmitted from one ring
to the other as well.
It is evident that ferrocene is a new aromatic system of the
non-benzenoid type.
POSSIBILITIES FOR TECHNOLOGICAL APPLICATION OF FERROCENt
In the patent literature ferrocene has been suggested for use
as an additive in mineral oils as an antidetonator143.9153, and as a
thermally stable heat transfer agent16. Ferrocene is also useful
for accomplishing the smokeless combustion of oilslso.
III. PROPERTIES OF DICYCLOPENTADIENYL COMPOUNDS OF METALS
At the present time dicyclopentadienyl compounds of the majority
of metals have been obtained. The methods for obtaining them were
discussed above. The physical and especially the chemical
properties have not been studied in as much detail as those of
ferrocene itself. The magnetic properties of all the compounds
obtained have been investigated and spectra have been taken
(usually infrared); for some of them X-ray crystallographic
alalysis has been carried out and polarographic measurements have
been made. Of the chemical properties which are usually investigated
there is the reaction with malefic anhydride and the ease of hydrolysis
of the bond between the cyclopentadiene rings and the metal, and
oxidation to the cation is described or conversely reduction of the
c;,.ion. The character of the spectrum and its agreement with the
spectrum of ferrocene usually serve as a basis (sometimes not
completely adequate) for judgement as to the three-dimensional
structure of the given dicyclopentadienylmetal. The ease of
hydrolysis, and the reaction with FeC1226 to form ferrocene serve as
criteria of the ionic nature of the bond between metal and cyclo-
pentadiene ring, while the absence of reaction with maleic anhydride
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of the Diels-Alder type serves as an indication of the aromaticity
of the rings and the presence of "sandwich" bonds between the metal
and the cyclopentadiene ring.
The reactions of. aromatic substitution have been studied in
detail only for ferrocene. Attempts were made to accomplish these
reactions with nickelocene, cobalticinium salts, and dicyclopenta-
dienyl. compounds of titanium. Negative results were obtained in all
cases,
It is possible that this is due to the decreased stability, in
comparison with ferrocene, of dicyclopentadienyl derivatives of
nickel and titanium, which is.confirmed for nickelocene by mass-
spectral investigations82 and theoretical calculations. The
question as to the possibility of electrophilic substitution
reactions for the cation has not been studied even for ferricinium
ion. Dunitz and Orgel6' calculate that in the cations of dicyclo-
pentadienyl compounds, the d-orbitals of the central atoms are
significantly more stable than the'T'_ orbitals of the C5H5 rings, and
therefore in compounds of tetravalent titanium and trivalent iron,
cobalt, and nickel, the character of the bonds is shifted in the
direction of more ionic character. This must lead to a decrease
in the stability and to diminishing of the reactivity toward aromatic
substitution.
The behavior of ruthenocene (the closest dicyclopentadienylmetal
in all properties and stability to ferrocene) in reactions of aromatic
electrophilic substitution has not been studied, possibly because of
the difficult accessibility of the metal itself.
Below, the physical and chemical properties of dicyclopentadien-
yl compounds, grouped according to their group in the periodic system
of elements, are discussed.
DICYCLOPENTADIENYL COMPOUNDS OF ELEMENTS OF
GROUP VII IN THE PERIODIC SYSTEM
Dicyclopentadienyl compounds have been obtained for all
elements of the eighth group except palladium (see table 1). The
physical and chemical properties of ferrocene were discussed above.
All dicyclopentadienyl compounds of elements of group VIII have
the centrally symmetrical antiprismatic structure, the cyclopentadiene
ring bound to the metal just as in ferrocenel8'19'31:'2'98.
Spectroscopic18'19'21-24'161 and mass-spectroscopic 82
investigations and polarographicl9'21'24'84 and magnetic measure-
ments 18'19'21'11'1''31'32'69'98 are in complete agreement with the
"sandwich" structure of dicyclopentadienyl compounds of metals of
group VIII.
For the ortho-para interconversion of hydrogen in the presence
of nickelocene and cofalticene see68.'
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The densities of nickelocene and cobalticene72 are equal to
d18 1.47 g./cm3 and d18 1.49 g./cm3 respectively.
The green nickelocene, (C5H5)2Ni, is paramagnetic, sublimes in
vacuum, dissolves readily in non-polar solvents, gradually is
oxidized in air, especially in solutions31,~does not dissolve in
water and is not decomposed by water, and does not form ferrocene with
ferrous chloride26. Nickelecinium cation, (C5H5)2Ni , yields water-
insoluble salts only with complex ions such as are shown below:
[(CsHs)2Ni][Cr(SCN)4(NH3)2), [(C5H5)2Ni][B(CGH5)4],
and is unstable in water, decomposing in several minutes19'31.
Comparison of mass-spectra shows that the bond between the nickel and
the cyclopentadienyl rings in nickelocene is much weaker than in
ferrocene 2. For the heat of formation of nickelocene from cyclopen-
tadiene radicals and the gaseous metal, see21.
Reactions of aromatic substitution are not known for nickelocene.
Wilkinson, Pauson, and Cotton21 unsuccessfully tried to acylate
nickelocene by the Friedel-Craft reaction. Our attempts to
accomplish acylation by acetylborontrifluoride, arylation, and
metalation of nickelocene under conditions analogous to those under
which these reactions were carried out for ferrocene, also gave
negative results. In the process, a significant part of the nickel-
ocene decomposed'even when the reaction was carried out under
nitrogen.
In the patent literature there is an indication that nickelocene
may be used as an antidetonator and as a 'catalyst in some organic
reactions44.
Cobalticene (C5H5)2Co is extremely easily oxidized32 to the
very stable diamagnetic cation (C5H5)2Co0, which is isoelectronic
with ferrocene and yields water-insoluble salts, similarly to
ferricinium and nickelecinium, only with large anions88. Cobalt-
icinium salts are not decomposed by concentrated sulfuric and nitric
acids, but in their presence, substitution in the nucleus does not
take place18'22. Cobaltcin.um nitrate'is not ozonized, even upon
prolonged passage of ozone into a solution of the salt in acetic
acid for many hours86. Our attempts to acylate by the Friedel-Crafts
method, arylate, sulfonate and nitrate cobalticinium picrate were also
unsuccessful, In all cases the cobalticinium salt was recovered
unchanged.:
In anhydrous solvents (C5H5)2Co?Br0 is reduced by-lithium
aluminum hydride to (C5Hs)2Co in good yield43.
The action of water does not cleave the bonds between the metal
and the rings in cobalticene; only slow oxidation to the cation takes
place26; with FeC12 ferrocene is not formed26.
By the action of an alkali metal cyclopentadienyl compound on
(C5H5)2Co'& , FischerlB2 obtained a substance
he t assigned r(XL)is with
the composition Co2(CSHs.)s gned
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dipole moment of this compound is zeros9.
01
= C5H5
Ruthenocene is similar to ferrocene in properties and
stability23's2's4. The reactions of substitution of the hydrogens
of the cyclopentadiene rings has not been studied. For the nuclear
.
magnetic resonance spectrum of ruthenocene see70
Wilkinson, Cotton, and Birmingham26 studied the reaction of
dicyclopentadienyl compounds of iron, ruthenium, cobalt, and nickel
with benzophenone, m-nitrobenzaldehyde, maleic anhydride, and methyl
maleate and found that only ferrocene and ruthenocene are inert to
all these reagents. Cobalticene forms colored products with
benzophenone; nickelocene does not react. Cobalticene and nickel-
ocene react witl! maleic anhydride; however the character of the
reaction has not been studied, and therefore it is impossible to
draw any conclusions.
Dicyclopentadienyl compounds of rhodium and'iridium24 have been
obtained only in the form of salts of the cations
(C5H5)2Rh and (C5H5)2Ir with [Cr(SCN)4(NH3)21,ClO4e
and others and the free bases (C5H5)2RhOH and (C5H5)2IrOH. The
cations of the dicyclopentadienyl compounds of rhodium and iridium
are similar in properties and stability to cobalticinium cation.
An attempt to isolate dicyclopentadienylrhodium, (C5H5)2Rh
by electrolytic reduction in aqueous solution was.not successful4;
a hydride of dicyclopentadienylrhodium is described163.
In his review Pauson13 refers to the private communication of
Lippincott concerning the obtaining of a dicyclopentadienyl compound
of osmium.
DICYCLOPENTADIENYL COMPOUNDS OF ELEMENTS OF
GROUP VII IN THE PERIODIC SYSTEM
Dicy.clopentadienyl compounds have been obtained for rhenium47
and manganese 25'26,33'46,16 '165
.
Dicyclopentadienylmanganese is paramagnetic26'69, has an
arrangement of atoms in space similar to ferrocene, in the form of a
pentagonal antiprism, but the bonds between manganese and the
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cyclopentadiene rings is of the ionic type 26'46'82'164. In chemical
properties, (C5H5)2Mn is similar to (C5H5)2Mg, with which it forms
mixed crystals. Upon heating, the brown dicyclopentadienylmanganese
changes color and is transformed into another modification26'46.
Mn(C5H5)2 decomposes upon attempts to oxidize it to the cation,
reacts with aldehydes, ketones, and maleic anhydride; forming
products which have not been investigated26.
Wilkinson, Cotton, and Birmingham26 mention the obtaining of
(CH3C5H4)2Mn by means of methylcyclopentadienylsodium (reference to
unpublished work).
A dicyclopentadienyl compound of rhenium is known47'166 only in
the form of the hydride, (C5H5)2ReH. The structure was confirmed
by nuclear magnetic resonance study47'7o'163. The hydride hydrogen
atom is located in the space between the cyclopentadiene rings.
(C5H5)2ReH does not react with water or with 6NNaOH, reacts slowly
with the oxygen of the air, dissolves in organic solvents. Solutions
in liquid ammonia do not conduct the electric current; upon reaction
with FeCl2, ferrocene is not formed. (C5H5)2ReH dissolves in
dilute hydrochloric or sulfuric acid with formation of the cation
[(CsH5)2ReH2]? which is precipitated in the form of the silicotung-
state or reineckeate.
Wilkinson and Birmingham47 believe that the hydride of
dicyclopentadienylrhenium has a structure similar to ferrocene.
DICYCLOPENTADIENYL COMPOUNDS OF GROUP VI
OF THE PERIODIC SYSTEM
Of the elements of group VI dicyclopentadienyl compounds have
been obtained for chromium26227143133270 1 molybdenum27 and tungsten27
Dicyclopentadienylchromium, (C5H5)2Cr, is paramagnetic68'69,
thermally stable to 3000, but is extremely easily oxidized in air,
ignites spontaneously in finely pulverized form; is not appreciably
decomposed by water26'34.; evolves cyclopentadiene on treatment with
dilute mineral acids, forming a dark blue solution34 in which neither
the chromium ion nor the cation (C5H5)2Cr+ is detected. Dicyclo-
pentadienylchromium reacts with FeC12 to form ferrocene (yield 70%)
and a blue-green substance of undetermined structure28; upon heating
under pressure with CO, dicyclopentadienylchromium forms first
chromium cyclopentadienylcarbonyls of various compositions and then
Cr(CO)e 35. Dicyclopentadienylchromium reacts with maleic anhydride,
aldehydes, and ketones; neither the products so formed nc?r the
nature of the reactions have been investigated26. By the action of
iodine dicyclopentadienylchromium is transformed into the iodide of
the cation, (C5H5)2CrI49. It was not possible to take the infrared
spectrum of dicyclopentadienylchromium34.
Thomas167 obtained the bromide of the cyclopentadienylacetyl-
acetonate of chromium and showed by this means the possibility of the
existence of compounds of chromium with one cyclopentadiene ring:
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/CH3
---- Cr,,,O-C~H
CH3
Dicyclopentadienyl compounds of tetra- and pentavalent molyb-
denum and pentavalent tungsten have been isolated in the form of
salts27.
(C5H5)2MoC12s [(CSHs)2MoC1]]Cr(SCN)4(NH3)2]?H20,
V V
[(C5H5)2MoC12][PtCle] (paramagnetic) and [(C5H5)2WC11][PtC16]
Cotton and Birmingham27 calculate on the basis of infrared
spectra that these compounds have structures similar to ferrocene.
DICYCLOPENTADIENYL COMPOUNDS OF ELEMENTS OF
GROUP V OF THE PERIODIC SYSTEM
Of the elements of group V, dicyclopentadienyl compounds of
vanadium19'20'26'43'50,68'168, niobium, 2O, tantalum20, bismuth51,
antimony, and arsenic51 are described; triphenylphosphonium
cyclopentadienylide has also been obtained s .
The dicyclopentadienyl compound of tetravelent vanadium has
been isolated in the form of the chloride and bromide.
The dichloride of dicyclopentadienylvanadium is paramagnetic,
dissolves in polar organic solvents, forms a green solution in water,
in which it decomposes rapidly upon addition of alkali; in acid
solution it is preserved for several hours. It is reduced by
LiAlH4 to. dicyclopentadienylvanadium, (C5H5)2V43.
The ion of the trivalent vanadium compound, (C5H02V?, oxidizes
rapidly in air20'28.
Dicyrclopentadienylvanadium, (C5H5)2V, is paramagnetic, rather
stable26, 2, is not decomposed by water, is hardly decomposed at all
even in acid medium, forms traces of ferrocene with FeC1228, reacts
with aldehydes, ketones, and maleic anhydride forming products which
were not investigated26, and with CO yields C5H5V(CO)4 0'169. The
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The data of X-ray crystallographic analysis indicate the "sandwich"
structurels9.
The dicyclopentadienyl compounds of pentavalent niobium and
tantalum2O were isolated in the form of salts:
(C5H5)2NbBr3, (C5H5)2Nb(OH)Br2 (diamagnetic), and (CsHs)2TaBr3
The infrared spectra of the dicyclopentadienyl compounds of V,
Nb, and Ta are consistent with each other and have bands characteristic
for "sandwich" compounds2os26.
Triphenylphosphonium cyclopentadienylide is obtained52 in the
reaction of bromocyclopentadiene with triphenylphosphine and
subsequent treatment of the reaction product with aqueous sodium
hydroxide. Ramirez and Levy52 calculate that the substance has the
ionic structure(XLI), The cyclopentadiene ring is aromatized.
Triphenyiphosphonium cyclopentadienylide is stable and almost
useless for the synthesis of olefins, in contrast to other phosphine-
methylenes, for example, (C6Hs)3P=CH2 and (C6Hs)3P=CHC6H5. In the
reaction of the cyclopentadienylide with benzenediazonium ion, azo
coupling takes place2 ?.
(C6H5)3P--4 e I +
C6H5N2X
CH3COONa,
- (C6H5)3 P--,/ A R + HX
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In acid medium, the azo compound (XLII) forms a salt (XLIII)
yielding upon hydrogenation compound XLIV, the structure of which
was proved by independent synthesise??.
4D P-C6Hs)3Bre
/.f ~..
N-NHC6H5
XLIII
H2
P9(CeH5)3GBr
" = N-NHC6H5
DICYCLOPENTADIENYL COMPOUNDS OF ELEMENTS OF
GROUP IV OF THE PERIODIC SYSTEM
Dicyclopentadienyl compounds of titanium19'2o,39,53 zirconium'9 "
tins', lead 54,59, and silicon56,57 have been obtained.
The salts of dicyclopentadienyltitanium (IV) cation (C5H5)2TiX2s
are diamagnetic19,2?'68, stable in air, dissolve in organic solvents
and water (hydrolyzes somewhat), and yield precipitates with the same
anions19a20 as do other cyclopentadienylmetal cations.
Attempts to acylate dicyclopentadienyltitanium bromide by the
Friedel-Crafts method gave no positive results20; it was also
impossible to isolate an alcoholate in the reaction with butyl
alcohol in the presence of pyridine2O. With phenyllithium,
dicyclopentadienyltitanium chloride forms diphenyldicyclopentadienyl-
titanium171,172, which gradually decomposes at room temperature.
(C5H5)2TiCl2 + 2CBH5Li -> (C5H5)2Ti(C6H5)2 + 2LiC1
By analogous means, meta- and para- (CH3C6H4)2Ti(C5H5)2 were
obtained. [g-(CH3)2NC8H4~2Ti(C5H5)2 172 and (CH3)2Ti(C5H5)2 70
are very unstable, yield lo.
Salts of dicyclopentadienyltitanium (III), (C5H5))2TiX, are
obtained by reduction of (C5H5?)2TiX2 electrolytically20 or with
LiA1H448.. The dicyclopentadienyl compound of divalent titanium53,
(C5H5)2Ti, is diamagnetic, decomposes in air, but can be preserved
well in an atmosphere of inert gas, is thermally unstable, upon
heating in an atmosphere of inert gas decomposes below its melting
point (--x130?),xeacts very slowly with water which does not contain
air, is transformed by dilute hydrochloric or sulfuric acid into
compounds of tetravalent titanium, and forms an etherate with
tetrahydrofuran. Solutions of dicyclopentadienyltitanium in
ammonia virtually do not conduct the electric current. In the
reaction of (C5H5)2Ti with FeC12 only traces of ferrocene are formed53.
The properties described for dicyclopentadienyltitanium and
also the similarity of infrared spectra19i ? of(C5H5)2TiBr2 with the
spectra of ferrocene and ruthenocene enable one to assert that
dicyclopentadienyl compounds of titanium are similar in structure
CONTINUED
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to ferrocene53.
Wilkinson and coworkers19a20 obtained dicyclopentadienylzirconium
(IV) bromide, (C5H5)2 ZrBr2, the properties of which have hardly been
studied; there is only the information that this compound is dia-
magnetic2O, the infrared spectrum is given, and mention is made of an
attempt at polarographic investigation-19.
Dicyclopentadienyltin, (C5H5)2Sn, and dicyclopentadienyllead,
(C5H5 2Pb, are organometallic compounds with an ordinary C-M bonds
(C5H5)2Sn is diamagnetic48, has a dipole moment of 1.01 debye59, and
reacts with maleic anhydride 45.. Cyclopentadienylphenyl compounds
of tetravalent tin have been described5 ; it was not possible to
isolate tetracyclopentadienyltin in pure form55.
Dicyclopentadienyllead is diamagnetic48, has a dipole moment of
163 debye59, is not hydrolyzed by water, but is easily oxidized in
air45..
Cyclopentadienyl compounds of silicon have been obtained:
(CsHS)Si(CH3)s and (CsH5)2Si(CH3)2 56,57
TRICYCLOPENTADIENYL COMPOUNDS OF ELEMENTS OF
GROUP III OF THE PERIODIC SYSTEM
Elements of group IIIcr the.periodic system in contrast to
others yield only tricyclopentadienyl compounds.
Thus tricyclopentadienyl compounds have been obtained for
scandium, yttrium, and the lanthanides-- lanthanum, cerium,
praseodymium, neodymium, samarium, gadolinium, dysprosium, erbium,
and ytterbium28'29. A hypothesis has been expounded, that in
these tricyclopentadienyl compounds the cyclopentadienyl rings are
arranged so that perpendiculars going through the centers of the
rings. intersect at the site of the metal atom and form angles of 1200
with each other58.
r
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The bonds between the rings and the metal are of the ionic type:
tricyclopentadienyl compounds of scandium, yttrium and the lanthanides
do not dissolve in hydrocarbons, react with FeC12 to yield ferrocene
in good yield, are decomposed by water 28,29; for a discussion of the
magnetic properties of these compounds seems.
Reynolds and Wilkinson58 obtained cyclopentadienyl compounds
of uranium and thorium. The dicyclopentadienyl derivative of
theorim was not isolated in pure form. in the reaction of anhydrous
ThC14 with cyclopentadieriylsoc:ium, a substance is formed in 1% yield
which is unstable in air and decomposes upon attempts to sublime it,
and which correspond atiproximately~ iii composition to to tracyclopenta-
dienylthorium, (C~H 4Th In the action of water upon this
substance an unstable solution is formed which nevertheless gives
precipitates with silicotun,gstic acid or with Reinecke's salt and
probably contains dicyclcpentadienylthorium. The infrared spectrum
of this compound recalls the spectrum of dicyclopentadienylzirconium,
which gives Reynolds and Wilk.nson the basis to suggest that in the
thorium compound there are'}--bonds between the rings and the metal58.
The cyclopentadienyl compounds of uranium are very interesting.
In the reaction of anhydrous UC13 with cyclopentadienylsodium, an
extraordinarily unstable compound is formed which does not contain
halogen and which corresponds approximately in composition to
(C5H5)3U. It was not investigated further58.
Upon reaction of cyclopentadienylsodium with UC14, the dark red
chloride (C5H5)3UC1 is formed in good yield. It decomposes in air,
but in an inert gas atmosphere is completely stable and withstands
heating to 3000. The paramagnetic moment of it corresponds
approximately to two unpaired electrons58. (C5H5)3UC1 does not
react with FeC12 at room temperature, but upon heating to 1000 for 8
days, it yields traces of ferrocene; it does not react with maleic
anhydride. Solutions of (C5H5)3UC1 in water which does not contain
oxygen give precipitates with silicotungstic acid, Reinecke's salt,
and other anions in a manner similar to that of the 'h'-dicyclopenta-
dienyl compounds of other metals.
All these data, and also the nature of the absorption spectra,
allow Reynolds and Wilkinson58 to calculate that in (C5H5)3UC1 there
are IT-bonds between metal and rings. The rings are oriented in
space just as in the tricyclopentadienyl compounds of the rare earth
elements (see above).
In the work of Reynolds and Wilkinson58 a calculation is shown
for the ion (C5H5)3Ua~, carried out by Moffitt by the molecular orbital
method.
Cyclopentadienylthallium (C5H5)T1 was obtained by Fischer49'173.
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CYCLOPENTADIENYL COMPOUNDS OF ELEMENTS OF
GROUPS I AND II OF THE PERIODIC SYSTEM
Cyclopentadienyl compounds of lithium, sodium, potassium and
magnesium have wide applicationsin organic synthesis, and, in
particular, are used to obtain ferrocene and compounds similar
to it (see "Methods of Obtaining Dicyclopentadienyl Compounds of
Metals").
Cyclopentadienyl compounds of elements of groups I and II are
ordinary organometallic compounds with an ionic or covalent bond
between metal and carbon and therefore will not be considered by us
in detail. We limit ourselves to mentioning the works which
appeared after the discovery of ferrocene in which methods are
described for obtaining cyclopentadienyl compounds of lithium175,
sodium174,175~ otassium174, rubidium, caesium173, calcium17s,176
ma esiuI1125-26.9168,P70.91649168 40' 57, 7o
~ , and mercury
It must be mentioned that dicyclopentadienylmagnesium is
arranged sterically in the form of a pentagonal antiprism similar
to ferrocene164, although the bonds between the magnesium and the
rings are ionic164.
The first attemptsto obtain a cyclopentadienyl compound of
divalent copper were unsuccessful, which was explained by the
presence in the copper atom of only one free d-orbital19. In 1956
Wilkinson and Piper 7, after a series of unsuccessful attempts to
prepare a cyclopentadienyl compound of copper by one of the general
methods of obtaining these compounds, found in one of the patents a
description of the synthesis of cyclopentadienyltripropylphosphine-
copper 77, C5H5CuP(C3H7)3s and by analogous methods (reaction of
P(C2H5)3 with a mixture of Cu2O and cyclopentadiene) prepared in
60% yield and studied in detail cyclopentadienyltriethylphosphine-
copper, C5H5CuP(C2H5)3. The Cu-C5H5 bond is probably covalent;
C5H5CuP(C2H5)3 does not react with water, dissolves in petroleum
ether, forms ferrocene with FeC12, reacts with maleic anhydride
(however the authors note that P(C2H5)3 also reacts with maleic
anhydride).
For the nuclear magnetic resonance spectrum of (CSH5)2Mg,
(CsH5)aHg, and C5H5CuP(C2H5)3 see7O.
IV. CYCLOPENTADIENYLCARBONYLS AND
CYCLOPENTADIENYLNITROSYLS OF METALS
It has already been mentioned above that in the reaction of
metal carbonyls with cyclopentadiene, cyclopentadienylcarbonyls of
metals are formed which can also be obtained by the action of
C5H5Li (or C5H5Na) on metal carbonyls, or by heating some dicyclo-
pentadienylmetals under pressure with CO.
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38'38s70s188,169s178'179s1800;1184
Cycloientadienylcarbonyls of iron '
cobalt36'16 '181'185,.manganese 35'36'46'70'169'181, mot bdenum34'35'70'
169,174,180 34'370'189'174'180'181 5'68'70'174'
tungsten , chromium
183, and vanadium 35'36'50'68'189 have been studied. Cycio entadienyl-
nitrosyls of metals are formed by the action of NO on (C5H512Me.
Cyclopentadienylnitrosyls of nicke138,70,186, manganese 70,1 7'188, and
chromium70'178'187 have been obtained, Cyclopentadienylcarbonyl-
nitrosyls of manganese36, chromium166, molybdenumlas'189 and Tungstenl8`
have also been described.
A discussion of the properties of these compounds demands a
separate review. We only mention the remarkable fact of the
existence of alkyl and aryl derivatives of iron 70'19?, mol bdenum70'
189, tungsten70,174 and chromium7O of the type (C5H5)Me(COy) R where
R=CH3, C2H5, or C6H5, n=2 for Fe or n=3 for Mo, W, and Cr.
Indene forms compounds similar in structure to ferrocene with
iron, nickel, cobalt, and ruthenium, but less stable.
Diindenyliron (XLV) is obtained in the reaction of indenyl-
lithium191 or indenylmagnesium bromide192 with FeC13.
+ FeC13
The black diindenyliron is diamagnetic, sublimes under high
vacuum at 120-130?, does not dissolve in water and does not react
with it, is rather stable in the solid state, but solutions of it in
benzene, ether, or alcohol rapidly decompose in air-91'192.
Diindenyliron is cleaved during oxidation, and one cannot
isolate191'192 the cation (C9H7)2Fe .
It must be-noted that the benzene rings in diindenyliron and
diindenylruthenium are more easily hydrogenated than the cyclopenta-
diene rings. Thus, in the hydrogenation of diindenyliron in the
presence of platinum, the liquid di(tetrahydroindenyl) iron is
formed114, which can be oxidized with hydrogen peroxide to the cation
(C9H11)2Fe~, which is precipitated in the form of a salt with the
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ion [B(C6H5)4 ]e.
H2/Pt H202
(C9H7)2Fe (C9H,1)2Fe
NaB(CeH5
a [(C9Hii)2Fe]4~ [B(C6H5)4]A
Concerning diindenylruthenium, (C9H7)2Ru, there is only the
indication of Fischer1s' ss , that upon hydrogenation of this compound,
the solid, diamagnetic48, almost colorless di(tetrahydroindenyl)
ruthenium is obtained. The dipole moment of diidenylruthenium is
zero59.
Diindenylcobalt is obtained similarly to cobalticene in the
reaction of Co(SCN)2(NH3)4 with indenylpotassium in liquid ammonia193:
2 C9H7K + Co(SCN)2(NH3)4 -~ CONH3)4(C9H7)2 + 2 KSCN
Co (NH3)4 (C9H7)2 -> Co(C9H7)2 + 4 NH3
The cation of diindenylcobalt, (C9H7)2CoQ) is also obtained in
a way similar to that of obtaining cobalticinium cation, by the
reaction of indenylmagnesium bromide with the acetylacetonate of
trivalent cobalt191 or with CoBr2 and subsequent oxidation with
hydrogen peroxide193.
Diindenylcobalt is oxidized by hydrogen peroxide or K2S208 to
the cation (C9HZ)2Co? which is very stable and resembles the cation
cobalticinium19 in its properties. In the reduction of
diindenylcobalt (III) perchlorate on the dropping mercury electrode
in a 0.1N sodium perchlorate solution, the half wave potential is
equal to -0.6V with reference to the normal calomel electrode, while
for cobalticinium perchlorate the half wave potential is - 1.16V..
Thus the addition of a benzene ring significantly decreases the
reduction potential; hence, the oxidation of neutral diindenyl-
cobalt to the cation must take place with greater difficulty191, than
that of cobalticene which was indeed observed by Fischer and
coworkers193. However, in the solid state as well as in solutions,
diindenylcobalt is stable only in the absence of air, sublimes under
high vacuum at 100-1200, and in contrast to cobalticene, it does
not dissolve in or react with water which has been saturated with:
nitrogen.
Debye crystallograms'92 and spectra191'192 of the diindenyl
derivatives of iron and cobalt indicate the structural similarity
of these compounds.
Diindenylnickel was obtained by the same methods as were used
for diindenylcobalt'93. Its properties were not described; mention
is made only of the fact that one unpaired electron has been
detected in it's for some unknown reason.
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German and Nelson194 note that the Ti-C bond with the indenyl
group is more stable than that with. the alkyl or aryl groups.
However, Wilkinson and Birmingham2O were not able to prepare the
individual diindenyl compound of titanium (C9H7)2 TIC a by the
reaction of TIC 4 with indenyllithium or indenylmagnesium bromide.
In Fischer's review article16 it is mentioned that diindenyl-
magnesium was studied by him in detail.
Tetraindenyltin195'196 and tetrafluorenyltinl96 are described,
as well as mixed phenylindenyl compounds of tetravalent tiny which
do not have structures similar to ferrocene.
No one has succeeded in obtaining fluorence derivatives simi-
lar in structure to ferrocene13.
VI. DIB:NZENECHIOMIUM: AND SIMILAR.CONY' OUNDS
In 1919-1920 Hetn204-207, by the action of phenylmagnesium
bromide on chromyl chloride and chromium salts, obtained a
series of chromium-organic compounds which from that time have been
considered derivatives of tri-, tetra-, and pentaphenylchromium.
After the discovery of ferrocene, Zeiss20a,203 expressed the
hypothesis , 2O7 that this ttimla flare derivatives
ferrocene -like mcmobtained pounds. by Thus
to tetraphenyl-and tripllenylchromium iodide he assigned respective-
ly structures (XLVII) and (X:LVIII)..
Cr I
Cry I0
The isolation of the corresponding amounts of benzene and
biphenyl upon reduction of (XLVII) and (?LVIII) with LIA1H42O8
served Zeiss as a proof of his hypothesis.
In 1955, Fischer 197 obtained dibenzenechromlum, the simplest
representative of the compounds in which a transition metal is
bound to two aromatic ring..
The dibenzenechromium (III) cation was synthesized173,19$ 199
by the so-called reductive Friedel-Crafts method:
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3 CrCa + 2A1 + AJC13 + 6C6H6 3[Cr(C6H6)2J AlC14
The reaction mixture was heated 15 hours at 1500 with careful
exclusion of the oxygen of the air. This method with some varia-
tions is general for obtaining similar compounds.
The cation can be precipitated in the form of the iodide198,
perchlorate'97, reineckeate197; picrate197, or in the form
[Cr(C6H6 )2 J? [C5H5 Cr(CO)a.le4 9 and [CrJC6H6 )2 J [ (C6Hs )4HJ
10 The reduction of the [Cr(C6H6)2J formed is accomplished by
sodium hydrosulfite (or other reducing agents) and leads to
electrically neutral dibenzenechromium in 39-60% yield:
2[Cr(C6H6)2J+ ? 5204_ + 4 0H' 2 Cr(C6H6)2 + 2 S03= + 2H20
The brownish-black dibenzenechromium198 is moderately soluble
in organic solvents, insoluble in water, sublimes under high
vacuum at 130-160?, has m.p. 2#54-2850, is easily oxidized to the
cations, and is thermally stable up to 300?. The cation is stable
198 in alkaline or neutral medium, unstable in acidic. [Cr(C6H6)2JOH
is a strong base197. The infrared spectrum of dibenzenechromium
has been taken'97. Cr(C6H6)2 is diamagnetic 48'98, (the cation
is paramagnetic', and its dipole moment is zero69. According to
x-ray crystallographic investigations200, dibenzenechromium has the
centrally-symmetrical "sandwich" structure (XLVI) with parallel
benzene rings and the chromium atom between them at the center of
the symmetry.
(ALVI)
Starting from these data, Fischer corn-ared dibenzenechromium
with complex compounds with ferrocene-like structures'98. Fischer
calculates 87,197 that the obtaining of dibenzene chromium is a
proof of his hypothesis as to the structure of sandwich-shaped
molecules.
In spite of the original suggestions of Fischer197, further
investigation showed201 that the benzene rings in Cr(C6H6)2 do not
retain their reactivity. Neither electrophilic, nor free radical,
nor nucleophilio substitution reactions proceed with dibenezene-
chromium.
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Fischer2O9 confirmed the Seuss hypothesis by obtaining?by his
method the bisbiphenylchromium (III) cation [Cr4.C6H5C6H5)2J and
by proving its identity with Hein's [Cr(C6H5)4j via precipitation
reactions and physico-chemical investigations.
By reduction of [Cr(C6Hi5C6H5)2j by means of formamidine-
sulfinic acid or salts of diaminomethanedisulfinic acid, the orange,
diamagnetic Cr(C6H5C6j5)2, melting at 112?, was obtained2O9. Hein
admitted 21? the correctness of this interpretation of his sub-
stances and.improved his method of synthesis of biphenylbenzene-
chromium (III) iodide (from C6H5 Mg3r and CrC13) and reduced this
compound to (C6H5C6H5) Cr(C6H6)211,212' and also showed by means
of paper chromatography 213 that dibenzenechromium can also be
obtained by the Grignard reaction. Later Seuss214 sug es et the
reaction of C6H5 Mg Br with CrC13 or CrO2C12 as a means of obtain-
ing dibenezenechromium and showed that in the reaction process
intermediate substances are probably formed of the type (C6H5 MgBr)2
CrCl or (C6H5 CrC12'2 CrCl, since carboxylationGof the reaction mix-
ture before hydrolysis led to [(HOOC C6H5)2 CrjJ .
Fazuvaev and coworkers215,218 accomplished the photodecomposi-
tion of Heins "tetraphenylchromium (III) iodide" (XLVII) and
pentaphenylchromium (III) hydroxide"
Cry OC6H5 (XLIX)
in which process the isolation of corresponding quantities of
phenol and biphenyl showed the correctness of the Fischer structures.
Besides the dibenzene-, bisbiphenyl-, and biphenylbenezene-
chromium already described, in one of FischerTs works'98 dimesity-
lenechromium,. di-(p-xylene)-chromium, ditetralinchromium, di-(hex,
amethylbenezene)-chromium, and ditoluenechromium are mentioned;
however detailed data about these compounds are absent thus far.
It is only known that their cations are paramagnetic while they
themselves are diamagnetic48 and also that ditoluenechromium,
like dibenzenechromium, does not take part in substitution reactions
202. The dipole moment of ditoluenechromium is zero59(
In group VI of the periodic table, besides chromium compounds,
molybdenum compounds are described. Dibenezenemolybdenum216 is
obtained from MoC15 and benzene in the presence of Al and A1C13
(15 hours at 120?) with subsequent reduction of the cation with
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formamidinesulfinic acid. The green Mo(6H6)2 ignites spontaneously
in air, decomposes without melting at 1150, sublimes under high
vacuum at 90_100?, is readily soluble in organic solvents, and is
diamagnetic48.- The dibenzenem@lybdenum (III) 8ation is precipitated
Q17 in the form of [No(C6H6)2J [C5H5 Mo(CO)3J
According to the latest data199 the best method of going from
[Mo(C6H6)2J to No(C6H6)2 is the reaction of disproportionation in
strongly alkaline medium:
6[Mo(.6H6)2J~D + g OHa 5 Mo(C6H6)2 +
+MoO4= + 2 C6H6 + 4H20
The obtaining of dimesityler-emclybdenum is merely mentioned
in the literature 16.. Also mentioned is the possibility of syn-
thesis of dibenzenetungsten173,217.
In group VII of the periodic system therdoubly.charged,-=++
diamagnetic dimesityleneiron (II) cation l ;Fe[C6H3 (CH3)3J2
is described in detail. It is obtained by the reduction at 9O_900
of FeBr2 with mesitylene and A1913. The reductant Al is not neces-
sary here, since the charge on the Fe++ ion does not change. The
cation is stable in weakly acidic medium, unstablg in alkaline.,
and is precipitated by the gollowing anions: PF6 , [B(C6n5)4J ,
IQ, C10 4W, [Cr(SCN)4 (NH3)-J-, and SnCl3e 217. It was not possible
to reduce the cation.
The dibenzeneiron (II) cation, [Fe(C6H6)2J++, could not be
isolated although it is probably formed217. The possibility is
mentioned- of obtaining ditetraliniron(IL) and di-(th-xylere) iron
(12)217; compounds of FSu,Co, and Hh199are also being investigated...
In Group V of the periodic system, dibenzenevanadium, V(C6H6)2
has been obtained 173,199. This compound is Immediately isolated
in the uncharged form. The authros explain this by the fact that
in the given case the reaction of disproportionation proceeds
easily:
V C14 + Al + 2 C6H6 A1C13_
[V (C6H6) 2 J? [ A1C14 Je
5 [V (C6H6)2J H20) 4 V(C6H6)2 + 2 C6H6 + V+++++
The reddish-brown dibenzenevanadium is easily oxidized, there-
upon decompsIng (the cation Is unknown). It is soluble in organic
solvents, melts at 277-278?,:decomposes at 3300, is paramagnetic,
and its infrared spectrum is similar to the spectra of the diben-
zene derivatives of chromium, tungsten and molybdenum.
Mention is made of the obtaining of dimesitylenevanadium for
which the cation has also been isolated in the form of the salt
~V[C6H3(CH3)3J2~? [AlCl4 )e 199
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Fischer assigned the sandwich structure to all such compounds
obtained, which in some cases is supported in sufficient detail
by physico0chemical measurements, and an electronic structure
similar to that of ferrocene was also assigned to these compounds.
In other words, in all the compounds studied Fischer suggests a
bond between the aromatic rings and the atoms of the transition
metals such that the 11-electrons of the rings enter into the
orbitals of the metal, forming six bonds (three on each ring).
Magnetic measurements in all cases formally agree with this hypo-
thesis.
Data, obtained for the more thoroughly investigated group VI
of the periodic system, show that the stability of the compounds
studied drops in the series Cr Mo W. that is with increase in
the atomic number of the metal200. As for the organic portion
of the molecule, the most stable of all are the compounds with
mesitylene217.
It can hardly be doubted that in ferrocene and the compounds
of the dibenzenechromium type, the nature of the bonding between
the metal and the organic part is related. However all data
indicate that this bond is not as stable in the dibenzenemetals as
in the dicyclopentadienyl.metals.
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Literature
1. A. N. Nesmeyanov, Uspekhie Khimii 14, 261 (1945).
2. F. A. Cotton, Chem. Revs. 55, 551 (1955).
3. J. A. Wanklin, L. Carius, Ann. 120, 69 (1861).
4. N. V. Kondratyev and D. A. Fomin, Journ. Russ. Phys. Chem. Soc.
47, 190 (1915).
5. A. Jobet, R. Reich, Comptes rendus 174, 1358 (1922).
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TABLE 1
Cyclopentadienyl Compounds of Metals
1
Group in
Cyclopentadienyl
Method of-'
Yield %
Literature
the
Compound*
Obtainingi
Reference
Periodic
System
t
VIII
(CsHS)2FeIIIX
Oxidation
,41
(C5H5)2FeII
34,52
10,17,42
almost quan-1
21
titative
85-90
26
84188
21,2 6,37
24-30
11,40
(CsHS)2CoIIIX
(CsHs)2CoII
(CSHS)2NiIIIX
(CsHs)2NiII
65
C
75-80
26
D
3
E
10
21
F
26
reduction
85
43
oxidation
A
19
42
45
60-70
31
traces
21
26
CONTINUED
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 Approved For Release 2009/03/26: CIA-RDP80T00246AO08000080002-3
V BL I (Continued)
Group in Cyclopentadtenyl {
Method of Yield % Literature
the Compound
Obtaining ! Reference
Periodic
System
VIII
( C H Ru IIX
Oxidation
23
(CcH RuII
B 20
23
CH Rh"X
B
24
C H IrIIIX
B
2
C H Os
1
VII
(C5H5)2 MnII
A
50
25146
25'
D
low
46
(C H ReIIIH
C
20
4
I
II
VI
X
(C H Cr
Oxidation
4904q
C5H5)2 CrII
C
70-80 1
26,27
D
low I
3
E
0
4
C1HF MoVX
A
2
(C5H5)2 MoIVX2
A !
27
C
27
(C5H5)2 WVX3
A
27
C
27
V
(C5H5 )2VNX2
A
16
199,20
C
6
20
(C.;HF VIIIX
Reduction
20
(C5H5)2VII
A
50-60
50
C
75
26
Seduc
tion
70
4
(C5H5)2NbVX3
C
70
20
-Copt
nued-
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 Approved For Release 2009/03/26: CIA-RDP80T00246A008000080002-3
TABLE I (Continued)
Group in
the
Periodic
System
Cyclopentadienyl
Compound
Method of Yield %
Obtaining
(C
H
)2TaVX3
19
A
5
5
2 i
C 6
H~)~BSIII
(CsHS) b III
(C,HS3AsIII
Literature
Reference
20
20
(CcH4 )PV(C6H~
(C5H5)aTi IV Xa
in
(CSHG 2TjII'X
Deduction
(C,,HS)2TiII C
(CH)2Z n A2
C H PbII C 2r- 4 4
C H SnII C 0_60 4
C H SnIV ( C H
r) r.
CSH )w SiN(CH:4)4_r
56.57
III
C HCIII
75
215.29
T T T
5
9r;
2 29
k(C,H,,)~LaIII
25
28,29
C Hti CeIII
_72
28. P
III
(CFH9)3Pr
A-3-
25.29
1(C5H.,)3NdIII
79
2#5,29
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 Approved For Release 2009/03/26: CIA-RDP80T00246A008000080002-3
TABLE I (Continued)
Group in Cyclopentadienyl Method of
the { Compound (Obtaining
Periodic
System
The
`(C5H5)aSmIII
1(C5H5)3GdIII ! C
(C5H ybIII
TCH TnN
CcH UIVX
CcHS sUIII
"Cyclopentla.dienyl
Yield % Literature
Reference
(CaH~, )T1.
I
I and II
See
groups I
and II of the Periodic
Rom n numberal indica
the formal
in theyclopeniraO.inJzyl compound. X is
In dime hylformam2.c7.c
Es of Elments of
yst2m?"
alence oft the metal
d moral ant anion.
Compo
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58
 Approved For Release 2009/03/26: CIA-RDP80T00246AO08000080002-3
T"BLE 2
Carbonyl Compounds of
the Ferrocene :series
GOTH GU D I , in ?C Method lield,%
Obtaining
1eference
C5H5 Fe C5H. CHC 1 120-123
(C5H5)2Fe +POC-(3 + CH3 N(CI_1C(C6H5 7G; 55_
122,123
transition 45; 124,5
(C5H5)2 e +M iOCk.3 + (Oh3)2 N(+G) 23
119
130_132
(C5h5)Fe C5I-5 CH2OH +1"n02 98
.147, 149
Oxime
91-93
76
147
transition 98; 133-
77
119
135
123
138_11}O
" Oximeacetate
9O-91
147
semicarbazone
200
123
203_2C4 dec.
59
119
217-219 dec.
147
" 2,4-dinitrophenyl.._
hydrazone
dec. 248
123
isonicotinylcarba_
zone
212-213
39
119
azine
245
47
119
rhodanone
245 dec.
70
119
Literature
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 Approved For Release 2009/03/26: CIA-RDP80T00246AO08000080002-3
Compound
C5H5I'e C03(CH3 )CHO-1f
C5H5Fe .C5H4 CCH3
C5ri5.1k'e- 5h.a (COCH3)2-
1,2
Fe(C5H4 1:(11.13)2
T-,-.BL.' 2_ (CC::TIfiU_D)
0
in C
85-96
169.170
198-201
105_106
130_131
200 dec.
Method of Cbtainin;:. field,I
Oxidation of C5I`5i1e C5H3 (CH3) H2
CH
(C5H5)21'e. + (C?{:3000)4 i.. ("n 04
5 ?5)2Fe +(CH3CC)2O(EI''Cr3)
(C5Hc )2i'e + (CH3CC)2C (H31 G4 )
(C5`+ (CH3CO)2G (~D-'3 )
(C5H5)2Fe + (CH3CO)20 (HF)
( ;5H5) Fe + C5H4 HgC.+ C;1"3 COCA'
(C5H5)2Fe + CH3 CC (;X WCk3)
(C5H5)2Fe + CH3 CCi3r (K C, 3)
n + (CH3CC)20 (~QC