Effect of catalyst structure on the reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane

Article abstract of DOI:10.1134/S107036320904015X

Reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane in the presence of the complexes of platinum(II), palladium(II) and rhodium(I) is explored. It is established that in the presence of platinum catalyst predominantly occurs hydrosilylation of α-methylstyrene leading to formation of β-adduct, on palladium catalysts proceeds reduction of α-methylstyrene, on rhodium catalysts both the processes take place. In the reaction mixture proceeds disproportion and dehydrocondensation of 1,1,3,3-tetramethyldisiloxane that leads to formation of long chain linear and cyclic siloxanes of general formula HMe₂Si(OSiMe₂) _n H and (-OSiMe₂-)m (n = 2-6, m = 3-7), respectively. Platinum catalysts promotes formation of linear siloxanes, while both rhodium and palladium catalysts afford linear and cyclic siloxanes as well. Structure of intermediate metallocomplexes is studied.

Full text of DOI:10.1134/S107036320904015X

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 4, pp. 762–777. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © D.A. de Vekki, N.K. Skvortsov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 4, pp. 598–613.
Effect of Catalyst Structure on the Reaction
of α-Methylstyrene with 1,1,3,3-Tetramethyldisiloxane
D. A. de Vekki and N. K. Skvortsov
St. Petersburg State Institute of Technology, Moskovskii pr. 26, St. Petersburg, 190013 Russia
e-mail: skvorn@mail.ru
Received December 11, 2008
Abstract―Reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane in the presence of the complexes
of platinum(II), palladium(II) and rhodium(I) is explored. It is established that in the presence of platinum
catalyst predominantly occurs hydrosilylation of α-methylstyrene leading to formation of β-adduct, on
palladium catalysts proceeds reduction of α-methylstyrene, on rhodium catalysts both the processes take place.
In the reaction mixture proceeds disproportion and dehydrocondensation of 1,1,3,3-tetramethyldisiloxane that
leads to formation of long chain linear and cyclic siloxanes of general formula HMe2Si(OSiMe2)nH and
(–OSiMe2–)m (n = 2–6, m = 3–7), respectively. Platinum catalysts promotes formation of linear siloxanes, while
both rhodium and palladium catalysts afford linear and cyclic siloxanes as well. Structure of intermediate
metallocomplexes is studied.
DOI: 10.1134/S107036320904015X
Reaction of catalytic hydrosilylation is the most
universal pathway for the synthesis of organosilicon
compounds that is applied both in preparative and
industrial chemistry. However, the catalysts used in the
industry are far from perfection. Therefore seems
promising finding the catalytic systems allowing to
synthesize the products of a given structure with high
chemical yield and selectivity.
interesting is application of the siloxanes with two Si–H
groups because at hydrosilylation with use of one Si–H
group the second one remains intact and can be
selectively used for the following hydrosilylation of
another substrate that is important for obtaining
unsymmetrical siloxanes. An example is the synthesis
by hydrosilylation of acetophenone silyl ester [9]
followed by hydrosilylation with these compounds of
liquid crystal compounds [10].
Now there are many enough publications on the
hydrosilylation of styrene and related compounds with
various hydrosilanes in the presence of the complexes
of cobalt, nickel, zirconium, palladium, platinum,
rhodium and so on [1–8]. The reaction products are
respective arylalkylsilanes (Scheme 1).
However, there are only a few publication
concerning synthesis of styrene derivatrives containing
Si–H group. For example, it has been described a
reaction of α-methylstyrene with α,ω-bis(trimethyl-
siloxy)methylhydrosiloxane in anhydrous toluene or
tetrahydrofuran resulted in the respective oligomers
[11, 12], and addition of 1,1,3,3-tetramethyldisiloxane
The more selective hydrosilylating agents com-
pared to hydrosilanes are hydrosiloxanes. The doubtless
Scheme 1.
SiR'R''R'''
SiR'R''R'''
SiR'R''R'''
R
R
R
R
R
catalyst
+ R'R''R'''SiH
+
+
+
X
X
X
X
X
R = H, CH3; X = H, Hal, Alk, NO2, OAlk; R', R'', R''' = H, Hal, OAlk, Ph.
762

EFFECT OF CATALYST STRUCTURE ON THE REACTION
763
Scheme 2.
H
Si
O
Si
Si
O
Si
O
Si
H
.
H2PlCl6 4H2O
+
+
EtOH, C4H8O2
Si
H
A
B
[(HMe2Si)2O] to two mole excess of α-methylstyrene
in the presence of solution of platinum hydrochloric
acid in a mixture ethanol–dioxane at 110°С [13]
(Scheme 2). In the last case the product of
disproportion is formed (compound B, yield 81%),
while the yield of the mono derivative (compound A),
which is of much greater significance is 3% or less.
addition of (HMe2Si)2O in the presence of platinum
and rhodium catalysts is β-carbon atom of α-
methylstyrene (adducts A and B), in the presence of
palladium the hydrosilylation leads to formation of α-
adduct (compound C). This direction of addition of
(HMe2Si)2O is well corresponds to the published data
on the effect of the metal nature on the direction of
addition of hydrosilans to alkens [2, 3, 14, 15], but and
exclusion is addition of triethoxysilane to styrene in
the presence of С60-fullerenethanolamine platinum
complex that yields α-adduct with 100% region-
selectivity [23].
For increasing the selectivity of the process of hydro-
silylation of styrene homologs with hydrosiloxanes
(optimization of the synthesis of adduct A) we attem-
pted to study influence of structure of the complexes
based on platinum(II), palladium(II) and rhodium(I) on
the reaction of α-methylstyrene with tetramethyl-
disiloxane. Use of α-methylstyrene is defined by the
presence of СН3 group, a convenient moiety for the
reaction monitoring with NMR spectroscopy.
The reaction of α-methylstyrene with (HMe2Si)2O
observed in our case can be described by Scheme 3.
The optimal method of monitoring the process of
conversion of reactants is gas-liquid chromatography,
but in the case of application of highly selective
As the catalyst we used versatile sulfoxide, tri-
phenylphosphine and cyclooctadiene complexes that
have been applied to the hydrosilylation [9, 14–20], as
well as pyridine coordination platinum compounds
with the catalytic activity suggested either moderate or
absent at all [18, 21]. The interest to the latter ones is
stipulated additionally by the recently found [22]
propensity of the platinum(II) di- and tetrapyridinium
complexes to the reactions of substitution of the
neutral ligand, that could play a positive role at
formation in situ of the real catalyst. For the
comparison of catalytic activity of platinum catalysts
with other metallocomplexes we used coordination
compounds of rhodium and palladium with triphenyl-
phosphine and 1-methylcycloocta-1,5-diene (MeCOD)
ligands.
1
platinum and palladium catalysts can be applied H
NMR spectroscopy. In the 1H NMR spectrum (CDCl3)
at the hydrosilylation of α-methylstyrene appear the
characteristic signals of СН2, ССН3 and CH groups in
1,1,3,3-tetramethyl-1-(2-phenylpropyl)disiloxane at δН
1.01 d.q (2Н, J 6.7, J 7.3 Hz), 1.34 d (3Н, J 7.5 Hz),
2.96 d.t (1H, J 6.5, J 7.0 Hz) ppm; while at the
reduction of α-methylstyrene the signals of cumene
СН3 and CH groups at δН 1.29 d (3Н, J 7.0 Hz) and
2.93 heptet (1Н, J 7.0 Hz) ppm.
A typical chromatogram of the reaction mixture
contains the peaks related to the initial compounds, α-
methylstyrene (retention time 12.6 min) and (HMe2Si)2O
(retention time 3.4 min); the adducts A (retention time
18.7 min), B (retention time 27.7 min) and C (retention
time 17.7 min); cumene (retention time 11.3 min); the
products of side transformations of (HMe2Si)2O:
trimethylsilane Me3SiH (retention time 2.6 min),
1,1,1,3,3-pentamethyldisiloxane HMe2SiOSiMe3 (reten-
tion time 4.0 min), linear dihydrosiloxanes with
terminal SiH groups with general structure HMe2Si–
(–OSiMe2–)n–H (n = 2–6) and cyclic siloxanes, hexa-
methylcyclotrisiloxanes (D3, retention time 8.6 min)
Reaction of α-methylstyrene with (HMe2Si)2O.
The direction of α-methylstyrene reaction with
(HMe2Si)2O in a great extent depends on the nature of
the complex forming atom. With platinum catalysts the
main process is hydrosilylation, with palladium ones
reduction of α-methylstyrene, rhodium complexes
catalyze both these processes (the hydrosilylation some
prevails over reduction). The main direction of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

764
DE VEKKI, SKVORTSOV
Scheme 3.
Si
O
Si
H
A
B
H
Si
O
catalyst
+
C
catalyst
Si
H
Si
O
Si
H
n
H
Si
O
Si
H
catalyst
n
D
n = 2_4
and octamethylcyclotetrasiloxane (D4, retention time
12.4 min) (the D3 : D4 ratio is about 1 : 80), and to
other products of α-methylstyrene hydrosilylation as
well, the hydrosiloxanes are formed as a result of
(HMe2Si)2O transformation. The main adduct in such
side hydrosilylation is 1,1,3,3,5,5-hexamethyl-1-(2-
phenylpropyl)trisiloxane (D, n = 2, retention time 20.8
min). Identification of the above compounds (except
adducts) is carried out by the method of chromato-
mass spectrometry with use NIST-2005 database.
which is also possible in our case is disproportion of
(HMe2Si)2O and HMe2SiOSiMe3 (Scheme 4). In favor
of such direction of join disproportion of siloxanes
attests the presence of Me3SiH in the reaction mixture.
Formation
in the
reaction
mixture
of
1,1,3,3,5,5,7,7-octamethyltetrasiloxane
HMe2SiOSi
(Me2)OSi(Me2)OSiMe2H (retention time 14.5 min) in
turn can be a result of disproportion of two
HMe2SiOSi(Me2)OSiMe2H
molecules
or
join
disproportion of (HMe2Si)2O (or HMe2SiOSiMe3) with
HMe2SiOSi(Me2)OSiMe2H (Scheme 4). The presence
in the reaction mixture of other terminal dihydro-
siloxanes HMe2Si–(–OSiMe2–)n–H (n = 4–6) in part
probably is a result of disproportion of respective
siloxanes, in correspondence with Scheme 4. However,
the presence in the reaction medium of cyclic siloxanes
D3 and D4 allows to assume an alternative pathway to
dihydrosiloxanes HMe2Si–(–OSiMe2–)n–H (n = 4–6).
It is the well known the insertion of cyclosiloxanes to
SiOSi bond proceeding in the presence of acids, bases
and other promoters [26]. The possible insertion
pathways D3 and D4 are reflected by the Scheme 5.
The mass-spectrum of the products of hydro-
silylation contains a peak of the molecular ion with
split off hydride (that is characteristic of electron
impact) and of a series of low molecular fragments
from the styrene and silicon parts of the molecule. For
the styrene part are characteristic the peaks of ions
with m/z 77 [C6H5]+, 91 (basic peak), 105
[C6H5СНMe]+ and 119 [С6Н5СН(Me)СН2]+; for the
silicon part 59 [Me2SiH or MeSiO]+ and 133 [HSi(Me)2·
OSiMe2]+.
The main direction of side pathway of (HMe2Si)2O
transformations in the presence of the considered
metallocomplexes is disproportion of its two molecules
into 1,1,3,3,5,5-hexamethyltrisiloxane HMe2SiOSi
(Me2)OSiMe2H (retention time 7.9 min) and
dimethylsilane Me2SiH2 (Scheme 4), as has been
reported [9, 24]. Under ambient conditions, Me2SiH2 is
gaseous [25], therefore the peak corresponding to it
does not occur in the chromatogram. The second
pathway of formation of HMe2SiOSi(Me2)OSiMe2H
One more cause for the appearance of HMe2SiOSi
(Me2)OSi(Me2)OSiMe2H in the reaction mixture is
dehydrocondensation of (HMe2Si)2O in the presence of
water traces [24] according to the reactions:
(HMe2Si)2O + Н2О → HMe2SiOSiMe2OH + H2,
HMe2SiOSiMe2OH + (HMe2Si)2O
→ HMe2SiOSi(Me2)OSi(Me2)OSiMe2H + H2.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

EFFECT OF CATALYST STRUCTURE ON THE REACTION
765
Scheme 4.
−Si−O−Si−H
H−Si−O−Si−H
H−Si−O−Si−H
H−Si−O−Si−H
H−Si
O−Si
H
H−Si−H
−Si−H
2
H−Si
O−Si
H
2
−Si−O−Si−H or H−Si−O−Si−H
−Si−H or H−Si−H
H−Si−O−Si−H
H−Si
H−Si
O−Si
H
3
O−Si
H
H−Si
O−Si
H
3
−Si−O−Si−H or H−Si−O−Si−H
2
H−Si−O−Si−H
H−Si
O−Si
H
−Si−H or H−Si−H
2
H−Si
O−Si
H
4
H−Si
O−Si
H
H−Si
O−Si
O−Si
H
2
3
H−Si−O−Si−H
H−Si
H
2
H−Si
O−Si
H
−Si−O−Si−H or H−Si−O−Si−H
H−Si
O−Si
H
5
5
H−Si
O−Si
H
H−Si
O−Si
H
H−Si
4
O−Si
H
2
3
H−Si−O−Si−H
H−Si
O−Si
H
−Si−H or H−Si−H
2
H−Si
O−Si
H
H−Si
O−Si
H
3
H−Si
O−Si
H
4
6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

766
DE VEKKI, SKVORTSOV
Scheme 5.
Si
H
O
Si
H
Si
H
O
Si
H
4
Si
H
O
Si
H
Si
H
O
Si
H
2
Si
O
Si
Si
O
Si
O
Si
O
O
O
Si
H
O
Si
H
5
Si
O
Si
Si
H
O
Si
H
6
Si
H
O
Si
H
Si
H
O
Si
H
2
3
This pathway of (HMe2Si)2O transformation is
confirmed indirectly by the existence in the reaction
mixture of D3 and D4, formed, according to publica-
tions [26, 27], at the presence of a source of ОН groups
(e.g., water) from HMe2SiOSi(Me2)OSiMe2H and HMe2Si·
OSi(Me2)OSi(Me2)OSiMe2H respectively (Scheme 6).
product of α-methylstyrene reduction, is formed in
trace amounts.
Kinetic monitoring of the reaction proceeding of
(HMe2Si)2O with α-methylstyrene allowed to elucidate
the most active catalysts of hydrosilylation (as a
measure of activity of a catalyst is taken conversion of
α-methylstyrene at the same duration period for all the
catalysts). The best are cis-dichlorobispyridinepla-
tinum(II) cis-[Pt(Py)2Cl2] and tetrapyridineplatinum(II)
[Pt(Py)4]Cl2. Conversion of α-methylstyrene at 90°С
Effect of platinum complexes. Reaction of α-
methylstyrene with (HMe2Si)2O in the presence of
platinum catalysts leads to predominate formation of
β-adducts (compounds A and B) while cumene, the
Scheme 6.
Si
Si
H
O
Si
H
H
O
Si
H
H2O
2
3
Si
O
Si
Si
O
Si
H2
O
O
O
O
Si
Si
O
Si
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

EFFECT OF CATALYST STRUCTURE ON THE REACTION
767
after 47 h in the presence of cis-[Pt(Py)2Cl2] was 89%,
with [Pt(Py)4]Cl2 95% (see the figure). That is, cis-
[Pt(Py)2Cl2] and [Pt(Py)4]Cl2 are of similar activity.
The addition selectivity with both these complexes by
the data of chromatography is 99%, the β-adduct :
cumene ratio is 380 : 1 and 250 : 1 for [Pt(Py)4]Cl2 and
cis-[Pt(Py)2Cl2], respectively.
[the optical activity bears (+)-Me-p-TolSO–(+)-methyl-
para-tolylsulfoxide] show catalytic activity com-
parable with that of cis-[Pt(Et2SO)(Py)Cl2] and cis-
[Pt(Et2SO)2Cl2], respectively, but their application
does not lead to asymmetric induction (the data of
polarimetry, 18°С, 7 days). Reasons of such behavior
of (–)-cis-[Pt(Me-p-TolSO)(Py)Cl2] and (–)-cis-[Pt
(Me-p-TolSO)2Cl2] will be considered below.
At 80°С trans-[Pt(Py)2Cl2] displays lower catalytic
activity than its cis-analog (after 73 h the conversion is
32% against 73% for the cis-isomer); increasing the
reaction temperature does not changes the observed
picture (see the figure). This effect of the
metallocomplex configuration on its catalytic pro-
perties is well consistent with the published data on the
catalysis in the presence of geometric isomers of
platinum(II) coordination compounds [3, 14, 18].
However, the fact that di- and tetrapyridine platinum(II)
coordination compounds possess catalytic properties is
rather unexpected, because earlier has been shown that
the presence of one pyridine molecule in the platinum(II)
coordination sphere decreases considerably the
catalytic activity of the metallo-complex at the
hydrosilylation of vinylsiloxanes [18, 20], alkenes [3,
15] and ketones [28], and [Pt(Py)2Cl2] does not
catalyze this reaction at all [15, 18, 21, 28]. By the
chromatographic data, selectivity of addition in the
presence of trans-[Pt(Py)2Cl2] is 99%, the ratio β-
adduct : cumene is 248 :1. Thus, the reaction of
(HMe2Si)2O with α-methylstyrene in the presence of
geometric isomers of [Pt(Py)2Cl2] proceeds similarly
by selectivity.
Dichloro-η4-(1-methylcycloocta-1,5-diene)platinum(II)
[Pt(MeCOD)Cl2] that catalyzes successfully the hydro-
silylation of siloxane [18] shows lower activity than
[Pt(Py)4]Cl2 and cis-[Pt(Py)2Cl2] in the earlier steps of
the reaction of (HMe2Si)2O with α-methylstyrene at
90°С, although the durations for achieving 99%
conversion are similar (see figure). But conversion of
α-methylstyrene at 80°С after 73 h in the presence of
[Pt(MeCOD)Cl2] is a bit lower (69%) than in the
presence of cis-[Pt(Py)2Cl2] (73%). Selectivity of β-
addition in the presence of [Pt(MeCOD)Cl2] is, by the
data of chromatography, 99%, and the ratio β-adduct :
cumene is 120:1.
The lowest catalytic activity displays triphenyl-
phosphine complex of platinum(II), that is typical for
its catalysis of the reaction of hydrosilylation [2, 3,
29]. However, in the initial steps of this reaction the α-
methylstyrene conversion in the presence of cis-
1
100
80
2
3
Diethylsulfoxide substitution for the pyridine ligand
in cis-[Pt(Py)2Cl2] leads to decrease in catalytic
activity of the complex: cis-[Pt(Et2SO)(Py)Cl2] is less
active catalyst of α-methylstyrene hydrosilylation than
cis-[Pt(Py)2Cl2] (see the figure). Replacement of the
second pyridine ligand by diethylsulfoxide {in going
from cis-[Pt(Et2SO)(Py)Cl2] to cis-[Pt(Et2SO)2Cl2]}
increases the rate of the reaction but the rate remains
lower than in the presence of cis-[Pt(Py)2Cl2] and
[Pt(Py)4]Cl2 {after 10.3 h at 80°С the α-methylstyrene
conversion is 25, 36 and 42% in the presence of cis-
[Pt(Et2SO)(Py)Cl2], cis-[Pt(Et2SO)2Cl2] and [Pt(Py)4]Cl2,
respectively}. The higher activity of bissulfoxide
catalyst as compared with the pyridinesulfoxide one is
well consistent with the published data on the hydro-
silylation of other unsaturated compounds [3, 18, 20].
4
60
5
40
6
20
0
10 20 30 40 50 60 70
Time, h
80
Change in time of α-methylstyrene conversion in the
reaction with (HMe2Si)2O in the presence of catalysts [90°С,
Сc 1×10–3 mol l–1, α-methylstyrene : (HMe2Si)2O = 1:3 mol]:
(1) [Pt(Py)4]Cl2; (2) [Pt(MeCOD)Cl2]; (3) cis-[Pt(Py)2Cl2];
(4) cis-[Pt(Et2SO)(Py)Cl2]; (5) trans-[Pt(Py)2Cl2]; and
(6) cis-[Pt(Ph3P)2Cl2].
The chiral complexes of similar structure, (–)-cis-
[Pt(Me-p-TolSO)(Py)Cl2] and (–)-cis-[Pt(Me-p-TolSO)2Cl2]
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768
DE VEKKI, SKVORTSOV
[Pt(Ph3P)2Cl2] prevails those in the presence of trans-
[Pt(Py)2Cl2] (see figure, curves 5, 6). A feature
distinguishing hydrosilylation of α-methylstyrene from
that of other unsarurated compounds [14, 16, 17, 19] in
the presence of cis-[Pt(Ph3P)2Cl2] is the absence of
induction period on the kinetic curve (see figure, curve
6), that indicates faster formation in the reaction
medium of catalytically active moieties. Effect of air
oxygen on the hydrosilylation in the presence of
phosphine complexes corresponds to that described in
literature [19, 30]: the presence of oxygen increases
activity of the catalyst (in our case, α-methylstyrene
conversion for 100 at 80°С in the presence of oxygen
is 43% against 7%).
[Rh(MeCOD)Cl]2 by the data of chromatography is
6:1, while α-adduct : cumene ratio in the presence of
[Pd(MeCOD)Cl2] is 1:160. The such high fraction of
the reduction product of α-methylstyrene in the case of
[Pd(MeCOD)Cl2] is a result of fast transformation of
the complex into colloidal palladium [at the adding
(HMe2Si)2O to the reaction mixture it appears as
abundant flaky brown precipitate] which does not
catalyze hydrosilylation with hydrosiloxanes [18, 31],
but by our data is active at reduction of double bonds
with the hydrosiloxanes.
The total yield of the products of hydrosilylation
with 1,1,3,3-tetramethyldisiloxane in the presence of
[Rh(MeCOD)Cl]2 according to the data of chromato-
graphy is only 34%, in the presence of [Rh(Ph3P)3Cl]
24%; the selectivity of β-addition at the catalysis with
[Rh(MeCOD)Cl]2 is 97%, with [Rh(Ph3P)3Cl] 87%.
Thus, the catalysis of α-methylstyrene hydro-
silylation with (HMe2Si)2O occurs the following order
of the effect of neutral ligands on the activity of
platinum(II) complexes:
Another feature of the reaction of α-methyl styrene
with (HMe2Si)2O in the presence of the considered
rhodium and palladium catalysts is formation in the
reaction mixture of long-chain linear and cyclic
siloxanes. By the data of chromato-mas spectrometry,
in the reaction mixture besides the mentioned above
siloxanes present 1,1,3,3,5,5,7,7,9,9,11,11,13,13-tetra-
decamethylheptasiloxane and 1,1,3,3,5,5,7,7,9,9,11,11,-
13,13,15,15-hexadecamethyloctasiloxane, decamethyl-
cyclopentasiloxane (D5), dodecamethylcyclohexasil-
oxane (D6) and tetradecamethylcycloheptasiloxane
(D7); the ratio of D5 : D6 : D7 is 6 : 4 : 1. Formation of
these substances obviously also is a result of
disproportion and dehydrocondensation of respective
siloxanes, which in this case proceeds along the
Schemes 4–6.
Py > MeCOD > Et2SO > Ph3P.
Influence of palladium and rhodium complexes.
Unlike the coordination compounds of platinum(II),
the selectivity of reaction of α-methylstyrene with
(HMe2Si)2O in the presence of rhodium(I) and
palladium(II) complexes is not very high.
The hydrosilylation of α-methylstyrene in the
presence of triphenylphosphine and methylcyclo-
octadiene rhodium catalysts
{[Rh(Ph3P)3Cl] and
[Rh(MeCOD)Cl]2 respectively} proceeds with reduc-
tion of the substrate in a great extent, while in the
presence of triphenylphosphine and methylcycloocta-
diene palladium complexes {cis-[Pd(Ph3P)2Cl2] and
[Pd(MeCOD)Cl2] respectively} formation of cumene
prevails.
Prolonged keeping of reaction solutions containing
rhodium and palladium catalysts leads to formation of
a gel due to stepwise increase in amount of linear and
cyclic high molecular siloxanes, that in the case of,
e.g., [Pd(MeCOD)Cl2] are registered by appearance in
1H NMR spectrum of three very strong singlet signals
of methylsilicon groups protons at δН 0.07, 0.08 and
1.00 ppm, and in the 13С NMR spectrum of a broad
singlet at δС 0.65 ppm.
Conversion of α-methylstyrene after 50 h at 80°С in
the presence of [Rh(Ph3P)3Cl] is 7%, with cis-
[Pd(Ph3P)2Cl2] 1%, while in the presence of cis-
[Pt(Ph3P)2Cl2] 17%. The β-adduct : cumene ratio in
the presence of [Rh(Ph3P)3Cl] is about 2:1. After 130 h
at 90°С the conversion of α-methylstyrene in the
presence of [Rh(Ph3P)3Cl] is 41% at the same β-
adduct : cumene ratio, while in the presence of cis-
[Pd(Ph3P)2Cl2] the conversion of α-methylstyrene is
not higher than 3%.
Reaction of the complexes with the reagents. To
reveal why absent the transfer of chirality at the
application of optically active platinum(II) complexes
containing coordinated (+)-Me-p-TolSO, and also for
elucidation the mechanism of action of highly active
pyridine complexes and low effective phosphine
complexes we studied their behavior in the presence of
The conversion of α-methylstyrene after 73 h at
80°С in the presence of [Rh(MeCOD)Cl]2 and
[Pd(MeCOD)Cl2] is the same (34%), but with both the
catalysts is lower than with [Pt(MeCOD)Cl2] (69%).
The β-adduct : cumene ratio in the presence of
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EFFECT OF CATALYST STRUCTURE ON THE REACTION
769
(HMe2Si)2O, α-methylstyrene and styrene excess by
by several factors. First, S–O bond in free ligand lies
almost in the plane of aromatic ring (as known [34],
such configuration is the most advantageous for the
sulfoxides with aromatic substituents at the sulfur atom
because this assists to partial conjugation of the
electrons of rig and S–O bond), while , e.g., in (–)-cis-
[Pt(Me-p-TolSO)2Cl2] the S–O bond of only one
sulfoxide ligands is in the plane of the ring (the
dihedral angle is 6.8°), while not of the second ligand
(the respective dihedral angle is 76°) [35]. Second, at
the reduction of coordinated (+)-Me-p-TolSO occurs
coordination of hydrosiloxane at the platinum atom
and hence the Si–H bond becomes activated. At the same
time, the fact that coordination of (+)-Me-p-TolSO
leads to a noticeable shortening of S–O bond {in free
(+)-Me-p-TolSO, in (–)-cis-[Pt(Me-p-TolSO)2Cl2] and
in (–)-cis-[Pt(Me-p-TolSO)(Py)Cl2] the S–O bond
length is respectively 1.493, 1.482 (in the second
sulfoxide 1.473) and 1.469 Ǻ [35–37]} does not affect
such considerably the rate of reduction of this bond.
1
the method of Н and 13С NMR spectroscopy. For the
phosphine containing coordination compounds was
also used 31Р NMR spectroscopy.
At keeping the solution of (–)-cis-[Pt(Me-p-TolSO)2Cl2]
[CDCl3; δН, ppm: 2.47 s (3H, Ph-CH3); 3.48 t (JPt–H
22.7 Hz, 3Н, S–CH3); 7.41 d (2Н, Ph, JH–H 8.2 Hz);
7.95 d (2Н, Ph, JH–H 8.3 Hz) in CH2Cl2 s (HMe2Si)2O
[the mole ratio complex : (HMe2Si)2O = 1:45.5] at
room temperature it initially becomes yellowish-green
and then brown. This change in color is explainable by
the formation of a platinum–silicon hydride complex
that then stepwise is transformed into colloidal
1
platinum [32, 33]. In the H NMR spectrum of the
yellowish-green solution occur the signals of free
Me-p-TolSO [δН, ppm: 2.42 s (3H, Ph–CH3); 2.71 s
(3Н, S–CH3); 7.35 d (2Н, Ph, JH–H 7.6 Hz); 7.53 d (2Н,
Ph, JH–H 7.7 Hz)] and of new complex cis-[Pt(MeS-p-
Tol)2Cl2] (MeS-p-Tol = methyl-para-tolylsulfide) [δН,
ppm: 2.36 s (3H, Ph–CH3); 2.66 t (3Н, S–CH3, JPt–H
40.6 Hz); 7.21 d (2Н, Ph, JH–H 8.1 Hz); 7.71 d (2Н, Ph,
Keeping a solution of (–)-cis-[Pt(Me-p-TolSO)2Cl2]
in CH2Cl2 with α-methylstyrene (the complex : α-me-
thylstyrene mole ratio is 1:10) at 20°С leads to changes
J
H–H 8.1 Hz)]. After 15-min keeping at 20°С the parent
complex disappears from the reaction mixture and the
ratio Me-p-TolSO : cis-[Pt(MeS-p-Tol)2Cl2] becomes
equal to 1:3. Heating the reaction mixture to 80°С
1
in the structure of the H NMR spectrum of the
solution. After 22 days in the NMR spectrum besides
the signals of coordinated and free Me-p-TolSO (7:1
ratio) occur singlets at δН 2.84, 4.79, 5.14 ppm in the
ratio 5:2:2.
1
accelerates the process of reduction. In the H NMR
spectrum after 15-min heating occur the signals of cis-
[Pt(MeS-p-Tol)2Cl2] and of free Me-p-TolSO and
MeS-p-Tol [δН, ppm: 2.31 s (3H, Ph-CH3); 2.46 s (3Н,
S–CH3); 7.10 d (2Н, Ph, JH–H 8.0 Hz); 7.18 d (2Н, Ph,
In distinct to α-methylstyrene, at keeping a solution
of (–)-cis-[Pt(Me-p-TolSO)2Cl2] in CH2Cl2 with
styrene (the complex : styrene mole ratio 1:10) at 20°С
J
H–H 7.9 Hz)] in 4:1:20 ratio. After 1.5-h heating at 80°
С the reaction mixture becomes consisting of cis-[Pt
(MeS-p-Tol)2Cl2] and free sulfide in the ratio 10 : 93.
In the case of (–)-cis-[Pt(Me-p-TolSO)(Py)Cl2] the
complex decomposition and formation of free Me-p-
TolSO and MeS-p-Tol proceeds slower, that is defined
by known higher stability of platinum(II) pyridine-
sulfoxide complexs as compared with bissulfoxide
complexes toward their reduction with silcon hydrides
[18].
1
in the H NMR spectrum appear the signals of free
Me-p-TolSO, probably due to replacement it in the
complex by styrene. After 22 days by the data of NMR
the ratio of coordinated Me-p-TolSO to free becomes
equal to 10:1.
Thus, the absence of asymmetric induction in the
presence of platinum(II) complexes with coordinated
(+)-Me-p-TolSO is due to chirality loss at fast
reduction of optically active (+)-Me-p-TolSO into
achiral sulfide under the action of (HMe2Si)2O [in (+)-
Me-p-TolSO the sulfur(IV) atom is chiral] or at its
elimination in the course of catalysis.
Heating of a mixture of non-coordinated (+)-Me-p-
TolSO в CH2Cl2 and (HMe2Si)2O [mole ratio (+)-Me-
p-TolSO : (HMe2Si)2O = 1 : 22.5] also leads to rapid
reduction of the sulfoxide into sulfide. By the data of
1H NMR spectroscopy, after 15 min at 80°С yield of
MeS-p-Tol is 48% against 80% at the reduction of (+)-
Me-p-TolSO in the coordination sphere; after 1.5 h
90% against 93%.
The scope of the data obtained and analysis of the
published data (other examples of desoxygenation of
coordinated sulfoxides are given in [38]) allow to
assume the following Scheme of transformation of
platinum(II) complexes with (+)-Me-p-TolSO in the
presence of silicon hydrides:
The faster reduction of coordinated (+)-Me-p-
TolSO as compared with the free sulfoxide is defined
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

770
DE VEKKI, SKVORTSOV
p-Tol
S
p-Tol
Cl
Si
H
i
Pt + L' +
S
Me
L'
Pt
Pt
p-Tol
O
Me
Cl
S
Cl
Si
H
Si
H
Me
Pt
H
Si
H
L
Cl
Si
Cl
p-Tol
O
ii
+
S
L
Cl
Me
L = Me-p-TolSO, Py; L' = MeS-p-Tol, Py.
Reaction of the sulfoxide-containing platinum(II)
complexes with silicon hydride proceeds in two
directions: (i) Reduction by the silicon hydride of Me-
p-TolSO located in the platinum inner coordination
shell into MeS-p-Tol and (ii) ligand exchange with
formation of silicon hydride platinum complex and
free sulfoxide. Further transformations of both the
metalloxcomplexes and free Me-p-TolSO consists in
their reduction into colloidal platinum and MeS-p-Tol
respectively, in the case of (–)-[Pt(Me-p-TolSO)(Py)Cl2]
into the colloidal Pt, MeS-p-Tol and pyridine.
are the same as the signals of extract with chloroform
of the polystyrene prepared for this experiment by
ionic polymerization of styrene. The polystyrene yield
in the presence of cis-[Pd(Ph3P)2Cl2] by the NMR data
is 100% after 23 h, in the presence of cis-[Pt(Ph3P)2Cl2]
50%.
Heating of [Rh(Ph3P)3Cl] (δP 29.42 ppm) with α-
methylstyrene (complex : α-methylstyrene mole ratio
is 1:100) at 90°С for 130 h does not lead to changes in
1Н, 13С and 31Р NMR spectra of the reaction mixture,
while at heating with styrene at the same mole ratio for
1
130 h in the Н and 13С NMR spectra appear the
Reaction of platinum, palladium and rhodium
phosphine complexes with silicon hydrides has been
studied to the moment in details. It is suggested that in
the course of the catalysis are formed both metal–silyl
intermediates [16] and metal–hydride complexes [39].
Other authors [19, 40] hold a hypothesis about η2-
coordination of silicon hydrides. However, behavior of
phosphine complexes in styrene systems has poorly
been studied.
signals of polystyrene. Heating of [Rh(Ph3P)3Cl] (δP
29.41 ppm) with (HMe2Si)2O [the complex to
(HMe2Si)2O mole ratio is 1:100] at 90°С for 31 h
damages the complex (the solution becomes dark-
brown and in its 31Р NMR spectrum occurs only one
signal at δP 20.68 ppm that responds to triphenyl-
phosphine oxide).
Study of reaction of the platinum pyridine com-
plexes with the reactants applied to hydrosiylation has
never been described, therefore we considered this
reaction with α-methylstyrene and styrene, and with
(HMe2Si)2O as well.
Heating of cis-[Pt(Ph3P)2Cl2] [δP 13.81 t (JPt–H
3677.4 Hz) ppm] and cis-[Pd(Ph3P)2Cl2] (δP 23.97 ppm)
with α-methylstyrene (the complex : α-methylstyrene
mole ratio is 1:160) at 90°С for 120 h does not lead to
1
any changes in Н, 13С and 31Р NMR spectra of the
Heating of trans-[Pt(Py)2Cl2] with styrene (the
complex : styrene mole ratio is 1:10) in CDCl3 at 50°С
for 35 h or at 90°С for 46 h leads to appearance in the
reaction mixture of polystyrene traces (1H NMR
monitoring), and probably to styrene η2-coordination
[δH 7.64 t (1Нγ, J 8.2 Hz), 7.90 d (2Нα, J 7.8 Hz), the
signals of 2Нβ and η2-СH=CH2 group are overlapped
with the signals of styrene and polystyrene]. By the
NMR data the ratio of coordinated pyridine : co-
ordinated styrene is 3 : 1. Heating of trans-[Pt(Py)2Cl2]
with α-methylstyrene (the complex : α-methylstyrene
mole ratio is 1:10) in CDCl3 at 90°С for 53 h also
reaction mixture. Heating these complexes with
styrene under the same conditions also do not lead to
appearance of new signals in 31Р NMR spectrum. But
appear increase in viscosity of the reaction mixture
containing cis-[Pt(Ph3P)2Cl2], and stepwise poly-
merization occurs of the reaction mixture containing
1
cis-[Pd(Ph3P)2Cl2]. In the H NMR spectra of both the
mixtures appear broad signals at δН 1.47 s, 1.84 s, 6.49 d
13
(J 16.9 Hz), 6.59 s and 7.06 d (J 17.2 Hz) ppm, in С
NMR spectrum at δС 40.45 s, 44.15 s, 125.64 s, 127.96 s,
145.31 s. These signals by shape and chemical shifts
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EFFECT OF CATALYST STRUCTURE ON THE REACTION
771
1
leads to appearance in the H NMR spectrum of new
signals, probably due to α-methylstyrene η2-coordina-
tion [δH 7.55 d (2Нβ, J 7.1 Hz), 7.79 t (1Нγ, J 7.4 Hz),
7.96 d (2Нα, J 7.7 Hz)].
some cases afford colloidal platinum. Such colorize-
tion commonly is suggested to be a result of formation
of platinum–hydrosiloxane complexes [32, 33]. Unlike
the platinum coordination compounds, after the
reaction of rhodium catalysts with (HMe2Si)2O the
reaction mixture becomes brown.
Heating of cis-[Pt(Py)2Cl2] and [Pt(Py)4]Cl2 with
styrene or α-methylstyrene (the complex : reactant
mole ratio is 1:10) in CDCl3 at 90°С for 126 h like the
case of trans-[Pt(Py)2Cl2] leads to appearance of
signals that we assigned to the traces of coordinated
reactant. Also, heating of [Pt(Py)4]Cl2 with the
reactants is accompanied with the pyridine elimination
leading to formation of cis-[Pt(Py)2Cl2]. However and
idle experiment of heating [Pt(Py)4]Cl2 in CDCl3
without the reactants at 90°С after 46 h also affords
cis-[Pt(Py)2Cl2] in 90% yield.
Analysis of the results listed in the table allows to
conclude the following.
The platinum complex with η4-methylcyclo-
octadiene or with two sulfoxide ligands being heated in
(HMe2Si)2O displays a bit higher catalytic activity than
the not treated one. On the contrary, the treatment of
the complexes with α-methylstyrene led to decrease of
α-methylstyrene conversion.
The tendency to decrease in activity of the catalyst
after heating it with α-methylstyrene occurs also in the
case of pyridinesulfoxide catalyst, and maximal
conversion of α-methylstyrene can be achieved
without its preliminary treatment.
Heating of [Pt(Py)4]Cl2 with styrene taken in a large
excess (the complex : styrene mole ratio is 1:100) at
90°С for 7 h induces styrene polymerization and forma-
tion of cis-[Pt(Py)2Cl2], while heating of [Pt(Py)4]Cl2
with α-methylstyrene under the same conditions
eliminates pyridine, the rate of the elimination is only a
bit higher than in the idle experiment.
Dipyridine platinum(II) complex with cis-structure
in distinct to cis-[Pt(Et2SO)(Py)Cl2] and cis-[Pt(Et2SO)2Cl2]
showed a bit higher activity after treatment with α-
methylstyrene than untreated complex, while heating
with (HMe2Si)2O leads to decrease in catalytic
properties. At the same time the maximal activity of
trans-[Pt(Py)2Cl2] occurs after its activation with
(HMe2Si)2O: conversion of α-methylstyrene after
treatment is 4-fold higher. This can be connected with
the difference in the initial steps of the mechanism of
action of the geometric isomers of the platinum(II)
complexes.
Heating of [Pt(Py)4]Cl2 with (HMe2Si)2O [the
complex : (HMe2Si)2O mole ratio is 1:10] in CDCl3 at
90°С for 53 h leads to formation of cis-[Pt(Py)2Cl2]. In
turn, cis-[Pt(Py)2Cl2] being heated under the same
conditions does not exert any changes while trans-
[Pt(Py)2Cl2] is damaged, as confirmed by the presence
in the 1H NMR spectrum of the signals of free pyridine
only.
Thus, phosphine and sulfoxide metallocomplexes
react more actively with (HMe2Si)2O, than with α-
methylstyrene; in the case of pyridine coordination
compounds occurs coordination of α-methylstyrene.
A good sensitivity toward the preliminary treatment
showed [Pt(Py)4]Cl2: its activation with α-methyl-
styrene is a bit more effective than with (HMe2Si)2O,
while without preliminary heating of the complex with
the reactants the α-methylstyrene conversion was two-
fold lower.
Preliminary activation of complexes. Uncertainty
of the data obtained on the reaction of the complex
with the reactants inclined us to carry out their
preliminary activation with α-methylstyrene or
(HMe2Si)2O and then estimate the catalytic activity of
the resulting substance.
The preliminary keeping of the platinum triphenyl-
phosphine complex with the reactants led to decrease
in α-methylstyrene conversion as compared to a not
activated system; in the case of [Rh(Ph3P)3Cl] the
catalyst becomes slightly activated in α-methylstyrene.
In all cases the preliminary activation of the
platinum complexes with tetramethyldisiloxane is
accompanied with colorization of the reaction solution
to yellow or yellowish-green {e.g., after the treatment
of trans-[Pt(Py)2Cl2], sulfoxide and methylcyclo-
octadiene complexes the color of solution is green, of
pyridinesulfoxide complexes yellowish-green, of [Pt
(Py)4]Cl2 and cis-[Pt(Ph3P)2Cl2] light yellow}, and in
The α-methylstyrene conversion in the presence of
not treated [Rh(MeCOD)Cl]2 turned to be a bit higher
than after its preliminary treatment with α-methyl-
styrene, while activation of the complex with (HMe2Si)2O
decreases its catalytic properties considerably.
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772
DE VEKKI, SKVORTSOV
Thus, in most cases the preliminary treatment of
With the above analysis of behavior of the
coordination compounds in the reaction mixtures and
assumption of η2-coordination of the reactants in mind,
we propose the following simplified Scheme of the
reaction mechanism of hydrosilylation (on an example
of formation of β-adduct):
catalysts leads to increase in the reaction rate, but in
some cases to decrease, that can be connected with
difference in the mechanism of formation of real
catalysts.
Hydrosilylation mechanism. Current view on the
mechanism of catalytic hydrosilylation of С=С bond is
based on several Schemes [29, 41–47]. The Scheme of
Chalk and Harrod [41] assumes reversible coordination
of alkene and oxidative addition of Si–H to the
platinum atom and insertion of the coordinated alkene
to the metal–hydrogen bond followed by reductive
elimination of alkyl and silyl ligand as a key step. Such
Scheme explains isotopic exchange between the alkene
and Si–D and isomerization of alkene in side process.
According to modified Scheme proposed by Chalk and
Harrod [42, 43] the insertion proceeds to the metal–
silicon bond and then occurs elimination of silyl and
hydride ligands. Also, there is another concept of the
Si–H bond activation based on the assumption of η2-
coordination of the hydrosilane without complete
cleavage of bonds (three-center bonding) [29, 44–47]
that has been confirmed by, e.g., of X-ray structural
analysis [48, 49]. This Scheme is consistent with the
general view on the essence of the catalytic process
that assumes only loosening of bonds and formation of
unstable intermediate structures that can not be
isolated by chemical means.
The initial transformation of the platinum(II)
complex at the action of reactants is competitive
coordination of the reactants for the formation of η2-
styrene (path i, complex E) or η2-hydrosiloxane com-
plexes (path ii, complex F), differ by their catalytic
activity. That is, occurs formation of two real catalysts
of the process. In the favor of proceeding the (i) step
attest two facts: the preliminary keeping of [Pt(Py)4]Cl2
and cis-[Pt(Py)2Cl2] with α-methylstyrene allows to
increase conversion of the latter at its reaction with
(HMe2Si)2O, and appearance in the NMR spectra of
the signals of coordinated α-methylstyrene. With
sulfoxide and cyclooctadiene catalysts the process is
defined by interaction with silicon hydride (path ii), as
confirmed by the increasing in α-methylstyrene
conversion in the reaction with (HMe2Si)2O in the
presence of the complexses treated preliminary with
(HMe2Si)2O, and this fact is consistent well with the
published data on the hydrosilylation mechanism in the
presence of sulfoxide and cyclooctadiene catalysts. But
we have to note that in the case of [Pt(MeCOD)Cl2]
the paths (i) and (ii) is differ slightly from the above
considered because here after formation of E and F
Conversion of α-methylstyrene [α-C9H11] in its reaction with (HMe2Si)2O in the presence of preliminary treated and
untreated complexes (88°С, 5 h)
Complex
Activation
Conversion, %
Complex
Activation
Conversion, %
[Pt(MeCOD)Cl2]
(HMe2Si)2O
α-C9H11
–
29.3
5.7
cis-[Pt(Py)2Cl2]
(HMe2Si)2O
α-C9H11
–
14.8
21.5
19.9
10.4
(HMe2Si)2O
α-C9H11
–
(HMe2Si)2O
α-C9H11
–
Traces
3.3
cis-[Pt(Me2SO)2Cl2]
cis-[Pt(Et2SO)2Cl2]
trans-[Pt(Py)2Cl2]
[Pt(Py)4]Cl2
26.2
9.8
[Rh(Ph3P)3Cl]
23.3
1.9
(HMe2Si)2O
(HMe2Si)2O
14.5
17.7
cis-[Pt(Et2SO)(Py)Cl2]
[Rh(MeCOD)Cl]2
cis-[Pt(Ph3P)2Cl2]
α-C9H11
–
2.9
7.5
α-C9H11
–
0.7
20.8
3.0
(HMe2Si)2O
(HMe2Si)2O
17.5
α-C9H11
3.7
α-C9H11
11.2
–
4.3
18.9
23.8
–
14.2
1.7
(HMe2Si)2O
α-C9H11
(HMe2Si)2O
α-C9H11
7.3
–
9.8
–
11.2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

EFFECT OF CATALYST STRUCTURE ON THE REACTION
773
H3C
C
CH2
L'
HSi
L'
Pt(L)(L')Hal2
Ph
ii
i
Hal
Hal
L
Hal
Hal
L
Pt
H
Pt
H3C
Si
C
F
Е
C
H
E
Д
H3C
HC CH2
Ph
Ph
Ph
Si
H
H2C
C
SiH
CH3
Ph
H2C
C
CH3
H3C
HC CH2
Ph
Si
SiH
Hal
L
Ph
CH3
H3C
Ph
Pt
C
H2C
L
C
C
Hal
H
Hal
Hal
H
SiH
H
Pt
H
Si
Si
G
Ж
H
З
Ph
L, L' = сульфоксид, алкен,
пиридин, фосфин.
H3C
HC CH2
Ph
Si
H2C
C
CH3
L, L' =
sulfox-
complexes the ligand does not leave the coordination
process (from active E complex the less active F or,
otherwise, from active F less active E) can be
confirmed at the consideration of kinetic curves of
hydrosilylation in the presence of tetrapyridine and
methylcyclooctadiene catalysts (see figure, curves 1,
2; the curves are typical logarithmic ones), that show
decrease in the process rate in the final steps, probably
due to the above considered reasons.
sphere remaining η2-coordinated.
In the next step the formed complexes (E and F)
react with the second reactant. Complex E probably
affords tetracoordinated transition state G that at the
action of next α-methylstyrene molecule regenerates
the catalyst and affords the final reaction product. In
the case of the complex F probably occurs coordina-
tion of α-methylstyrene at the platinum unoccupied
orbital that affords respective platinum–siloxane–
styrene intermediate H. The latter in turn reacts with
next hydrosiloxane molecule affording the final
product of the hydrosilylation reaction and
regenerating one of the forms of the real catalysts of
the process.
It is a sophistical problem to decide which form of
the real catalyst is formed from cis-[Pt(Ph3P)2Cl2] is
the most active one. First, the α-methylstyrene
conversion in the reaction with (HMe2Si)2O in the
presence of the complex treated preliminary with the
reactants falls compared to the same reaction in the
presence of the untreated complex. But conversion of
α-methylstyrene at the hydrosilylation in the presence
of complex treated with α-methylstyrene turned to be
The formation of less active form of the catalyst
from the more active one in the course of the catalytic
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

774
DE VEKKI, SKVORTSOV
H3C
H3C
Ph
C
CH2
HSi
Cl
Pt
Cl
H3C
H3C
Cl
Cl
Cl
Cl
Pt
C
Pt
Si
H
C
H
H
H3C
Ph
higher than in the presence of the complex treated with
(HMe2Si)2O. However, e.g. in [28] was reported that
induction period of the reaction of hydrosilylation of
para-substituted styrenes with methyldichlorosilane
disappeared when the reaction was carried out in the
presence of cis-[Pt(Ph3P)2Cl2] treated preliminary with
methyldichlorosilane. By our data, keeping of cis-
[Pt(Ph3P)2Cl2] with (HMe2Si)2O is accompanied by
partial reduction of the parent complex. In this con-
nection, it is the most probable that the initial
transformation of planar-square phosphine complexes
of platinum leads to the formation of the real catalysts,
the complexes E and F with comparable catalytic
activity, and the Scheme of the catalysis is little differ
from the considered above.
In the case of rhodium catalyst, the first step of the
hydrosilylation cycle depends on the structutre of the
complex: with mononuclear [Rh(PPh3)3Cl] it is the
elimination of triphenylphosphine, with binuclear is
thermal destruction. In both these cases is formed
coordanationally unsaturated center that is instantly
occupied by a molecule of solvent–reactant.
Thus, in the reaction of α-methylstyrene with
(HMe2Si)2O in the presence of the considered
complexes occurs formation of two forms of real
catalyst (active and little active). Structure and
catalytic activity of each form depends not only on the
geometry of the parent complex and the nature of the
complex forming atom but also on the nature of ligand
environment. In a general case, at the decrease in σ-
donor and increase in p-acceptor contributions of a
neutral ligand (sulfoxide ≈ alkene > Py > phosphine [3,
18]) the real catalyst E activity grows and that of the
second real catalyst F falls.
The mechanism of interaction of the coordination
compounds of palladium with the reactants probably
differ from that of platinum catalysts. A feature of the
palladium complex is much higher rate of their
primary interaction with (HMe2Si)2O (path ii) than
with α-methylstyrene (path i). That is, formation of the
palladium catalyst with the structure analogous to that
of complex F prevails. This complex, in turn,
predominantly is transformed into metallic palladium
at the action of not coordinated (HMe2Si)2O molecules
rather than react with α-methylstyrene. At the same
time when palladium catalyst analogous by structure to
the E complex is formed, occurs hydrosilylation and
reduction of α-methylstyrene. Thus, the real active
palladium catalyst is its complex with η2-α-
methylstyrene.
EXPERIMENTAL
1
The Н, 13С and 31Р NMR spectra were registered
on Bruker АС-200 and WМ-400 spectrometers from
samples dissolved in CDCl3 or (CD3)2CО, at the
operating frequencies 200.13 and 400.14 (1Н), 50.33
(13С), 81.01 (31Р) МHz. Spectra of samples were
registered without additional reference substances,
referring to the signal of deuterated solvent.
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EFFECT OF CATALYST STRUCTURE ON THE REACTION
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The IR spectra were taken on Shimadzu FTIR-
8400S (4000–400 cm–1) and Hitachi FIS-3 (400–100 cm–1)
spectrometers from KBr tablets.
cooling, to the solution was added 0.54 ml of 1-
methylcycloocta-1,5-diene in 40 ml of ethanol. The
formed yellow precipitate was kept for 15 min, then
filtered off, washed on the filter with 3 ml of ice water
and 20 ml of diethyl ether and then dried at room
temperature for 24 h. 427 mg of [Pd(MeCOD)Cl2] was
obtained (yield 83.7%). The 1H NMR spectrum
(CDCl3; δН, ppm): 2.12 s (3Н, СН3), 2.41 m (4Н, СН2,
J 98 Hz), 3.05 m (4Н, СН2, J 94 Hz), 6.28 m (3Н, СН,
J 44 Hz). The 13С NMR spectrum (CDCl3; δС, ppm):
28.9 s (1С, СН3), 29.5 s (1С, СН2), 30.7 s (1С, СН2),
31.5 s (1С, СН2), 36.8 s (1С, СН2), 96.1 t (1С, СН, JPt–C
150 Hz), 107.8 s (1С, СН), 113.9 s (1С, СН), 115.9 s
(1С, С). The IR spectrum, cm–1: ν(СН) 3390–3350;
2920–2850; ν(С=С) 1515, 1485; δ(СН, Ме) 1460,
1405; 1357; 1332; 1305; 1238; 1185; 1165; 1140;
1090; δ(СН, COD) 1010, 987; τ(Me) 960, 920; δ(СН,
COD) 880, 862, 843; 807; 782; 725; 543. Far IR
spectrum, cm–1: ν(Pd–Cl) 336, 310; 293; 246; δ(Pd–Cl)
197.
The polarometric investigations were carried out on
a Perkin–Elmer 241MC polarimeter in thermostated
cells 10 cm length.
Hydrosilylation of α-methylstyrene with three mole
excess of 1,1,3,3-tetramethyldisiloxane was carried out
in sealed ampoules followed by analysis of the reaction
1
mixture by the method of H NMR spectroscopy in a
tentative time moment. The complex concentration in
the reaction mixture was varied in the range 5×10–4–
2×10–3 mol l–1.
The catalyst preliminary activation was carried out
with α-methylstyrene or (HMe2Si)2O in sealed
ampoules at 88°С for 5 h. Then the second reactant
was added and the mixture was kept 5 h next. For the
comparison were taken untreated catalysts and a
preliminary prepared mixture of α-methylstyrene and
(HMe2Si)2O. The catalyst concentration in the reaction
mixture was 0.85 mmol l–1.
Tetrapyridineplatinum(II) chloride. To a mixture
of 43.8 mg of cis-[Pt(Py)2Cl2] and 5 ml of water was
added 1.5 ml of pyridine and the mixture was heated
on a boiling water bath to formation of transparent
solution. The solution was then aerated to dryness and
the formed white precipitate was dried in a thermostat
at 40°С. 59.7 mg (yield 99.3%) of [Pt(Py)4]Cl2 was
obtained. The 1H NMR spectrum [(CD3)2CО; δН, ppm]:
7.54 t (2Нβ, Py, J 6.7 Hz), 8.04 t (1Нγ, Py, J 7.4 Hz);
8.89 d.t (2Нα, Py, J 5.3, J 17.7 Hz); (CDCl3; δ, ppm):
7.53 t (2Нβ, Py, J 6.4 Hz); 8.04 t (1Нγ, Py, J 7.3 Hz);
8.90 d.t (2Нα, Py, J 5.8, J 16.8 Hz). The IR spectrum,
cm–1: 3117; 3089; ν(СН) 3065, 3028; 3004; 2993;
2979; 2961 sh; 2925; 2847; ν(С=С and C=N) 1610,
1600; ν(С=С and C=N) 1478, 1452; δ(СН) 1222;
1162; 1138; δ(СН) 1084, 1070, 1025; 971, δ(СН) 898,
799, 770, 698. The far IR spectrum, cm–1: νs (Pt–N)
305.
Chromato-mass spectrometric investigation was
carried out on an Agilent 6890N chromatograph with
mass-selective deterctor Agilent 5973N, EI ionization
(70 eV). The column is of quartz capillary DB-5MS
(60 m×0.25 mm, phase film thickness 0.25 µm),
injector temperature 280°С, interface temperature 290°С,
the column temperature was varied from 150°С to
280°С with the rate 10 deg/min; carrier gas helium,
flow dividing 1:20; sample value 0.5 µl. For identifica-
tion of compounds was used NIST-2005 database.
The ratio of the formed products is calculated from
their weight yields.
In the experiments were used ethanol, diethyl ether,
styrene, α-methylstyrene, PdCl2, RhCl3·3H2O, MeCOD,
and hydrochloric acid of “chemically pure” grade;
1,1,3,3-tetramethyldisiloxane
from Acros; cis-
1,1,3,3-Tetramethyl-1-(2-phenylpropyl)disiloxane
(A). In a sealed ampoule was heated at 85°С for 150 h
a mixture of 11 mg of [Pt(Py)4]Cl2, 2 ml of α-methyl-
styrene and 8 ml of 1,1,3,3-tetramethyldisiloxane.
Then the reaction mixture was distilled in a vacuum, a
fraction boiling at 112°С (12 mm Hg). (published bp
80°С at 1 mm Hg. [13]) was selected. Product (2.52 g,
[Pt(Et2SO)2Cl2], cis-[Pt(Et2SO)(Py)Cl2], cis- and trans-
[Pt(Py)2Cl2], cis-[Pt(Ph3P)2Cl2], [Rh(Ph3P)3Cl] along
the data in [50], [Pt(MeCOD)Cl2], in [51], (–)-cis-
[Pt(Me-p-TolSO)(Py)Cl2] in [52], cis-[Pt(Me-p-
TolSO)2Cl2] in [53].
[Rh(MeCOD)Cl]2 was presented courtesy by dr.
Uvarov, St. Petersburg Technological Institute.
Dichloro(1,2:5,6-η4-1-methylcycloocta-1,5-diene)
palladium (II). In 1.5 ml of conc. hydrochloric acid
was dissolved at heating 303.4 mg of PdCl2. After
1
yield 53.7%) was obtained. The H NMR spectrum
(CDCl3, δН, ppm): –0.02 s (3H, Si–CH3), 0.00 s (3H,
Si–CH3), 0.18 s (3H, Si–CH3), 0.19 s (3H, Si–CH3),
1.01 d.q (2H, SiCH2, J 6.7, J 7.3 Hz), 1.34 d (3Н, СН3,
J 7.5 Hz), 2.96 d.t (1H, СH, J 6.5, J 7.0 Hz), 4.70 m
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776
DE VEKKI, SKVORTSOV
8. Ura, Y., Gao, G., Bao, F., Ogasawara, M., Takahashi, T.,
Organometallics, 2004, vol. 23, no. 21, p. 4804.
9. Zuev, V.V., de Vekki, D.A., Kuchaev, E.A., Vorob’ev, M.V.,
and Skvortsov, N.K., Zh. Obshch. Khim., 2004, vol. 74,
no. 11, p. 1804.
10. Zuev, V.V. and de Vekki, D.A., Phosph., Sulfur,
Silicon, and Relat. Elem., 2006, vol. 181, no. 9, p. 2063.
11. Titvinidze, G., Tatrishvili, T., Mukbaniani, N., and
Mukbaniani, O., Sakartvelos Mecnierebata Akademiis
Macne, Kimiis Seria, 2004, vol. 30, no. 1–2, p. 53.
12. Mukbaniani, O., Tatrishvili, T., Titvinidze, G., and
Mukbaniani, N., J. Appl. Polym. Sci., 2006, vol. 101,
p. 388.
(1H, SiH), 7.18 t (1Н, Ph, J 7.1 Hz), 7.28 m (4Н, Ph).
The 13С NMR spectrum (CDCl3, δС, ppm): 0.54 s (1С,
SiCH3), 0.89 s (2C, SiCH3), 0.96 s (1С, SiCH3), 26.03 s
(1С, CH3), 28.30 s (1С, CH2), 35.64 s (1С, CH),
125.76 s (1С, CНarom), 126.61 s (2С, CНarom), 128.30 s
(2С, CНarom), 149.77 s (1С, Carom). The mass-spectrum:
m/z (relative intensity of the ion,%) 251(1) [M – H]+;
239(5); 208(3); 193(2); 176(3) [M – H – HSi(CH3)2O]+
and (or) [M – H – 5(СН3)]+, and (or) [M – С6Н5]+; 149(22);
133 (30) [HSi(CH3)2OSi(CH3)2]+; 119(15) [С6Н5СН·
(СН3)СН2]+; 112(9); 105(81) [С6Н5СН(СН3)]+; 91(100);
77(11) [С6Н5]+; 59(4) [HSi(CH3)2]+ and/or [OSiCH3]+;
51(3) [(СН)4–H]+; 43(3) [SiCH3]+; 28 4) [CH2CH2]+;
18(1).
13. Ryan, J.W. and Speier, J.L., J. Org. Chem., 1959, vol. 24,
no. 12, p. 2052.
14. Trofimov, A.E., Spevak, V.N., Lobadyuk, V.I., Skvor-
tsov, N.K., and Reikhsfel’d, V.O., Zh. Obshch. Khim.,
1989, vol. 59, no. 9, p. 2048.
15. Trofimov, A.E., Skvortsov, N.K., Spevak, V.N., Loba-
dyuk, V.I., Komarov, V.Ya., and Reikhsfel’d, V.O., Zh.
Obshch. Khim., 1990, vol. 60, no. 2, p. 276.
16. Skvortsov, N.K., Trofimov, A.E., Titov, K.E., Spe-
vak, V.N., and Vasil’ev, V.V., Zh. Obshch. Khim.,
1991, vol. 61, no. 3, p. 574.
1,1,3,3-Tetramethyl-1,3-бис(2-phenylpropyl)di-
siloxane (B). The 1H NMR spectrum (CDCl3, δН, ppm):
1.05 s (12H, Si–CH3), 0.99 d (2H, SiCH2, J 6.9 Hz),
1.00 d (2H, SiCH2, J 7.0 Hz), 1.30 d (6Н, СН3, J 7.0 Hz),
2.94 q (2H, СH, J 6.4, J 7.3 Hz), 7.17 t (2Н, Ph, J 7.5 Hz),
7.24 m (8Н, Ph). The 13С NMR spectrum (CDCl3, δС,
ppm): 0.68 s (1С, SiCH3), 1.05 s (3C, SiCH3), 25.94 s
(2С, CH3), 28.40 s (2С, CH2), 35.61 s (2С, CH),
125.69 s (2С, CНarom), 126.59 s (4С, CНarom), 128.25 s
(4С, CНarom), 149.84 s (2С, Carom).
17. Titov, K.E., Gavrilenko, F.A, Vorob’ev-Desyatov-
skii, N.V., and Skvortsov, N.K., Zh. Obshch. Khim.,
1992, vol. 62, no. 9, p. 1942.
18. de Vekki, D.A., Ol’sheev, V.A., Spevak, V.N., and
Skvortsov, N.K., Zh. Obshch. Khim., 2001, vol. 71,
p. 2017.
19. de Vekki, D.A., and Skvortsov, N.K., Zh. Obshch.
Khim., 2004, vol. 74, no. 2, p. 224.
ACKNOWLEDGMENTS
This work was financially supported by the Russian
Foundation for Basic research (grants nos. 06-03-
32137а and 09-03-00341) and the government of St.
Petersburg (grant no. 36-MKN).
20. de Vekki, D.A. and Skvortsov, N.K., Zh. Obshch.
Khim., 2006, vol. 76, no. 1, p. 119.
REFERENCES
21. Astrakhanov, M.I. and Reikhsfel’d, V.O., Zh. Obshch.
Khim., 1973, vol. 43, no. 11, p. 2439.
22. de Vekki, D.A., Zh. Neorg. Khim., 2008, vol. 53, no. 8,
p. 1331.
1. Comprehensive Handbook on Hydrosilylation, Mar-
ciniec, B., Ed.,Oxford: Pergamon Press, 1992.
2. Pukhnarevich, V.B., Lukevits, E., Kopylova, L.I., and
Voronkov, M.G., Perspektivy gidrosililirovaniya
(Perspectives of Hydrisilylation), Lukevits, E., Ed.,
Riga: Inst. Org. Synthesis, Latv. Akad. Sci., 1992.
23. Fang, P.-F., Chen, Y.-Y., Wang, Z.-H., and Lu, Q.-S.,
Youji Huaxue, 1999, vol. 19, no. 6, p. 600.
24. de Vekki, D.A., Viktorovskii, I.V., and Skvortsov, N.K.,
Zh. Obshch. Khim., 2004, vol. 74, no. 9, p. 1426.
3. Skvortsov, N.K., Zh. Obshch. Khim., 1993, vol. 63, no. 5,
25. Bažant, V., Chvalovsky, V., and Rathousky, J.,
Organosilicon Compounds, Prague: Publ. House of
Czechoslovak Academy of Sciences, 1965, vol. 2/1, p. 56.
26. Voronkov, M.G., Mileshkevich, V.P., and Yuzhelev-
skii, Yu.A., Siloksanovaya svyaz’ (Siloxane Bond),
Novosibirsk: Nauka, 1976.
27. Bažant, V., Chvalovsky, V., and Rathousky, J.,
Organosilicon Compounds, Prague: Publ. House of
Czechoslovak Academy of Sciences, 1965, vol. 2/2.
p. 961.
4. Bringmann, G., Wuzik, A., Breuning, M., Henschel, P.,
Peters, K., and Peters, E.-M., Tetrahedron: Asymmetry,
1999, vol. 10, no. 15, p. 3025.
5. Hayashi, T., Hirate, S., Kitayama, K., Tsuji, H., Torii, A.,
and Uozumi, Y., J. Org. Chem., 2001, vol. 66, no. 4,
p. 1441.
6. Fontaine, F.-G., Nguyen, R.-V., and Zargarian, D.,
Canad. J. Chem., 2003, vol. 81, no. 11, p. 1299.
7. Tsuchiya, Y., Uchimura, H., Kobayashi, K., and
28. Lasitsa, N.A., Skvortsov, N.K., Lobadyuk, V.I., Spe-
vak, V.N., Esina, G.A., Abramova, I.P., and Lazarev, S.Ya.,
Zh. Obshch. Khim., 1992, vol. 62, no. 8, p. 1864.
Nishiyama, H., Synlett, 2004, no. 12, p. 2099.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 4 2009

EFFECT OF CATALYST STRUCTURE ON THE REACTION
777
29. Bergens, S.H., Noheda, P., Whelan, I., and Bosnich, B.,
J. Am. Chem. Soc., 1992, vol. 114, no. 6, p. 2128.
30. Faltynek, R.A., Inorg. Chem., 1981, vol. 20, no. 5, p. 1357.
43. Reikhsfel’d, V.O., Gel’fman, M.I., Khvatova, T.P.,
Astrakhanov, M.I., and Gavrilova, I.V.., Zh. Obshch.
Khim., 1977, vol. 47, no. 9, p. 2093.
31. Andrianov, K.A., Souchek, I., Getfleish, I., and
Khananashvili, L.M., Zh. Obshch. Khim., 1975, vol. 45,
no. 10, p. 2215.
32. Stein, J., Lewis, L.N., Gao, Y., and Scott, R.A., J. Am.
Chem. Soc., 1999, vol. 121, no. 15, p. 3693.
44. Skvortsov, N.K., Reznikov, A.N., de Vekki, D.A.,
Abstract of Papers,, 6-th All-Russian Conference
“Mechanisms of Chemical Reactions,” October 1–5,
2002, Moscow: p. 147.
45. Lewis, L.N., J. Am. Chem. Soc., 1990, vol. 112, no. 16,
33. Huang, J., Liu, Z., Liu, X., He, C., Chow, S.Y., and Pan, J.,
Langmuir, 2005, vol. 21, no. 2, p. 699.
p. 5998.
46. Chernyshev, E.A., Belyakova, Z.V., Knyazeva, L.K.,
Pomerantseva, M.G., and Efimova, L.A., Izv. Akad.
Nauk, Ser. Khim., 1998, no., p. 1413.
34. Panina, N.S. and Kukushkin, Yu.N., Zh. Neorg. Khim.,
1997, vol. 42, no. 3, p. 466.
35. Spevak, V.N., Skvortsov, N.K., Bel’skii, V.K., Kono-
valov, V.E., and Lobadyuk, V.I., Zh. Obshch. Khim.,
1992, vol. 62, no. 12, p. 2646.
47. Chernyshev, E.A., Belyakova, Z.V., Yagodina, L.A.,
Nikitinskii, E.V., and Bykovchenko, V.G., Izv. Akad.
Nauk, Ser. Khim., 1998, no. 10, p. 2048.
36. De la Camp, U. and Hope, H., Acta Crystallogr., (B),
1970, vol. 26, no. 6, p. 846.
48. Ciriano, M., Green, M., Haward, J.A.K., Proud, J.,
Spencer, J.L., Stone, F.G.A., and Tsipis, C.A., J. Chem.
Soc., Dalton Trans., 1978, no. 7, p. 801.
37. Skvortsov, A.N., de Vekki, D.A., Stash, A.I., Bel-
sky, V.K., Spevak, V.N., and Skvortsov, N.K., Tetra-
hedron: Asymmetry, 2002, vol. 13, no. 15, p. 1663.
38. Skvortsov, N.K., Spevak, V.N., Lobadyuk, V.I., Ti-
tov, K.E., Konovalov, V.E., and Bel’skii, V.K., Zh.
Obshch. Khim., 1994, vol. 64, no. 10, p. 1663.
49. Schubert, U., Adv. Organomet. Chem., 1990, vol. 30,
p. 151.
50. Manual on Inorganic Syntheses, Brauer, G., Ed.,
Moscow: Mir, 1986, vol. 6, p. 1867.
39. Reznikov, A.N. and Skvortsov, N.K., Zh. Obshch.
Khim., 2004, vol. 74, no. 10, p. 1639.
40. Akita, M., Mitani, O., and Morooka, Y., J. Chem. Soc.,
Chem. Commun., 1989, no. 9, p. 527;
41. Chalk, A.J. and Harrod, J.F., J. Am. Chem. Soc., 1965,
vol. 87, no. 1, p. 16.
51. de Vekki, D.A., Uvarov, V.M., and Skvortsov, N.K.,
Zh. Obshch. Khim., 2005, vol. 75, no. 3, p. 353.
52. de Vekki, D.A., Spevak, V.N., and Skvortsov, N.K.,
Koord. Khim., 2001, vol. 27, no. 8, p. 617.
53. Trofimov, A.E., Lobadyuk, V.I., Skvortsov, N.K.,
Spevak, V.N., and Reikhsfel’d, V.O., Zh. Obshch.
Khim., 1989, vol. 59, no. 12, p. 2792.
42. The Chemistry of Organic Silicon Compounds, Rap-
poport, Z. and Apeloig, Y., Eds., New York: Willey,
1998, vol. 2, part 2, p. 1687.
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