Thermal and photochemical silicon-carbon bond activation in donor-stabilized platinum(0)-alkyne complexes

Article abstract of DOI:10.1021/om010984g

Reaction of Pt(COD)₂ with Me₃SiC≡CPh and a bidentate chelating ligand leads to the formation of the corresponding donor-stabilized Pt-η²-alkyne complexes (PN)Pt(η²-Me₃SiC≡CPh) (1) and (dcpe)Pt(η²-Me₃SiC≡CPh) (3) (PN = (diisopropylphosphinodimethylamino)-ethane; dope = bis(dicyclohexylphosphino)ethane). The nitrogen donor ligand in 1 facilitates the cleavage of the Si-C(sp) bond, and the Pt(II) complex (PN)Pt(SiMe₃)(C≡CPh) (2) is formed at room temperature. In contrast, the bisphosphino-substituted compound 3 has been isolated as a thermally robust Pt(0) complex. However, the silicon-carbon bond in the latter compound can be photochemically activated, and the oxidative addition product (dcpe)Pt-(SiMe₃)(C≡CPh) (4) is generated. Both Si-C(sp) bonds in Me₃Si-C≡C-C≡C-SiMe₃ have been thermally activated by a (PN)Pt fragment to afford the dinuclear Pt(II) species (PN)-Pt(SiMe₃)-C≡C-C≡C-Pt(SiMe₃)(PN) (6).

Full text of DOI:10.1021/om010984g

1190
Organometallics 2002, 21, 1190-1196
Th er m a l a n d P h otoch em ica l Silicon -Ca r bon Bon d
Activa tion in Don or -Sta bilized P la tin u m (0)-Alk yn e
Com p lexes
Christian Mu¨ller, Rene J . Lachicotte, and William D. J ones*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received November 13, 2001
Reaction of Pt(COD)2 with Me3SiCtCPh and a bidentate chelating ligand leads to the
formation of the corresponding donor-stabilized Pt-η2-alkyne complexes (PN)Pt(η2-Me3SiCt
CPh) (1) and (dcpe)Pt(η2-Me3SiCtCPh) (3) (PN ) (diisopropylphosphinodimethylamino)-
ethane; dcpe ) bis(dicyclohexylphosphino)ethane). The nitrogen donor ligand in 1 facilitates
the cleavage of the Si-C(sp) bond, and the Pt(II) complex (PN)Pt(SiMe3)(CtCPh) (2) is formed
at room temperature. In contrast, the bisphosphino-substituted compound 3 has been isolated
as a thermally robust Pt(0) complex. However, the silicon-carbon bond in the latter
compound can be photochemically activated, and the oxidative addition product (dcpe)Pt-
(SiMe3)(CtCPh) (4) is generated. Both Si-C(sp) bonds in Me3Si-CtC-CtC-SiMe3 have
been thermally activated by a (PN)Pt fragment to afford the dinuclear Pt(II) species (PN)-
Pt(SiMe3)-CtC-CtC-Pt(SiMe3)(PN) (6).
In tr od u ction
alkynylsilanes with coordination of both the SiR3 and
the alkynyl fragment is much less common and has been
reported only in some isolated cases.8
The scission of silicon-carbon bonds by transition
metal complexes has recently attracted much interest
due to its potential application in functionalization and
transformation reactions of organosilanes.1 Further-
more, detailed studies on the interaction of organo-
silanes with transition metal centers provide better
insight into important processes, such as the hydro-
silylation of alkenes,1a,2 the dehydrogenative coupling
of primary and secondary silanes,3 or the dehydroge-
native silylation of olefins.4
We report here on the synthesis of 1-phenyl-2-tri-
methylsilylacetylene and 1,4-bis(trimethylsilyl)-1,3-
butadiyne complexes of Pt(0) in which the Pt(η2-Me3-
SiCtCR) fragment is stabilized by the chelating donor
(iPr)2PCH2CH2NMe2 (PN)9 or (Cy)2PCH2CH2P(Cy)2 (bis-
(dicyclohexylphosphino)ethane, dcpe). The PN-substi-
tuted compounds show remarkable differences in Si-
C(sp) bond activation and reductive elimination reactions
compared to the bisphosphino-substituted complexes.
While the oxidative addition of Si-C(sp3) bonds to
transition metal centers is still quite rare,5 Si-C(sp2)
bond cleavage has been studied much more frequently.6
Several examples of Si-C(sp) bond activation reactions
in LnM(η2-Me3SiCtCR) complexes have also been docu-
mented in the literature so far. However, migration of
the silyl group to the metal center is generally not
observed in these systems. Instead, 1,2-silyl migration
occurrs to form vinylidene complexes under thermal or
photochemical conditions.7 Cleavage of Si-C bonds in
Resu lts a n d Discu ssion
We recently reported on the synthesis of the zero-
valent platinum complexes (PN)Pt(η2-PhCtCPh) and
(PP)Pt(η2-PhCtCPh) (PP ) dcpe; bis(diisopropylphos-
phino)ethane, dippe).10 These compounds undergo oxi-
dative addition of the C(sp)-C(sp2) bond in diphenyl-
acetylene to the metal center under photochemical
conditions. However, a thermal reaction with dipheny-
lacetylene to form a platinacyclopentadiene complex was
only observed for (PN)Pt(η2-PhCtCPh).11 This indicates
an enhanced reactivity of the platinum atom due to the
hemilabile character of the bidentate P,N hybrid ligand.12
(1) (a) Ojima, I. In The Chemistry of Organosilicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, 1989; Vols. 1 and 2.
(b) Comprehensive Organometallic Chemistry I and II; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1982, 1995.
(2) (a) Speier, J . L. Adv. Organomet. Chem. 1979, 407. (b) Harrod,
J . F.; Chalk, A. J . In Organic Synthesis via Metal Carbonyls; Wender,
I., Pino, P., Eds.; Wiley: New York, 1977; p 673. (c) Chalk, A. J .;
Harrod, J . F. J . Am. Chem. Soc. 1965, 87, 16.
(3) Braunstein, P.; Knorr, M. J . Organomet. Chem. 1995, 500, 21,
and refs 10, 12-25 therein.
(4) Kakiuchi, F.; Yamada, A.; Chatani, N.; Murai, S. Organometallics
1999, 18, 2033.
(5) (a) Hofmann, P.; Heiss, H.; Neiteler, P.; Mu¨ller, G.; Lachmann,
J . Angew. Chem., Int. Ed. Engl. 1990, 29, 880. (b) Lin, W.; Wilson, S.
R.; Girolami, G. S. Organometallics 1994, 13, 2309. (c) Hua, R.; Akita,
M.; Moro-oka, Y. Chem. Commun. 1996, 541.
(6) (a) Steenwinkel, P.; Gossage, R. A.; Maunula, T.; Grove, D. M.;
van Koten, G. Chem. Eur. J . 1998, 4, 763. (b) Mintcheva, N.; Nishihara,
Y.; Tanabe, M.; Hirabayashi, K.; Mori, A.; Osakada, K. Organometallics
2001, 20, 1243, and refs 12 and 13 therein.
(7) (a) Bantel, H.; Powell, A. K.; Vahrenkamp, H. Chem. Ber. 1990,
123, 661. (b) Rappert, T.; Nu¨rnberg, O.; Werner, H. Organometallics
1993, 12, 1359. (c) Werner, H.; Baum, M.; Schneider, D.; Windmu¨ller,
B. Organometallics 1994, 13, 1089. (d) Werner, H.; Lass, R. W.; Gevert,
O.; Wolf, J . Organometallics 1997, 16, 4077.
(8) (a) Ciriano, M.; Howard, J . A. K.; Spencer, J . L.; Stone, F. G. A.;
Wadepohl, H. J . Chem. Soc., Dalton Trans. 1979, 1749. (b) Huang, D.;
Heyn, R. H.; Bollinger, J . C.; Caulton, K. G. Organometallics 1997,
16, 292.
(9) Werner, H.; Hampp, A.; Peters, K.; Peters, E. M.; Walz, L.; von
Schnering, H. G. Z. Naturforsch. 1990, 45b, 1548.
(10) Mu¨ller, C.; Iverson, C. N.; Lachicotte, R. J .; J ones, W. D. J .
Am. Chem. Soc. 2001, 123, 9718.
(11) Mu¨ller, C.; Lachicotte, R. J .; J ones, W. D. Organometallics 2002,
in press.
10.1021/om010984g CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/09/2002

Silicon-Carbon Bond Activation
Organometallics, Vol. 21, No. 6, 2002 1191
We were further interested in the reactivity of donor-
stabilized Pt(0) fragments toward SiMe3-substituted
alkynes, such as 1-phenyl-2-trimethylsilylacetylene13
and 1,4-bis(trimethylsilyl)-1,3-butadiyne13b,e,14 com-
plexes. Reaction of Pt(COD)2 with 1 equiv of Me3SiCt
CPh and 1 equiv of (iPr)2CH2CH2NMe2 in C6D6 led to
the formation of the η2-alkyne complex (PN)Pt(η2-Me3-
SiCtCPh) (1) (eq 1). A singlet with platinum satellites
F igu r e 1. Molecular structure of (PN)Pt(SiMe3)(CtCPh)
(2) (ORTEP diagram; 30% probability ellipsoids). The
-CH2NMe2 portion of the P,N ligand showed some disor-
der. Only one contributor is shown.
at δ ) 66.4 ppm (1J Pt-P ) 3952 Hz) was observed for 1
1
in the 31P{1H} NMR spectrum. The H NMR spectrum
displayed the characteristic ortho-, meta-, and para-
protons of Me3SiCtCPh in the ratio of 2:2:1. However,
the η2-alkyne complex 1 quantitatively rearranged to a
new compound (2) within approximately 5 days at room
temperature (24 h at T ) 70 °C). 2 was obtained as a
colorless solid after recrystallization from C6D6/pentane.
The 31P{1H} NMR spectrum (C6D6) of 2 showed a singlet
with platinum satellites at δ ) 59.3 ppm (1J Pt-P ) 2760
Hz). The comparatively smaller platinum-phosphorus
coupling constant is indicative for a Pt(II) species with
substitutents σ-bonded to the metal center. Further-
more, a SiMe3 group with platinum satellites was
observed for 2 in the 1H NMR spectrum, suggesting that
the SiMe3 group is attatched to the platinum center. The
NMR spectroscopic data are consistent with an oxidative
addition of the silicon-carbon bond in Me3SiCtCPh to
the donor-stabilized platinum fragment at ambient
temperature (eq 2). A crystal of 2 suitable for X-ray
F igu r e 2. 31P NMR spectrum (162 MHz) of the thermal
Si-C bond activation reaction in 1 at t ) 48 h (T ) rt).
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 2
Bond Lengths
Pt(1)-N(1B)
Pt(1)-P(1)
Pt(1)-Si(1)
2.25(4)
2.262(2)
2.313(2)
Pt(1)-C(1)
C(1)-C(2)
C(2)-C(3)
1.998(8)
1.199(11)
1.440(11)
Bond Angles
Si(1)-Pt(1)-C(1)
Si(1)-Pt(1)-P(1)
C(1)-Pt(1)-N(1B)
82.9(2)
N(1B)-Pt(1)-P(1)
84.0(9)
176.4(7)
176.3(9)
101.63(8) Pt(1)-C(1)-C(2)
91.8(9)
C(1)-C(2)-C(3)
diffraction was obtained by recrystallization from C6D6/
pentane. The molecular structure of 2 is illustrated in
Figure 1; selected bond lengths and distances are
summarized in Table 1. The structural analysis con-
firmed that 2 is the Si-C(sp) cleavage product (PN)Pt-
(SiMe3)(CtCPh). Interestingly, the insertion of the
metal center into the Si-C bond is selective. Only one
isomer with the alkynyl group trans to the phosphorus
atom and the SiMe3 group trans to the nitrogen atom
was generated.
Although 1 is quantitatively converted to 2 within ∼5
days at room temperature, two transient intermediates
(I and II) were observed during the course of the
reaction. Figure 2 displays a 31P{1H} NMR spectrum
(C6D6) of the reaction mixture, recorded after t ) 48 h.
Two doublets with platinum satellites at δ ) 33.2 ppm
(12) For the concept of hemilability see for example: (a) J effrey, J .
C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658. (b) Okuda, J .
Comments Inorg. Chem. 1994, 16, 185. (c) Slone, C. S.; Weinberger,
D. A.; Mirkin, C. A. Prog. Inorg. Chem. 1999, 48, 233. (d) Mu¨ller, C.;
Vos, D.; J utzi, P. J . Organomet. Chem. 2000, 600, 127. (e) Braunstein,
P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680.
(13) For zerovalent group-10-(η2-Me3SiCtCPh) complexes see: (a)
Boag, N. M.; Green, M.; Grove, D. M.; Howard, J . A. K.; Spencer, J .
L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1980, 2170. (b) Butler,
G.; Eaborn, C.; Pidcock, A. J . Organomet. Chem. 1981, 210, 403. (c)
Hoffman, D. M.; Hoffmann, R. J . Chem. Soc., Dalton Trans. 1982, 1471.
(d) Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.;
Heimbach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11,
1235. (e) Rosenthal, U.; Nauck, C.; Arndt, P.; Pulst, S.; Baumann, W.;
Burlakov, V. V.; Go¨rls, H. J . Organomet. Chem. 1994, 484, 81. (f)
Rosenthal, U.; Pulst, S.; Kempe, R.; Po¨rschke, K.-R.; Goddard, R.; Proft,
B. Tetrahedron 1998, 54, 1277.
2
(1J Pt-P ) 3626 Hz, J P-P ) 37.3 Hz) and δ ) 35.8 ppm
(1J Pt-P ) 3468 Hz, J P-P ) 37.3 Hz) were detected for
2
1
intermediate I. The H NMR spectrum of the reaction
mixture, however, revealed a ratio of complexed alkyne
to P,N ligand of 1:2 for compound I, as well as 1 equiv
of free alkyne. The spectroscopic data are consistent
with an asymmetric Pt(η2-Me3SiCtCPh) complex, con-
taining two monodentate P,N ligands which coordinate

1192 Organometallics, Vol. 21, No. 6, 2002
Mu¨ller et al.
F igu r e 4. Schematic structures of intermediate II and the
triplatinum compound A.
lites for a SiMe3 group. The resonances of the trimethyl-
silyl group, the P,N ligand, and the phenylalkynyl group
were detected in a ratio of 1:1:1. Again, these data are
consistent with a silicon-carbon bond activation prod-
uct. We were able to isolate intermediate II from the
reaction mixture by fractional crystallization. The com-
pound was obtained as a pale yellow solid. Unfortu-
nately, any attempt to grow crystals of II suitable for
X-ray diffraction failed. However, heating a solution of
pure II in C6D6 for 48 h at T ) 100 °C resulted in the
quantitative formation of (PN)Pt(SiMe3)(CtCPh) (2).
Interestingly, the color of the solution changed from
yellow to dark gray upon heating, suggesting the
generation of colloidal platinum. Furthermore, an el-
emental analysis as well as an electrospray-MS of
compound II is consistent with the formula C42H76N2P2-
Pt3Si2 and the mass 1312.2 g/mol, respectively. We
propose that II is the platinum-bridged dimer shown
in Figure 4. The additional platinum atom in II balances
the stoichiometry for the formation of I and free alkyne
from two molecules of the starting material 1 (vide
supra). Similar triplatinum compounds with the sche-
matic structure A are known and have been reported
by Stone et al. before (Figure 4).18
F igu r e 3. Molecular structure of (NP)2Pt(η2-Me3SiCtCPh)
(I) (ORTEP diagram; 30% probability ellipsoids).
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for I
Bond Lengths
Pt(1)-P(1)
Pt(1)-P(2)
Pt(1)-C(1)
Pt(1)-C(2)
2.2955(10)
2.2820(11)
2.047(4)
C(1)-C(2)
Si(1)-C(2)
C(1)-C(3)
1.304(6)
1.848(5)
1.460(6)
2.100(4)
Bond Angles
36.63(17) C(2)-Pt(1)-P(1) 108.44(12)
110.08(4) Si(1)-C(2)-C(1) 134.3(4)
140.1(4)
C(1)-Pt(1)-C(2)
P(2)-Pt(1)-P(1)
C(1)-Pt(1)-P(2) 104.87(13) C(2)-C(1)-C(3)
to the metal center via the diisopropylphosphino group.
Intermediate I was independently synthesized by reac-
tion of Pt(COD)2 with 1 equiv of Me3SiCtCPh and 2
equiv of (iPr)2PCH2CH2NMe2 in C6D6 according to eq
3. This compound was isolated as an air- and moisture-
We assume that the initial step in the silicon-carbon
bond cleavage reaction in 1 is migration of the metal
fragment with subsequent oxidative addition of the Si-
C(sp) bond to the platinum(0) center. Additionally, an
equilibrium between 1 and intermediate I, which con-
tains two P,N ligands, must also exist according to the
(14) For zerovalent group-10-(Me3SiCtC-CtCSiMe3) complexes
see: (a) Klein, H.-F.; Beck-Hemetsberger, H.; Reitzel, L.; Rodenha¨user,
B.; Cordier, G. Chem. Ber. 1989, 122, 43. (b) Rosenthal, U.; Pulst, S.;
Arndt, P.; Baumann, W.; Tillack, A.; Kempe, R. Z. Naturforsch. 1995,
50b, 368. (c) Rosenthal, U.; Pulst, S.; Arndt, P.; Baumann, W.; Tillack,
A.; Kempe, R. Z. Naturforsch. 1995, 50b, 377. (d) Rosenthal, U. Pulst,
S.; Arndt, P.; Ohff, A.; Tillack, A.; Baumann, W.; Kempe, R.; Bulakov,
V. V. Organometallics 1995, 14, 2961. (e) Tillack, A.; Pulst, S.;
Baumann, W.; Baudisch, H.; Kortus, K.; Rosenthal, U. J . Organomet.
Chem. 1997, 532, 117. (f) Bruce, M. I.; Low, P. J .; Werth, A.; Skelton,
B. W.; White, A. H. J . Chem. Soc., Dalton Trans. 1996, 1551.
(15) (a) Dewar, M. J . S. Bull. Soc. Chim. Fr. 1951, 18, C79. (b) Chatt,
J .; Duncanson, L. A. J . Chem. Soc. 1953, 2939. (c) Greaves, E. O.; Lock,
C. J . L.; Maitlis, P. M. Can. J . Chem. 1968, 46, 3879. (d) Otsuka, S.;
Nakamura, A. Adv. Organomet. Chem. 1976, 14, 245, and references
therein. (e) Rosenthal, U., Schulz, W. J . Organomet. Chem. 1987, 321,
103.
sensitive, colorless solid. Crystals of I suitable for X-ray
diffraction were obtained after recrystallization from
petroleum ether at T ) -30 °C. The molecular structure
of I is illustrated in Figure 3; selected bond lengths and
distances are listed in Table 2. The structural analysis
revealed that intermediate I is indeed the Pt(η2-Me3-
SiCtCPh) complex with two P,N ligands coordinated
to the platinum atom in a monodentate fashion. Com-
pound I adopts the expected distorted square-planar
geometry at the metal center with the alkyne ligand in
the P(1)-Pt-P(2) plane. The bending of the CtC-C(Si)
angles reflects a major contribution of Ptfπ* back-
donation.15 The P(1)-Pt(1)-P(2) angle of 110.1° is
similar to the one reported for (Ph3P)2Pt(η2-PhCtCPh)
(102.0°),16 but about 24° larger compared to Pt(η2-
alkyne) complexes bearing chelating R2PCH2CH2PR2
ligands.17
(16) Glanville, J . O.; Stewart, J . M.; Grim, S. O. J . Organomet. Chem.
1967, 7, P9.
(17) The P-Pt-P angles in (dippe)Pt(η2-PhCtCPh) and (dippe)Pt-
(η2-tBuCtCPh) are 86.84(3)° and 87.20(3)°, respectively: ref 11 and
unpublished results.
(18) (a) Boag, N. M.; Green, M.; Howard, J . A. K.; Spencer, J . L.;
Stansfield, R. F. D.; Stone, F. G. A.; Thomas, M. D. O.; Vicente, J .;
Woodward, P. J . Chem. Soc., Chem. Commun. 1977, 930. (b) Boag, N.
M.; Green, M.; Howard, J . A. K.; Spencer, J . L.; Stansfield, R. F. D.;
Thomas, M. D. O.; Stone, F. G. A.; Woodward, P. J . Chem. Soc., Dalton
Trans. 1980, 2182. (c) Boag, N. M.; Green, M.; Howard, J . A. K.; Stone,
F. G. A.; Wadepohl, H. J . Chem. Soc., Dalton Trans. 1981, 862.
For intermediate II, however, a singlet with broad
platinum satellites at δ ) 53.5 ppm (1J Pt-P ) 2631 Hz)
was observed in the 31P{1H} NMR spectrum. The 1H
NMR spectrum showed a singlet with platinum satel-

Silicon-Carbon Bond Activation
Organometallics, Vol. 21, No. 6, 2002 1193
Sch em e 1
to room temperature, only the silicon-carbon bond
cleavage product 2 could be detected by NMR spectros-
copy. This suggests that rearrangement of 2a to 2 had
occurred, which is the thermodynamically favored prod-
uct (eq 4). In the photochemical Si-C(sp) bond scission,
only small amounts (<5%) of the intermediates I and
II were recorded by 31P{1H} NMR spectroscopy. The
formation of I and II in this reaction is most likely due
to a thermal conversion of 1 to compound 2 (vide supra).
We extended our investigations on thermal and
photochemical silicon-carbon bond activation to Pt(η2-
Me3SiCtCPh) species, which are stabilized by a chelat-
ing bisphosphino ligand. Reaction of Pt(COD)2 with 1
equiv of Me3SiCtCPh and 1 equiv of bis(dicyclohexyl-
phosphino)ethane (dcpe) in C6D6 led to the quantitative
formation of the η2-alkyne complex (dcpe)Pt(η2-Me3SiCt
CPh) (3) (eq 1). The 31P{1H} NMR spectrum of 3 showed
two doublets with platinum satellites at δ ) 67.7 ppm
data recorded by 31P{1H} NMR spectroscopy (Figure 2).
The remaining fragment “Pt(η2-Me3SiCtCPh)” would
react with the Si-C bond activation product 2 to form
the second intermediate II together with free alkyne
(Scheme 1). The temporary presence of free Me3SiCt
CPh during the course of the reaction was indeed
2
(1J Pt-P ) 3274 Hz, J P-P ) 53.9 Hz) and δ ) 69.1 ppm
2
(1J Pt-P ) 3116 Hz, J P-P ) 53.9 Hz). In contrast to 1,
compound 3 was isolated as a yellow solid after recrys-
tallization from pentane/dichloromethane at T ) -30
°C. A solution of 3 in C6D6 showed no thermal Si-C(sp)
bond activation at room temperature. Even prolonged
heating for 8 days at T ) 100 °C resulted in no
significant change in the 31P NMR spectrum. These
observations support the assumption that the enhanced
reactivity of the (PN)Pt(0) fragment toward thermal
bond scission is mainly due to the NR2 donor functional-
ity.
1
verified by H NMR spectroscopy. The latter reaction
is also reversible, leading again to a decrease of II as
well as of I to form the final product 2 quantitatively
after ∼5 days at room temperature.
The reactivity of the metal fragment toward Si-C
bond activation is most likely due to the differences in
σ-donor and π-acceptor capabilities of the donor func-
tionalities in (iPr)2PCH2CH2NMe2. While the PR2 group
is a good σ-donor and π-acceptor, the NR2 group lacks
in π-acceptor character. The increased electron density
at the metal center might facilitate the oxidative addi-
tion reaction. This assumption is based on the fact that
intermediate I, in which two monodentate P,N ligands
coordinate to the Pt(η2-Me3SiCtCPh) fragment via the
diisopropylphosphino group, does not show any thermal
Si-C bond activation at all. Another possibility for the
increased reactivity of 1 is that a coordinatively unsat-
urated Pt species is required for the oxidative addition
process. The -NMe2 group as a “hard” Lewis-basic
functionality offers this lability.
Silicon-carbon bond activation in 3, however, was
achieved under photochemical conditions. A solution of
3 in C6D6 was irradiated with UV light, and the reaction
was monitored by 31P{1H} NMR spectroscopy. After 1
h of photolysis the formation of a new species was
observed. Within 6 h, 3 was quantitatively converted
into the product (4), which was obtained as a pale yellow
solid after recrystallization. The 31P{1H} NMR spectrum
of 4 displayed two doublets with platinum satellites at
2
δ ) 67.2 ppm (1J Pt-P ) 2593 Hz, J P-P ) 5.2 Hz) and δ
2
) 71.3 ppm (1J Pt-P ) 1113 Hz, J P-P ) 5.2 Hz).
We were further interested in the reactivity of (PN)-
Pt(η2-Me3SiCtCPh) under photochemical conditions. A
solution of 1 in THF-d8 was irradiated with UV light at
T ) -30 °C to prevent thermal rearrangement of 1 to
compound 2. Within 8.5 h of photolysis, the starting
material was quantitatively converted to an approxi-
mately 1:1 mixture of the products 2 and 2a . The 31P-
{1H} NMR spectrum of 2a displayed a singlet with
platinum satellites at δ ) 66.0 ppm (1J Pt-P ) 1126 Hz)
as well as coupling to silicon (2J P-Si ) 191 Hz). We
assume that 2a is an isomer of 2 with the SiR3 group
trans to phosphorus and the alkynyl group trans to
nitrogen. However, on warming the mixture of isomers
Additionally, a SiMe3 group with platinum satellites
was recorded in the 1H NMR spectrum of 4. The
spectroscopic data are again consistent with the forma-
tion of an asymmetric Pt(II) species with a SiMe3 and
alkynyl group σ-bonded to the platinum center (eq 5).

1194 Organometallics, Vol. 21, No. 6, 2002
Mu¨ller et al.
F igu r e 6. Molecular structure of (PN)Pt(SiMe3)-CtC-
CtC-Pt(SiMe3)(PN) (6) (ORTEP diagram).
Sch em e 2
F igu r e 5. Molecular structure of (dcpe)Pt(SiMe3)(CtCPh)
(4) (ORTEP diagram; 30% probability ellipsoids).
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 4
Bond Lengths
Pt(1)-P(1)
Pt(1)-P(2)
Pt(1)-Si(1)
2.2711(15)
2.3302(15)
2.3910(17)
Pt(1)-C(27)
C(27)-C(28)
C(28)-C(29)
2.007(6)
1.200(8)
1.445(8)
Bond Angles
Si(1)-Pt(1)-C(27) 81.64(17) C(27)-Pt(1)-P(2)
90.68(17)
P(1)-Pt(1)-P(2)
86.50(5) Pt(1)-C(27)-C(28) 176.3(5)
Si-C bond cleavage was confirmed by single-crystal
X-ray diffraction. Although we were not able to obtain
satisfying structural analysis data (R1 ) 9.70%), the
activation of both silicon-carbon bonds in 1,4-bis-
(trimethylsilyl)-1,3-butadiyne by the (PN)Pt fragments
was obvious. The molecular structure of 6 is illustrated
in Figure 6. Bond activation reactions in Me3Si-CtC-
CtC-SiMe3 with early transition metal fragments have
been reported by Rosenthal et al. before. Interestingly,
the cleavage of the central C(sp)-C(sp) single bond
instead of the Si-C(sp) bond was observed with in situ-
generated “Cp2M” species (M ) Ti, Zr).19
Si(1)-Pt(1)-P(1) 101.55(6) C(27)-C(28)-C(29) 177.2(6)
Crystals of 4 suitable for X-ray diffraction were obtained
after recrystallization from C6D6/pentane. The molecu-
lar structure of 4 is depicted in Figure 5; selected bond
lengths and distances are summarized in Table 3. The
structural analysis confirmed the oxidative addition of
the Si-C(sp) bond in Me3SiCtCPh to the metal center
under photochemical conditions. However, the bond
cleavage reaction turned out to be a reversible process.
On thermal activation reductive elimination occurred
and the Pt-η2-alkyne complex 3 was regenerated (eq 5).
The thermal accessibility of this reverse reaction indi-
cates that the oxidative addition of the Si-C(sp) bond
in 3 is uphill thermodynamically, whereas it is downhill
in complex 1! This conclusion also argues against chelate
lability as being responsible for the thermal reactivity
of 1.
Using 1,4-bis(trimethylsilyl)-1,3-butadiyne instead of
1-phenyl-2-trimethylsilylacetylene, both silicon-carbon
bonds were activated by a (PN)Pt fragment. Reaction
of (CODPt)2(η2;η2-Me3Si-CtC-CtCSiMe3) (5) with 2
equiv of (iPr)2PCH2CH2NMe2 in C6D6 and subsequent
heating to T ) 70 °C for 16 h led to the formation of a
yellow precipitate (6), which was isolated and character-
ized by NMR spectroscopy. A SiMe3 group with plati-
num satellites and coupling to phosphorus at δ ) 0.98
ppm was observed for compound 6 in the 1H NMR
spectrum. The 31P{1H} NMR spectrum showed a singlet
with platinum satellites at δ ) 58.6 ppm (1J Pt-P ) 2734
Hz), while a silicon resonance with silicon-phosphorus
coupling (2J Si-P ) 8.0 Hz) was observed at δ ) -16.6
ppm in the 29Si NMR spectrum. The spectroscopic data
indicate that oxidative addition of both silicon-carbon
bonds to the platinum center occurred, with the SiMe3
group in a cis position to phosphorus (Scheme 2). The
Con clu sion s
In this paper we described the synthesis of novel
zerovalent Pt(η2-Me3SiCtCR) complexes which are
stabilized by a chelating donor molecule. Thermal
silicon-carbon bond activation was observed in those
compounds which are substituted by a bidentate P,N
hybrid ligand to afford the thermodynamically favored
Pt(II) species. In contrast, cleavage of the Si-C bond
in bisphosphino-stabilized Pt complexes is possible only
under photochemical conditions. The latter reaction is
uphill thermodynamically and can be reversed ther-
mally. The differences in reactivity of (PN)Pt fragments
compared to (PP)Pt systems is attributed to electronic
effects.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out under a nitrogen atmosphere in a Vacuum Atmospheres
(19) (a) Rosenthal, U.; Go¨rls, H. J . Organomet. Chem. 1992, 439,
C36. (b) Rosenthal, U.; Ohff, A.; Baumann, W.; Kempe, R.; Tillack, A.;
Burlakov, V. V. Organometallics 1994, 13, 2903. (c) Rosenthal, U.; Ohff,
A.; Tillack, A.; Baumann, W. J . Organomet. Chem. 1994, 468, C4. (d)
Rosenthal, U.; Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V. Acc.
Chem. Res. 2000, 33, 119.

Silicon-Carbon Bond Activation
Organometallics, Vol. 21, No. 6, 2002 1195
3
2
i
Corporation glovebox unless otherwise stated. The solvents
were commercially available and distilled from dark purple
solutions of benzophenone ketyl. A Siemens-SMART 3-Circle
CCD diffractometer was used for the X-ray crystal structure
determinations. All photolysis experiments were conducted
with an Oriel arc source using a 200 W Hg(Xe) bulb in NMR
tubes. The elemental analyses were obtained from Desert
1.31 (dd, J H-H ) 7.1 Hz, J H-P ) 15.3 Hz, 6 H, Pr), 1.90 (m,
2 H, -CH-), 2.09 (m, 2 H, -CH-), 2.11 (s, 6 H, N-CH3), 2.17
(s, 6 H, N-CH3), 2.21 (m, 4 H, PCH2-), 2.47 (m, 2 H, NCH2-
), 2.54 (m, 2 H, NCH2-), 6.98 (t, 3J H-H ) 6.5 Hz, 1 H, p-C6H5),
3
7.19 (pseudo-t, 2 H, m-C6H5), 7.29 (d, J H-H ) 7.7 Hz, 2 H,
o-C6H5). 31P{1H} NMR (C6D6): δ (ppm) 33.2 (d, with platinum
1
2
satellites, J Pt-P ) 3626 Hz, J P-P ) 37.3 Hz), 35.8 (d, with
1
1
2
Analytics. H, 31P, and 29Si NMR spectra were recorded on a
platinum satellites, J Pt-P ) 3468 Hz, J P-P ) 37.3 Hz).
P r epar ation of [(P N)P t(SiMe3)(CtCP h )]2P t (II). 1-Phen-
yl-2-trimethylsilylacetylene (13.1 mg, 0.075 mmol) was dis-
solved in 0.3 mL of THF-d8 and added to Pt(COD)2 (30.9 mg,
0.075 mmol) at T ) -25 °C. A yellow solution was formed,
and (iPr)2PCH2CH2NMe2 (14.2 mg, 15.9 µL, 0.075 mmol) was
added. The initial generation of the η2-alkyne complex 1 was
Bruker AMX-400 or Bruker Avance-400 spectrometer, and all
1H chemical shifts are reported relative to the residual proton
resonance in the deuterated solvents. The positive electro-
spray-MS was recorded on a Hewlett-Packard 1100 Series LC/
20
MS (fragmentor set to 70 eV). Pt(COD)2 and (iPr)2PCH2CH2-
NMe2 (PN)9 were synthesized according to published procedures.
(Cy)2PCH2CH2P(Cy)2 was purchased from STREM Chemicals,
and Me3SiCtC-CtCSiMe3 was obtained from Aldrich. Both
compounds were used without further purification. Me3SiCt
CPh was purchased from Aldrich and was degassed prior to
use.
confirmed by H and 31P{1H} NMR spectroscopy. The orange
1
solution was filled in a vial, and diffusion of pentane into the
reaction mixture led to the formation of a white solid within
24 h. The mother liquid was decanted, and the remaining solid
was again recrystallized from THF/pentane at T ) -30 °C.
Pure II was obtained as a white solid. Yield: 7.2 mg (0.006
In Sit u P r ep a r a t ion of (P N)P t (η2-Me3SiCtCP h ) (1).
1-Phenyl-2-trimethylsilylacetylene (7.5 mg, 0.043 mmol) was
dissolved in C6D6 (0.5 mL) and added to Pt(COD)2 (17.7 mg,
0.043 mmol). A yellow solution was formed, and (iPr)2PCH2-
CH2NMe2 (8.1 mg, 9.1 µL, 0.043 mmol) was subsequently
added. The 1H and 31P{1H} NMR spectrum of the orange
1
mmol, 22%). H NMR (C6D6): δ (ppm) 0.67 (s, with platinum
3
3
satellites, J H-Pt ) 29.0 Hz, 18 H, SiMe3), 0.79 (dd, J H-H
)
2
i
3
6.8 Hz, J P-H ) 11.8 Hz, 6 H, Pr), 0.92 (dd, J H-H ) 6.9 Hz,
2J H-P ) 13.5 Hz, 6 H, Pr), 1.10 (m, 4 H, -CH-), 1.13 (dd,
i
3J H-H ) 7.3 Hz, J H-P ) 16.2 Hz, 6 H, Pr), 1.18 (dd, J H-H
)
2
i
3
2
i
1
7.3 Hz, J H-P ) 17.7 Hz, 6 H, Pr), 1.81-1.99 (2×m, 2×4 H,
solution was immediately recorded. H NMR (C6D6): δ (ppm)
-CH2-), 2.53, 2.60 (2×s, br, 2×6 H, N-CH3), 7.07 (t, 3J H-H
)
3
2
0.50 (s, 9 H, SiMe3), 0.87 (dd, J H-H ) 6.9 Hz, J H-P ) 13.0
i
3
2
7.5 Hz, 2 H, p-C6H5), 7.23 (pseudo-t, 4 H, m-C6H5), 8.16 (d,
Hz, 6 H, Pr), 1.08 (dd, J H-H ) 7.1 Hz, J H-P ) 16.4 Hz, 6 H,
3J H-H ) 8.0 Hz, 4 H, o-C6H5). 31P{1H} NMR (C6D6): δ (ppm)
iPr), 1.15 (m, 2 H, -CH-), 1.91 (m, 4 H, -CH2-), 2.21 (s, br,
1
3
53.5 (s, with platinum satellites, J Pt-P ) 2631 Hz). MS
16 H, COD-CH2-), 2.82 (s, with Pt satellites, J H-Pt ) 19.4
(positive electrospray): m/z (%) 1312.2 (15) (M+). Anal. Calcd
for C42H76N2P2Pt3Si2 (1312.2 g/mol): C, 38.43; H, 5.84; N, 2.13.
Found: C, 38.27; H, 5.74; N, 1.97.
3
Hz, 6 H, N-CH3), 5.58 (s, br, 8 H, COD-CH-), 7.11 (t, J H-H
) 7.3 Hz, 1 H, p-C6H5), 7.27 (pseudo-t, 2 H, m-C6H5), 7.91 (d,
3J H-H ) 7.3 Hz, 2 H, o-C6H5). 31P{1H} NMR (C6D6): δ (ppm)
1
66.4 (s, with platinum satellites, J Pt-P ) 3952 Hz).
P h otoch em ica l Si-C Bon d Activa tion in (P N)P t(η2-
Me3SiCtCP h ) (1). Pt(COD)2 (29.7 mg, 0.072 mmol) was
dissolved in a solution of 1-phenyl-2-trimethylsilylacetylene
(12.6 mg, 0.072 mmol) in THF-d8 (0.5 ml) at T ) -30 °C. A
dark yellow solution was formed, and (iPr)2PCH2CH2NMe2
(13.7 mg, 15.3 µL, 0.072 mmol) was added. The formation of 1
was confirmed by 1H and 31P{1H} NMR spectroscopy (vide
supra). The NMR tube was cooled to T ) -30 °C and irradiated
with UV-light. The reaction was monitored by NMR spectros-
copy.
P r ep a r a tion of (d cp e)P t(η2-Me3SiCtCP h ) (3). 1-Phenyl-
2-trimethylsilylacetylene (18.2 mg, 0.1 mmol) was dissolved
in 0.3 mL of C6D6 and added to Pt(COD)2 (43.0 mg, 0.1 mmol).
A yellow solution was formed. Subsequently a solution of bis-
(dicyclohexylphosphino)ethane (44.1 mg, 0.1 mmol) in 0.3 mL
of C6D6 was added, and the formation of 3 was confirmed by
1H and 31P{1H} NMR spectroscopy. The solvent and all
volatiles were evaporated in vacuo, and the remaining yellow
solid was dissolved in pentane/CH2Cl2. Yellow crystals were
formed after recrystallization at T ) -30 °C. The mother liquor
was decanted, and the product was dried in vacuo. 3 was
obtained as an air- and moisture-sensitive, yellow solid.
P r ep a r a tion of (P N)P t(SiMe3)(CtCP h ) (2). 1-Phenyl-2-
trimethylsilylacetylene (11.1 mg, 0.064 mg) was dissolved in
C6D6 (0.5 mL) and added to Pt(COD)2 (26.2 mg, 0.064 mmol).
Subsequently (iPr)2PCH2CH2NMe2 (12.1 mg, 13.5 µL, 0.064
mmol) was added, and the orange solution was heated to T )
70 °C. The reaction was monitored by 1H and 31P{1H} NMR
spectroscopy, and 2 was obtained in 97% spectroscopic yield
within 24 h. 2 was obtained as a white solid after recrystal-
lization from C6D6/pentane. Yield: 22.2 mg (0.040 mmol, 62%).
3
2
1H NMR (C6D6): δ (ppm) 0.74 (dd, J H-H ) 6.9 Hz, J H-P
)
)
)
i
3
12.8 Hz, 6 H, Pr), 0.86 (s, with platinum satellites, J Pt-H
3
15.2 Hz, 9 H, SiMe3), 0.99 (m, 2 H, -CH-), 1.05 (dd, J H-H
7.3 Hz, 2J P-H ) 17.1 Hz, 6 H, iPr), 1.79 (m, 4 H, -CH2-), 2.40
3
(s, br, with platinum satellites, 6 H, N-CH3), 7.01 (t, J H-H
)
7.4 Hz, 1 H, p-C6H5), 7.13 (pseudo-t, 2 H, m-C6H5), 7.75 (d,
3J H-H ) 7.0 Hz, 2 H, o-C6H5). 31P{1H} NMR (C6D6): δ (ppm)
59.3 (s, with platinum satellites, J Pt-P ) 2760 Hz). 29Si NMR
1
2
(C6D6): δ (ppm) 0.03 (d, J Si-P(cis) ) 8.0 Hz). Anal. Calcd for
21H38NPPtSi (558.72 g/mol): C, 45.14; H, 6.86; N, 2.51.
C
Found: C, 44.97; H, 6.83; N, 2.39.
P r ep a r a tion of (NP )2P t(η2-Me3SiCtCP h ) (I). Pt(COD)2
(26.2 mg, 0.064 mmol) was dissolved in a solution of 1-phenyl-
2-trimethylsilylacetylene (11.1 mg, 0.064 mmol) in C6D6 (0.5
mL). Subsequently (iPr)2PCH2CH2NMe2 (24.1 mg, 27.0 µL,
0.127 mmol) was added, and the generation of I was confirmed
by 1H and 31P{1H} NMR spectroscopy. The solvent and all
volatiles were evaporated in vacuo, and the residue was
dissolved in petroleum ether (0.2 mL) and cooled to T ) -30
°C. I was obtained as a colorless, air- and moisture-sensitive
1
Yield: 50.0 mg (0.063 mmol, 61%). H NMR (C6D6): δ (ppm)
0.56 (s, 9 H, SiMe3), 0.91, 1.18, 1.33, 1.42, 1.56, 1.80, 1.96, 2.11,
3
2.23 (9×m, 48 H, Cy-H, -CH2-CH2-), 7.11 (t, J H-H ) 7.3
Hz, 1 H, p-C6H5), 7.35 (pseudo-t, 2 H, m-C6H5), 7.93 (d, 2 H,
3J H-H ) 7.6 Hz, o-C6H5). 31P{1H} NMR (C6D6): δ (ppm) 67.7
1
2
(d, with platinum satellites, J Pt-P ) 3274 Hz, J P-P ) 53.9
1
2
Hz), 69.1 (d, with platinum satellites, J Pt-P ) 3116 Hz, J P-P
) 53.9 Hz). Anal. Calcd for C37H62P2PtSi (792.08 g/mol): C,
56.11; H, 7.89. Found: C, 56.55; H, 8.12.
1
solid. Yield: 28.2 mg (0.038 mmol, 59%). H NMR (C6D6): δ
3
2
P r ep a r a tion of (d cp e)P t(SiMe3)(CtCP h ) (4). 3 (21.0 mg,
0.027 mmol) was dissolved in C6D6 (0.5 mL) and transferred
to a resealable NMR tube. The yellow solution was irradiated
with UV-light, and the reaction was monitored by 1H and 31P-
{1H} NMR spectroscopy. Pale yellow crystals of 4 were formed
during photolysis, and the product was quantitatively formed
within 6 h. Recrystallization from C6D6/pentane afforded 15.0
(ppm) 0.37 (s, 9 H, SiMe3), 0.97 (dd, J H-H ) 7.0 Hz, J H-P
)
i
3
2
13.0 Hz, 6 H, Pr), 1.07 (dd, J H-H ) 7.1 Hz, J H-P ) 15.4 Hz,
6 H, Pr), 1.15 (dd, J H-H ) 7.0 Hz, J H-P ) 12.8 Hz, 6 H, Pr),
i
3
2
i
(20) (a) Green, M.; Howard, J . A. K.; Spencer, J . L.; Stone, F. G. A.
J . Chem. Soc., Dalton Trans. 1977, 271. (b) Osborn, J . A.; Wilkinson,
G.; Mrowca, J . J . Inorg. Synth. 1990, 28, 77.

1196 Organometallics, Vol. 21, No. 6, 2002
Mu¨ller et al.
1
mg (0.019, 70%) of 4. H NMR (C6D6): δ (ppm) 0.98 (d, with
of the reaction, a yellow precipitate was formed. The suspen-
sion was concentrated to ∼0.1 mL and filtered. The yellow solid
was washed twice with petroleum ether (0.3 mL) and dried in
3
4
platinum satellites, J H-Pt ) 33.6 Hz, J H-P(trans) ) 2.6 Hz, 9
H, SiMe3), 1.03-1.30, 1.39-1.75, 2.06, 2.30 (4×m, 48 H, Cy-
H, -CH2-), 6.99 (t, 3J H-H ) 7.4 Hz, 1 H, p-C6H5), 7.18 (pseudo-
1
vacuo. Yield: 20.5 mg (0.021 mmol, 58%). H NMR (THF-d8):
t, 2 H, m-C6H5), 7.76 (d, J H-H ) 2 H, o-C6H5). 31P{1H} NMR
δ (ppm) 0.26 (s, with platinum satellites, 18 H, SiMe3, 3J Pt-SiCH
3
(C6D6): δ (ppm) 67.2 (d, with platinum satellites, 1J Pt-P ) 2593
) 13.8 Hz), 1.20 (dd, J H-P ) 7.1 Hz, J H-H ) 3.4 Hz, 12 H,
3 3 i
3
3
Hz, 2J P-P ) 5.2 Hz), 71.3 (d, with platinum satellites, 1J Pt-P
)
iPr), 1.21 (dd, J H-P ) 33.0 Hz, J H-H ) 6.9, 12 H, Pr), 1.87
(m, 4 H, P-CH2-), 2.16 (m, 4 H, -CH-), 2.50 (m, 4 H,
N-CH2-), 2.65 (s, br, 12 H, N-CH3). 31P NMR (C6D6): δ (ppm)
1113 Hz, J P-Si ) 166 Hz, J P-P ) 5.2 Hz). 29Si NMR (C6D6):
2
2
2
2
δ (ppm) 0.03 (dd, J Si-P(trans) ) 161.0 Hz, J Si-P(cis) ) 10.0 Hz).
Anal. Calcd for C37H62P2PtSi (792.08 g/mol): C, 56.11; H, 7.89.
Found: C, 56.20; H, 8.01.
58.6 (s, with platinum satellites, J Pt-P ) 2734 Hz). 29Si NMR
1
2
(THF-d8): δ (ppm) -16.6 (d, J Si-P(cis) ) 8.0 Hz). Anal. Calcd
P r ep a r a tion of [(COD)P t]2(SiMe3)2C4 (5). Compound 5
was synthesized according to the preparation of (COD)Pt(η2-
diphenylacetylene).13a 1,4-Bis(trimethylsilyl)-1,3-butadiyne (50.0
mg, 0.26 mmol) was dissolved in petroleum ether (2.5 mL) and
added dropwise to a suspension of Pt(COD)2 (212.0 mg, 0.52
mmol) in petroleum ether (3 mL) at T ) -40 °C. The color
changed to dark brown, and the reaction mixture was allowed
to warm to T ) -5 °C within 45 min. The suspension was
concentrated to ∼3 mL, and the brown solution was decanted.
The remaining dark orange solid was dried in vacuo at T )
-5 °C and stored at T ) -30. 5 was used without further
purification. Yield: 64 mg (0.08 mmol, 31%).
P r ep a r a tion of (P N)P t(SiMe3)-CtC-CtC-P t(SiMe3)-
(P N) (6). A solution of (iPr)2PCH2CH2NMe2 (13.8 mg, 15.4 µL,
0.073 mmol) in C6D6 (0.5 mL) was added to 5 (29.2 mg, 0.037
mmol). The brown solution was transferred to a resealable
NMR tube and heated to T ) 70 °C for 16 h. During the course
for C30H66N2P2Pt2Si2 (963.23/mol): C, 37.40; H, 6.91; N, 2.91.
Found: C, 37.00; H, 6.98; N, 2.65.
Ack n ow led gm en t is made to the U.S. Department
of Energy, grant FG02-86ER13569, for their support of
this work. C.M. thanks the Deutsche Forschungsge-
meinschaft (DFG) for a postdoctoral fellowship. We
further thank Dr. Carl N. Iverson for crystallographical
help.
Su p p or tin g In for m a tion Ava ila ble: Details of data
collection parameters, bond lengths, bond angles, fractional
atomic coordinates, and anisotropic thermal parameters for
2, I, 4, and 6. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM010984G