Transition metal silyl complexes. 59. Oxidative addition of nonactivated Si-C bonds to platinum(0) centers

Article abstract of DOI:10.1021/om9805335

Reaction of Ph₂PCH₂CH₂SiPh_3-nMe_n (n = 0, 1) with (Ph₃P)₂Pt(π-C₂H₄) at elevated temperatures results in the formation of (Me_nPh_3-nSiCH₂CH₂Ph ₂-P)Pt(PPh₂CH₂CH₂SiPh _2-nMe_n)Ph by oxidative addition of the Si-C_phenyl group. Oxidative addition of Si-Me groups is not observed. Therefore, no chelate complex is obtained with Ph₂PCH₂CH₂SiMe₃. The complex (Et₃P)Pt(PPh₂CH₂CH₂SiPhMe)Ph is formed when a mixture of PEt₃ and Ph₂PCH₂CH₂SiPh₂Me is reacted with (Ph₃P)₂Pt(π-C₂H₄).

Full text of DOI:10.1021/om9805335

4760
Organometallics 1998, 17, 4760-4761
Tr a n sition Meta l Silyl Com p lexes. 59.1 Oxid a tive
Ad d ition of Non a ctiva ted Si-C Bon d s to P la tin u m (0)
Cen ter s
Hilmar Gilges and Ulrich Schubert*
Institut fu¨r Anorganische Chemie, Technische Universita¨t Wien, Getreidemarkt 9,
A-1060 Wien, Austria
Received J une 24, 1998
Summary: Reaction of Ph2PCH2CH2SiPh3-nMen (n ) 0,
1) with (Ph3P)2Pt(π-C2H4) at elevated temperatures
results in the formation of (MenPh3-nSiCH2CH2Ph2-
ature, only the Si-Si bond was oxidatively added to
the metal, and the chelate complexes (Ph3P)Pt[PPh2-
(CH2)nSiMe2]SiPh3 were exclusively formed.7 The al-
ternative oxidative addition of a Si-Ph group was not
observed, although this would lead to a less strained
five-membered ring for n ) 1. This is experimental
proof that oxidative addition of a Si-Si bond is distinctly
more favorable than a Si-C bond when both compete
with each other. In the present communication we
show, however, that the chelate-assisted oxidative ad-
dition of Si-C bonds is observed in the absence of
competing Si-Si bonds.
The compounds Ph2PCH2CH2SiR2R′ (R ) R′ ) Ph,
Me; R ) Ph, R′) Me) were synthesized by irradiation
of Ph2PH and the corresponding vinyltriorganosilane in
the absence of a solvent in a quartz vessel. The reaction
of (Ph3P)2Pt(π-C2H4) with any of the three (phosphino-
ethyl)silanes at ambient temperature under identical
conditions led to the immediate formation of highly
dynamic phosphine complexes Pt(P )x (x ) 3, 4; P )
PPh3, Ph2PCH2CH2SiR2R′). This was indicated by the
spontaneous evolution of ethylene, a color change to
orange-red, and a very broad resonance in the 31P NMR
spectrum. The NMR spectrum of the reaction mixture
did not change over 2 days at room temperature.
However, if the reaction mixture containing the SiPh3
derivative was heated to 70 °C after the ethylene
evolution had stopped, a subsequent reaction was
observed by 31P NMR spectroscopy. Prolonged heating
resulted in the almost quantitative formation of (Ph3-
P)Pt(PPh2CH2CH2SiPh2-nMen)Ph by oxidative addition
of the Si-Cphenyl group. Oxidative addition of Si-Me
groups is not observed. Therefore, no chelate complex
is obtained with Ph2PCH2CH2SiMe3. The complex
(Et3P)Pt(PPh2CH2CH2SiPhMe)Ph is formed when a
mixture of PEt3 and Ph2PCH2CH2SiPh2Me is reacted
with (Ph3P)2Pt(π-C2H4).
There is a growing interest in Si-C or Si-Si activa-
tion processes, partially due to the interest in the
catalytic formation of new organosilicon polymers.2
Several examples for the oxidative addition of Si-Si
bonds to transition-metal centers are now known,
compared to only a few for that of Si-C bonds. Two
strategies were mainly used to promote the oxidative
addition of Si-C bonds (the case of intramolecular
addition of the Si-C bond of a silyl ligand in binuclear
complexes is not considered here). The first is to
enhance of the reactivity of the transition-metal frag-
ment, for example by geometric distortions as in
(But PCH2But P)Pt.3 The second strategy is to use
2
2
compounds with activated Si-C bonds4 or to increase
the reactivity of the Si-C bond by ring strain as in
silacyclobutanes.5
In recent publications we utilized the promoting and
stabilizing effect of chelation to obtain stable complexes
by intramolecular oxidative addition of the Sn-C, Si-
Sn, or Si-Si (E-E′) bonds in (phosphinoalkyl)silane and
-stannane complexes of the type LnM-PR2(CH2)n-
ER′2E′R′′3.6-8 When (Ph3P)2Pt(π-C2H4) was reacted
with Ph2P(CH2)nSiMe2SiPh3 (n ) 1, 2) at room temper-
SiCH2CH2Ph2P)Pt(PPh2CH2CH2SiPh2)Ph (1a ) (eq 1).
(1) Part 58: Schubert, U.; Kalt, D.; Gilges, H. Monatsh. Chem., in
press.
(2) Yamashita, H.; Tanaka, M. Bull. Chem. Soc. J pn. 1995, 68, 403.
(3) Hofmann, P.; Heiss, H.; Neiteler, P.; Mu¨ller, G.; Lachmann, J .
Angew. Chem. 1990, 102, 935; Angew. Chem., Int. Ed. Engl. 1990, 29,
880.
(1)
(4) Huang, D.; Heyn, R. H.; Bollinger, J . C.; Caulton, K. G.
Organometallics 1997, 16, 292. Osakada, K.; Koizumi, T.; Yamamoto,
T. Bull. Chem. Soc. J pn. 1997, 70, 189.
(5) Cundy, C. S.; Lappert, M. F.; Dubac, J .; Mazerolles, P. J . Chem.
Soc., Dalton Trans. 1976, 910. Cundy, C. S.; Lappert, M. F. J . Chem.
Soc., Dalton Trans. 1976, 665. Yamashita, H.; Tanaka, M.; Honda, K.
J . Am. Chem. Soc. 1995, 117, 8873. Tanaka, Y.; Yamashita, H.;
Shimada, S.; Tanaka, M. Organometallics 1997, 16, 3246.
(6) Mu¨ller, C.; Schubert, U. Chem. Ber. 1991, 124, 2181.
(7) Gilges, H.; Kickelbick, G.; Schubert, U. J . Organomet. Chem.
1997, 548, 57.
The identity and structure of 1a were unequivocally
established by elemental analysis and NMR spectra.9
In contrast to this, the SiMe3 derivative showed no
subsequent reaction after the formation of the Pt(P )x
species, according to the 31P NMR spectra, even if the
reaction mixture was heated to 70 °C for 72 h or refluxed
(8) Gilges, H.; Schubert, U. Eur. J . Inorg. Chem. 1998, 897.
10.1021/om9805335 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 10/08/1998

Communications
Organometallics, Vol. 17, No. 22, 1998 4761
in toluene. It is assumed that this different behavior
was due to the lower activity of Si-Me bonds toward
oxidative addition compared with Si-Ph bonds, because
the same order of reactivity was already observed for
the corresponding tin compounds.8 To test this notion,
Ph2PCH2CH2SiPh2Me was analogously reacted. The
31P NMR spectra showed that the complex (MePh2-
doublet at about 50 ppm can be assigned to the
phosphorus atom of the five-membered ring because of
the significant low-field shift. This is also clear proof
2
that chelation has occurred. The value J PPtP ≈ 15 Hz
is typical for a cis arrangement of the phosphane
ligands.
The comparison of the results reported in this com-
munication with our previous work on the reactions of
(Ph3P)2Pt(π-C2H4) with Ph2PCH2CH2ER2-E′R′3 (E-E′ )
Si-Si, Si-Sn,7 and Sn-C8) allows conclusions about the
order of reactivity of E-E′ bonds toward the same metal
complex fragment in the same electronic and steric
environment. Oxidative addition of the Si-Si, Si-Sn,
Sn-Cphenyl, or Sn-Cmethyl bond of Ph2PCH2CH2SiR2-
EPh3 (E ) Si, Sn; R ) Me, Ph) and Ph2PCH2CH2SnR3
(R ) Me, Ph) proceed even at room temperature, but
the reaction rates are different. Oxidative addition of
Si-C bonds in Ph2PCH2CH2SiR3 is only observed for
Si-phenyl groups at higher temperatures. Thus, the
order of reactivity is Sn-Si > Sn-Cphenyl > Sn-Cmethyl
≈ Si-Si . Si-Cphenyl. No oxidative addition reaction
was observed for Ph2PCH2CH2SiMe3; therefore, even
chelate assistance is not sufficient to add the least
reactive Si-Cmethyl bonds to Pt(0). It is known that Si-
aryl groups are more easily cleaved by electrophiles than
Si-alkyl groups. Si-alkyl bonds are less polarized
because of the hydrogen substituents at the carbon
atom. This may be the explanation for the selectivity
of Si-Ph over Si-Me in the reaction reported in this
paper.
SiCH2CH2Ph2P)Pt(PPh2CH2CH2SiPhMe)Ph (1b) was
almost quantitatively formed after heating for 40 h.10
Si-Ph addition could only be spectroscopically observed,
because solutions of the complex showed a marked
tendency to eliminate the Si-C bond again and re-
form Pt(P )x with nonchelated PPh2CH2CH2SiPh2Me
ligand(s). To suppress this reductive elimination by
increasing the electron density at the metal center, a
1:1:1 mixture of (Ph3P)2Pt(C2H4), PEt3, and Ph2PCH2-
CH2SiPh2Me was reacted, which resulted in the forma-
tion of (Et3P)Pt(PPh2CH2CH2SiPhMe)(Ph) (2).11 Ac-
cording to the 31P NMR spectra, the solution of 2 was
stable toward reductive elimination, due to the more
electron-donating properties of the PEt3 ligand. There
was also no indication for a byproduct originating from
the oxidative addition of the Si-Me group in this
modification of the reaction.
The stereochemisty of the complexes 1 and 2 is the
same as previously observed for the corresponding
complexes (R′′3P)Pt(PPh2CH2CH2SiR2)ER′3 (E ) Si, Sn;
R′′3P ) R′3ESiR2CH2CH2Ph2P, Ph3P). There are two
doublets in the 31P NMR spectra for the nonequivalent
phosphorus nuclei, accompanied by Pt satellites. The
Ack n ow led gm en t . We thank the Fonds zur Fo¨r-
derung der wissenschaftlichen Forschung (FWF) for
supporting this work.
(9) An amount of 134 mg (282 mmol) of Ph2PCH2CH2SiPh3 was
added to a solution of 106 mg (142 mmol) of (Ph3P)2Pt(C2H4) in 8 mL
of benzene under an atmosphere of dry argon. An immediate color
change to orange occurred, and gas was evolved. The solution was
stirred for 15 min and then slowly heated to 70 °C and held at this
temperature for 12 h. After the solution was cooled to room temper-
ature, all volatiles were then removed in vacuo, leaving a yellow oil.
The residue was extracted three times with 8 mL portions of pentane.
When the combined pentane solutions were concentrated to 4 mL, a
yellow precipitate was formed. Precipitation was completed by cooling
to -20 °C. The yellow powder was separated at -20 °C and dried in
vacuo. Yield: 84 mg (52%). Anal. Calcd for C64H58P2PtSi2: C, 67.40;
H, 5.13. Found: C, 67.15; H, 5.27. 31P{1H} NMR (101.25 MHz, C6D6):
Su p p or tin g In for m a tion Ava ila ble: 31P NMR spectra of
1b and 2 (2 pages). Ordering information is given on any
current masthead page.
OM9805335
(11) A solution of 51 mg (123 mmol) of Ph2PCH2CH2SiPh2Me in 1.5
mL of benzene and then a solution of 21 mg (177 mmol) of PEt3 in 1.0
mL of benzene was added to a solution of 92 mg (123 mmol) of (Ph3P)2-
Pt(C2H4) in 8 mL of benzene under an atmosphere of dry argon. An
immediate color change to orange occurred, and gas was evolved. The
solution was stirred for 30 min and then slowly heated to 75 °C and
held at this temperature for 21 h. After the solution was cooled to room
temperature, all volatiles were then removed in vacuo, leaving a yellow
2
1
1
δ 49.1 (d, J PPtP ) 14.6 Hz, J PtP ) 2023.8 Hz), 25.2 (d, J PtP ) 1354.9
Hz). 29Si NMR (49.69 MHz, C6D6): δ 28.7 (dd, J PPtSi ) 160.0 Hz, J PSi
2
) 10.2 Hz), -9.2 (d, J PCCSi ) 24.0 Hz). 1H NMR (250.13 MHz, C6D6):
3
δ 1.05-1.35 (m, 2 H, SiCH2), 1.58-1.69 (m, 2 H, SiCH2), 2.09-2.39
2
oil. 31P{1H} NMR (101.25 MHz, C6D6): δ 50.6 (d, J PPtP ) 14.6 Hz,
(m, 2 H, PCH2), 2.47-2.58 (m, 2 H, PCH2), 6.77-7.73 (m, 20 H, Ph).13
C
1
2
1J PtP ) 2054.5 Hz), 13.4 (d, J PtP ) 1390.4 Hz, J PPtSi ) 156.2 Hz). 1H
2
NMR (62.90 MHz, C6D6): δ 19.7 (d, SiCH2, J PCC ) 18.5), 21.6 (dd,
4
NMR (250.13 MHz, C6D6): δ 0.59 (d, 3 H, SiMe, J PPtSiCH ) 2.1 Hz,
SiCH2 [chel.], J PC ) 19.9 Hz, J PC ) 3.8 Hz), 29.3 (d, PCH2, 1J PC ) 27.2
3J PtSiCH ) 24.7 Hz), 0.69-0.75 (m, 9 H, CMe), 0.95-1.15 (m, 6 H, PCH2-
Me), 1.31-1.54 (m, 2 H, SiCH2), 2.25-2.45 (m, 2 H, PCH2), 6.99-7.76
1
1
Hz), 32.1 (dd, PCH2 [chel.], J PC ) 36.8 Hz, J PC ) 9.5 Hz), 127.3-
144.4 (Ph).
(m, 10 H, Ph).13C NMR (62.90 MHz, C6D6): δ -0.4 (d, SiCH3, J PPtSiC
3
(10) 31P{1H} NMR (101.25 MHz, C6D6): main product 1b, δ 49.7
3
2
) 3.7 Hz, J PPtSiC ) 68.4 Hz), 15.1, 15.2 (SiCH2 and CCH3, J PCC
)
2
1
1
(d, J PPtP ) 13.4 Hz, J PtP ) 2074.0), 24.7 (d, J PtP ) 1307.4 Hz).
Byproduct (∼10%). [(Ph3P)Pt(Ph2PCH2CH2SiPhMe)Ph], δ 50.1 (d, 2J PPtP
1
1
20.3 Hz), 20.1 (d, PCH2, J PC ) 65.7 Hz), 20.1 (dd, PCH2, J PC ) 37.9
4
Hz, J PPtPC ) 10.6 Hz), 127.0-147.1 (Ph), 162.3 (dd, ipso-CPh
,
2J PPtC
)
1
1
2
) 12.2 Hz, J PtP ) 2036.2 Hz), 26.5 (d, J PtP ) 1328.1 Hz).
96.2 Hz, J PPtC ) 13.4).