Pd-Pt heterobimetallic and Pd-Pd or Pt-Pt dinuclear complexes with bridging diphenylsilyl ligands

Article abstract of DOI:10.1021/om030081i

The reaction of Pt(SiHPh₂)₂(dmpe) (dmpe = 1,2-bis(dimethylphosphino)ethane) with Pd(PCy₃)₂ forms (Cy₃P)Pd(μ-η²-HSiPh₂)₂Pt (PCy₃) (1), which contains two diphenylsilyl ligands bridged to Pd and Pt centers. A comparison of the crystallographic results and the NMR spectra of 1 with those of [(Cy₃P)Pd(μ-η²-HSiPh₂)]₂ (3) and [(Cy₃P)Pt(μ-η²-HSiPh₂)]₂ (4) indicates that the structure of 1 contains two inequivalent Si-H hydrogens, Pd-H-Si and Pt-H-Si, with three-center two-electron bonds.

Full text of DOI:10.1021/om030081i

2190
Organometallics 2003, 22, 2190-2192
P d -P t Heter obim eta llic a n d P d -P d or P t-P t Din u clea r
Com p lexes w ith Br id gin g Dip h en ylsilyl Liga n d s
Makoto Tanabe, Tetsuyuki Yamada, and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, J apan
Received February 4, 2003
Summary: The reaction of Pt(SiHPh2)2(dmpe) (dmpe )
1,2-bis(dimethylphosphino)ethane) with Pd(PCy3)2 forms
(Cy3P)Pd(µ-η2-HSiPh2)2Pt(PCy3) (1), which contains two
diphenylsilyl ligands bridged to Pd and Pt centers. A
comparison of the crystallographic results and the NMR
spectra of 1 with those of [(Cy3P)Pd(µ-η2-HSiPh2)]2 (3)
and [(Cy3P)Pt(µ-η2-HSiPh2)]2 (4) indicates that the
structure of 1 contains two inequivalent Si-H hydro-
gens, Pd-H-Si and Pt-H-Si, with three-center two-
electron bonds.
reaction of H2SiR2 with the zerovalent complexes of
these metals.7,8 In this paper, we report the preparation
of a new Pd-Pt heterodinuclear complex with two
diphenylsilyl ligands and a comparison of its spectro-
scopic properties with those of analogous dipalladium
and diplatinum complexes.
An equimolar reaction of Pt(SiHPh2)2(dmpe) (dmpe
) 1,2-bis(dimethylphosphino)ethane) with Pd(PCy3)2 in
toluene at room temperature produces a mixture of the
complexes (Cy3P)Pd(µ-η2-HSiPh2)2Pt(PCy3) (1), [(dmpe)-
Pt(µ-SiPh2)]2 (2),6b and [(Cy3P)Pd(µ-η2-HSiPh2)]2 (3) (eq
1).9 The new Pd-Pt heterobimetallic complex 1 is the
major product and is isolated as pale yellow crystals in
28% yield from the recrystallization of the product
separated from the reaction mixture. The reactions of
H2SiPh2 with Pd(PCy3)2 and with PtMe2(PCy3)2 produce
an analogous dipalladium complex, [(Cy3P)Pd(µ-η2-
HSiPh2)]2 (3), and a diplatinum complex, [(Cy3P)Pt(µ-
η2-HSiPh2)]2 (4),7 respectively (eqs 2, 3). Dinuclear
complexes 1, 3, and 4 are air-stable in solid and CD2-
Cl2 or C6D6 solution.
Primary (-SiH2R) and secondary (-SiHR2) organo-
silyl ligands of di- and multinuclear transition-metal
complexes were reported to coordinate to two or more
metal centers as the bridging ligands with both M-Si
σ-bonds and M-H-Si three-center two-electron (3c-2e)
bonds.1,2 The bridging silyl ligand, which is bonded
unsymmetrically to two metal centers, often causes a
change in the structure of the complex due to flexible
M-H-Si bonding. Heterobimetallic complexes with
such bridging organosilyl ligands are of significant
interest because the coordination mode of the ligands
and their dynamic behavior are influenced by the
presence of two different metals.3 Although there are a
number of diplatinum complexes with bridging µ-silyl
ligands,4 only a few heterobimetallic complexes contain-
ing Pt are known. Braunstein et al. reported Fe-Pt
complexes in which the two metals are bridged by Si-
(OMe)3 ligands.5 Recently, we have reported the syn-
thesis of Rh-Pt heterobimetallic complexes through the
reaction of Pt(SiHPh2)2(PMe3)2 with RhCl(PMe3)3, which
involves the coordination of the Si-H group of the silyl
ligand to the Rh(I) center.6 On the other hand, dinuclear
homometallic complexes of Pd and Pt, [(R′3P)M(µ-η2-
HSiR2)]2 (M ) Pd, Pt), were prepared easily by the
(1) (a) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151. (b)
Braunstein, P.; Knorr, M. J . Organomet. Chem. 1995, 500, 21. (c)
Tobita, H.; Ogino, H. Adv. Organomet. Chem. 1998, 42, 223. (d) Corey,
J .-Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175. (e) Braunstein,
P.; Boag, N. M. Angew. Chem., Int. Ed. 2001, 40, 2427.
(2) Choi, S.-H.; Lin, Z. J . Organomet. Chem. 2000, 608, 42.
(3) (a) Malisch, W.; Weckel, H.-U.; Grob, I.; Ko¨hler, F. H. Z. Natur-
forsch. 1982, 37b, 601. (b) Powell, J .; Sawyer, J . F.; Shiralian, M.
Organometallics 1989, 8, 577. (c) Bodensieck, U.; Braunstein, P.; Deck,
W.; Faure, T.; Knorr M.; Stern, C. Angew. Chem., Int. Ed. Engl. 1994,
33, 2440. (d) Sakaba, H.; Ishida, K.; Horino, H. Chem. Lett. 1998, 149.
(4) (a) Levchinsky, Y.; Rath N. P.; Braddock-Wilking, J . Organo-
metallics 1999, 18, 2583. (b) Braddock-Wilking, J .; Levchinsky, Y.;
Rath, N. P. Organometallics 2000, 19, 5500. (c) Sanow, L. M.; Chai,
M.; McConnville, D. B.; Galat, K. J .; Simons, R. S.; Rinaldi, P. L.;
Youngs, W. J .; Tessier, C. A. Organometallics 2000, 19, 192.
(5) (a) Knorr, M.; Braunstein, P.; Tiripicchio, A.; Ugozzoli, F. Organo-
metallics 1995, 14, 4910. (b) Knorr, M.; Strohmann, C.; Braunstein,
P. Organometallics 1996, 15, 5653. (c) Knorr, M.; Hallauer, E.; Hush,
V.; Veith, M.; Braunstein, P. Organometallics 1996, 15, 3868. (d)
Braunstein, P.; Faure, T.; Knorr, M. Organometallics 1999, 18, 1791.
(6) (a) Tanabe, M.; Osakada, K. Chem. Lett. 2001, 962. (b) Tanabe,
M.; Osakada, K. Inorg. Chim. Acta, in press.
Figure 1a depicts the molecular structure of Pd-Pt
heterobimetallic complex 1 as determined by X-ray
(7) Auburn, M.; Ciriano, M.; Howard, J . A. K.; Murray, M.; Pugh,
N. J .; Spencer, J . L.; Stone, F. G. A.; Woodward, P. J . Chem. Soc.,
Dalton Trans. 1980, 659.
(8) (a) Kim, Y.-J .; Lee, S.-C.; Park, J .-I.; Osakada, K.; Choi, J .-C.;
Yamamoto, T. Organometallics 1998, 17, 4929. (b) Kim, Y.-J .; Lee, S.-
C.; Park, J .-I.; Osakada, K.; Choi, J .-C.; Yamamoto, T. J . Chem. Soc.,
Dalton Trans. 2000, 417.
10.1021/om030081i CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/02/2003

Communications
Organometallics, Vol. 22, No. 11, 2003 2191
F igu r e 2. 31P{1H} NMR spectra of (a) 1, (b) 3, and (c) 4
at 25 °C in benzene-d6. Peaks with asterisks are due to
195Pt satellite signals.
F igu r e 1. ORTEP drawings of complex (a) 1 and (b) 3 as
determined by X-ray crystallography with 50% probability
thermal ellipsoids. Hydrogens except for SiH hydrogen
were omitted for simplicity. Atoms with asterisks are
crystallographically equivalent to those having the same
number without asterisks. M ) Pd and Pt with equal
occupancy. Two SiH hydrogens of 1 were not found due to
the disorder of two metal centers. Selected bond distances
(Å) and angles (deg) for 1: M-M* 2.691(2), M-P 2.299(3),
M-Si 2.377(3), M-Si* 2.328(4), M*-M-P 160.68(8), M*-
M-Si 55.97(8), M*-M-Si* 54.27(8), P-M-Si 106.72(11),
P-M-Si* 141.87(11) Si-M-Si* 110.24(11), M-Si-M*
69.8(1). Selected bond distances (Å) and angles (°) for 3:
Pd-Pd* 2.691(1), Pd-P 2.316(2), Pd-Si 2.326(2), Pd-Si*
2.384(2), Pd-H 1.61, Si-H 1.63. Pd*-Pd-P 161.40(7),
Pd*-Pd-Si 56.19(6), Pd*-Pd-Si* 54.14(6), P-Pd-Si
107.69(8), P-Pd-Si* 140.66(8), Si-Pd-Si* 110.32(7), Pd-
Si-Pd* 69.68(7).
bridged to the metals (Pd and Pt) in the former bond,
forming an M-H-Si, 3c-2e bond. Dipalladium complex
3 also has a C2-symmetrical Pd2Si2 core with two Pd-
H-Si bonds (Figure 1b),11 which is quite similar to that
of the reported [(Me3P)Pd(µ-η2-HSiPh2)]2.8a
Figure 2a-c depicts the 31P{1H} NMR spectra for 1,
3, and 4. Two inequivalent phosphine signals for 1 are
observed as two sets of doublets (3J (PP) ) 59 Hz) at δ
55.2 and 46.7. The former doublet with the larger J (PPt)
(3588 Hz) than the latter (2J (PPt) ) 239 Hz) is assigned
to the phosphorus nucleus directly bonded to Pt. The
31P NMR signal for the PCy3 bonded to the Pt in 1 is
close to that of diplatinum complex 4 (δ 54.2), and the
chemical shift of the phosphorus bonded to Pd is similar
1
to that of dipalladium analogue 3 (δ 45.1). The H NMR
spectrum for 1 exhibits the signals for the Si-H
hydrogens at δ 2.49 and 1.70 due to the inequivalent
environmets of the two SiH hydrogens (Figure 3a). The
2H NMR spectrum of (Cy3P)Pd(µ-η2-DSiPh2)2Pt(PCy3)
(1-d 2), which is prepared from Pt(SiDPh2)2(dmpe) and
Pd(PCy3)2, shows two resonances of deuterium bonded
to Si at δ 2.51 and 1.72. The peak positions clearly
crystallography.10 The molecule has a crystallographic
center of symmetry at the midpoint of the two metal
centers, which causes a disorder of the Pd and Pt centers
at the two metal positions with equal occupancy. Thus
each M-Si bond distance is an average of the Pd-Si
and Pt-Si bonds. Different lengths between two crys-
tallographically independent M-Si bonds, 2.377(3) and
2.328(4) Å, are ascribed to the presence of hydrogen
1
indicate that the above H peaks are due to the Si-H
hydrogens rather than to the hydrogens of PCy3 ligands.
The 1H NMR peak for 1 at δ 2.49 is observed with
relatively small coupling to the 195Pt nucleus (2J (HPt)
) 73 Hz), which is assigned to the hydrogen involved
in the Pd-H-Si, 3c-2e bond and is shifted to a lower
(9) Complex 2 was characterized by NMR spectroscopy. 31P{1H}
NMR of 2 (122 MHz, C6D6, rt): δ 39.0 (J (PPt) ) 1263 Hz, 2J (PPt) )
222 Hz, 3J (PP) ) 29 Hz).
(10) X-ray data of 1: C60H88P2Si2PdPt, Mr ) 1228.96, monoclinic,
P21/c (No. 14), a ) 10.202(5) Å, b ) 13.930(8) Å, c ) 20.010(11) Å, â )
(11) X-ray data of 3: C60H88P2Si2Pd2, Mr ) 1140.28, monoclinic, P21/c
(No. 14), a ) 10.188(3) Å, b ) 14.141(2) Å, c ) 20.184(4) Å, â ) 94.46-
(2)°, V ) 2899.2(9) Å3, Z ) 2, µ(Mo KR) ) 0.753 mm-1, Dc ) 1.306 g
cm-3, F(000) ) 1196, 6934 unique reflections, 298 variables, R ) 0.050,
Rw ) 0.042, GOF ) 1.50 using 2806 I > 3σ(I).
92.746(8)°, V ) 2840.4(27) Å3, Z ) 2, µ(Mo KR) ) 2.902 mm-1, Dc
)
1.437 g cm-3, F(000) ) 1260, 6229 unique reflections, 341 variables,
R ) 0.073, Rw ) 0.097, GOF ) 1.00 using 3826 I > 2σ(I).

2192 Organometallics, Vol. 22, No. 11, 2003
Communications
magnetic field (δ 1.70) shows a large J (HPt) value (601
Hz). These J (HPt) values are similar to those of diplati-
num complex 4 with two sets of 195Pt satellites (2J (HPt)
) 88 Hz, J (HPt) ) 605 Hz) (Figure 3c). The Pt-H-Si
signals for 1 are observed as doublets, whereas those
of 3 and 4 appear as apparent triplets due to virtual
coupling. The Pd-H-Si hydrogen signal for 1 is at a
lower field than that of 3, whereas the Pt-H-Si
hydrogen signal for 1 is shifted from 4 to a higher field.
The reaction of Pd(SiHPh2)2(dmpe) with Pt(PCy3)2
forms a mixture of the diplatinum and dipalladium
complexes 2 and 3. The 31P{1H} NMR study of the
reaction mixture showed that complex 1 was formed
initially in a much smaller amount than 2 and 3 and
that the heterobimetallic complex diminished soon to
give a mixture of 2 and 3 in approximately 6:4 molar
ratio. The low yield of 1 in the reaction, which causes
exchange of the phosphine ligands between Pd and Pt,
and conversion of 1 into other products in the reaction
mixture are contrasted with the reaction in eq 1 to form
1 as the major product among the three complexes.
In summary, this study provided a new Pd-Pt het-
erobimetallic complex 1 with organosilyl ligands. The
two SiH hydrogens of 1 are unsymmetrically coordi-
nated to Pd and Pt centers via 3c-2e bonds. The complex
prefers a structure having Pt-Si, Pd-Si, Pt-H-Si, and
Pd-H-Si bonds rather than that with two Pt-Si and
Pd-H-Si bonds (or two Pd-Si and two Pt-H-Si
bonds).
Ack n ow led gm en t . This work is supported by
Grants-in-Aid for Scientific Research from the Ministry
of Education, Science, Sports, Culture, and Technology,
J apan, and from J apan Society for the Promotion of
Science (J SPS). We thank Dr. Kunihisa Sugimoto at
Rigaku Co. for help with the X-ray structure solution.
M.T. is grateful for the fellowship from J SPS.
F igu r e 3. 1H NMR spectra of (a) 1 at 40 °C, (b) 3 at 25
°C, and (c) 4 at 25 °C in benzene-d6. The signals without
assignment are due to PCy3 hydrogens. Peaks with aster-
isks are due to 195Pt satellite signals.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures for the synthesis of the complexes of 1-4 and results
of X-ray crystallography for 1 and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
field than the observed chemical shift of 3 (δ 2.07)
(Figure 3b). The bridging Pt-H-Si signal at a higher
OM030081I