Activation of Si-Si and Si-H bonds at Pt: A catalytic hydrogenolysis of silicon-silicon bonds

Article abstract of DOI:10.1039/c3dt32530j

The activation of Ph₂HSiSiHPh₂ and Me ₃SiSiMe₃ at [Pt(PEt₃)₃] (1) yielded the products of oxidative addition. The formation of [Pt(SiHPh₂) ₂(PEt₃)₂] (2) as a mixture of the cis and trans isomers appears to proceed quantitatively, whereas a conversion to give cis-[Pt(SiMe₃)₂(PEt₃)₂] (3) was not complete. Treatment of 1 with one equivalent of H₂SiPh₂ led to cis-and trans-[Pt(H)(SiHPh₂)(PEt₃)₂] (cis-4, trans-4) together with the dinuclear complex [(Et₃P) ₂(H)Pt(μ-SiPh₂)(μ-η²-HSiPh ₂)Pt(PEt₃)] (5). In contrast, HSiMe₃ reacts with [Pt(PEt₃)₃] to yield cis-[Pt(H)(SiMe ₃)(PEt₃)₂] (7) exclusively. Catalytic reactions of dihydrogen with the disilanes Ph₂HSiSiHPh₂ or Me ₃SiSiMe₃ in the presence of catalytic amounts of [Pt(PEt₃)₃] (1) led to the products of hydrogenolysis, H₂SiPh₂ and HSiMe₃. The conversion of Me ₃SiSiMe₃ is much slower and needs higher temperature to proceed.

Full text of DOI:10.1039/c3dt32530j

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Activation of Si–Si and Si–H bonds at Pt: a catalytic
hydrogenolysis of silicon–silicon bonds†
Cite this: Dalton Trans., 2013, 42, 4052
Jan Voigt, Maren A. Chilleck and Thomas Braun*
The activation of Ph2HSiSiHPh2 and Me3SiSiMe3 at [Pt(PEt3)3] (1) yielded the products of oxidative
addition. The formation of [Pt(SiHPh2)2(PEt3)2] (2) as a mixture of the cis and trans isomers appears to
proceed quantitatively, whereas a conversion to give cis-[Pt(SiMe3)2(PEt3)2] (3) was not complete. Treat-
ment of 1 with one equivalent of H2SiPh2 led to cis-and trans-[Pt(H)(SiHPh2)(PEt3)2] (cis-4, trans-4)
together with the dinuclear complex [(Et3P)2(H)Pt(μ-SiPh2)(μ–η2-HSiPh2)Pt(PEt3)] (5). In contrast, HSiMe3
reacts with [Pt(PEt3)3] to yield cis-[Pt(H)(SiMe3)(PEt3)2] (7) exclusively. Catalytic reactions of dihydrogen
with the disilanes Ph2HSiSiHPh2 or Me3SiSiMe3 in the presence of catalytic amounts of [Pt(PEt3)3] (1) led
to the products of hydrogenolysis, H2SiPh2 and HSiMe3. The conversion of Me3SiSiMe3 is much slower
and needs higher temperature to proceed.
Received 23rd October 2012,
Accepted 9th January 2013
DOI: 10.1039/c3dt32530j
www.rsc.org/dalton
{Si(OEt)3}(PEt3)2] and trans-[Pt(H){Si(OEt)3}(PEt3)2] as well as
HSi(OEt)3. However, no subsequent reaction of the Pt com-
Introduction
The cleavage of Si–H and Si–Si bonds by transition metal com- plexes with dihydrogen was observed.11 Previously, we also
plexes1,2 can be considered as one of the key steps in various reported a cyclic process for the reaction of ClMe2SiSiMe2Cl
catalytic reactions like hydrosilylations3,4 or disilylations5 of with dihydrogen to yield HSiMe2Cl.12 Treatment of the bissilyl
unsaturated compounds. The catalytic dehydrogenative coup- complex cis-[Pt(SiMe2Cl)2(PEt3)2] with dihydrogen gave trans-
ling of silanes is a well recognized process.6 Thus, the coupling [Pt(H)2(PEt3)2] and two equivalents of HSiMe2Cl. In the pres-
of primary or secondary silanes can be applied for the syn- ence of H2 complex trans-[Pt(H)2(PEt3)2] does not react with
thesis of polysilanes.7 However, the reverse reaction, catalytic Me2ClSiSiClMe2 to give again the activation product cis-
hydrogenolysis of disilanes with H2, still represents a major [Pt(SiMe2Cl)2(PEt3)2]. This inhibition reaction by dihydrogen
challenge. The reaction usually proceeds under harsh reaction hampered a catalytic conversion. However, by adding PEt3 and
conditions such as high pressure or high temperature and a subsequent removal of H2 in vacuo it is possible to regain the
with low selectivities. Most of the procedures are covered by complex [Pt(PEt3)3], which then reacts again with ClMe2Si-
patent specifications.8 In 1972 Atwell et al. described a cataly- SiMe2Cl to give [Pt(SiMe2Cl)2(PEt3)2].
tic process with palladium on charcoal as a catalyst at 3.8 bar
In this paper we describe Si–Si activation reactions of
hydrogen pressure to produce HSiMe3 with a turnover number Ph2HSiSiHPh2 and Me3SiSiMe3 at [Pt(PEt3)3] (1). In addition,
of 16.9 Note that to the best of our knowledge only one cataly- the reactivity of the bissilyl complexes cis-[Pt(SiHPh2)2(PEt3)2]
tic process in a homogeneous phase which proceeds under (cis-2) and trans-[Pt(SiHPh2)2(PEt3)2] (trans-2) towards dihydro-
moderate pressure and temperature conditions was published gen was investigated. The reactivity of the hydrido silyl com-
by Rosenberg et al.10 They described the catalytic conversion plexes cis-[Pt(H)(SiHPh2)(PEt3)2] (cis-4) and trans-[Pt(H)-
of Ph2HSiSiHPh2 and H2 to yield H2SiPh2 within one week by (SiHPh2)(PEt3)2] (trans-4) and cis-[Pt(H)(SiMe3)(PEt3)2] (7),
using 0.8 mol% [Rh(Cl)(PPh3)3] as a catalyst.
which are possible intermediates in a catalytic process, was
An example for the conversion of a disilane to give one also studied. These investigations led to the development of a
equivalent of the corresponding tertiary silane is represented catalytic process for the hydrogenolysis of Ph2HSiSiHPh2 and
by the reaction of (OEt)3SiSi(OEt)3 with [Pt(PEt3)3] (1) in the Me3SiSiMe3.
presence of H2 to give the hydrido–silyl complexes cis-[Pt(H)-
Results
Department of Chemistry, Humboldt-Universitat Berlin, Brook-Taylor-Str. 2, Berlin,
Germany. E-mail: thomas.braun@cms.hu-berlin.de; Fax: +49 (0)30 2093 7468;
Si–Si activation at [Pt(PEt3)3] (1)
Tel: +49 (0)30 2093 3913
A mixture of the bissilyl complexes cis-[Pt(SiHPh2)2(PEt3)2]
(cis-2) and trans-[Pt(SiHPh2)2(PEt3)2] (trans-2) was synthesized
†Electronic supplementary information (ESI)
available. See DOI:
10.1039/c3dt32530j
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Scheme 2 Formation of cis-4, trans-4 and 5.
Scheme 1 Formation of the bissilyl complexes cis-2, trans-2 and 3.
Reactions of H2SiPh2 and HSiMe3 with [Pt(PEt3)3] (1)
Treatment of 1 with one equivalent of H2SiPh2 at room temp-
erature led instantly to a reaction. However, the products are
highly dynamic in solution on the NMR time-scale. At room
temperature a very broad feature from 5 ppm to 22 ppm
was observed in the 31P{1H} NMR spectrum (121.5 MHz). In
the 1H NMR spectrum a broad resonance at δ −1.8 ppm with a
by the oxidative addition of Ph2HSiSiHPh2 at [Pt(PEt3)3] (1)
(Scheme 1). The reaction proceeds at room temperature, in
benzene and is completed after 10 minutes. The ratio for cis-
2 : trans-2 is 1 : 0.27. The 31P{1H} NMR spectrum for cis-2
shows a singlet with 195Pt satellites at δ 15.3 ppm (1JPtP = 1706
Hz). The coupling constant is in a typical range of cis-substi-
tuted platinum phosphine bissilyl complexes.11–13 In contrast,
the resonance for complex trans-2 at δ 6.80 ppm in the 31P{1H}
NMR spectrum shows a much larger phosphorus–platinum
1
coupling constant of JPtH = 932 Hz was observed. The low
temperature (190 K) 31P{1H}, 1H, and 1H,29Si HMBC NMR
spectra indicate the presence of the three complexes cis-[Pt(H)-
(SiHPh2)(PEt3)2] (cis-4), trans-[Pt(H)(SiHPh2)(PEt3)2] (trans-4)
and the dinuclear compound [(Et3P)2(H)Pt(μ-SiPh2)(μ–η2-
HSiPh2)Pt(PEt3)] (5) as well as of hydrogen and PEt3 in the
reaction mixture (Scheme 2), the ratio cis-4 : trans-4 : 5 is
approximately 2 : 0.58 : 3.2. At low temperature, the signals of
trans-4 and 5 sharpened whereas the resonances of cis-4
remained broad. The generation of 5 can be explained by the
elimination of H2 and PEt3 from 2 equivalents of cis-4/trans-4.
Nevertheless, free H2 might induce an isomerisation between
cis-4 and trans-4 via a Pt(IV) compound. Reductive elimination
processes of tertiary silanes at Pt(II) are also known.19 In
addition, a photochemical isomerization of Pt(II) hydrido–silyl
complexes was reported.19,20
1
coupling of JPtP = 2436 Hz, because of the weaker trans-influ-
ence of the phosphine ligands compared to the silyl groups.14
The 1H NMR spectrum of cis-2 displays a virtual triplet with
platinum satellites at δ 5.82 ppm (JPH,apparent = 15.7 Hz) for the
silicon-bound hydrogen atoms. 31P decoupling experiments
2
reveal the JPtH coupling constant to be 68.8 Hz. A triplet at
3
δ 5.54 ppm with platinum satellites (2JPtH = 23.6 Hz and JPH
=
10.9 Hz) for the silicon bound hydrogen atoms reveals the
presence of trans-2. Note that Lee et al. prepared the same
complexes by treatment of [Pt(PEt3)4] with 2 equivalents of
H2SiPh2 followed by drying the reaction mixture in vacuo.15
It was described before that the oxidative addition of
Me3SiSiMe3 at [Pt(PEt3)3] (1) leads to the bissilyl complex cis-
[Pt(SiMe3)2(PEt3)2] (3) (Scheme 1).12 In contrast to the reactivity
of 1 towards Ph2HSiSiHPh2, the reaction with Me3SiSiMe3 is
much slower. After 3 weeks at room temperature we observed
approximately 50% conversion to give the bissilyl complex 3.
Other examples for the activation of Si–Si bonds at plati-
num complexes and the formation of bissilyl complexes
were reported before.2 For instance, Goto et al. showed that
[Pt(PEt3)3] (1) reacts with HMe2SiSiMe2H at 243 K in pentane
to yield the bissilyl compound cis-[Pt(SiMe2H)2(PEt3)3].16
Ito et al. reported that the reaction of [Pt3(CNAd)6] (Ad = 1-ada-
mantyl) with Me3SiSiMe3 at 353 K yields the bissilyl complex
[Pt(SiMe3)2(CNAd)2] in nearly quantitative yields.17 Note that
the activation of Ph2HSiSiHPh2 might proceed via an initial
Si–H activation step and is therefore more facile.18
Note that even by evaporation of the volatiles and drying of
the reaction mixture for 24 hours in a high vacuum it was not
possible to achieve a quantitative formation of 5. To verify the
identity of cis-4 and trans-4, we synthesised the complexes by
an alternative route which involves a replacement of the silyl
group in cis-[Pt(H)(SiPh3)(PEt3)2] (6). Thus, the reaction of 6
with one equivalent of H2SiPh2 resulted at room temperature
in broad signals in the 31P{1H} NMR spectrum in a ratio of
1 : 0.22 for cis-4 and trans-4. Free HSiPh3 was also observed
(Scheme 2).
At 190 K a resonance at δ 18.0 ppm with a coupling con-
1
stant of JPtP = 2536 Hz was found for complex trans-4 in the
31P{1H} NMR spectrum. As mentioned above, the resonances
for the complex cis-4 are broad even at low temperature and
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appear at δ 22.5 ppm and δ 16.6 ppm. The signals exhibit
1
coupling constants of JPPt ∼ 2260 Hz (cis to a silyl ligand) and
1JPPt ∼ 1700 Hz (trans to a silyl ligand). The latter value is in a
typical range for complexes in which the metal bound silyl
group exerts a strong trans influence.14,19 The 1H,29Si HMBC
NMR spectrum reveals cross resonances at δ 6 ppm in the 29Si
domain for cis-4 and at δ −3 ppm for trans-4.
The 31P{1H} NMR spectrum of 5 at 190 K shows two reso-
nances for the inequivalent phosphine ligands; a triplet at δ
Scheme 4 Reactivity of 1 with HSiMe3.
2
13.3 ppm (1JPPt = 3874 Hz, JPPt = 258 Hz) and a doublet at δ
2
−1.15 ppm (1JPPt = 3500 Hz, JPPt = 105 Hz). The phosphorus–
3
phosphorus coupling constant is JPP = 23 Hz. The 1H NMR
spectrum displays a triplet resonance at δ −7.4 ppm with coup-
ling constants of 1JHPt = 537 Hz, 2JHPt = 79 Hz, and 2JHP = 13 Hz
for the non-bridging hydrido ligand. The signal for the brid-
ging hydrogen atom is covered by the resonances of the ethyl
1
groups, but the H,29Si HMBC NMR spectrum reveals a corre-
lation at δ 1.2 ppm in the 1H domain. The 1H,29Si HMBC NMR
spectrum also shows a large downfield shift of the resonances
at δ 179 ppm and δ 178 ppm in the 29Si domain for the silicon
containing groups compared to the signals cis-4/trans-4. Equi-
librium reactions between hydrido–silyl complexes and unsym-
metric binuclear platinum silyl complexes (Scheme 2) were
Scheme 5 Reactivity of cis-2 and trans-2 towards dihydrogen.
described before by Braddock-Wilking et al.21 and by Mochida that Trogler et al. synthesized 7 by reaction of [Pt(C2F4)(PEt3)2]
1
et al.22 The 31P, H, and 29Si NMR data for 5 are in good agree- with an excess of HSiMe3 at room temperature.26
ment with the reported literature data.
Reactivity of cis-[Pt(SiHPh2)2(PEt3)2] (cis-2) and
trans-[Pt(SiHPh2)2(PEt3)2] (trans-2) towards dihydrogen
The observation of the broad resonances in the 31P NMR
spectrum of cis-4 even at 190 K indicates a further equilibrium.
VT NMR studies revealed no significant change of the chemi- The reaction of cis-2 and trans-2 with H2 under ambient con-
cal shift of the signals. We suggest a dynamic behaviour which ditions led to the formation of cis-[Pt(H)(SiHPh2)(PEt3)2] (cis-4)
is characterized by an intramolecular exchange of the hydrido and trans-[Pt(H)(SiHPh2)(PEt3)2] (trans-4) in a ratio of 1 : 0.1 as
and silyl ligands that involves free triethylphosphine well as of H2SiPh2 (Scheme 5). After one hour 80% of the start-
(Scheme 3). The latter is always present in the solution, ing material was converted according to the 1H NMR spec-
because of the equilibrium with 5 (see above). A similar trum. The trans isomer trans-2 could not be detected anymore
1
broadening in the 31P{1H} and H NMR spectra for the signals which indicates a higher reactivity of trans-2, which might be
of triethylphosphine hydrido–silyl complexes can be observed caused by the strong trans influence of the silyl groups. In con-
after treatment of [Pt(PEt3)3] (1) with other silanes such as trast, cis-2 does not convert completely even at higher dihydro-
HSiMe2Cl,12 HSiEt3,23 HSiPh3,24 HSiMePh2,11 and HSi(OEt)3
gen pressure. After removal of the volatiles in vacuo the bissilyl
11
as long as residual PEt3 is still present in the reaction mixture. complexes cis-2 and trans-2 (ratio 1 : 0.2) were regenerated by
The NMR resonances are broadened also by adding PEt3 to elimination of dihydrogen and consumption of the free silane
solutions of the cis-[Pt(H)(SiR3)(PEt3)2] (R3 = Me2Cl, Et3, Ph3, (Scheme 5).
Me3, MePh2, OEt3, Ph2H) complexes. Intramolecular phos-
Development of catalytic processes for the formation of
H2SiPh2 and HSiMe3
phine exchange on platinum hydrido silyl complexes was
reported before.19
NMR studies of a reaction of 1 with HSiMe3 at room temp- Based on the stoichiometric reactions described above, we
erature revealed after work-up 5% conversion to yield cis-[Pt(H)- studied the reactivity of cis-2 and trans-2 (ratio 1 : 0.27)
(SiMe3)(PEt3)2] (7) (Scheme 4).25 However, at 193 K free towards a possible catalytic hydrogenolysis of Ph2HSiSiHPh2
phosphine reacts with complex 1 to form [Pt(PEt3)4] (8), which for producing H2SiPh2. The reaction of cis-2 and trans-2 with
precipitates. Repeating this procedure yielded 50% conversion 10 equiv. of Ph2HSiSiHPh2 was carried out at different temp-
of 1 into 7. Complex 7 can be isolated as a dark red oil. Note eratures and dihydrogen pressures (Table 1). The progress of
the reactions was monitored by NMR spectroscopy and GC-MS
analysis. Note that the formation of H2SiPh2 at room tempera-
ture and one atmosphere of dihydrogen is very slow. After
12 hours only one equivalent of Ph2HSiSiHPh2 was converted.
By increasing the temperature the reaction accelerated at 1.7 bar
Scheme 3 Fluxionality in complex cis-4.
hydrogen pressure, but more products of a redistribution
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Table 1 Silane products (mol%) after a reaction of Ph2HSiSiHPh2 with hydrogen in the presence of cis-2 and trans-2 (10 mol%) after 2 h
Pressure
Temp.
Consumption of disilane
HSiPh3
H2SiPh2
H3SiPh
Others
1 bar
298 K
298 K
323 K
353 K
298 K
10% (after 12 h)
2%
6%
33%
36%
1.5
0.7
50
49
0.9
97
98.6
42
45
98.2
1.5
0.7
8
5
0.9
—
—
—
1.7 bar
1.7 bar
1.7 bar
6 bar
PhH2SiSiPh3
—
dihydrogen to the solution of 1 and disilane the NMR signals
became very broad, and it was not possible to identify
any platinum compounds. On cooling to 213 K only signals
for [Pt(H)2(PEt3)3] (9) were observed by 1H and 31P{1H} NMR
spectroscopy.31 After removal of the solvent and the excess
silane under vacuum only complex 1 was present. Note that
there are very few examples for the hydrogenolysis of
Me3SiSiMe3 reported in the literature.9
Conclusions
Scheme 6 Catalytic formation of H2SiPh2 and HSiMe3.
Catalytic processes for the hydrogenolysis of Ph2HSiSiHPh2
and Me3SiSiMe3 were developed. Conceivable intermediates of
the catalytic process were synthesised and identified by NMR
spectroscopy. We consider the use of dihydrogen as a hydro-
gen source as superior to alternative methods for the trans-
formation of silicon–silicon bonds into hydrogen–silicon
bonds, which often include the reaction of disilanes with HCl
at high temperature and high pressure resulting in a mixture
of chloro and hydrido silanes.32 The development of a reaction
route for the hydrogenolysis of disilanes is of certain impor-
tance, because it opens up new opportunities to access higher-
value silanes which can be applied for further synthesis.12,33
Note that in the Müller–Rochow process chlorinated disilanes
and polysilanes are produced, which might be converted into
monosilanes by hydrogenolysis.34 Other catalytic reactions
which involve the activation of the Si–Si bond in Me3SiSiMe3
include the bissilylation of double bonds,35 triple bonds,36 or
α,α-diketones.37 The Si–Si bond in Me3SiSiMe3 can also be
cleaved stoichiometrically on using for instance Br2, B2H6,
MeLi or KOMe.38
of the phenyl groups at the silane such as HSiPh3, PhH2SiSiPh3
and H3SiPh were formed (Table 1).
For a catalytic conversion, the reaction was finally per-
formed at 6 bar dihydrogen pressure in an autoclave at room
temperature with 25 equiv. of disilane. According to the
1
GC-MS and H NMR spectroscopic data, a turnover number of
18 was achieved after 50 hours, based on the disilane con-
sumption (Scheme 6). In addition to the product H2SiPh2 less
than 2% of HSiPh3 and H3SiPh were present as impurities.
Notably, the amount of redistribution products is very low,
although such reactions were observed frequently at transition
1
metal centres.10,27 The H and 31P NMR spectroscopic data of
the resulting reaction mixture also showed the presence of the
complexes cis-2 and trans-2 in a ratio of 1 : 0.27.
Rosenberg et al. estimated an equilibrium constant of Kc =
104 at room temperature for the reaction of Ph2HSiSiHPh2
with dihydrogen to form two equivalents of H2SiPh2 with [Rh-
(Cl)(PPh3)3] as a catalyst.10 This shows that the hydrogenolysis
of Ph2HSiSiHPh2 is an exergonic process. For comparison,
DFT calculations for the analogous reaction of Me3SiSiMe3
with dihydrogen at the B3LYP/cc-pVTZ level28–30 suggest
that the hydrogenolysis yielding HSiMe3 is also exergonic with
an equilibrium constant of approximately K = 109 (ΔG =
−54.0 kJ mol−1) at 293 K. However, a reaction of Me3SiSiMe3
with dihydrogen in the presence of 1 at room temperature and
6 bar H2 yielded only small amounts of HSiMe3, but by
increasing the temperature to 392 K a catalytic reaction was
achieved. The conversion was monitored by NMR spectroscopy
and GC-MS analysis. In a reaction of 1 with 100 equivalents of
Me3SiSiMe3 at 393 K and a dihydrogen pressure of 1.7 bar a
turnover number of 18, based on the disilane consumption,
was achieved after 90 hours (Scheme 6). Monitoring the
reaction by NMR spectroscopy revealed that after adding
Experimental
The synthetic work was carried out on a Schlenk line or in a
glovebox. Toluene and pentane were purified by distillation
from Na/K and stored under argon over molecular sieves (3 Å).
High pressure experiments were performed in an autoclave
HR-100 with a PTFE insert (Berghof instruments). NMR high
pressure tubes were purchased from Wilmad Lab glass. NMR
spectra were acquired on a Bruker DPX 300 or a Bruker AV 400
spectrometer. 1H NMR spectra were referenced to residual
C6D5H at δ 7.15 ppm. 31P{1H} NMR spectra were referenced to
external 85% H3PO4 at δ 0 ppm, respectively. 19F NMR spectra
were referenced to C6F6 at δ −162.9 ppm. GC-MS data were
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obtained at an Agilent Technologies GC 6890N which 190 K): δ 18.0 (s + 195Pt satellites, JPPt = 2536 Hz); 1H,29Si
was equipped with a 5973 mass spectrometer as a detector. HMBC NMR (300.1 MHz/59.6 MHz, toluene-d8, 190 K): δ 7.9/
[Pt(PEt3)3] (1) was prepared according to the literature.39 −3 (s + 195Pt satellites, 1JPtSi = 995 Hz, ortho Ar), 5.3/−3 (s, SiH).
Hexamethyldisilane and tetraphenyldisilane were purchased NMR data for 5: 1H NMR (300.1 MHz, toluene-d8, 190 K):
from ABCR.
−7.41 (1 H, t + 195Pt satellites, 1JPtH = 536 Hz, 2JPtH = 79 Hz, 2JPH
= 13 Hz, PtH), 8.07 (4 H, m, ortho Ar, PtHSi), 8.16 (4 H, m, ortho
Ar), the signal for PtHSi hydrogen is covered by resonances
of the Et groups; 31P{1H} NMR (121.5 MHz, toluene-d8, 190 K):
Synthesis of cis-[Pt(SiHPh2)2(PEt3)2] (cis-2) and
trans-[Pt(SiHPh2)2(PEt3)2] (trans-2)
A red solution of [Pt(PEt3)3] (1) (400 mg, 0.73 mmol) in δ −1.2 (d + 195Pt satellites, 1JPPt = 3500 Hz, 2JPPt = 105 Hz, 4JPP
=
benzene (5 ml) was treated with 267 mg (0.73 mmol) 23 Hz, Pt(PEt3)2), 13.3 (t + 195Pt satellites, JPPt = 3874 Hz, JPPt
1
2
Ph2HSiSiHPh2. After stirring for 10 min the colour of the solu- = 258 Hz, JPP = 23 Hz, Pt(PEt3); 1H,29Si HMBC NMR
3
tion turned yellow. The reaction mixture was then evaporated (300.1 MHz/59.6 MHz, toluene-d8, 190 K): δ −7.4/179 (s, PtH),
to dryness. A pale yellow highly viscous oil was obtained. 8.2/179 (s, ortho Ar), −7.4/178 (s, PtH), 1.2/178 (s, Pt–H–Si),
Yield: 565 mg (97%). Ratio: cis-2 : trans-2 = 1 : 0.27 (Found C, 8.1/178 (s, ortho Ar).
54.38; H, 6.55. C36H52P2PtSi2 requires C, 54.18; H, 6.57%).
1
Reaction of cis-[Pt(SiHPh2)2(PEt3)2] (cis-2) and
trans-[Pt(SiHPh2)2(PEt3)2] (trans-2) with H2
NMR data for cis-2: H NMR (400.1 MHz, C6D6): δ 0.91 (18 H,
m, t in the 1H{31P} NMR spectrum, JHH = 7.6 Hz, PCH2CH3),
1
1.73 (12 H, m, q in the H{31P} NMR spectrum, JHH = 7.6 Hz, Hydrogen gas was bubbled into a bright yellow solution of
PCH2CH3), 5.82 (2 H, vt + 195Pt satellites, JPH,apparent = 15.7 Hz, cis-[Pt(SiHPh2)2(PEt3)2] (cis-2) and trans-[Pt(SiHPh2)2(PEt3)2]
JPtH = 68.8 Hz, SiH), 7.25 (12 H, m, meta and para Ar), 7.87 (trans-2) (48 mg, 0.06 mmol) in C6D6. Within one hour the
(8 H, m, ortho Ar); 31P{1H} NMR (161.9 MHz, C6D6): δ 15.3 solution turned colourless. The NMR spectrum shows the pres-
(s + satellites, JPPt = 1706 Hz), 1H,29Si HMBC NMR (400.1 MHz/ ence of cis-[Pt(H)(SiHPh2)(PEt3)2] (cis-4) and trans-4 in a ratio
79.5 MHz, C6D6): δ 7.8/−11 (s + 195Pt satellites, 1JSiPt = 1330 Hz, of 1 : 0.1 as well as of H2SiPh2.
ortho Ar), 5.8/−11 (s, SiH). NMR data for trans-2: 1H NMR
Reaction of cis-[Pt(H)(SiPh3)(PEt3)2] (6) with H2SiPh2
(400.1 MHz, C6D6): δ 0.83 (18 H, m, t in the 1H{31P} NMR
spectrum, JHH = 7.4 Hz, PCH2CH3), 1.99 (12 H, m, q in the 112 mg (0.16 mmol) 6 were suspended in 3 ml C6D6 and 30 μl
1H{31P} NMR spectrum, JHH = 7.4 Hz, PCH2CH3), 5.54 (2 H, t + (0.16 mmol) H2SiPh2 were added at room temperature. The
1
1
195Pt satellites, JPH = 10.9 Hz, JPtH = 23.6 Hz, SiH), 7.20 (4 H, m, reaction mixture became clear. The H, 31P and H,29Si HMBC
para Ar), 7.37 (8 H, m, meta Ar), 8.04 (8 H, m, ortho Ar); 31P{1H} NMR spectroscopic data of the solution revealed the presence
NMR (161.9 MHz, C6D6): δ 6.80 (s + 195Pt satellites, JPPt
=
of the complexes cis-4 and trans-4 as well as of HSiPh3. Ratio:
2436 Hz); 1H,29Si HMBC NMR (400.1 MHz/79.5 MHz, C6D6): cis-4 : trans-4 = 1 : 0.22.
δ 8.0/5 (s + 195Pt satellites, JSiPt = 875 Hz, ortho Ar), 5.5/5 (s, SiH).
Reaction of [Pt(PEt3)3] (1) with HSiMe3
Reaction of [Pt(PEt3)3] (1) with H2SiPh2
A red solution of [Pt(PEt3)3] (1) (125 mg, 0.23 mmol) in toluene
A red solution of 48.6 mg (0.09 mmol) 1 in 1 ml benzene was (3 ml) was cooled to −80 °C and an excess of HSiMe3 was con-
treated with 16.3 μl (0.09 mmol) H2SiPh2. The colour of the densed to the solution. The resulting suspension was filtered
solution changed rapidly to pale yellow. After stirring for and the filtrate was treated a second time with HSiMe3 and fil-
30 min all volatiles were removed in vacuo. A yellow highly tered again. After removing the solvent from the filtrate a dark
1
viscous oil was obtained. Yield: 49 mg (90%). Selected NMR red oil was obtained. The H and 31P NMR spectroscopic data
1
data (in the H NMR spectrum the signals for the PEt3 ligands reveal the formation of cis-[Pt(H)(SiMe3)(PEt3)2] (7).26
at cis-4, trans-4 and 5 overlap). NMR data for cis-4: 1H NMR
Catalytic formation of H2SiPh2 by reaction of Ph2HSiSiHPh2
with dihydrogen in the presence of cis-2 and trans-2
(300.1 MHz, toluene-d8, 190 K): δ −1.81 (1 H, br, d + 195Pt satel-
1
2
lites, JPtH = 925 Hz, JPH(trans) = 132 Hz, PtH), 5.41 (1 H, m +
195Pt satellites, 1JSiH = 155 Hz, 2JPtH = 25 Hz, SiH), 7.14 (2 H, m, 87 mg (0.11 mmol) of a mixture of cis-2 and trans-2 in a ratio
para Ar), 7.31 (4 H, meta Ar), 8.11 (4 H, m, ortho Ar); 31P{1H} of 1 : 0.27 were dissolved in C6D6 (3 ml). The resulting yellow
NMR (121.5 MHz, toluene-d8, 190 K): δ 16.6 (s, br, + 195Pt satel- solution was combined with 1 g (2.75 mmol) Ph2HSiSiHPh2 in
lites, JPPt = 2260 Hz, P cis to Si), 22.5 (s, br, + 195Pt satellites, 20 ml C6D6 and the mixture was then transferred into an auto-
1JPPt = 1700 Hz, P trans to Si); 1H,29Si HMBC NMR (300.1 MHz/ clave. 6 bar dihydrogen were fed. The reaction was monitored
59.6 MHz, toluene-d8, 190 K): δ 8.1/6 (s + 195Pt satellites, 1JPtSi
=
by NMR spectroscopy and GC-MS measurements. After
1
1140 Hz, ortho Ar), 7.3/6 (s + 195Pt satellites, JPtSi = 1140 Hz, 50 hours the reaction was interrupted, the mixture dried in a
1
meta Ar), 5.4/6 (s + 195Pt satellites, JPtSi = 1140 Hz, SiH). NMR vacuum and the resulting oily solid was dissolved in C6D6 and
data for trans-4: 1H NMR (300.1 MHz, toluene-d8, 190 K): investigated by NMR spectroscopy. The GC-MS and 1H NMR
1
2
δ 0.45 (1 H, t + 195Pt satellites, JPtH = 750 Hz, JPH = 18 Hz, spectroscopic data revealed the formation of H2SiPh2 (TON =
PtH), 5.52 (1 H, m + 195Pt satellites, 2JPtH = 27 Hz, 29Si satellites 18, based on the disilane consumption, 36 equiv. silane
1
not observed, SiH), 7.20–7.30 (6 H, m, meta and para Ar), 7.91 H2SiPh2 with respect to the amount of a catalyst). The H and
(4 H, m, ortho Ar); 31P{1H} NMR (121.5 MHz, toluene-d8, 31P NMR spectroscopic data of the residue showed the
4056 | Dalton Trans., 2013, 42, 4052–4058
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presence of the complexes cis-2 and trans-2 (ratio cis-2 : trans- 15 Y. J. Kim, J. I. Park and S. C. Lee, Organometallics, 1999, 18,
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Catalytic formation of HSiMe3 by reaction of Me3SiSiMe3 with
dihydrogen
A mixture of 10 mg (0.018 mmol) of 1 in toluene (0.7 ml) and
0.036 ml (1.8 mmol) Me3SiSiMe3 in C6D6 (0.1 ml) was trans-
ferred into an NMR pressure tube. 1.7 bar hydrogen pressure
was then applied. The NMR tube was heated to 120 °C. After
90 hours the solution was investigated by 1H NMR
spectroscopy and by GC-MS. The spectroscopic data reveal the
formation of HSiMe3 (TON 18, based on the disilane consump-
tion, 36 equiv. silane HSiMe3 with respect to the amount of
catalyst). After evaporating the volatiles and drying the solution
in a vacuum the residue was dissolved in C6D6, and complex
[Pt(PEt3)3] (1) was observed in the NMR spectrum.
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Acknowledgements
We would like to acknowledge the Deutsche Forschungs-
gemeinschaft for financial support. We also thank the BASF SE
for a gift of solvents.
25 After removing the volatiles from the solution the starting
compound [Pt(PEt3)3] (1) is regenerated, because 1 is in
equilibrium with 7 and HSiMe3, and HSiMe3 is highly
volatile.
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