Synthesis and reactivity of platinum group metal complexes featuring the new pincer-like bis(phosphino)silyl ligand [K3-(2-Ph 2PC6H4)2SiMe]- ([PSiP]): Application in the ruthenium-mediated

Article abstract of DOI:10.1021/om7009528

The synthesis of coordinatively unsaturated Ru, Rh, Pd, and Pt complexes supported by the new pincer-like bis(phosphino)silyl ligand [k ³-(2-Ph₂PC₆H₄)₂SiMe] ^- ([PSiP]) is described. In the

Full text of DOI:10.1021/om7009528

6522
Organometallics 2007, 26, 6522–6525
Synthesis and Reactivity of Platinum Group Metal Complexes
Featuring the New Pincer-like Bis(phosphino)silyl Ligand
[K3-(2-Ph2PC6H4)2SiMe]- ([PSiP]): Application in the
Ruthenium-Mediated Transfer Hydrogenation of Ketones
Morgan C. MacInnis,†,‡ Darren F. MacLean,†,‡ Rylan J. Lundgren,†,‡ Robert McDonald,§
and Laura Turculet*,‡
Department of Chemistry, Dalhousie UniVersity, Halifax, NoVa Scotia, Canada B3H 4J3, and
X-Ray Crystallography Laboratory, Department of Chemistry, UniVersity of Alberta,
Edmonton, Alberta, Canada T6G 2G2
ReceiVed September 25, 2007
anticipation that such novel ligand architectures will impart
unique physical and reactivity properties to the ensuing complexes.
Summary: The synthesis of coordinatiVely unsaturated Ru, Rh,
Pd, and Pt complexes supported by the new pincer-like
bis(phosphino)silyl ligand [κ3-(2-Ph2PC6H4)2SiMe]- ([PSiP])
is described. In the first application of silyl pincer-type
complexes in transfer hydrogenation catalysis, [PSiP]Ru species
were shown to be effectiVe in mediating the reduction of ketones
In this contribution, we report the synthesis and preliminary
coordination chemistry studies of the new pincer-like bis(phos-
phino)silyl ligand [κ3-(2-Ph2PC6H4)2SiMe]- ([PSiP]). Although
metal-silicon chemistry is well-precedented across the transition
series,3 relatively little attention has been given to the incorpora-
tion of silyl donor fragments into the framework of a preformed
tridentate ancillary ligand.4 A notable exception is the work of
Stobart and co-workers,5 who have reported late transition metal
complexes featuring bi-, tri-, and tetradentate phosphinosilyl
ligands. In addition, Tilley and co-workers have recently
reported Rh and Ir complexes featuring a rigid, tridentate NSiN
ligand framework.6 While it has been proposed that the
incorporation of strongly electron donating and trans-labilizing
silyl groups into such multidentate ligand architectures may
promote the formation of coordinatively unsaturated complexes
that exhibit enhanced reactivity properties, the catalytic utility
of metal complexes supported by such ancillary ligands has not
been widely demonstrated.6c,7 Herein we report the synthesis
and characterization of coordinatively unsaturated Ru, Rh, Pd,
and Pt complexes featuring [PSiP], as well as a preliminary
investigation of the catalytic utility of [PSiP]Ru species in the
transfer hydrogenation of ketones. In contrast to the phosphi-
nosilyl complexes previously reported by Stobart and co-workers
that feature an aliphatic or benzylic ligand backbone, we
anticipated that the reduced conformational flexibility and lack
of ꢀ-hydrogens associated with the rigid o-phenylene backbone
i
employing basic PrOH as the hydrogen source.
Cyclometalated phosphine-based “PCP” pincer complexes of
the platinum group metals have been the subject of intense
research in recent years, owing to the remarkable stoichiometric
and catalytic reactivity exhibited by such complexes.1 With the
goal of discovering new metal-mediated reactivity patterns and
extending the versatility of metal pincer chemistry, significant
effort has been devoted to the synthesis of structurally and/or
electronically related systems where strategic alterations have
been introduced to the pincer ligand architecture, including
variation of the central and peripheral donor fragments, as well
as the ancillary ligand backbone.1b,c,2 In this context, we are
interested in the synthesis and study of pincer-like metal
complexes supported by new tridentate ancillary ligands featur-
ing formally anionic heavier main group element donors, in
* To whom correspondence should be addressed. Tel: 1-902-494-6414.
Fax: 1-902-494-1310. E-mail: laura.turculet@dal.ca.
† These authors contributed equally to this work.
‡ Dalhousie University.
§ University of Alberta.
(1) (a) For selected recent examples and reviews see: Jensen, C. M.
Chem. Commun. 1999, 2443. (b) Albrecht, M.; van Koten, G. Angew. Chem.,
Int. Ed. 2001, 40, 3750. (c) van der Boom, M. E.; Milstein, D. Chem. ReV.
2003, 103, 1759. (d) Singleton, J. T. Tetrahedron 2003, 59, 1837. (e) Zhao,
J.; Goldman, A. S.; Hartwig, J. F. Science 2005, 307, 1080. (f) Goldman,
A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.; Brookhart, M.
Science 2006, 312, 257.
(3) (a) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S.,
Rappoport, Z. Eds.; Wiley: New York, 1991. (b) Corey, J. Y.; Braddock-
Wilking, J. Chem. ReV. 1999, 99, 175.
(4) (a) Balakrishna, M. S.; Chandrasekaran, P.; George, P. P. Coord.
Chem. ReV. 2003, 241, 87. (b) While the manuscript was in preparation,
Fe complexes supported by a structurally related tetradentate tris(phosphi-
no)silyl ligand were reported. Mankad, N. P.; Whited, M. T.; Peters, J. C.
Angew. Chem., Int. Ed. 2007, 46, 5768.
(2) For selected examples and reviews highlighting structural versatility
see: (a) Fryzuk, M. D. Can. J. Chem. 1992, 70, 2839. (b) Liang, L.-C.
Coord. Chem. ReV. 2006, 250, 1152. (c) Pugh, D.; Danopoulos, A. A. Coord.
Chem. ReV. 2006, 251, 610. (d) Gerisch, M.; Krumper, J. R.; Bergman,
R. G.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123, 5818. (e) Lin, G.; Jones,
N. D.; Gossage, R. A.; McDonald, R.; Cavell, R. G. Angew. Chem., Int.
Ed. 2003, 42, 4054. (f) Ozerov, O. V.; Guo, C.; Papkov, V. A.; Foxman,
B. M. J. Am. Chem. Soc. 2004, 126, 4792. (g) Yao, Q.; Sheets, M. J. Org.
Chem. 2006, 71, 5384. (h) Frech, C. M.; Ben-David, Y.; Weiner, L.;
Milstein, D. J. Am. Chem. Soc. 2006, 128, 7128. (i) Fischer, J.; Schürmann,
M.; Mehring, M.; Zachwieja, U.; Jurkschat, K. Organometallics 2006, 25,
2886. (j) Kuklin, S. A.; Sheloumov, A. M.; Dolgushin, F. M.; Ezernitskaya,
M. G.; Peregudov, A. S.; Petrovskii, P. V.; Koridze, A. A. Organometallics
2006, 25, 5466. (k) Weng, W.; Parkin, S.; Ozerov, O. Organometallics
2006, 25, 5345. (l) Ma, L.; Imbesi, P. M.; Updegraff, J. B. III; Hunter,
A. D.; Protasiewicz, J. D Inorg. Chem. 2007, 46, 5220. (m) Aydin, J.; Senthil
Kumar, K.; Sayah, M. J.; Wallner, O. A.; Szabó, K. J. J. Org. Chem. 2007,
72, 4689. (n) Guananathan, C.; Ben-David, Y.; Milstein, D. Science 2007,
317, 790.
(5) (a) Auburn, M. J.; Stobart, S. R. Inorg. Chem. 1985, 24, 318. (b)
Joslin, F. L.; Stobart, S. R. J. Chem. Soc., Chem. Commun. 1989, 504. (c)
Auburn, M. J.; Holmes-Smith, R. D.; Stobart, S. R.; Bakshi, P. K.; Cameron,
T. S. Organometallics 1996, 15, 3032. (d) Gossage, R. A.; McLennan, G. D.;
Stobart, S. R. Inorg. Chem. 1996, 35, 1729. (e) Brost, R. D.; Bruce, G. C.;
Joslin, F. L.; Stobart, S. R. Organometallics 1997, 16, 5669. (f) Zhou, X.;
Stobart, S. R. Organometallics 2001, 20, 1898.
(6) (a) Stradiotto, M.; Fujdala, K. L.; Tilley, T. D. Chem. Commun.
2001, 1200. (b) Sangtrirutnugul, P.; Stradiotto, M.; Tilley, T. D. Organo-
metallics 2006, 25, 1607. (c) Sangtrirutnugul, P.; Tilley, T. D. Organome-
tallics 2007, 26, 5557.
(7) A report on the use of phosphinoalkylsilyl metal complexes as
catalysts for hydroformylation of olefins appears in the patent literature:
Stobart, S. R.; Grundy, S. L.; Joslin, F. L. U.S. Patent 4,950,798, 1990;
Canadian Patent 1,327,365, 1994.
10.1021/om7009528 CCC: $37.00
2007 American Chemical Society
Publication on Web 11/22/2007

Communications
Organometallics, Vol. 26, No. 26, 2007 6523
Scheme 1. Synthesis of [PSiP]Ru Chloride (2) and Hydride
(3a) Complexesa
a
Reagents: (i) RuCl2(PPh3)3, Et3N; (ii) LiEt3BH.
of [PSiP] could provide enhanced stability and selectivity in
metal-mediated substrate transformations.
Figure 1. Crystallographically determined structure of 2 · (OEt2)1.5
,
The parent tertiary silane, [PSiP]H (1), was obtained by
lithiation of 2-Ph2PC6H4Br with nBuLi, followed by in situ
treatment with 0.5 equiv of MeSiHCl2.8 Isolated 1 was obtained
as a peach-colored solid in 90% yield. The 1H NMR spectrum
of 1 (benzene-d6) features a multiplet at 6.03 ppm corresponding
to the Si-H, as well as a doublet at 0.81 ppm (3JHH ) 3 Hz)
corresponding to the silyl methyl substituent. The 31P NMR
resonance of 1 is found at -10.9 ppm, while the 29Si NMR
resonance occurs at -23.2 ppm (benzene-d6).
shown with 50% displacement ellipsoids. All H atoms as well as
the diethyl ether solvate have been omitted for clarity. Selected
interatomic distances (Å) and angles (deg) for 2 · (OEt2)1.5: Ru-Cl
2.4492(6); Ru-P1 2.3040(6); Ru-P2 2.2093(6); Ru-P3 2.3891(6);
Ru-Si 2.3361(6); Cl-Ru-P1 89.26(2); Cl-Ru-P2 119.66(2);
Cl-Ru-P3 87.42(2); Cl-Ru-Si 160.41(2); P1-Ru-P3 156.79(2);
P1-Ru-Si 81.53(2); P2-Ru-Si 79.23(2); P3-Ru-Si 94.24(2).
31P{1H} NMR spectrum of 2 (300 K, 202.5 MHz) features three
resonances in a 1:1:1 ratio, consisting of a broad singlet at 96.8
ppm, a broad doublet at 67.1 ppm (J ) 289 Hz), and a doublet
at 29.1 ppm (J ) 258 Hz). Upon cooling of the solution to 223
Treatment of 1 with RuCl2(PPh3)3 in the presence of Et3N
resulted in quantitative (by 31P NMR) formation of the cyclo-
metalated 16-electron Ru complex 2, which was isolated in 89%
yield (Scheme 1). The X-ray crystal structure of 2 · (OEt2)1.5
(Figure 1) confirms the formation of a five-coordinate fac-[PSiP]
complex with distorted square-pyramidal geometry at Ru,8 in
which a phosphine arm of the [PSiP] ligand occupies the apical
coordination site, while the remaining phosphine arm and the
silyl group occupy basal sites. The Si donor in 2 is positioned
trans to Cl, with a Ru-Si distance of 2.3361(6) Å. These
structural features differ somewhat from those of the related
complex (biPSi)RuCl(CO) (biPSi ) κ3-MeSi(CH2CH2CH2-
PPh2)2),9 which features the biPSi ligand in a mer-type
configuration with Si positioned trans to the vacant coordination
site (Ru-Si, 2.339(5) Å). While the acute P2-Ru-Si angle of
79.23(2)° in 2 may arise due to the geometric constraints of
the rigid [PSiP] ligand (P1-Ru-Si, 81.53(2)°), it is also feasible
that the structure of 2 might be influenced by previously
described electronic effects involving the distortion of five-
coordinate d6 complexes.10 Such distortion results in a “Y-
shaped” molecular geometry in which a ligand with poor
σ-donor but good π-donor properties (such as Cl-) is positioned
opposite the acute angle of the “Y”. However, in the case of 2
the chloride ligand is positioned significantly closer to P2 than
to Si (Cl-Ru-P2, 119.66(2)°; Cl-Ru-Si, 160.41(2)°), such
that the complex is better represented as square pyramidal, with
the arrangement of Si, Cl, and P2 described by a distorted
T-shape.10c
K, the 31P NMR resonances (101.3 MHz) sharpen significantly,
2
revealing further PP coupling (98.5 ppm, apparent t, JPPcis
)
25 Hz; 69.9 ppm, dd, JPPcis ) 27 Hz, 2JPPtrans ) 281 Hz; 32.4
2
2
2
ppm, dd, JPPcis ) 24 Hz, JPPtrans ) 282 Hz). No further
decoalescence phenomena are observed at temperatures below
223 K. The resonances observed at low temperature in the 31P
NMR spectrum of 2 are consistent with the structure observed
in the solid state, where the three phosphine donors are arranged
in a T-type configuration. These temperature-dependent NMR
line shape changes may arise due to intramolecular rearrange-
ment processes (e.g., pseudorotation) and/or Ru-P dissociation.
Complex 2 reacted with LiEt3BH to form a mixture of three
Ru hydride species (3a-c) that each exhibit Cs symmetry in
solution (31P NMR). In benzene-d6 solution, the major hydride
1
product (3a) features a Ru-H H NMR resonance at -13.66
2
2
ppm (td, JHP ) 10 Hz, JHP ) 27 Hz) and two 31P NMR
resonances in a 2:1 ratio at 64.6 (d, 2JPP ) 19 Hz) and 34.8 (t,
2JPP ) 19 Hz) ppm, corresponding to the [PSiP] and PPh3
ligands, respectively.11 The ratio of 3a:b:c observed in situ was
approximately 2:1:1, and heating of the mixture (20 h, 70 °C,
benzene-d6) did not change the observed ratio of these three
Ru-H species. In a preparative scale reaction of 2 with
LiEt3BH, 3a was readily isolated in 64% yield by washing of
the crude product (which also contained 3b and 3c) with diethyl
ether.12 On the basis of spectroscopic and microanalytical data,
complex 3a is assigned as a dinitrogen adduct of the type
[PSiP]RuH(N2)(PPh3) (Scheme 1). Facile formation of dinitro-
In methylene chloride-d2 solution, both the 1H and 31P NMR
spectra of 2 exhibit significant line broadening at 300 K. The
(8) Full experimental details, including spectroscopic characterization
data for the new compounds reported herein and crystallographic details
for 2 · (OEt2)1.5 are provided in the Supporting Information. Selected crystal
j
data for 2 · (OEt2)1.5: triclinic (P1); a ) 11.2541(9) Å; b ) 3.4722(11) Å;
c ) 17.6235(14) Å; R ) 85.0100(11)°; ꢀ ) 85.5172(11)°; γ ) 85.8870(11)°;
V ) 2648.1(4) Å3; Z ) 2; GOF ) 1.050; R1 ) 0.0369; wR2 ) 0.0975.
(9) Bushnell, G. W.; Casado, M. A.; Stobart, S. R. Organometallics
2001, 20, 601.
(11) Complex 3b (300 K, benzene-d6): Ru-H 1H NMR resonance at
-7.18 ppm (br s) and two 31P NMR resonances at 71.0 ppm (d, 2 P, [PSiP],
2JPP ) 14 Hz) and 47.7 ppm (t, 1 P, PPh3, 2JPP ) 14 Hz). Complex 3c (300
K, benzene-d6): Ru-H 1H NMR resonance at -11.04 ppm (br d, J ≈ 140
Hz), and two 31P NMR resonances at 71.3 ppm (br, 2 P, [PSiP]) and 54.7
(10) (a) Thorn, D. L.; Hoffmann, R. New J. Chem. 1979, 3, 39. (b)
Riehl, J.-F.; Jean, Y.; Eisenstein, O.; Pelissier, M. Organometallics 1992,
11, 729. (c) Chin, B.; Lough, A. J.; Morris, R. H.; Schweitzer, C. T.;
D’Agostino, C. Inorg. Chem. 1994, 33, 6278. (d) Johnson, T. J.; Folting,
K.; Streib, W. E.; Martin, J. D.; Huffman, J. C.; Jackson, S. A.; Eisenstein,
O.; Caulton, K. G. Inorg. Chem. 1995, 34, 488. (e) Lam, W. H.; Shimada,
S.; Batsanov, A. S.; Lin, Z.; Marder, T. B.; Cowan, J. A.; Howard, J. K.;
Mason, S. A.; McIntyre, G. J. Organometallics 2003, 22, 4557.
2
ppm (t, 1 P, PPh3, JPP ) 16 Hz).
(12) We attribute the 64% isolated yield of 3a to the conversion of 3b
and/or 3c to 3a upon workup. Efforts to definitively identify 3b and 3c are
ongoing.

6524 Organometallics, Vol. 26, No. 26, 2007
Communications
Scheme 2. Synthesis of [PSiP]Rh Complexesa
Scheme 3. Synthesis of [PSiP]PtCl (7) and [PSiP]PdCl (8)a
a
Reagents: (i) PtCl2(SEt2)2; (ii) 0.5 [PdCl(C3H5)]2.
Table 1. Transfer Hydrogenation of Ketonesa
a
Reagents: (i) (COD)Rh(CH2Ph) (COD ) 1,5-cyclooctadiene); (ii)
PPh3; (iii) RhCl(PPh3)3, PhCH2K.
entry
catalyst
substrate
time (h)
conv (%)b
1
2
3
4
5
6
2
2
2
2
2
3a
acetophenone
benzophenone
2-heptanone
cyclopentanone
cyclohexanone
cyclohexanone
6
6
4.5
3
3
96
92
99
>99
>99
94
gen adducts has been reported in related [PCP]Ru and [PNP]Ru
pincer chemistry.13
In an effort to explore further the coordination chemistry of
[PSiP], we also pursued the synthesis of group 9 and 10
complexes featuring this new tridentate ligand. The treatment
of 1 with (COD)Rh(CH2Ph)14 in THF solution at room
temperature led to the formation of [PSiP]Rh(COD) (4), which
was isolated in 49% yield (Scheme 2). The 31P{1H} NMR
spectrum of 4 (benzene-d6) features a doublet at 58.5 ppm (1JPRh
) 140 Hz), consistent with a Cs-symmetric complex in solution.
3
a Reactions were performed on a 1 mL scale (0.1 M ketone, 0.2 mol
% Ru, 2 mol % KOtBu) in PrOH at 82 °C under N2. b Determined by
i
GC-FID.
of Si for C in a rigid tridentate ancillary ligand framework
influences metal-mediated reactivity, given the strong electron-
donating and trans-labilizing abilities of Si. Previous work has
established that Ru(II) PCP-, NCN-, CNC-, and CNN-pincer
complexes are effective catalysts for the transfer hydrogenation
of ketones, and it has been proposed that the Ru-C σ-bond
plays an important role in the formation of long-lived, catalyti-
cally active species.13b,16 In this context, we became interested
in surveying the catalytic activity of [PSiP]RuCl(PPh3) (2) and
[PSiP]RuH(N2)(PPh3) (3a) in the transfer hydrogenation of
The reaction of 1 with RhCl(PPh3)3 led to quantitative (by 31
P
NMR) formation of what we tentatively assign as a 1:1 mixture
of two isomeric [PSiP]RhHCl(PPh3) species (5a,b) that each
exhibit Cs symmetry in solution.15 Although Et3N proved
incapable of dehydrohalogenating 5a,b, treatment of in situ
generated 5a,b with 1 equiv of PhCH2K led to clean formation
of [PSiP]RhPPh3 (6), which was isolated in 49% yield (Scheme
2). The 31P NMR spectrum of 6 (benzene-d6) features two
1
2
resonances at 58.6 ppm (dd, 2 P, [PSiP], JPRh ) 173 Hz, JPP
i
ketones, employing basic PrOH as the hydrogen source; the
) 22 Hz) and 24.9 ppm (dt, 1 P, PPh3, 1JPRh ) 130 Hz, 2JPP
)
results obtained in our preliminary survey are summarized in
Table 1. Although the conditions have not yet been optimized,
the activity of 2 as a precatalyst in this reaction is comparable
to that of related Ru pincer catalysts that lack an NH
functionality.13b,16 When employing 0.2 mol % of 2 with 2 mol
% of KOtBu at 82 °C, high conversion to the corresponding
secondary alcohols was observed for several ketone substrates,
including diaryl, dialkyl, and alkyl/aryl ketones. As is the case
for most metal-catalyzed transfer hydrogenation processes
22 Hz), consistent with Cs symmetry in solution. Complex 6
was also formed cleanly (by 31P NMR) in the reaction of 4
with PPh3 (Scheme 2).
Group 10 [PSiP] complexes were readily synthesized by
treatment of 1 with an appropriate Pt or Pd starting material
(Scheme 3). Thus, the reaction of 1 with 1 equiv of PtCl2(SEt2)2
in benzene solution resulted in the precipitation of [PSiP]PtCl
(7) as a colorless microcrystalline solid (95% isolated yield).
Similarly, treatment of 1 with 0.5 equiv of [PdCl(C3H5)]2 in
benzene solution led to precipitation of [PSiP]PdCl as a colorless
microcrystalline solid (96% isolated yield). Each complex
exhibits a single 31P NMR resonance (chloroform-d, for 7, 51.7
i
conducted in PrOH, less than 5% conversion was observed in
the absence of KOtBu as base. The preformed Ru hydride
complex 3a was similarly inactive for transfer hydrogenation
of cyclohexanone in the absence of added KOtBu, although 94%
conversion was obtained when using 2 mol % KOtBu along
with 0.2 mol % 3a (entry 6, Table 1). These preliminary results
establish [PSiP]Ru complexes as a promising class of precata-
lysts for transfer hydrogenation. Further mechanistic studies of
this reaction, as well as catalytic studies featuring these and
other [PSiP] derivatives, are currently in progress.
1
ppm (with Pt satellites, JPPt ) 3074 Hz); for 8, 46.9 ppm),
consistent with Cs symmetry in solution.
Building on our synthetic investigations of [PSiP]-ligated
metal complexes, we have begun to examine the utility of such
species as catalysts in a range of substrate transformations. In
particular, we are interested in exploring how the substitution
In summary, the facile synthesis of platinum group metal
complexes supported by the versatile new pincer-like bis(pho-
sphino)silyl ligand [κ3-(2-Ph2PC6H4)2SiMe]- ([PSiP]) has been
described. In one of the first applications of silyl pincer-type
complexes in catalysis to be documented in the academic
literature, both chloro- and hydrido-[PSiP]Ru species were
(13) (a) Gusev, D. G.; Dolgushin, F. M.; Antipin, M. Y. Organometallics
2000, 19, 3429. (b) Amoroso, D.; Jabri, A.; Yap, G. P. A.; Gusev, D. G.;
dos Santos, E. N.; Fogg, D. E. Organometallics 2004, 23, 4047. (c) Zhang,
J.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.; Milstein, D.
Organometallics 2004, 23, 4026.
(14) Generated in situ from 0.5 [Rh(COD)Cl]2 and PhCH2K in THF
(COD ) 1,5-cyclooctadiene). See: Fryzuk, M. D.; McConville, D. H.; Rettig,
S. J. J. Organomet. Chem. 1993, 445, 245.
(15) Complex 5a (300 K, methylene chloride-d2): Rh-H 1H NMR
resonance at -16.66 ppm (m) and two 31P NMR resonances at 59.3 ppm
(16) (a) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten,
G. Angew. Chem., Int. Ed. 2000, 39, 743. (b) Danopoulos, A. A.; Winston,
S.; Motherwell, W. B. Chem. Commun. 2002, 1376. (c) Baratta, W.;
Chelucci, G.; Gladiali, S.; Siega, K.; Toniutti, M.; Zanette, M.; Zangrando,
E.; Rigo, P. Angew. Chem., Int. Ed. 2005, 44, 6214. (d) Weng, W.; Parkin,
S.; Ozerov, O. Organometallics 2006, 25, 5345. (e) Gagliardo, M.; Chase,
P. A.; Brouwer, S.; van Klink, G. P. M.; van Koten, G. Organometallics
2007, 26, 2219.
1
2
(dd, 2 P, [PSiP], JRhP ) 117 Hz, JPP ) 20 Hz) and 20.3 ppm (dt, 1 P,
1
2
PPh3, JRhP ) 78 Hz, JPP ) 21 Hz). Complex 5b (300 K, methylene
chloride-d2): Rh-H 1H NMR resonance at -18.14 ppm (apparent quart, J
) 19 Hz) and two 31P NMR resonances at 50.0 ppm (dd, 2 P, [PSiP], 1JRhP
) 115 Hz, 2JPP ) 19 Hz) and 11.5 ppm (dt, 1 P, PPh3, 1JRhP ) 69 Hz, 2JPP
) 20 Hz).

Communications
Organometallics, Vol. 26, No. 26, 2007 6525
shown to be effective in mediating the transfer hydrogenation
of ketones to secondary alcohols, employing basic PrOH as
the hydrogen source. These preliminary studies establish [PSiP]-
ligated platinum group metal complexes as promising candidates
for further catalytic studies.
Trust Fund, and Dalhousie University for their generous
support of this work. We also thank Dr. Michael Lumsden
(Atlantic Region Magnetic Resonance Center, Dalhousie) for
his assistance in the acquisition of NMR data.
i
Supporting Information Available: Experimental details and
characterization data, including crystallographic data for 2 · (OEt2)1.5.
(CIF). This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. We are grateful to the Natural Sciences
and Engineering Research Council (NSERC) of Canada
(including a Discovery Grant for L.T. and Postgraduate
Scholarships for D.F.M. and R.J.L.), the Canada Foundation
for Innovation, the Nova Scotia Research and Innovation
OM7009528