Si-H and Si-Si activation at Pt: Synthesis and reactivity of neutral and cationic silyl complexes

Article abstract of DOI:10.1039/c1dt11351h

Reactions of [Pt(PEt₃)₃] (1) with the silanes HSiPh₃, HSiPh₂Me and HSi(OEt)₃ led to the products of oxidative addition, cis-[Pt(H)(SiPh₃)(PEt ₃)₂] (2), cis-[Pt(H)(SiPh₂Me)(PEt ₃)₂] (3), cis-[Pt(H){Si(OEt)₃}(PEt ₃)₂] (cis-4) and trans-[Pt(H){Si(OEt)₃} (PEt₃)₂] (trans-4). The complexes cis-4 and trans-4 can also be generated by hydrogenolysis of (EtO)₃SiSi(OEt)₃ in the presence of 1. Furthermore, the silyl compounds cis-4 and trans-4 react with B(C₆F₅)₃ and CH₃CN by hydride abstraction to give the cationic silyl complex trans-[Pt{Si(OEt) ₃}(NCCH₃)(PEt₃)₂][HB(C ₆F₅)₃] (8). In addition, the reactivity of the complexes cis-4, trans-4 and 8 towards alkenes and CO was studied using NMR experiments.

Full text of DOI:10.1039/c1dt11351h

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PAPER
Si–H and Si–Si activation at Pt: synthesis and reactivity of neutral and
cationic silyl complexes
Jan Voigt and Thomas Braun*
Received 18th July 2011, Accepted 1st September 2011
DOI: 10.1039/c1dt11351h
Reactions of [Pt(PEt3)3] (1) with the silanes HSiPh3, HSiPh2Me and HSi(OEt)3 led to the products of
oxidative addition, cis-[Pt(H)(SiPh3)(PEt3)2] (2), cis-[Pt(H)(SiPh2Me)(PEt3)2] (3), cis-[Pt(H){Si(OEt)3}-
(PEt3)2] (cis-4) and trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4). The complexes cis-4 and trans-4 can also
be generated by hydrogenolysis of (EtO)3SiSi(OEt)3 in the presence of 1. Furthermore, the silyl
compounds cis-4 and trans-4 react with B(C6F5)3 and CH3CN by hydride abstraction to give the
cationic silyl complex trans-[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HB(C6F5)3] (8). In addition, the reactivity
of the complexes cis-4, trans-4 and 8 towards alkenes and CO was studied using NMR experiments.
activation product cis-[Pt(SiMe2Cl)2(PEt3)2], but not in the pres-
ence of H2. Thus, inhibition by dihydrogen hampered a catalytic
Introduction
The cleavage of Si–H and Si–Si bonds by transition metal
conversion.
complexes can be considered as one of the key steps in various
In this paper we describe Si–H activation reactions as well as the
reactions like hydrosilylations,1,2 disilylations3,4 or the dehydro-
stoichiometric hydrogenolysis of (EtO)3SiSi(OEt)3 by Si–Si activa-
coupling of hydrosilanes.5 In particular, the formation of hydrido
silyl platinum complexes by Si–H activation reactions at Pt(0)
species is well known.6,7 For instance, the reactions of [Pt(PCy3)2]
tion. The reaction of (EtO)3SiSi(OEt)3 with [Pt(PEt3)3] in the pres-
ence of H2 led to the formation of the hydrido silyl complexes cis-
[Pt(H){Si(OEt)3}(PEt3)2] (cis-4), trans-[Pt(H){Si(OEt)3}(PEt3)2]
with tertiary silanes, such as HSiEt3, HSiMe2Et or H2SiEt2, led
(trans-4) and the silane HSi(OEt)3. In addition, we report
to the formation of cis-[Pt(H)(SiR2R¢)(PCy3)2] (R = R¢ = Et;
R = Me, R¢ = Et; R = Et, R¢ = H).7 Osakada and Yamamoto
reported that a reaction of [Pt(PEt3)4] with the rhodium hydrido
silyl complex [Rh(Cl)(H)(SiPh3)(PiPr3)2] gives the Pt(II) complex
[Pt(H)(SiPh3)(PEt3)2], as well as [Rh(Cl)(PEt3)3] as the major
rhodium-containing product.8 The reaction pathway presumably
involves a reductive elimination of the silane HSiPh3 at rhodium,
followed by an oxidative addition at platinum. Examples for
the activation of Si–Si bonds at platinum complexes and the
formation of disilyl complexes have also been described befor◦e.4,9,10
Thus, Goto et al. showed that [Pt(PEt3)3] (1) reacts at -30 C in
pentane with HMe2SiSiMe2H to yield the silyl compound cis-
[Pt(SiMe2H)2(PEt3)2].10
The hydrogenolysis of disilanes with H2 still represents a major
challenge. Catalytic processes, which involve such a conversion
are rare. Most of them are covered by patent specifications.11 The
reactions normally proceed under harsh reaction conditions such
as high pressure or high temperature, but with low selectivities.
Previously, we reported on a cyclic process for the reaction of
ClMe2SiSiMe2Cl with hydrogen to yield HSiMe2Cl.9 Treatment
of the disilyl complex cis-[Pt(SiMe2Cl)2(PEt3)2], which is available
from ClMe2SiSiMe2Cl, with dihydrogen gave trans-[Pt(H)2(PEt3)2]
and two equivalents of HSiMe2Cl. Complex trans-[Pt(H)2(PEt3)2]
reacted subsequently with ClMe2SiSiMe2Cl to give again the
on the generation of an unprecedented cationic silyl com-
plex trans-[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HB(C6F5)3] (8), which
can be synthesized by hydride abstraction from the hydrido
silyl complexes cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and trans-
[Pt(H){Si(OEt)3}(PEt3)2] (trans-4).
Results
Si–Si and Si–H activation at [Pt(PEt3)3]
The hydrido silyl complexes cis-[Pt(H)(SiPh3)(PEt3)2] (2), cis-
[Pt(H)(SiPh2Me)(PEt3)2] (3) cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4)
and trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) were synthesized
by oxidative addition of silanes at [Pt(PEt3)3] (1) (Scheme
1). Thus, reactions of HSiPh3 or HSiPh2Me with [Pt(PEt3)3]
(1) yielded the complexes cis-[Pt(H)(SiPh3)(PEt3)2] (2) or cis-
[Pt(H)(SiPh2Me)(PEt3)2] (3), respectively (Scheme 1). Note that
other routes to furnish hydrido silyl complexes include the treat-
ment of [Pt(Cl)2(PEt3)2] with LiSiPh3 followed by an alcoholysis
reaction with methanol to give cis-[Pt(SiPh3)(H)(PEt3)2].12
Single crystals of 2, which were suitable for X-ray analysis, were
grown from a benzene/n-hexane solution at room temperature.
Comparison of the unit cell and results of the X-ray crystallo-
graphic analysis with the literature data revealed the presence of 2.
Complex 3 was characterized by its NMR spectroscopic data. The
Humboldt-Universita¨t zu Berlin, Department of Chemistry, Brook-Taylor-
Str. 2, 12489 Berlin, Germany. E-mail: thomas.braun@chemie.hu-berlin.de
1
31P{ H} NMR spectrum shows two mutually coupled resonances,
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lents of HSiMe2Cl and complex trans-[Pt(H)2(PEt3)2].9 Initially,
the complex trans-[Pt(H)(SiMe2Cl)(PEt3)2] and one molecule of
HSiMe2Cl was formed, but in contrast to the behaviour of cis-4
and trans-4 (see also below), trans-[Pt(H)(SiMe2Cl)(PEt3)2] reacts
further with H2 to generate another molecule of HSiMe2Cl.
Note that Trogler et al. synthesized cis-[Pt(SiEt3)(H)(PEt3)2] by
reacting cis-/trans-[Pt(H2)(PEt3)2] with HSiEt3.16 The conversion
is accompanied by hydrogen elimination.
Reactivity of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and
trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4)
To gain some information on the reactivity of cis-4 and trans-4,
they were treated with alkenes, CO and H2. Thus, a reaction of cis-
4 and trans-4 with CO at 1 atm led immediately to the formation
of [Pt(CO)2(PEt3)2] (5) and HSi(OEt)3 (Scheme 2). Complex 5
was characterized by comparison of its NMR data with those
in the literature.16 Treatment of cis-4 and trans-4 with ethene or
norbornene did not lead to hydrosilylation of the olefins.17 Instead,
the formation of the olefin complexes [Pt(C7H10)(PEt2)2] (6) and
[Pt(C2H4)(PEt2)2] (7) was observed, as well as the generation of
HSi(OEt)3 (Scheme 2). Note that [(Cp*)Rh(H)2(SiEt3)2] also reacts
with ethene to yield free silane and [(Cp*)Rh(H)(SiEt3)(C2H4)].18
The complexes 6 and 7 were identified by comparison of their
NMR spectroscopic data with the literature.19,20
Scheme 1 Formation of hydrido silyl complexes at platinum.
each with 195Pt satellites at d 23.7 ppm (JPPt = 1552.6 Hz) and at
d 22.7 ppm (JPPt = 2382.8 Hz). The signal with the smaller P–Pt
coupling corresponds to the PEt3 group in the trans position to
the silyl ligand, which has a larger trans influence than the hydride
1
ligand.13 The H NMR spectrum of 3 displays a signal at d -2.3
ppm with a platinum–hydrogen coupling of 908.8 Hz, which can be
assigned to the metal bound hydrogen nucleus. The signal appears
as a doublet of doublets with JHP(trans) = 147.0 Hz and JHP(cis)
=
21.5 Hz. A 1H,29Si HMBC NMR spectrum shows a resonance at
d 0.2 ppm in the 29Si domain, which correlates with the resonances
for the hydrido ligand and for the SiPh2Me group. The platinum–
silyl coupling is 1100 Hz. The infrared spectrum of 3 displays an
absorption band at n = 2031 cm-1 for the Pt–H vibration.
A reaction of [Pt(PEt3)3] with HSi(OEt)3 afforded the iso-
meric compounds cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and trans-
[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) in approximately a ratio of 10 : 1
(Scheme 1). Notably, the same complexes cis-4 and trans-4 as well
as HSi(OEt)3 were obtained in a similar ratio by reaction of 1
and (EtO)3SiSi(OEt)3 in the presence of hydrogen (Scheme 1).
After irradiation of a mixture of cis-4 and trans-4 for 5 h, the
cis : trans ratio changed from 10 : 1 to 5 : 1. Storage of the reaction
mixture at room temperature led to the original distribution. It
is known that complexes of the type cis-[Pt(H)(SiR2R¢)(PCy3)2]
undergo quantitative cis–trans isomerization when irradiated by a
UV source.7,14
Scheme 2 Reactivity of cis-4 and trans-4.
The treatment of a mixture of cis-4 and trans-4 with H2 in
toluene did not lead to the formation of HSi(OEt)3, even at high
pressure (5 atm) or high temperature (80 ◦C). This observation is in
contrast to the behaviour of trans-[Pt(H)(SiMe2Cl)(PEt3)2] which
gave, with H2, the silane HSiMe2Cl and the dihydrido complex
trans-[Pt(H)2(PEt3)2].9
The 31P NMR spectrum of cis-4 displays two doublets with
platinum satellites for the non-equivalent phosphines at d 23.5
ppm (JPPt = 1546.2 Hz, PEt3 in the trans-position to the silyl ligand)
and d 22.7 ppm (JPPt = 2341.7 Hz, PEt3 in the cis-position to the
silyl ligand). A singlet at d 23.3 ppm with platinum satellites (JPPt
=
2590 Hz) reveals the presence of trans-4. The 1H NMR spectrum
of cis-4 and trans-4 shows two signals for the hydrido ligands.
A doublet of doublets with 195Pt satellites (JHPt = 926.5 Hz) at d
-2.6 ppm can be assigned to cis-4. For trans-4 a triplet with 195Pt
satellites (JHPt = 678.8 Hz) appears at d 0.7 ppm.
Synthesis of cationic silyl complexes
The reaction of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and trans-
[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) with one equivalent of the
Lewis acid B(C6F5)3 in 1,2 difluorobenzene at -30 ◦C yielded, after
subsequent addition of acetonitrile, the cationic silyl compounds
trans-[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HB(C6F5)3] (8) and trans-
[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HOB(C6F5)3] (9) which exhibit
two different anions. We presume that 9 was generated by traces
of adventitious water. However, on treatment of the reaction
Mechanistically, the reaction of 1 with disilane and hydrogen
might proceed via [Pt{Si(OEt)3}2(PEt3)2]. It has been reported
before that cis-[Pt(SiMePh2)2(PMe2Ph)2] reacts with hydrogen to
yield trans-[Pt(H)(SiMePh2)(PMe2Ph)2] and HSiMePh2.15 How-
ever cis-[Pt(SiMe2Cl)2(PEt3)2] gives with dihydrogen two equiva-
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mixture of 8 and 9 with an excess of HSi(OEt)3, complex 8
was furnished only (Scheme 3). The formation of siloxanes was
detected by GC-MS and NMR measurements. Mechanistically, we
described before.26 An analogous reaction was observed by
Bullock et al. with molybdenum hydrido complexes.27 Formation
of Gomberg’s dimer implies the generation of a Ph3C∑ radical
by a one-electron oxidation of cis-4/trans-4 to yield the radical
cation [Pt(H){Si(OEt)3}(PEt3)2]∑+ (Scheme 4). Two equivalents
of Ph3C∑ recombine to give Gomberg’s dimer.28 Protonation
of cis-4/trans-4 by [Pt(H){Si(OEt)3}(PEt3)2]∑+ might furnish
H2 as well as [Pt{Si(OEt)3}(PEt3)2]+ and [Pt{Si(OEt)3}(PEt3)2]∑
or, as an alternative, HSi(OEt)3 as well as [Pt(H)(PEt3)2]+
and [Pt{Si(OEt)3}(PEt3)2]∑. The latter can again be oxidized
-
assume that HSi(OEt3)3 reacts in an initial step with HOB(C6F5)3
-
to give HOSi(OEt)3 and HB(C6F5)3 . The silanol HOSi(OEt)3
reacts then with itself to give the siloxane (OEt)3SiOSi(OEt)3
and H2O. Alternatively, HOSi(OEt)3 might react with HSi(OEt)3
to yield H2 and the siloxane (OEt)3SiOSi(OEt)3. Examples for
a comparable conversion of a B–O bond into a B–H bond
are very rare. Parvez et al. found that a reaction of 2,2,6,6-
tetramethylpiperidine (TMPH) with B(C6F5)3 and CO2 yields
[TMPH2][(TMP)C(O)OB(C6F5)3]. Treatment of the latter with
HSiEt3 led to a cleavage of the B–O bond and the compounds
[TMPH2][HB(C6F5)3] and [(TMP)C(O)OSiEt3] were formed.21
by
a
trityl cation to give [Pt{Si(OEt)3}(PEt3)2]+. Finally,
[Pt{Si(OEt)3}(PEt3)2]+ and [Pt(H)(PEt3)2]+ convert in the presence
of acetonitrile into 10 and 11, respectively.
Treatment of trans-[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HB(C6F5)3]
(8) with CO at
1 atm led to the formation of trans-
[Pt{Si(OEt)3}(CO)(PEt3)2][HB(C6F5)3] (12) (Scheme 3). One sin-
glet in the 31P NMR spectrum with 195Pt satellites at d 24.8
ppm (JPPt = 2263 Hz) reveals the presence of two phosphine
ligands in a mutual trans position. The 31P NMR spectrum
of [Pt{Si(OEt)3}(13CO)(PEt3)2][HB(C6F5)3] shows an additional
doublet coupling of JPC = 8 Hz. The coupling constant for the
carbon–phosphorus coupling is in a good agreement with a cis
configuration of CO and PEt3. The IR spectrum of 12 displays
an absorption band for the CO stretching vibration of n = 2029
cm-1. The value is unexpected low compared with other cationic
platinum carbonyl complexes.29 One possible explanation could be
the high trans-influence of the Si(OEt)3 ligand.13
It should be mentioned that square-planar cationic
platinum silyl complexes are rare. The occurrence of
[Pt(SiH2Cl)(PEt3)3][BPh4] was suggested, but the compound
was never isolated.30 Tilley et al. observed the complex cis-
[Pt{Si(StBu)2H}(NCCH3)(PEt3)2][OTf] by NMR spectroscopy.31
In addition, there are a number of cationic silyl complexes
which exhibit a silyl entity as part of a multidentate chelating
ligand. Examples of such ligands are the pincer ligands bis(8-
quinolyl)methylsilyl32 or (2-R2PC6H4)2SiMe.33
Scheme 3 Formation and reactivity of 8.
Compound 8 was characterised by its NMR and IR spectro-
scopic data as well as by mass spectrometric studies. The 31P NMR
spectrum of 8 displays a singlet at d 22.6 ppm with 195Pt satellites
and a platinum–phosphorus coupling constant of 2600 Hz. The
1H,29Si HMBC NMR spectrum shows a cross peak between a
signal in the 29Si domain at d -56 ppm and the resonances for the
OCH2 groups of the silyl group at d(1H) 4 ppm. The 1JSiPt coupling
constant is 2150 Hz. The 31P,29Si HMBC shows a cross peak at
d(29Si) -56 ppm and d(31P) 23 ppm. The IR spectrum of 8 displays
an absorption band for the CN stretching vibration at n = 2294
cm-1 and a band for the B–H vibration at n = 2376 cm-1. The former
is in good agreement with literature values for other platinum
cationic complexes, such as [Pt(Ph)(NCCH3)(PEt3)2]BF4.22 The
anion [HB(C6F5)3]- was identified by comparison of the 11B and
19F NMR spectroscopic data with the literature.23 Conductivity
measurements of a solution of 8 in CH3CN are also in accordance
with the presence of an ionic compound.24
In contrast to the observations which are described above, the
trityl cation Ph3C+ did not induce any hydride abstraction as
it was observed with B(C6F5)3. Instead it acts as an oxidation
agent. Hence, a reaction of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4)
and trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) with Ph3CPF6 in
acetonitrile gave the cationic complex trans-[Pt{Si(OEt)3}-
(NCCH3)(PEt3)2][PF6] (10) together with Gomberg’s dimer
(C38H30; Ph2C C6H5CPh3)25 as the organic product. We could
also identify trans-[Pt(H)(NCCH3)(PEt3)2][PF6] (11) in the re-
action solution (ratio 10 : 11 = 1 : 0.5). The latter has been
Conclusions
In conclusion, we reported on the syntheses of the hy-
drido silyl complexes cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4), trans-
[Pt(H){Si(OEt)3}(PEt3)2] (trans-4), cis-[Pt(H)(SiPh3)(PEt3)2] (2)
and cis-[Pt(H)(SiPh2Me)(PEt3)2] (3) by oxidative addition reac-
tions of Si–H bonds. The activation of a Si–Si bond in the presence
of H2 has also been achieved. The conversion involves an unusual
hydrogenolysis of the Si–Si bond to give cis-4 and trans-4 as well
as HSi(OEt)3. On treatment of cis-4 and trans-4 with norbornene,
ethylene or CO, a second equivalent of silane was formed.
Furthermore, unique cationic silyl complexes such as trans-
[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HB(C6F5)3] were characterized.
Experimental
General considerations
The synthetic work was carried out on a Schlenk line or a glovebox.
Toluene and pentane were purified by distillation from Na/K and
stored under argon over molecular sieves. Acetonitrile was freshly
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Scheme 4 Proposed mechanism of the reaction of cis-4 with Ph3CPF6; trans-4 will react in a similar fashion; ꢀ represents a free coordination site.
distilled at Sicapent from CaH2. Then it was distilled again and
stored over a molecular sieve.
Synthesis of cis-[Pt(H)(SiPh2Me)(PEt3)2] (3)
[Pt(PEt3)3] (1) (80 mg, 0.15 mmol) was dissolved in toluene to give
a red solution. Then 32 ml (0.17 mmol) HSiPh2Me was added.
After stirring for 15 min the solution turned orange–red, and
colourless after 12 h. The solvent was then removed in vacuum to
yield 3 as a colourless oily solid. Yield: 0.085 g (93%). n (ATR,
diamond)/cm-1: 2031 (PtH); 1H NMR (400.1 MHz, C6D6): d -2.3
(1 H, dd + satellites, JHPt = 908.8 Hz, JHP = 153.0 Hz, JHP = 22.0 Hz,
NMR spectra were acquired on a Bruker AV 400 spectrometer.
1H NMR spectra were referenced to residual C6D5H at d 7.15
ppm. 11B NMR spectra were referenced to external BF3·OEt3 at
1
d 0 ppm. 31P{ H} NMR spectra were referenced externally using
85% H3PO4 at d 0 ppm. 19F NMR spectra were referenced to C6F6
at d -162.9 ppm. Infrared spectra were recorded on a Bruker
Vektor 22 spectrometer which was equipped with a diamond
ATR unit. X-ray data for compound 3 were collected with a Stoe
IPDS 2T diffractometer. [Pt(PEt3)3] was prepared according to the
literature.34
PtH), 0.73–0.99 (18 H, m, PCH2CH3), 1.2 (3 H, d + satellites, JHPt
32.4 Hz, JHP = 2.6 Hz, SiCH3), 1.3–1.6 (12 H, m, PCH2), 7.3 (2
=
H, t, JHH = 7.5 Hz, Hpara), 7.2 (4 H, m, Hmeta), 7.9 (4 H, m, Hortho);
1
31P{ H} NMR (161.9 MHz, C6D6): d 23.7 (1 P, d + satellites, JPPt
=
1552.6 Hz, JPSi = 161 Hz, JPP = 15.7 Hz, trans to Si), 22.7 (1 P, d +
satellites, JPPt = 2382.8 Hz, JPP = 15.7 Hz, cis to Si); 1H,29Si HMBC
Synthesis of cis-[Pt(H)(SiPh3)(PEt3)2] (2)
NMR (400.1 MHz/79.5 MHz, C6D6): d -2/0 (s + satellites, JSiPt
=
1100 Hz, HPtSi), 1/0 (s, PtSiCH3), 8/0 (s, Si/Hortho).
A red solution of [Pt(PEt3)3] (1) (800 mg, 1.46 mmol) in 6 ml
n-pentane was treated with 379 mg (1.5 mmol) HSiPh3. After
stirring for 1 h, the colour of the solution turned yellow. The
reaction mixture was then evaporated to dryness. The colourless
solid was dissolved in a 1 : 1 mixture of benzene/n-hexane (5 ml).
Slow evaporation of the solvent at room temperature led, after 2
weeks, to the formation of colourless crystals. Yield: 0.99 g (98%).
(Found C, 52.76; H, 6.69%. C30H46P2PtSi requires C, 52.08, H,
Synthesis of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and
trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4)
(a) A red solution of [Pt(PEt3)3] (1) (448 mg, 0.82 mmol) in 4 ml n-
pentane was treated with 180 ml (0.8 mmol) HSi(OEt)3. The colour
of the solution changed rapidly to pale yellow. After stirring for
15 min, the volatiles were removed in vacuo. A pale yellow highly
viscous oil was obtained. Yield: 476 mg (98%). Ratio cis-4 : trans-
4 = 10 : 1.
(b) 320 mg (0.58 mmol) [Pt(PEt3)3] (1) was dissolved in 5 ml
pentane. 200 ml (0.6 mmol) (EtO)3SiSi(OEt)3 was added. After
refluxing for 3 days, H2 gas was bubbled for 5 min into the bright
red solution until it turned pale yellow. The volatiles were removed
in vacuo. A pale yellow, highly viscous oil was obtained. Ratio: cis-
4 : trans-4 = 10 : 1.
1
6.70%); n (ATR, diamond)/cm-1: 2048 (PtH); H NMR (400.1
MHz, C6D6): d -2.4 (1 H, dd + satellites, JHPt = 873.4 Hz, JHP
=
31
150.4 Hz, JHP = 20.4 Hz, PtH), 0.8 (9 H, m, t in the 1H{ P} NMR
31
spectrum, JHH = 7.6 Hz, CH3), 1.0 (9 H, m, t in the 1H{ P} NMR
31
spectrum, JHH = 7.7 Hz, CH3), 1.3 (6 H, m, q in the 1H{ P} NMR
31
spectrum, JHH = 7.6, PCH2), 1.5 (6 H, m, q in the 1H{ P} NMR,
JHH = 7.7 Hz, PCH2), 7.3 (3 H, t, JHH = 7.3 Hz, Hpara), 7.4 (6 H, m,
1
Hmeta), 8.2 (6 H, m, Hortho); 31P{ H} NMR (161.9 MHz, C6D6): d
23.2 (1 P, d + satellites, JPPt = 1617.2 Hz, JPSi = 162.2 Hz, JPP = 15.8
Hz, trans to Si), 19.6 (1 P, d + satellites, JPPt = 2413.8 Hz, JPSi
=
Analytical data: (found: C, 36.73; H, 7.68%. C18H46O3P2PtSi
requires C, 36.29; H, 7.78%); n (ATR, diamond)/cm-1 2024 (PtH,
cis-4), 1851 (PtH, trans-4); selected NMR data of cis-4: 1H NMR
16 Hz, JPP = 15.8 Hz, cis to Si); 1H,29Si HMBC NMR (400.1/79.5
MHz, C6D6): d -2/6 (s + satellites, JSiPt = 1300 Hz, HPtSi).
12702 | Dalton Trans., 2011, 40, 12699–12704
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(400.1 MHz, C6D6): d -2.6 (1 H, dd + satellites, JHPt = 926.5 Hz,
volatiles were removed at room temperature in vacuo. The residue
was washed twice with 5 ml hexane, and 3 ml CH3CN was added.
The spectroscopic data revealed the presence of 8 and 9 in a ratio
of 1 : 0.6.
JHP = 147.0 Hz, JHP = 21.5 Hz, PtH)), 1.4 (9 H, t + satellites, JHH
=
31
7.2 Hz, JHPt = 1.8 Hz, OCH2CH3), 1.6 (6 H, m, q in the 1H{ P}
NMR spectrum, JHH = 7.7 Hz, PCH2CH3), 2.0 (6 H, m, q in the
31
1H{ P} NMR spectrum, JHH = 7.7 Hz, PCH2CH3), 4.2 (6 H, q +
(b) 100 mg (0.17 mmol) of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4)
and trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) were dissolved in 3 ml
CH3CN and the solution was cooled to -30 ◦C. The solution was
then treated with B(C6F5)3 (86 mg, 0.17 mmol in 2 ml CH3CN) at
-30 ◦C. After stirring for 16 h at room temperature, the volatiles
were removed in vacuo. The residue was extracted with CD3CN.
100 ml (0.56 mmol) HSi(OEt)3 was then added and the solution
was stirred again for 1 day at room temperature. The residue was
Pt satellites, JHH = 7.7 Hz, JHPt = 4.3 Hz, OCH2) one resonance for
1
the methyl groups is covered by signals of trans-4; 31P{ H} NMR
(161.9 MHz, C6D6): d 23.5 (1 P, d + satellites, JPPt = 1546.2 Hz, JPSi
=
=
239.2 Hz, JPP = 17.9 Hz, trans to Si), 22.7 (1 P, d + satellites, JPPt
1
2341.7 Hz, JPSi = 21.8 Hz, cis to Si); 29Si{ H} NMR (79.5 MHz,
C6D6): d -2.3 (dd + satellites, JSiPt = 1844 Hz, JSiP = 239.2 Hz, JSiP
=
1
21.8 Hz); selected NMR data of trans-4: H NMR (400.1 MHz,
1
C6D6): d 0.7 (1 H, t + satellites, JHPt = 678.8 Hz, JHP = 19.5 Hz,
dried in vacuum and washed with pentane. The H, 11B, 19F and
PtH), 1.9 (12 H, m, q in the 1H{ P} NMR spectrum, JHH = 7.5 Hz,
31P NMR spectroscopic data reveal the presence of 8.
31
PCH2CH3), 4.0 (6 H, q, JHH = 6.8 Hz, OCH2), the resonances for
n (ATR, diamond)/cm-1 2294 (CH3CN), 2376 (B–H); 1H NMR
(400.1 MHz, C6D6): d 1.0–1.1 (18 H, m, PCH2CH3), 1.16 (9 H,
t, JHH = 7.0 Hz, OCH2CH3), 1.9 (3 H, s, CH3CN), 2.1 (12 H, m,
PCH2), 3.6 (1 H, q, JBH = 91.5 Hz, BH), 3.9 (6 H, q, JHH = 7.1 Hz,
OCH2); 11B NMR (128.3 MHz, C6D6): d -24.7 (d, JBH = 91.2 Hz),
19F NMR (282.4 MHz, C6D6): d -133.9 (m, Fortho), -164.3 (m, Fpara),
1
the methyl groups are covered by signals of cis-4; 31P{ H} NMR
(161.9 MHz, C6D6): d 23.3 (s + satellites, JPPt = 2590 Hz, JPSi
=
1
18.9 Hz); 29Si{ H} NMR (79.5 MHz, C6D6): d 11.5 (t, JSiP = 19
Hz, Pt satellites were not observed, because of the low intensity of
the signal).
1
-167.6 (m, Fmeta); 31P{ H} NMR (161.9 MHz, C6D6): d 22.6 (s +
satellites, JPPt = 2600 Hz); 1H,29Si HMBC NMR (400.1 MHz/79.5
MHz, C6D6): d 4/-56 (s + satellites, JSiPt = 2150 Hz PtSiOCH2);
31P,29Si HMBC NMR (161.9 MHz/79.5 MHz, C6D6): d 23/-57
(s, PPtSi); The data for 9 are similar except for the resonances for
Reaction of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and
trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) with CO
CO gas was bubbled into a bright yellow solution of cis-
[Pt(H){Si(OEt)3}(PEt3)2] (cis-4)/trans-[Pt(H){Si(OEt)3}(PEt3)2]
(trans-4) (40 mg, 0.075 mmol) in 0.5 ml 1,2-difluorobenzene until
1
the anion: H NMR (400.1 MHz, C6D6): d 3.2 (1 H, m, BOH),
11B NMR (128.3 MHz, C6D6): d -2.2 (s); 19F NMR (282.4 MHz,
C6D6): d -134.5 (m, Fortho), -158.0 (m, Fpara), -163.8 (m, Fmeta);
ESI-MS found: m/z 594.222 (M+-CH3CN), Requires: m/z 594.226
(M+-CH3CN). Molar conductivity (Km/S cm2 mol-1) = 36.
1
the solution turned orange. The H and 31P NMR spectroscopy
data reveal the formation of trans-[Pt(CO)2(PEt3)2]16 (5) and
HSi(OEt)3.
Reaction of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and
trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) with norbornene
Reaction of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and
trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) with Ph3CPF6:
formation of trans-[Pt{Si(OEt)3}(NCCH3)(PEt3)2]PF6 (10)
50 mg (0.091 mmol) 4 cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4)/trans-
[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) in 0.6 ml 1,2-difluorobenzene
was treated with 8.5 mg (0.091 mmol) norbornene. The solution
was transferred into an NMR tube and the mixture was heated to
80 ◦C for 4 days. The 1H and 31P NMR spectroscopic data reveal
the presence of 4 and [Pt(norbornene)(PEt3)2]19 (6) in a 1 : 1 ratio
as well as of HSi(OEt)3.
A solution of 76 mg (1.3 mmol) cis-[Pt(H){Si(OEt)3}(PEt3)2]
(cis-4)
and
trans-[Pt(H){Si(OEt)3}(PEt3)2]
(trans-4) in
acetonitril/C6D6 (2 : 1) was treated with 54 mg (1.4 mmol)
Ph3CPF6 at -30◦ C. A white solid precipitated. The solution was
filtered and all volatiles were removed in vacuo from the filtrate.
The residue was washed with 5 ml pentane and CH3CN was
added. The H, 19F and 31P NMR spectroscopy data reveal the
1
Reaction of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and
trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) with ethene
presence of 10 and trans-[Pt(H)(NCCH3)(PEt3)2][PF6] (11).26 The
white solid was dissolved in C6D6. The 1H NMR data confirm the
formation of Gomberg’s dimer.35 NMR data for the PF6 anion
-
Ethene was bubbled for 10 min into
a
solution of
of 10 and 11: 19F NMR (282.4 MHz, C6D6): d -72.3 (d, JFP
=
130 mg (23 mmol) cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4)/trans-
[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) in acetonitrile/C6D6 (5 : 1). Af-
ter 20 min at room temperature only traces of [Pt(ethene)(PEt3)2]20
(7) were formed. After 5 days at room temperature the 1H and 31
706.8 Hz); 31P{ H}NMR (161.9 MHz, C6D6): d -143.2 (septet,
JPF = 706.8 Hz).
1
P
NMR spectroscopic and GC-MS data revealed the presence of 2
and 7 (1 : 1) as well as of HSi(OEt)3.
Formation of trans-[Pt{Si(OEt)3}(CO)(PEt3)2][HB(C6F5)3] (12)
A solution of 47 mg (0.09 mmol)) [cis-[Pt(H){Si(OEt)3}(PEt3)2]
(cis-4) and trans-[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) in acetonitrile
was treated with 56 mg (0.1 mmol) B(C6F5)3 at -30 ◦C. The
solution was kept at this temperature for 1 day and then all volatiles
were removed in vacuo. The oily product was then dissolved in
1,2-difluorobenzene and the solution was treated with CO at 1
atm. The solution was brought to dryness, 0.1 ml toluene-d8 were
added. n (ATR, diamond)/cm-1 2029 (CO); 1H NMR (300.1 MHz,
Formation of trans-[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HB(C6F5)3]
(8) and trans-[Pt{Si(OEt)3}(NCCH3)(PEt3)2][HOB(C6F5)3] (9)
(a) A solution of cis-[Pt(H){Si(OEt)3}(PEt3)2] (cis-4) and trans-
[Pt(H){Si(OEt)3}(PEt3)2] (trans-4) (90 mg, 0.17 mmol) in 3 ml 1,2-
difluorobenzene was treated with 85 mg (0.17 mmol) B(C6F5)3 at
-30 ◦C. The solution was stored for 3 days at -30 ◦C. Afterwards all
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toluene-d8): d 0.8–1.1 (27 H, m, PCH2CH3, OCH2CH3), 1.6–1.9
16 R. S. Paonessa, A. L. Prignano and W. C. Trogler, Organometallics,
1985, 4, 647–657.
17 B. Marciniec, H. Maciejewski, C. Pietraszuk and P. Pawhuc´, Hydrosily-
lation. A Comprehensive Review and Recent Advances, ed. B. Marciniec,
Springer, London, 2008.
1
(12 H, m, PCH2), 3.9 (6 H, q, JHH = 6.9 Hz, OCH2); 31P{ H} NMR
(121.5 MHz, toluene-d8): d 24.8 (s + satellites, JPPt = 2263 Hz).
18 P. O. Bentz, J. Ruiz, B. E. Mann, C. M. Spencer and P. M. Maitlis, J.
Acknowledgements
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We would like to acknowledge the Deutsche Forschungsgemein-
schaft for financial support. We also thank the BASF SE for a gift
of solvents.
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