Hydrosilylation of cyclohexene and allyl chloride with trichloro-, dichloro(methyl)-, and chlorodimethylsilanes in the presence of Pt(0) complexes

Article abstract of DOI:10.1134/S1070363206060120

Hydrosilylation of cyclohexene and allyl chloride in the presence of Pt(0) complexes with tetramethyldivinyldisiloxane (Karstedt catalyst) and hexavinyldisiloxane was studied. It was shown that these catalysts are much more active in the hydrosilylation of cyclohexene with trichloro-, dichloro(methyl)-, and chlorodimethylsilane than the Pt(II)-containing Speier catalyst. In the hydrosilylation of allyl chloride in the presence of Pt(0) complexes, the ratio of the fraction of addition products to the fraction of reduction products increases from 5.7 (Speier catalyst) to 10-16. Quantum-chemical calculations showed that Pt(0) complexes are more active than Pt(II) complexes on the stage of formation of platinum silicon hydride complexes. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S1070363206060120

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 6, pp. 925 930.
Pleiades Publishing, Inc., 2006.
Original Russian Text Z.V. Belyakova, E.A. Chernyshev, P.A. Storozhenko, S.P. Knyazev, G.N. Turkel’taub, E.V. Parshina, A.V. Kisin, 2006, published
in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 6, pp. 967 972.
Hydrosilylation of Cyclohexene and Allyl Chloride
with Trichloro-, Dichloro(methyl)-, and Chlorodimethylsilanes
in the Presence of Pt(0) Complexes
Z. V. Belyakovaa, E. A. Chernysheva, P. A. Storozhenkoa, S. P. Knyazevb,
G. N. Turkel’taubb, E. V. Parshinab, and A. V. Kisina
a State Research Institute of Chemistry and Technology of Organoelement Compounds,
sh. Entuziastov 30, Moscow, 111123 Russia
e-mail: eos2004@inbox.ru
fax: 007 (095)2731323
b Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow, Russia
Received August 1, 2005
Abstract Hydrosilylation of cyclohexene and allyl chloride in the presence of Pt(0) complexes with tetra-
methyldivinyldisiloxane (Karstedt catalyst) and hexavinyldisiloxane was studied. It was shown that these
catalysts are much more active in the hydrosilylation of cyclohexene with trichloro-, dichloro(methyl)-, and
chlorodimethylsilane than the Pt(II)-containing Speier catalyst. In the hydrosilylation of allyl chloride in the
presence of Pt(0) complexes, the ratio of the fraction of addition products to the fraction of reduction products
increases from 5.7 (Speier catalyst) to 10 16. Quantum-chemical calculations showed that Pt(0) complexes are
more active than Pt(II) complexes on the stage of formation of platinum silicon hydride complexes.
DOI: 10.1134/S1070363206060120
Previously [1] we showed that Pt(0) complexes
with tetramethylvinyldisiloxane (Karstedt catalyst)
and hexavinyldisiloxane are more active in hydrosilyla-
tion of ethylene with triethoxysilane than a solution
of chloroplatinic acid in 2-propanol [Speier catalyst
(I)]. The aim of this work was to assess the efficiency
of these complexes in hydrosilylation of other un-
saturated compounds, cyclohexene and allyl chloride,
which are less active in addition reactions as com-
pared to unsaturated compounds of the CnH2n homo-
logous series. Sufficiently high yields in the hydro-
silylation of cyclohexene with trichlorosilane and di-
chloro(methyl)silane in the presence of catalyst I
could only be obtained at long reaction times, some-
times in sealed ampules or in autoclave. For example,
the reaction of cyclohexene with trichlorosilane in the
presence of catalyst I for 20 h at 100 C gave 78% of
trichloro(cyclohexyl)silane [2]. Dichloro(cyclohexyl)-
methylsilane was obtained in 100% yield upon heat-
ing of starting materials in a sealed ampule on a water
bath for 20 h [3]. No data on the hydrosilylation of
cyclohexene with chlorodimethylsilane are available.
After 16 h the reaction mixture contained 57.6% of
trichloro(hexyl)silane and as little as 0.6% of trichloro-
(cyclohexyl)silane. We carried out hydrosilylation of
cyclohexene with trichlorosilane, dichloro(methyl)-
silane, and chlorodimethylsilane.
SiRR2
(1)
+ HSiRR2
IIa IIc
R = R = Cl (a); R = Me, R = Cl (b); R = Cl, R = Me (c).
The results of hydrosilylation are listed in Table 1.
In the presence of Karstedt catalyst III, the yield of
trichloro(cyclohexyl)silane under reflux for 1.5 h was
69.1%, and in the presence of platinum hexavinyldi-
siloxane complex IV, 93.8%. In the presence of
catalyst I under the same conditions, no product was
obtained. Chromatographic analysis and IR spectro-
scopy showed that the hydrosilylation of cyclohexene
with trichlorosilane gives no dehydrogenative hydro-
silylation by-products. Analogously in the presence
of catalyst I the yield of dichloro(cyclohexyl)methyl-
silane is 92.4%, while in the presence of catalyst I,
95.4%. The hydrosilylation of cyclohexene with di-
chloro(methyl)silane, too, gives no dehydrogenative
With the purpose to compare the activity of cyclo-
hexene and hexane, we performed competing hydro-
silylation of these compounds with trichlorosilane in
the presence of Pd(0) hexavinyldisiloxane complex.
925

926
BELYAKOVA et al.
Table 1. Hydrosilylation of cyclohexene with trichloro-, dichloro(methyl)-, and chlorodimethylsilane
Catalyst
Reaction time, h
Final temperature, C Yield of adduct, %
Method
comp. no
MPt 106
R = R = Cl
53
I
III
IV
IV
I+ V
I+ V
10.2
20.4
10.2
1.7
1.7
1.7
5
1.5
5
27
72
7
0
a, b
100
116
115
20
69.1
93.8
92.1
89
b
b
b
c
92
78.1
b
R = Me, R = Cl
III
IV
IV
IV
I+ V
I+ V
I+ V
I+ V
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
23.5
8
120
64
64
20
20
20
20
92.4
41.4
81.2
95.4
13.4
53.3
80.1
93.2
d
b
b, c
b
c
c
c
c
70a
1152
6
24
48
72
20
R = R = Me
105
II
1.7
34.5
18.6
b
a
Including 62 h by procedure c.
1
hydrosilylation products. But in some experiments
one additional product was formed boiling by about
30 C lower than the main compound. Evidently, it
was chloro(cyclohexyl)methylsilane. The latter might
form from chloro(methyl)silane generated by dispro-
portionation of dichloro(methyl)silane.
by NMR spectroscopy. The H NMR spectrum of tri-
chloro(cyclohexyl)silane contained two multiplets of
ring protons at 1.2 1.4 and 1.7 2.0 ppm. The 13C
NMR spectrum contained cyclohexyl proton signals
at 33.5 (C1), 26.8 (C2 or C3), 26.0 (C4), and 25.4 ppm
(C2 and C3). The H NMR spectrum of dichloro-
1
(cyclohexyl)methylsilane contained a singlet of the
methyl group at 0.72 ppm and two complex signals at
1.2 1.3 and 1.7 1.9 ppm related to the cyclohexyl
2MeSiHCl2
MeSiH2Cl + MeSiCl3.
(2)
1
The hydrosilylation of cyclohexene with trichlo-
rosilane and dichloro(methyl)silane also easily pro-
ceeds in the presence of catalyst I plus allyl glycidyl
ether (V). The yields of trichloro(cyclohexyl)silane
and dichloro(cyclohexyl)methylsilane at room tem-
perature within 72 h reach 89.0 and 93.2%, respec-
tively.
substituent. The H NMR spectrum of chloro(cyclo-
hexyl)dimethylsilane displayed two methyl singlets at
0.72 and 0.78 ppm and two complex signals at 1.2
1.3 and 1.7 1.9 ppm related to the cyclohexyl sub-
stituent. The 13C NMR spectrum showed methyl
carbon signals at 1.05 and 0.35 ppm, as well as sig-
nals at 28.18 (C1), 27.54 (C2 and C3), 26.62 (C4), and
26.36 ppm (C2 and C3), related to the cyclohexyl
substituent.
The hydrosilylation of cyclohexene with chlorodi-
methylsilane in the presence of catalyst IV was
studied both at elevated and at room temperature. At
room temperature, no changes were observed within
one month. After 34.5 h under reflux, the final reaction
temperature reached 105 C, and chloro(cyclohexyl)-
dimethylsilane was isolated in 18.5% yield. The re-
sulting data show that the activity of silanes in cyclo-
hexene hydrosilylation decreases in the series HSiCl3
MeHSiCl2 > Me2HSiCl.
Cyclohexyltriethoxysilane is usually prepared in
two stages. The first stage involves hydrosilylation of
cyclohexene with trichlorosilane, and the second,
reaction of the resulting product with ethanol. With
rhodium catalysts, the hydrosilylation of cyclohexene
(80 100 C, 2 8 h) provides as little as 9% of cyclo-
hexyltriethoxysilane [4]. No data on hydrosilylation
in the presence of catalyst I were reported.
The structure of cyclohexylsilanes was confirmed
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HYDROSILYLATION OF CYCLOHEXENE AND ALLYL CHLORIDE
927
1
1
1
Table 2. Total energies (E, kcal mol ), enthalpies (H, kcal mol ), Gibbs energies (G, kcal mol ), and entropies
(S, cal mol 1 K ) of the intermediate and final products (platinum silicon hydride complexes) of reactions (5) and (6),
1
in relation to reagents
1
1
1
1
System
E, kcalmol
H, kcalmol
S, kcalmol 1 K
G, kcalmol
Reaction (5), X = Cl
Pt H Si complex
Reaction products
5.43
11.45
4.56
10.01
25.35
15.72
3
5.32
Reaction (5), X = OCH3 [C3 symmetry HSi(OCH3)3]
Intermediate complex
1.15
(Pt H 3.2
)
Reaction products
0.75
0.08
27.86
8.39
Reaction (5), X = Cl
6.15
Intermediate complex
(Pt H 3.6
)
Reaction products
6.36
7.41
34.30
41.50
17.64
12.02
Reaction (6), X = OCH3 [C3 symmetry HSi(OCH3)3]
Reaction products
1.35
0.35
the presence of catalyst IV under reflux. In the pre-
sence of cyclohexene this reaction proceeds 75% more
actively. Therefore, we failed to hydrosilylate cyclo-
hexene with triethoxysilane.
(3)
Si(OEt)3
+ HS(OEt)3
Note that despite of numerous studies of hydrosy-
lylation many specific features of this process remain
unclear, e.g., the higher activity of Pt(0) complexes
compared to Pt(II) and of chlorosilanes compared to
alkoxysilanes.
We carried out reaction (3) in the presence of
catalyst IV at 95 100 C and atmospheric pressure.
Monitoring by GLC showed that under these condi-
tions only tetraethoxysilane and siloxanes were
formed. Prolonged heating increased the fraction of
tetraethoxysilane in the mixture.
To find out the regularities and specific features of
the hydrosilylation of unsaturated compounds with
chlorosilanes and alkoxysilanes in the presence of
Pt(0) and Pt(II) complexes, we carried out quantum-
chemical calculations (GAUSSIAN-98, B3LYP/
lanL2DZ) of the first reaction steps, that is, formation
of platinum silicon hydride complexes. Model systems
including Pt(0) and Pt(II) olefin complexes, trichloro-
silane, and trimethoxysilane were studied.
7HSi(OEt)3
Si(OEt)4 + (EtO)3SiOSi(OEt)3
+ (EtO)3SiOSi(OEt)2OSi(OEt)3 + 3EtH + 2H2. (4)
With the other platinum catalysts, analogous results
were obtained. Gas chromatography mass spectro-
metry revealed in the resulting mixture 25.1% of
hexamethyldisiloxane {molecular ion peak with m/z
342 and a peak with m/z 297 [M OEt]+ (100%)}
and 49.4% of octaethoxytrisiloxane {molecular ion
peak is absent, peaks with m/z 405 [M C2H3 OEt]+
1
(C2H4)3Pt0 + H SiX3
(C2H4)3Pt2H(SiX3),
(C2H4)3Pt H SiX3
(5)
(5.8%), 368 [M EtOEt OH
281 [EtO(Et)Si OSi(OEt)3]+ (56.9%), 253 [EtO
SiH
Si(OEt)3]+ (22.6%), and 207 [EtOSi=
H2O]+ (23.1%),
(C2H4)2Pt2Cl2 + H SiX3 (C2H4)2Cl2Pt1 H SiX3
(C2H4)2Cl2Pt4H(SiX3),
(6)
X = Cl, OCH3.
O
+
Si(OEt)2 (100%)}.
1
The H NMR spectrum of siloxanes contained two
The calculated parameters of the intermediate states
and products of the platinum silicon hydride complex
formation reactions are listed in Table 2.
triplets of methyl protons at 1.25 ppm, and two
quartets of methylene protons at 3.85 ppm with the
intensity ratio 3:2. The presence of two sets of signals
can be explained by the formation of two different
siloxanes, which agrees with the GC MS data.
New features of the structure and formation of
ethylene and silicon hydride platinum complexes were
revealed. Reaction (5) (X = Cl) can proceed through
intermediate formation of a stable complex (C2H4)3Pt
Triethoxysilane was found to disproportionate in
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 6 2006

928
BELYAKOVA et al.
Cl
Cl
Cl
Cl
Cl
Cl
H
Si
Si
H
H
H
C
H
H
Pt
H
C
H
C
H
H
H
H
H
C
H
Pt
C
C
C
C
C
C
H
H
C
C
H
H
H
H
H
H
H
H
H
H
Structures of the molecular systems on the separate steps of reaction (1) (GAUSSIAN-98, B3LYP/LanL2DZ)
H SiCl3 including a Pt H Si bridging three-center
bond (see figure), and its subsequent rearrangement
to a platinum silicon hydride complex. Finally, the
most stable reaction product occurs to be a platinum
silicon hydride complex with Pt H and Pt Si bonds.
Therewith, one of the ethylene ligands leaves Pt and
no longer coordinated to it (see figure). As follows
from the total energy surface of the rearrangement of
the (C2H4)3Pt H SiCl3 complex to H Pt SiCl3(C2H4)3,
this reaction has a fairly low potential barrier (15
1
2
ClCH2CH2CH2SiR3,
ClCH2CH=CH2 + HSiR3
CH3CH=CH2 + ClSiR3.
HSiR3
(7)
PrSiR3
The fraction of reduction products increases on
methyl substituents for chlorine in the silicon hydride
molecule [4].
1
20 kcal mol ).
It is known that decreased temperature decrease
improves the yield of hydrosilylation products and
suppresses reduction. The latter pathway is also sup-
pressed when the reaction is performed at increased
pressure (8 atm). Hence, the reaction of allyl chloride
with trichlorosilane at atmospheric pressure provides
64% of the adduct and 36% of the reduction product
(addition/reduction ratio 1.8:1). At increased pressure
this ratio reaches 5.6 (83.5:16.5) [5]. Some additives
to the Speier catalyst favor hydrosilylation. Addition
of N,N-dimethylacetamide [6], tributylamine [7], tri-
phenylphosphine [8] increases the yield of trichloro-
( -chloropropyl)silane from 57 64% to 85%.
Characteristic changes take place in the type of
intermediate structures and parameters of reaction
products in the case of triethoxysilane and a Pt(II)
complex. No stable bridge structures are formed. The
minimum point on the coordinate of approach of two
reaction centers corresponds to formation of van der
Waals complexes at a distance of 3.2 3.6 . Further
approach causes an exponential growth of the energy
of the system. Analysis of the energy and thermo-
dynamic parameters of platinum silicon hydride com-
plexes with Pt H and Pt Si bonds points to their
lower stability as compared to the initial system
including isolated molecules (see Table 2).
The data on the hydrosilylation of allyl chloride in
the presence of catalyst I, Pt(0) complexes, and
catalyst I plus triphenylphosphine and trichlorophos-
phine oxide are listed in Table 3. As seen, in the
presence of catalysts III and IV the yield of trichloro-
( -chloropropyl)silane increases from 62.2 to 67.5
75.0%, and the addition/reduction (A/R) ratio changes
from 5.7 to 14.6 16.3. Triphenylphosphine and trichlo-
rophisphine oxide additives to the Speier catalyst do
not give a positive effect. The hydrosilylation of allyl
chloride with chlorodimethylsilane in the presence of
Hence, the higher activity of Pt(0) complexes and
trichlorosilane in hydrosilylation can be associated
with the easier formation and higher stability of pla-
tinum silicon hydride complexes.
It is known from the literature that allyl chloride
reacts with trichloro-, dichloro(methyl)-, triethoxy-,
and chlorodimethylsilane. Hydrosilylation of allyl
chloride is accompanied by reduction leading to pro-
pylene and chlorosilane. Propylene enters hydrosilyla-
tion to form corresponding propylsilanes.
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HYDROSILYLATION OF CYCLOHEXENE AND ALLYL CHLORIDE
929
Table 3. Hydrosilylation of allyl chloride with trichlorosilane and chlorodimethylsilane
Synthesis conditions
Content of products in the mixture, %
R
Yield, %
A/Rb
catalysta
time, h
C3H7SiR2Cl
ClCH2CH2CH2SiR2Cl
Cl
Cl
Cl
Cl
Cl
I
4.2
5.5
8.25
5.6
5.5
8.2
10.8
15.9
2.9
5.1
5.2
61.6
62.4
30.8
74.4
84.4
75.7
71.2
62.2
62.9
31.0
75.0
85.1
80.6
75.7
5.7
3.9
I + PPh3
I + POCl3
III
IV
III
IV
10.6
14.6
16.3
11.5
10.8
Me
Me
7.0
6.6
10.5
a
b
One drop (0.017 0.018 ml) of the catalyst was added.
Addition/reduction ratio.
catalyst III leads to high yields of ( -chloropropyl)-
dimethylsilane (75.7 80.6%). The A/R ratio is 10.8
11.5.
b. One drop (0.017 0.018 ml) of a 0.1 M solution
of platinum catalyst was treated with 1/10 of a mix-
ture of 0.03 mol of unsaturated compound and
0.033 mol of hydrosilane. The resulting mixture was
heated to reflux, and the residual reagent mixture was
added in portions after the temperature of the reaction
mixture reached 80 C. The mixture was refluxed until
it reached 120 C and then kept at this temperature for
1 h and cooled. If the temperature did not reach
120 C, the reaction mixture was kept at the highest
reached temperature for 1 h and then cooled.
EXPERIMENTAL
Gas chromatography was performed on an LHM-
80 chromatograph with a thermal conductivity detec-
1
tor, carrier gas helium (30 ml min ), 1000 3-mm
stainless-steel column packed with 5% SE-30 on
Chromaton N-AW-DMCS (0.25-0.31 mm). The oven
temperature was programmed from 20 to 300 C at a
c. A mixture of 0.03 mol of unsaturated compound,
0.033 mol of hydrosilane, and one drop of catalyst
(0.017 0.018 ml) was kept at room temperature and
then analyzed.
1
rate 8 deg min , injector temperature 350 C, detector
temperature 250 C.
The mass spectra were obtained on a Hewlett
Packard HP-5971A GC MS system at an ionizing
voltage of 70 V. Gas chromatography was performed
on a 25000 0.32-mm quartz capillary column, sta-
tionary phase DV-5 (film thickness 25 nm). The oven
temperature was programmed from 50 to 280 C at a
d. One drop (0.017 0.018 ml) of a 0.1 M
solution of platinum catalyst was mixed with unsa-
turated compound (0.03 mol), and the mixture was
heated to 80 C. In the course of the heating,
0.033 mol of hydrosilane was added in 6 equal
portions.
1
rate 7 C min ; carrier gas helium.
The NMR spectra were taken on a Bruker AM-360
1
The final reaction mixtures were fractionated by
distillation.
Fourier spectrometer (360 MHz for H and 90 MHz
for 13C).
Trichloro(cyclohexyl)silane. Distillation of the
mixture resulting from the reaction of cyclohexene
with trichlorosilane gave a fraction with bp 92 95 C
(20 mm Hg), containing 97.7% of trichloro(cyclo-
hexyl)silane, n2D0 1.228; MRD 50.18; calc. MRD 50.76.
The Karstedt catalyst was prepared by the proce-
dure in [9], catalyst I with the allyl glycidyl ether
additive was heated for 0.5 h at 50 C prior to use.
Hydrosilylation of unsaturated compounds.
a. A mixture of 0.03 mol of unsaturated compound
and 0.033 mol of hydrosilane was treated with a
catalyst and heated to slight reflux. In the course of
the reaction increase in the boiling point of the mix-
ture was observed. After it reached 120 C, the reac-
tion mixture was kept at this temperature for 1 h and
then cooled. If the temperature of the reaction mixture
did not reach 120 C. it was kept for 1 h at the highest
reached temperature and then cooled.
1
Published data [10]: n2D0 1.4774; d420 1.2211. H NMR
spectrum (CDCl3), , ppm: 1.2 1.4 m (6H), 1.7
2.0 m (5H). 13C NMR spectrum (CDCl3), Cm ppm:
33.5 (C1), 26.8 (C2 or C3), 26.0 (C4), 25.4 (C2 or C3)
(all signals belong to the cyclohexyl substituent).
Dichloro(cyclohexyl)methylsilane: bp 100 C
(20 mm), n2D0 1.4722, d420 1.091; MRD 50.63, calc.
MRD 50.64. Published data [11]: n2D0 1.4724; d420
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 6 2006

930
BELYAKOVA et al.
1
1.0953. H NMR spectrum (CDCl3), , ppm: 0.72 s
(3H, Me), 1.2 1.3 m (4H), 1.7 1.9 m (5H).
REFERENCES
1. Chernyshev, E.A., Belyakova, Z.V., Knyazev, S.P.,
and Parshina, E.V., Abstracts of Papers, Tezisy dok-
ladov X mezhdunarodnoi konferentsii Naukoemkie
khimicheskie tekhnologii ((X Int. Conf. High
Chemical Technologies 2004 ), Volgograd, 2004,
vol. 1, p. 335.
Chloro(cyclohexyl)dimethylsilane: bp 72 74 C,
n2D0 1.4620; d420 0.955; MRD 50.88, calc. MRD 51.16.
1H NMR spectrum (CDCl3), , ppm: 0.34 s (6H, Me),
1.2 1.3 m (5H), 1.7 1.9 m (6H).
2. Benkeser, R.A. and Kong, J.J., J. Organomet. Chem.,
1980, vol. 185, no. 1, p. 9.
Reaction of cyclohexene with triethoxysilane.
Syntheses were carried out in the presence of catalysts
3. Speier, J.L., Webster, J.A., and Barnes, G.H., J. Am.
Chem. Soc., 1957, vol. 79, no. 4, p. 974.
4. Belyakova, Z.V., Pomerantseva, M.G., and Beliko-
va, Z.V., Zh. Obshch. Khim., 1974, vol. 44, no. 11,
p. 2439.
5. DE Patent 2815316, Chem. Abstr., 1980, vol. 91,
19341y.
6. US Patent 4736049, Chem. Abstr., 1988, vol. 109,
54954.
II and III by procedures a, b, and c. No changes were
observed in the reaction mixture at room temperature.
The mixtures resulting from the syntheses were frac-
tionated by distillation to obtain a fraction with bp
118 C (3 mm Hg), nD20 1.406, and d240 0.983, contain-
ing 21.5% of hexamethyldisiloxane, 49.4% of octa-
ethoxytrisiloxane, and unidentified admixtures.
The hydrosilylation of allyl chloride was carried
out by procedure a.
7. Hu, Ch., Yang, R., and Jiang, Y., J. Mol. Catal., 1988,
vol. 2, no. 2, p. 38.
8. Hu, Ch., Zhao, D., and Jiang, Y., J. Catal., 1989,
vol. 2, no. 10, p. 213.
ACKNOWLEDGMENTS
9. Lewis, L.N., Sy, K.G., Bryant, G.L.Jr., and Do-
nahue, P.E., J. Organomet. Chem., 1991, vol. 10,
no. 10, p. 3750.
The authors express their gratitude to N.N. Khro-
mykh for recording the mass spectra.
10. Kolesova, V.A. and Voronkov, M.G., Collect. Czech.
Chem. Commun., 1957, vol. 22, no. 3, p. 851.
11. Petrov, A.D., Ponomarenko, V.A., Sokolov, V.A.,
and Odabashyan, G.O., Izv. Akad. Nauk SSSR, 1957,
no. 10, p. 1206.
The work was financially supported by the Pre-
sidential Program for Support of Young Russian
scientists and Leading Scientific Schools (project
no. NSh-1811.2003.3).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 6 2006