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Formation and Properties of Carbosilanes.

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(R = alkyl) presumably involves the direct participation
of the triple bond, and, as with the allene derivatives,
proceeds via a vinyl cation (99). This is supported by
the fact that, despite the strong inductive effect of the
triple bond, the rates of solvolysis of the acetylene
derivatives (98), R = alkyl, are only slightly lower
than those of the corresponding saturated compounds.
The formation of the cyclobutanones (100) could
also be explained by addition of the solvent to the
triple bond and subsequent homoallyl rearrangement.
In the presence of Hg2+ salts, which are known to
catalyse the addition to the triple bond, solvolysis of
(98), R = alkyl, leads mainly via ( l o r ) , R = alkyl, to
cyclopropyl ketones (102), R = alkyl. This indicates
that the uncatalysed solvolysis of (98), R = alkyl,
proceeds via a direct participation of the triple
bond [1121.
Conclusion
The present survey of the reactions of cyclopropylmethyl, cyclobutyl, and homoallyl compounds has had
to be confined to selected typical examples. The large
number of articles published even very recently shows
that this field is not yet closed. The present article has
been concerned only with cationic reactions. No
mention has been made of numerous publications e.g.
from the steroid field, or of the interesting rearrangements of carbanions, free radicals, and carbenes [la].
Finally, it should be pointed out that cyclizations
involving a double bond have been observed, not only
with homoallyl compounds, but also with other
unsaturated systems [ * c , 1131.
We are grateful to the Deutsche Forschungsgemeinschaft and to the Fonds der Chemischen Industrie for
their support of our own work, which was carried out by,
Helmut Allmendinger, Heinz Eggensperger, Klaus Giirler, Jiirgen Hafner, Inge Herterich, Rudolf Hiittinger
Sungrong Kang, Wolfgang Keberle, Karl Riedlinger,
Hans-Jorg Schneider, Helga Schneider-Bernlohr, and
Volker Vott.
Received: June 27th, 1966; revised: February 23rd, 1967 [A 586 IEi
German version: Angew. Chem. 79, 709 (1966)
Translated by Express Translation Service, London
[112] M . Hanack, I. Herterich, and V. V f f t t ,unpublished.
[I 131 P. D . Bartlett, Liebigs Ann. Chern. 653, 45 (1962).
Formation and Properties of Carbosilanes [*I
BY G . FRITZ [*I
The present paper describes the formation of silicon-carbon compounds (carbosilanes),
the moIecular skeletons of which consist of alternate Si and C atoms, and which can
be obtained by thermal decomposition of Si(CH3)4, CH3SiCI3, (CH3)2SiCIz, and
(CH3)3SiCl. The description of the formation of carbosilanes is followed by a discussion
of the reactions of polychlorinated carbosilanes with organometallic compounds.
1. Synthesis of Carbosilanes by Pyrolysis
Carbosilanes are compounds with alternate Si and C
atoms in their molecular skeletonrz]. They may be
open-chain or cyclic compounds,e.g.(C13Si-CH2)2SiC12
(1,1,1,3,3,5,5,5 - octachloro - 1,3,5 - trisilapentane) or
(SiC&-CH2)3
(1,1,3,3,5,5-hexachloro-1,3,5-trisilacyclohexane). The work described in this article arose
from experiments in which compounds containing SiH
were pyrolysed and made to react with hydrogen
compounds of other elements [31. Such reactions can
I'] Prof. Dr. G. Fritz
Institut fur Anorganische Chemie der Technischen Hochschule
Englerstrasse 11
75 Karlsruhe (Germany)
[I] Lecture at the 151st National Meeting of the American
Chemical Society in Pittsburg (USA) on March 28, 1966, on the
occasion of the presentation of the ACS Frederic Stanley Kipping
Award, 1966.
[2] G . Fritz, J. Grobe, and D. Kummer, Advances inorg. Chem.
Radiochem. 7, 349 (1965).
Angew. Chem. internat. Edit.
1 Vol. 6 (1967) / No. 8
in fact be carried out once H atoms and silyl radicals
have been produced, as is shown by the formation of
numerous organosilicon compounds on reaction of
SiH4 with ethylene 141 and with vinyl chloride fS1 above
400 "C, as well as by the reaction of SiH4 with PH3 to
form H3Si-PH2 and other silylphosphines 161. Since
these and other observations on silicon chemistry
pointed to the possibility of obtaining complicated
silicon compounds from simple compounds by freeradical reactions, we tried to utilize the thermal cleavage
of Si-CH, and C-H groups for the synthesis of
silicon-carbon compounds.
The Si-C bond in simple alkylsilanes is much more
stable to heat than the Si-H bond"]. The thermal
[3] G. Fritz, Fortschr. chem. Forsch. 4 , 459 (1963).
141 G. Fritz, Z . Naturforsch. 7b, 207 (1952).
[5] G. Fritz, Z. Naturforsch. 76, 379, 507 (1952).
161 G. Fritz, Z. Naturforsch. 8b, 776 (1953); Z. anorg. allg. Chem.
280, 332 (1955).
[7] G . Fritz, Z. anorg. allg. Chem. 273, 275 (1953).
677
decomposition of Si(CH& o r Si(C2H& can be
readily followed only above 650 "C 181, whereas Hz is
split off from the Si-H groups at 400°C. When the
alkylsilanes are heated for several hours in the gaseous
phase at about 700°C, they are almost completely
decomposed, with deposition of silicon, carbon, silicon
carbide and similar products, while hydrogen and
lower hydrocarbons (mainly methane) escape. However, if the pyrolysis mixture is removed from the
reaction zone after a short time and cooled, the
primary radicals produced in the gaseous phase can
form a series of silicon compounds191. The products
are mainly compounds having an Si-C-Si skeleton.
The proportion of high molecular weight compounds
in the reaction mixture increases with rising pyrolysis
temperature and with increasing residence time in the
reaction vessel.
To prepare these products in reasonable quantities we used a
system consisting of a storage vesseI containing tetramethylsilane or methylchlorosilanes, a rotary pump (to transport
the evaporating starting material through the reaction vessel,
which is heated in a furnace), and traps situated under the
reaction vessel to collect the reaction products [9,101. Since
the pressure in the reaction vessel very quickly reaches atmospheric pressure, owing to the relatively high vapor pressures of tetramethylsilane and of the methylchlorosilanes,
the conditions remain constant so long as the storage vessel
still contains liquid starting material.
2. Treatment of the Pyrolysis Mixture
The pyrolysis mixture was worked up by distillation
followed by gas chromatography [lo]. Approximately
half of the pyrolysis mixture can be distilled off and
resolved into more than 50 compounds, each of which
accounts for between 0.01 and 1 0 % of the total
pyrolysis product. The undistillable residue consists
of higher silicon compounds. The liquid fraction also
contains very small quantities of lower hydrocarbons
(up to hexane). All the higher fractions contain
silicon compounds having large molecules and with
several Si atoms. The principal gaseous products are
hydrogen and methane. The products containing more
than two Si atoms per molecule are listed in Table 1.
The higher products (> 5 Si atoms per molecule) in
the undistillable residue, which account for about
50 % of the reaction mixture in the pyrolysis of
S i ( C H 3 ) 4 , are particularly interesting. Before being
further investigated, the residue must be resolved into
pure compounds. However, this cannot be achieved
by distillation or by gas chromatography, particularly
since further reactions take place when the pyrolysis
mixture is heated above 280 "C. In order to isolate and
investigate further the various compounds, and t o
study, firstly, the influence of the reaction conditions
on the composition of the pyrolysis mixture and,
secondly, the secondary changes of the pyrolysis
181 D. F. Helm and E. Muck jr., J. Amer. chem. SOC. 59, 60
(1937); E. Wuring, Trans. Faraday SOC. 36, 1142 (1940).
191 G. Fritz and B. Ruube, Z . anorg. allg. Chem. 286,149 (1956);
299, 232 (1959).
[lo] G. Fritz and J. Grobe, 2. anorg. alig. Chem. 315, 157 (1962).
678
-
Table 1. Compounds formed on pyrolysis of Si(CH,)d (700 "C, residence time in reaction vessel
1 min).
Compound
(CH3)zSi-CHz-SiH(CH,)2
l11,3,3-Tetramethyl-l,3-disilacyclobutane 1111
(CHI)~S~-CH~-S~(CH~)~
1,1,3,3-Tetramethyl-l,3-disila4-cyclopentene [12]
C~HSS~(CHI)~
1,I .3,3,5,5-Hexamethyl1,3,S-trisilacyclohexane
1 .I ,3,3,5-Pentamethyl1,3,5-trisilacyclohexane
[(CHp)zSi-CH21,Si(CHs)z
1,3,5,7-TetramethyI1,3,5,7-tetrasilaadamantane
Si~Cd34
Si6C14H36
Si7C18H46 1131
S~~CZOHSO
Si~C24H66
Si9C27H74
SbC16H36
SbCi9H46
B.p.
( "C/mm)
(m.p. ( "C))
Proportion
of total
PyrolYSis
product
(v0l.- %)
120/768
122.8/745
2.4
3.2
135.5/750
138.5/745
6.9
0.7
172/745
205/745
5.6
7.5
201/767
7.5
206/760
103/1
7.5
10.1
(m.p. 122)
126-132/1
150--153/1
170- 195/l
200--230/1
230-240/1
245-300/1
Compound (12) consists of three six-membered rings with alternating
Si and C atoms. The Si valences that are not involved in the skeleton are
occupied by CH3 groups or by an H atom, while the carbon valences are
satisfied by hydrogen atoms. (16) and (17) consist of six-membered
rings in a three-dimensional arrangement and joined by Si-C groups.
The entire skeleton consists of alternate Si and C atoms. The Si valences
that are not involved in the skeleton are occupied by CH3 groups and
the carbon valences by H atoms [14al.
products, it was necessary to develop new chromatographic methods for their separation. A considerable
proportion of our work was devoted to the solution
of these problems.
2.1. Chromatographic Separation of the Pyrolysis
Products
Preliminary experiments showed that after the
distillable fractions have been removed, the higherboiling products of the pyrolysis of S i ( C H 3 ) 4 can be
separated into three groups on alumina columns. The
first group (A) is not adsorbed on the column from
a solution of the reaction mixture in benzene. The
second group (B) can be eluted with benzene, and the
third group (C), which remains in the column on
elution with benzene, can be washed out with benzenemethanol mixtures. Group C can be further resolved
on the column by successive elution with benzenemethanol mixtures having increasing methanol contents1141 (cf. Fig. 1).
Group A can be further resolved on an alumina
column with pentane. This group includes two crys[ll] G. Fritz, W . Kemmerling, G . Sonntag, H. J . Recker, E. A . V.
Ebsworth, and J. Grobe, 2. anorg. allg. Chern. 321, 10 (1963).
[12] G. Fritz, D. Kumrner, and G. Sonnfug, 2. anorg. allg. Chern.
342, 114, 121 (1966).
[I31 G. Fritz and J . Grobe, Z . anorg. allg. Chem. 299, 302 (1959).
1141 G. Fritz and D . Wick, Z.anorg. allg. Chern. 342, 130 (1966).
(14af G. Fritz, H. Kohler, and. H. Scheer, unpublished.
Angew. Chem. internat. Edit. 1 Vol. 6 (1967) I No. 8
0
h
Ln
I
I
I
I
I
I
I
I
A
50
rn
f
l
u
Fig. 1. Resolution of group C of the products from the pyrolysis of
Si(CH,)* (A1203 column neutral activity grade I, length 66 cm, diameter 3.5 cm) with benzene-methanol mixtures (140: l , 120: l , 100: l ,
80:1, 70:1,60:1, 50:1,40:1, 30:l); volumeofsolvent per fraction: 51.
Ordinate: quantity m of substance eluted (mg);
Abscissa: number of fractions n.
The quantities of the various fractions were determined after the solvents had been distilled off.The molecular weights are given against the
broken lines and the atomic ratios found by elemental analysis are given
in many cases together with the empirical formulae. These empirical
formulae are "averages" since it is not yet known whether the fractions
were pure [141.
talline substances (Si7C&36 and Si9C19H40, (16) and
(17) in Table 1). The solid products formed on
pyrolysis of Si(CH3)4 are deep brown, and fluoresce
in organic solvents. The fluorescence of individual
compounds and mixtures becomes more clearly
visible on separation and further resolution of the
groups, and can be used as a means of following the
separation processes [141, particularly in the case of
the compounds of group B.
2.2. Changes in the Pyrolysis Products on
Distillative Separation
The development of the chromatographic separation
method makes it possible to study the secondary
changes that take place on distillation of the pyrolysis
mixture. These changes can be represented as follows
(see Table 2) [14,151:
The products formed when Si(CH3)4 was heated were distilled
in a high vacuum t o remove as much as possible of the more
volatile products, the temperature of the pyrolysis mixture
not being allowed t o exceed 20°C (Column 1). A second
portion of the original pyrolysis mixture was then freed from
all the components that distilled off up to 210 "Cjl-2 m m Hg;
to achieve this, it was necessary t o heat the pyrolysis mixture
to 200-260 O C (Column 2). Part of the residue was distilled
further to remove all the components that distilled off up to
260 "Cjl m m H g ; this involved heating the pyrolysis mixture
to 340-400 OC (Column 3). Part of this last residue was heated
for 4 hours at 430 t o 450 OC (Column 4), and part for 5 min at
600 "C (Column 5).
The composition of the pyrolysis mixture clearly
becomes more complex with rising temperature on
separation by distillation, since the quantities of high
molecular-weight components increase rapidly. This
is particularly true of the substances of groups D and
E, which are initially almost entirely absent. The
quantity of substances of group C also increases (but
without formation of insoluble products) when the
temperature in the distillation vessel is raised from
260 to 400°C. Group B forms only a very small part
of the mixture; this group appears to be formed only
on heat treatment, and is destroyed again when heated
further.
The investigation showed that the mixtures of higher
molecular-weight compounds formed on pyrolysis of
tetramethylsilane are simpler than was originally
thought, and that complex chemical changes take
place on distillation of the reaction mixtures.
To obtain an insight into the secondary changes that
take place on distillation of the pyrolysis mixture, the
thermal stabilities of a number of substances and
groups of substances were studied. The temperature
ranges in which changes begin were determined, and
the changes were followed by means of molecularweight determinations. The gases formed during the
heat treatment were collected with a view to obtaining
[15] C. Fritz and N. GGfz, unpublished.
Table 2. Composition of the pyrolysis products of Si(CHd4 after being heated to various temperatures. After
heat treatment the mixture was cooled and resolved by chromatography.
u p to
20°C
Col. 2
Heated for
10 h a t
200-260 "C
Col. 3
Heated for
5 h at
340-400 "C
-
48
11
515
1:2.8:5.0
traces
550
1:3.6:5.4
0.56
800
-
550
10
Col. 1
Group
Proportion of total
pyrolysis product
(v0l.- %)
Molecular weight
Si:C:H
Proportion of total
pyrolysis product
(v0l.- %)
Molecular weight
Proportion of total
pyrolysis product
(vol. - %)
Molecular weight
Si:C:H
Proportion of total
pyrolysis product
(v0l.- %)
Proportion of total
pyrolysis product
fv0l.- %)
40
30
770
1:2.8:4.0
10
-
0.2
Col. 5
Heated for
5 min at
600 "C
1.4
-
26.5
660
1:3.3:6.5
40
[a] Mixture of substances of higher molecular weight.
Col. 4
Heated for
4 h at
430-450 "C
1370
62.3
-
not
determined
85
[bl Low solubility in benzene.
Angew. Chem. internal. Edit. J Vol. 6 (1967) J No. 8
679
information about the processes which bring about
the increase in molecular size. The substances used in
the investigation were an untreated reaction mixture
from the pyrolysis of Si(CH3)4, the substances of group
A obtained by column chromatography of the pyrolysis mixture, and the compounds Si4C10H24 [Table 1,
(9)1, Si9C16H36, and ((CH3)3Si)zCH2 [Table 1, (3)l.
The experiments showed that the untreated pyrolysis
mixture changed appreciably even when heated to
about 400 "C (increase in the average molecular
weight, formation of benzene-insoluble components;
group E), while only small quantities of gas are formed.
When a sample of the pyrolysis mixture was heated
at 430 to 490 "C for 46 hours, 72 % of the product was
converted into benzene-insoluble residues, with formation of only very small quantities of methane and
hydrogen. The separated group A exhibits similar
behavior only at about 230°C, though no benzeneinsoluble material is formed [151.
On the other hand, Si4C10H24, which has a tetrasilaadamantane skeleton (9), was found to have an
extremely high thermal stability, and showed practically no change when heated for 37 hours at 520 to
540 "C. No extensive decomposition occurred, even
when the substance was heated at 550 to 560°C
(70 hours). Marked decomposition is observed only
at 580"C, and after 24 hours at this temperature a
benzene-insoluble residue can be isolated \about 33
By far the greatest part of the benzene-soluble fraction
consists of unchanged Si7CloH24.
x).
The crystalline compound Si7C16H36, the structure of
which has not yet been fully elucidated, resembles
Si4C10H24 in its thermal stability. It shows practically
no change after 54 hours at temperatures up to 490 "C,
and forms an insoluble residue (42 % of the original
substance) only when heated at 560 "C (55 hours); the
benzene-soluble fraction still contains the unchanged
compound. The decomposition temperature
of
[(CH3)3Si]zCH2 is about 500 "C, i.e. somewhat lower
than that of the more symmetrical, crystalline compounds Si4C10H24 and Si7C16H36.
These investigations 1151 show that the observed molecular-weight changes in the pyrolysis mixtures are due
to changes in carbosilanes of a few structural types.
3. Synthesis of Chlorinated Czubosilanes by
Pyrolysis
Many carbosilanes of various molecular weights are
obtainable by the pyrolysis of tetramethylsilane. Most
of these compounds are unreactive, since they contain
no functional groups. However, compounds with the
same basic skeleton, but with reactive groups attached
to the Si atoms, are required in many investigations.
Compounds of this nature can be obtained by the
pyrolysis of the three methylchlorosilanes [161. The
thermal decomposition of the methylchlorosilanes is
1161 G . Fritz, D. Habel, D. Kummer, and G. Teichmann, Z. anorg.
allg. Chem. 302, 60 (1959).
680
reasonably fast at about 700 OC. The pyrolysis products
are obtained in useful amounts by the principle used
in the pyrolysis of tetramethylsilane. Of the products
formed on pyrolysis of (CH3)3SiCI, some 60 v01-x
consist of fractions that boil at temperatures between
163 and 200°C at normal pressure, while 40 vol-%
are oily and solid fractions that dissolve in non-polar
solvents. About 85 P: of the pyrolysis products of
CH3SiC1 are colorless liquids, while 15 % are oils or
solids that are fusible and colored. All the compounds
that were formed on pyrolysis of the three methylchlorosilanes and that have boiling points below 250 "C
have been detected by gas chromatography, and their
relative proportions have been determined [17,*81.
The carbosilanes obtained from the methylchlorosilanes are listed in Table 3. All the possible chlorinated
and methylated compounds having the basic structure
Si-CH2-Si have been isolated from the pyrolysis
products of (CH3)3SiCI. The distribution of the 1,3disilapropanes (I 7) to (26) in the pyrolysis products
of the three methylchlorosilanes are compared in
Table 3. The 1,3-disilapropanes accounted for 32 %
of the total pyrolysis product from (CH&SiCl, 43 %
of that from (CH3)2SiC12, and 60 % of that from
CH3SiC13.
4. Reduction of the Chlorinated Carbosilanes
In order to investigate the high molecular weight
products from the pyrolysis of the methylchlorosilanes,
it was necessary to separate the various compounds
from the mixture. However, even for substances
containing three Si atoms per molecule, the distillative
separation of Si-chlorinated carbosilanes is difficult,
owing to the high boiling points of the compounds.
The chromatographic methods are also unsuitable for
the same reason. Attempts were therefore made to
replace the chlorine by hydrogen in Si-chlorinated
carbosilanes by treatment with LiAlH4. The corresponding compounds with SiH groups boil at lower
temperatures, and can be separated by distillation
and gas chromatography. The hydrogenation takes
place with no change in the Si-C-Si skeleton, as was
shown by the investigation of Si-chlorinated 1,3disilapropanes having known structure, and of
1,1,3,3,5,5-hexachloro-1,3,5-trisilacyclohexane, (30),
which crystallizes well 1191.
The fractions of the pyrolysis products containing the compounds (27) to (40) were hydrogenated. Comparison of the
proportions of the various compounds in the hydrogenated
pyrolysis mixtures shows that the tendency toward the formation of six-membered rings with alternating Si and C atoms
increases with the number of SiCH3 groups in the starting
compound.
In the high molecular weight compounds formed o n pyrolysis
of the methyichlorosilanes, the Sic1 groups can again be converted into SiH groups without modification of the skeleton,
[17] G . Fritz and D. Ksinsik, Z . anorg. allg. Chern. 304,241 (1960).
[18] G. Fritz and D . Ksinsik, Z. anorg. allg. Chem. 322,46 (1963).
1191 G. Fritz, H. J. Buhl, and D. Kummer, Z. anorg. allg. Chern.
327, 165 (1964).
Angew. Chem. internat. Edit.
Vol. 6 (1967) 1 No. 8
Table 3. Carbosilanes from the pyrolysis of CHSiCl3, (CH9zSiCI2, and (CH3)3SiCI. The compounds containing Sic1 groups and the SiH compounds
obtained from them by hydrogenation with LiAIH4 are listed together.
Sickcontaining compound
in pyrolysis mixture
B.P.
[ "Clmm)
of the
SiH-comp.
Hydrogenated compound
Parts by volume in the pyrolysis
nixture from
ZH3SiCI3
I
(CH3)2SiCIz/ (CH,)$iiCI
with respect to (CI3Si)zCHz = 100
17/757
70.5-7 11768
(2 :3)
(30)
(31)
(32)
(33)
(34)
(35)
(36)
(37)
(38)
0.8
33
23.7
10.7
-
1031768
1201768
H3Si-CH2-SiH2-CH2-SiH3
ClsSi-ClJ-SiC12-CH2-SiCI3
C I ~ S ~ - - C H ~ - S ~ C I ~ - C H Z - S ~ C ~ ~ ( C HH~~) S ~ - C H ~ - S ~ H ~ - C H Z - S ~ H ~ ( C H ~ )
[a]
C13Si-CHz-SiClz-CHz-SiCl(CH3)2 la1 H,Si-CHz-SiHz-CHz-SiH(CH&
[CH~)JS~-CH~-S~(CH,)~
1,1,3,3,5,5-Hexachloro1,3,5-Trisilacyclohexane
1,3,5-trisilacyclohexane
CI~S~-CCHZ-S~CIZ-S~(CH~)~
[a]
H3Si-CHz-SiHz-CH2-Si(CH3)3
[a]
1,1,3.3,5-Pentachloro-5-methyl1-Methyl- 1,3,5-trisilacyclohexane
1,3,5-trisilacyclohexane
1,1,3,5-Tetrachloro-3,5-diniethylI ,3-Dimethyl-l,3,5-trisilacyclohexane
1.3,5-trisilacyclohexane
1.3,5-Trichloro-1,3,5-trimethyl1,3,S-Trimethyl-1,3,5-trisilacyclohexane
1,3,5-trisilacyclohexane
1,1.3-Trimethyl- 1,3,5-trisilacyclohexane
1,1,3-Trichloro-3,5,5-trimethyl1,3,5-trisilacyclohexane
1.3-DichIoro-1,3,S,5-tetramethyl1,1,3,5-Tetramethyl1,3,5-trisilacyclohexane
1,3,5-trisilacyclohexane
1,1,3,3,S-Pentametbyll-Chloro-1,3,3,5,5-pentamethylI ,3.S-trisilacyclohexane
1,3,5-trisilacycIohexane
1.3-Disilaindan
1.1,3,3-Tetrachloro-l,3-disilaindan
100
-
711768
91-921768
88.5/768
1071768
(1:3)
(27)
(28)
(29)
100
0.66
-
44.7
141
71.4
41.9
13.9
13.6
100/760
123/758
1331762
1351768
1421760
14
69
155
64
100
1541756
1591766
69
960
1661764
1690
1801764
1000
1901764
168
65
20 11767
(29) t (19)
65
2041746
129)+ (19)
(39)
(40)
1,3.3-Trichloro-l -methyl-l,3-disilaindan
l-Methyl-l,3-disilaindan
1.3-Dichloro-l,3-dimethyl-l,3-disilaindan 1,3-Dimethyl-l,3-disilaindan
(41)
2,2.4,4,6,6,8.8-0ctachIoro-2,4,6,8-tetrasilabicyclo[3.3.0loct-l(5)-ene [ZOal
59
14
2101767
not
determined
Metbylation product
2,2,4,4,6,6,8,8-0ctamethyl2,4,6.8-tetrasilabicyclo[3.3.0loct1(5)-ene (201 [mp. = 1421
1,3,5,7-Tetrahydro-l,3,5,7-tetrasilaadamantane
[a] The distribution of the CHI groups on the Si atoms of the molecule has not yet been established unambiguously.
[bl (44) consists of four condensed six-membered rings with alternating Si and C atoms. The Si valences that are not involved in the skeleton are
occupied by C1, and the carbon valences by H atoms. (43) has a similar structure.
Icl This compound has been obtained by the reaction of SiCI4 and (CH3)3SiCI in the presence of ucI3 at high pressures. - A. Lee Smith and H. A.
Clark, J. Amer. chem. SOC. 83, 3345 (1961).
so that these compounds containing SiH groups, which are
less sensitive to hydrolysis, can also be separated. The mixture is again resolved into three groups of substances by
chromatography on A1203 columns. Group C can be further
resolved by elution with benzene-methanol mixtures having
increasing methanol contents, The fractions obtained by
chromatographic separation (molecular weights between 400
and 800) all contain compounds having relatively small differences in their molecular weights (e.g. 544 to 571; 817 to
834) [21J.
thought to be reaction (1). This is followed by reaction
(2).
Si(CH3)d
+ (CH3)&
(CH3)3Si-CH3
+ CH3
+ cH3
+ (CH&Si-CHz
(1)
+ CH4
(2)
These processes yield the free radicals required for the
formation of the Si-C-Si skeleton. The parent cornpound is probably formed in accordance with (3).
5. Conclusions Concerning the Formation of
Pyrolysis Products
(CH3)3Si-?H2
The formation of compounds in the gaseous phase at
about 700°C is assumed to be a free-radical processR3,101. The initial step of the decomposition is
1201 G. Fritz, E. Krahe, and H . G . v. Schnering, unpublished.
[20a] G. Fritz and R. Haase, unpublished.
[21] G . Fritz and W. Kiinig, unpublished.
Angew. Chem. internat. Edit. I Val. 6 (1967) 1 No. 8
+ >i(CH&
+ (CH~)~S~-CHZ-S~(CH
(3)~ ) ~
68 1
This does not explain the preferential formation of
cyclic carbosilanes. The isolation of 1,3-disilacyclobutane from the pyrolysis products 1111 seems particularly significant; this product could be formed by
reactions (4)and (5).
can be split by reaction with halogens or hydrogen halides,
depending on the other substituents on the Si a t o m [ W This
principle was used for the preparation of a number of carbosilanes containing functional groups 1251, e.g. :
..
The formation of the six-membered ring can also be
explained as proceeding via the radical (CH&Si-CHz.
The Si-chlorinated carbosilanes could be formed in a
similar manner from the three methylchlorosilanes in
the gaseous phase [2,31. As in the pyrolysis of Si(CH3)4,
the S i c and C H bonds may be expected to be cleaved.
However, the products isolated show that the Sic1
bond must also be broken, since the pyrolysis products
of (CH3)3SiCl and (CH3)2SiC12 include compounds in
which the Si atom carries more C1 atoms than in the
starting material. Moreover, the 1,3-disilapropanes
formed in the greatest quantities are those whose
formation involves large transpositions, e.g.
C13Si-CHz-SiC13 and (CH&Si-CHz-SiC13
from
(CH3)3SiCI or (CH3)zSiCIz. Further assumptions are
necessary in order to explain the formation of these
compounds. If it is assumed that Sic1 bonds are
broken, the formation of the compounds could be
explained by the recombination of suitable radicals;
however, this assumption is open to certain objections.
It should be stressed that we have never found pyrolysis
products containing Si-Si bonds, which could possibly have arisen by the recombination of radicals
such as (CH3)3Sio (see eq. (1)).Since the bond energy
of the Si-C bond (76 kcal) is higher than that of the
Si-Si bond (53 kcal), the arrangement Si-C-Si is
energetically favored in relation to Si-Si-C. This is
confirmed by a series of catalytic and even thermal
rearrangements 1221.
The four-membered ring has now also been synthesized from
(CH3)2CISiCHzCI and Mg [2Sal.
The chemical properties of the carbosilanes are
determined largely by the groups attached to the Si
atoms and to the skeletal C atoms. The compounds
in which the Si atoms are fully methylated are (generally) inert. Reactions are observed only under
extreme conditions or where strained ring systems are
involved. Thus 1,1,3,3-tetramethyI-l,3-disilacyclobutane undergoes ring cleavage with HBr. The corresponding six-membered ring compound does not
exhibit this reaction.
Photochlorination leads to chlorination of the C H
groups of the carbosilane skeleton, the reaction
proceeding as far as steric factors allow[26,27] (cf.
eqs. (6)-(8)). Intermediates can be isolated in only
a very few cases[28], one such substance being
C13Si-CHCl-SiC13 Q7al.
6. Synthesis of Carbosilanes Containing
Functional Groups
The stepwise organometallic synthesis of carbosilanes
with functional groups on the Si atomtz33,23Jis made
difficult by the fact that functional groups on Si
readily undergo undesirable side reactions with organolithium or organomagnesium compounds.
The obvious remedy was to carry out the synthesis of the
organometallic compounds, and as far as possible their
further reaction, with derivatives having protective groups
on the Si atom. These groups must prevent undesirable condensations, and it must be possible to remove them at a later
stage to give a n Si atom carrying a functional group. A
suitable group for this purpose is the Si-CsHs group, which
[22] K . Shiina and M . Kumada, J. org. Chemistry 23, 139 (1958).
1231 G. Fritz and H . Burdt, Z . anorg. allg. Chem. 314, 35 (1962).
682
[24] G. Fritz and D. Kummer, Z . anorg. allg. Chem. 308, 105
(1961); 310, 327 (1961).
[25] G. Fritz and W. Kemmerling, Z . anorg. allg. Chem. 322, 34
(1963); G. Fritz, W . Kemmerling, G . Sonnrag, H . J . Becker, E. A.
V . Ebsworth, and J. Grobe, Z . anorg. allg. Chem. 321, 10 (1963).
[25a] W . A . Kriner, J. org. Chemistry 29, 1601 (1964); R. MiilIer,
R . Kahne, and H . Beyer, Chem. Ber. 95, 3030 (1962); H . Gilman,
personal communication.
[26] R . Muller and G. Seitz, Chem. Ber. 91,22 (1958).
1271 G. Fritz, D. Habel, and G . Teichmann, 2. anorg. allg. Chem.
303, 85 (1960).
[27a] G . Fritz and R. Riekens, unpublished.
[28] G. Fritz et a/., unpublished.
Angew. Chem. internat. Edit. I Vol. 6 (1967) 1 No.8
These C-chlorinated carbosilanes are particularly
interesting in their reaction with organometallic
compounds. While methylation of C-chlorinated
methylchlorosilanes with CH3MgCI or CH3Li
leads mainly to the Si-methyl compound, e. g .
the reaction of (CH3)2CISi-CHC12 with CH3MgCl
yields (CH3)3Si-CHC12, a similar reaction is
hardly ever observed with chlorosilanes in which
the skeletal C atom is chlorinated. After the
methylation of (C1$3)2CC12 with CH3MgC1 or
CH3Li, not even small quantities of the Simethylated compound [(CH3)3Si]2CC12 can be
isolated. Reaction under a wide range of conditions
leads
instead
to
[(CH&Si]2CHz,
[(CH3)$i]zCHCH3,
[(CH3)3Si]2C=CHz,
and
[(CH3)3Si]zC(CH3)2, as well as other compounds
that have not yet been fully characterized[29]. Although these transformations cannot be satisfactorily
interpreted at present they have opened up new
avenues in carbosilane chemistry.
The above investigations were carried out with the
support of the Fonds der Chemie, the Deutsche Forschungsgemeinschaft, and Farbenfabriken Bayer, Leverkusen. I am particularly grateful to my co-workers.
Received: September 26th 1966
[A 587 IEl
German version: Angew. Chem. 79. 657 (1967)
Translated by Express Translation Service, London
[291 G . Fritz and J . Crobe, Z. anorg. allg. Chem. 309, 77
(1961).
Siloxane Compounds of the Transition Metals
BY F. SCHINDLER AND H. SCHMLDBAUR [*I
Heterosiloxanes of transition metals contafn the characteristic grouping S i - 0 - X ; in
the compounds known so far, X may be Au, Zn, Cd, Hg, Ti, Zr, Hf, V, Nb, Ta, Cr,
U , Re, Fe, Co, Ni, or Pt. Most of these compounds are obtained from silanols, metal
silanolates, acyloxysilanes, disiloxanes, or alkoxysilanes, 1.e. from compounds that
already contain an Si-0 bond. The transition metal may be introduced e.g. as a halide,
as an organometarlic compound, as an alkoxy compound, or as an oxide. Heterosiloxanes
are also formed on reaction of many silicon compounds that do not contain oxygen with
transition metal compounds containing oxygen. Some of these compounds, e.g. some
titanosiloxanes, are very stable, whereas others decompose explosively. Oligomeric and
polymeric heterosiloxanes exist in addition to the monomeric compounds.
I. Siloxanes of Copper, Silver, and Gold
The heterosiloxane grouping Si-0-X (X = hetero
atom) is one of the most important structural units of
inanimate nature. The various metal silicates are built
up from such units, and profit from their high chemical
and thermal stability. Numerous attempts have been
made to prepare organometallic polymers from metalsubstituted silicones, in order to make use of the
advantageous properties of the heterosiloxane group.
Heterosiloxanes of elements of the main groups were
discussed in an earlier article 111. The present article
deals with the corresponding compounds of the transition elements, which were almost unknown until a
few years ago. Efforts to synthesize new inorganic
polymers [2,31 have also led to fundamental investigations in this field.
Preliminary experiments with copper and silver were
not very promising. Thus the reaction of disodium
diphenylsilanediolate with copper(I1) chloride gives an
intermediate product presumed to have the composition [ ~ i ( ~ ~ ~ ~ ) ~ - ~ ] , [ but
- ~ uthis
- ~ immediately
],,
decomposes into copper(I1) oxide and octaphenylcyclotetrasiloxane [41.
Attempts to prepare siloxanes of silver by reaction of
silver perchlorate or nitrate with sodium trimethylsilanolate in many different solvents did not yield a
definite silver trimethylsilanolate, but only silver oxide
and hexamethyldisiloxane [51.
[*I Dr. F. Schindler and Prof. Dr. H . Schmidbaur
2 AgC104+ 2 NaOSi(CH3)3 + 2 NaC104
Institut fur Anorganische Chemie der Universitat
Rontgenring 11
87 Wiirzburg (Germany)
[l] H . Schmidbaur, Angew.Chem.77, 206 (1965); Angew. Chem.
internat. Edit. 4, 201 (1965).
(21 F. G . A. Srone and W. A. G. Graham: Inorganic Polymers.
Academic Press, New York 1962.
[3] M . F. Lappert and G. J. Leigh: Development in Inorganic
Polymer Chemistry. Elsevier, Amsterdam 1962.
Angew. Chem. internat. Edit.
VoI. 6 (1967) 1 No. 8
+ AgZO + [(CH3)3Si]~0
It is not certain whether AgOSi(CH& occurs as an
unstable intermediate in this reaction.
141 E . D . Hornbaker and F. Conrad, I. org. Chemistry 24, 1858
(1959).
[5] H. Schmidbaur and M . Bergfeld, unpublished ; M . Bergfeld,
Dissertation, Universifat Wiirzburg 1967.
683
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