Au (i) complexes supported by donor-functionalized indene ligands: Synthesis, characterization, and catalytic behavior in aldehyde hydrosilylation

Article abstract of DOI:10.1021/om060948n

New Au (i) complexes featuring ligands of the type κ¹-3- R₂-indene (κ¹-1a, R = ⁱPr; κ¹-1b, R = Ph) and κ¹-1-R₂P-2- Me₂N-mdene (κ¹-1c, ⁱPr; κ¹-1d, R = Ph) were prepared and structurally characterized. Dicoordinate neutral complexes (κ¹-1)AuCl (2-5) were prepared by reacting 1 with Me₂SAuCl, with isolated yields ranging from 56 to 88%. Addition of a second equivalent of 1a to 2 resulted in formation of the tricoordinate neutral species (κ¹-1a)₂AuCl (6; 69%). By treating 6 with AgOTf, the corresponding cationic complex [(κ¹-1a)₂Au]⁺OTf^- ([7] ⁺OTf^-; 72%) was obtained. The catalytic performance of these new Au (i) compounds in the hydrosilylation of various aldehydes was compared to that of catalyst systems derived from a combination of R ₃P (R = Et, ⁿBu, ^tBu, Cy, or Ph) or N-heterocyclic carbene ligands and Me₂SAuCl. While for the phosphine-substituted indene complexes, a catalyst mixture of 3 mol % 2 and 20 mol % 1a was found to be optimal, a catalyst derived from 3 mol % Mc ₂SAuCl and 20 mol % Et₃P, ⁿBu₃P, or ^tBu₃P proved to be the most effective overall, especially for reactions conducted at 24°C. Single-crystal X-ray diffraction data are provided for 2, 4, 6, and [7]⁺OTf^-.

Full text of DOI:10.1021/om060948n

Organometallics 2007, 26, 1069-1076
1069
Au(I) Complexes Supported by Donor-Functionalized Indene
Ligands: Synthesis, Characterization, and Catalytic Behavior in
Aldehyde Hydrosilylation
Bradley M. Wile,† Robert McDonald,‡ Michael J. Ferguson,‡ and Mark Stradiotto*,†
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 October 14, 2006
i
New Au(I) complexes featuring ligands of the type κ1-3-R2P-indene (κ1-1a, R ) Pr; κ1-1b, R ) Ph)
and κ1-1-R2P-2-Me2N-indene (κ1-1c, R ) iPr; κ1-1d, R ) Ph) were prepared and structurally characterized.
Dicoordinate neutral complexes (κ1-1)AuCl (2-5) were prepared by reacting 1 with Me2SAuCl, with
isolated yields ranging from 56 to 88%. Addition of a second equivalent of 1a to 2 resulted in formation
of the tricoordinate neutral species (κ1-1a)2AuCl (6; 69%). By treating 6 with AgOTf, the corresponding
cationic complex [(κ1-1a)2Au]+OTf- ([7]+OTf-; 72%) was obtained. The catalytic performance of these
new Au(I) compounds in the hydrosilylation of various aldehydes was compared to that of catalyst systems
derived from a combination of R3P (R ) Et, nBu, tBu, Cy, or Ph) or N-heterocyclic carbene ligands and
Me2SAuCl. While for the phosphine-substituted indene complexes, a catalyst mixture of 3 mol % 2 and
20 mol % 1a was found to be optimal, a catalyst derived from 3 mol % Me2SAuCl and 20 mol % Et3P,
t
nBu3P, or Bu3P proved to be the most effective overall, especially for reactions conducted at 24 °C.
Single-crystal X-ray diffraction data are provided for 2, 4, 6, and [7]+OTf-.
centered reactivity and may ultimately enable the development
of new or improved Au-catalyzed substrate transformations.
In the pursuit of new classes of metal complexes that are
capable of mediating synthetically useful chemical transforma-
tions involving the activation of E-H bonds (E ) main group
fragment), we are exploring the reactivity behavior of coordina-
tion complexes supported by donor-substituted indene ligands,
Introduction
While soluble platinum-group metal catalysts are employed
widely in mediating a diversity of synthetically useful chemical
reactions,1 the application of Au complexes in homogeneous
catalysis had, until relatively recently, received little attention.
However, the numerous reports documenting Au-catalyzed
substrate transformations that have emerged over the past decade
serve to confirm the utility of such catalyst complexes; indeed,
soluble Au complexes in some instances have provided access
to reaction manifolds that cannot be reached by use of more
traditional catalysts.2 Notwithstanding this remarkable progress,
and despite an early report by Hayashi and co-workers3 that
highlights the reactivity benefits of employing appropriately
selected phosphine ancillary ligands in Au-mediated transforma-
tions, one consequence associated with the delayed recognition
of Au catalysis is that the influence of supporting ligands on
metal-centered reactivity has not been explored thoroughly.2,4
Given the central role that fundamental ligand design studies
have played in advancing the field of transition metal-mediated
homogeneous catalysis,1,5 related studies involving Au are likely
to further our understanding of the factors that influence Au-
i
including 3-R2P-indene (1a, R ) Pr; 1b, R ) Ph) and 1-R2P-
2-Me2N-indene (1c, R ) iPr; 1d, R ) Ph).6 In Rh-based studies,
we have observed that while lithiation of 1a followed by
treatment with 0.5 equiv of [(COD)RhCl]2 affords the corre-
sponding η5-indenylrhodium complex,6e under analogous condi-
(4) For a selection of reports examining the influence of supporting
ligands on Au-mediated reactivity, see: (a) Han, X.; Widenhoefer, R. A.
Angew. Chem., Int. Ed. 2006, 45, 1747. (b) Marion, N.; D´ıez-Gonza´lez, S.;
de Fre´mont, P.; Noble, A. R.; Nolan, S. P. Angew. Chem., Int. Ed. 2006,
45, 3647. (c) Xing, D.; Guan, B.; Cai, G.; Fang, Z.; Yang, L.; Shi, Z. Org.
Lett. 2006, 8, 693. (d) Marion, N.; de Fre´mont, P.; Lemie`re, G.; Stevens,
E. D.; Fensterbank, L.; Malacria, M.; Nolan, S. P. Chem. Commun. 2006,
2048. (e) Lo, V. K.-Y.; Liu, Y.; Wong, M.-K.; Che, C.-M. Org. Lett. 2006,
8, 1529. (f) Comas-Vives, A.; Gonza´lez-Arellano, C.; Corma, A.; Iglesias,
M.; Sa´nchez, F.; Ujaque, G. J. Am. Chem. Soc. 2006, 128, 4756. (g) Zhou,
C.-Y.; Chan, P. W. H.; Che, C.-M. Org. Lett. 2006, 8, 325. (h) Guan, B.;
Xing, D.; Cai, G.; Wan, X.; Yu, N.; Fang, Z.; Yang, L.; Shi, Z. J. Am.
Chem. Soc. 2005, 127, 18004. (i) Gonza´lez-Arellano, C.; Corma, A.; Iglesias,
M.; Sa´nchez, F. Chem. Commun. 2005, 1990. (j) Gonza´lez-Arellano, C.;
Corma, A.; Iglesias, M.; Sa´nchez, F. Chem. Commun. 2005, 3451. (k) Ito,
H.; Takagi, K.; Miyahara, T.; Sawamura, M. Org. Lett. 2005, 7, 3001. (l)
Nieto-Oberhuber, C.; Lo´pez, S.; Echavarren, A. M. J. Am. Chem. Soc. 2005,
127, 6178. (m) Hashmi, A. S. K.; Rudolph, M.; Weyrauch, J. P.; Wo¨lfle,
M.; Frey, W.; Bats, J. W. Angew. Chem., Int. Ed. 2005, 44, 2798. (n) Mun˜oz,
M. P.; Adrio, J.; Carretero, J. C.; Echavarren, A. M. Organometallics 2005,
24, 1293. (o) Hashmi, A. S. K.; Weyrauch, J. P.; Rudolph, M.; Kurpejoviæ,
E. Angew. Chem., Int. Ed. 2004, 43, 6545. (p) Baker, R. T.; Nguyen, P.;
Marder, T. B.; Westcott, S. A. Angew. Chem., Int. Ed. 1995, 34, 1336. (q)
Baker, R. T.; Calabrese, J. C.; Westcott, S. A. J. Organomet. Chem. 1995,
498, 109. (r) Pastor, S. D.; Togni, A. J. Am. Chem. Soc. 1989, 111, 2333.
(s) Dube´, P.; Toste, F. D. J. Am. Chem. Soc. 2006, 128, 12062. (t) Horino,
Y.; Luzung, M. R.; Toste, F. D. J. Am. Chem. Soc. 2006, 128, 11364.
(5) Yoon, T. P.; Jacobsen, E. N. Science 2003, 299, 1691.
* To whom correspondence should be addressed. Fax: (902) 494-1310.
Tel: (902) 494-7190. E-mail: mark.stradiotto@dal.ca.
† Dalhousie University.
‡ University of Alberta.
(1) For some prominent examples, see: (a) Grubbs, R. H. Angew. Chem.,
Int. Ed. 2006, 45, 3760. (b) Knowles, W. S. Angew. Chem., Int. Ed. 2002,
41, 1998. (c) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008.
(2) For selected reviews on the use of Au complexes in homogeneous
catalysis, see: (a) D´ıaz-Requejo, M. M.; Pe´rez, P. J. J. Organomet. Chem.
2005, 690, 5441. (b) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2005, 44,
6990. (c) Hoffmann-Ro¨der, A.; Krause, N. Org. Biomol. Chem. 2005, 3,
387. (d) Hashmi, A. S. K. Gold Bull. 2004, 37, 51. (e) Dyker, G. Angew.
Chem., Int. Ed. 2000, 39, 4237.
(3) Ito, Y.; Sawamura, M.; Hayashi, T. J. Am. Chem. Soc. 1986, 108,
6405.
10.1021/om060948n CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/13/2007

1070 Organometallics, Vol. 26, No. 4, 2007
Wile et al.
tions employing 1c, the formally zwitterionic (COD)Rh(κ2-3-
iPr2P-2-Me2N-indenide) is formed quantitatively.6f Correspond-
ingly, we became interested in preparing Au(I) derivatives of
1a-d, with an aim toward evaluating how the introduction of
structural modifications to the indene framework can influence
the coordination behavior of the ligand and/or the reactivity
characteristics of the associated metal fragments. Furthermore,
we sought to evaluate the utility of such complexes as catalysts
for the addition of various E-H bonds to unsaturated organic
molecules. Although several such Au-mediated addition reac-
tions have been documented,7 the addition of Si-H bonds is
limited to a single communication in 2000 by Hosomi and co-
workers, in which the hydrosilylation of various aldehydes
catalyzed by a Ph3PAuCl/nBu3P mixture at 70 °C was described.8a
We report herein the synthesis and characterization of neutral
and cationic Au(I) coordination complexes of 1a-d. Also
described are our efforts to evaluate further the influence of
ancillary ligands on the progress of Au-mediated Si-H addition
reactions, including a head-to-head comparison of the catalytic
abilities of these new Au(I) derivatives of 1a-d with those of
Me2SAuCl/L mixtures (L ) 1,3-diisopropyl-4,5-dimethylimi-
Figure 1. ORTEP diagram for 2 shown with 50% displacement
ellipsoids and with the atomic numbering scheme depicted; selected
hydrogen atoms have been omitted for clarity. Selected interatomic
distances (Å) and angles (deg) for 2: Au-P 2.2409(8); Au-Cl
2.2941(8); P-C3 1.802(3); C1-C2 1.509(4); C2-C3 1.345(4); and
Cl-Au-P 177.20(3).
n
t
dazol-2-ylidene or R3P, R ) Et, Bu, Bu, Cy, or Ph) in the
hydrosilylation of aldehydes at both 24 and 70 °C.
Results and Discussion
Synthesis and Characterization of New Au(I) Complexes
of 1a-d. Treatment of 1a or 1b with 1 equiv of Me2SAuCl
i
afforded (κ1-P-1)AuCl (2, R ) Pr; 3, R ) Ph) in 88 and 75%
isolated yield, respectively (eq 1). The proposed structures of 2
and 3 are supported by data obtained from solution NMR
studies, with the CS symmetry of these complexes being evident
1
in the H and 13C{1H} NMR spectra. In the case of 2, the
connectivity was confirmed on the basis of data obtained from
single-crystal X-ray diffraction studies. An ORTEP9 diagram
of 2 is presented in Figure 1, and relevant experimental
parameters for each of the crystallographically characterized
complexes reported herein are collected in Table 1. The structure
Figure 2. ORTEP diagram for 4 shown with 50% displacement
ellipsoids and with the atomic numbering scheme depicted; selected
hydrogen atoms have been omitted for clarity. Selected interatomic
distances (Å) and angles (deg) for 4: Au-P 2.247(2); Au-Cl
2.294(2); Au‚‚‚N 3.667; P-C1 1.879(8); C1-C2 1.51(1); C2-C3
1.36(1); and Cl-Au-P 177.60(8).
(6) For selected examples, see: (a) Wile, B. M.; Burford, R. J.;
McDonald, R.; Ferguson, M. J.; Stradiotto, M. Organometallics 2006, 25,
1028. (b) Rankin, M. A.; McDonald, R.; Ferguson, M. J.; Stradiotto, M.
Organometallics 2005, 24, 4981. (c) Cipot, J.; McDonald, R.; Stradiotto,
M. Chem. Commun. 2005, 4932. (d) Wile, B. M.; McDonald, R.; Ferguson,
M. J.; Stradiotto, M. Organometallics 2005, 24, 1959. (e) Cipot, J.;
Wechsler, D.; Stradiotto, M.; McDonald, R.; Ferguson, M. J. Organome-
tallics 2003, 22, 5185. (f) Stradiotto, M.; Cipot, J.; McDonald, R. J. Am.
Chem. Soc. 2003, 125, 5618.
of 2 is quite similar to that of the related complex iPr3PAuCl,10
with the Au center in 2 deviating only modestly from linearity
(177.20(3)°).
(7) For selected examples, see: (a) Brouwer, C.; He, C. Angew. Chem.,
Int. Ed. 2006, 45, 1744. (b) Youn, S. W. J. Org. Chem. 2006, 71, 2521. (c)
Zhang, J.; Yang, C.-G.; He, C. J. Am. Chem. Soc. 2006, 128, 1798. (d)
Nguyen, R.-V.; Yao, X.-Q.; Bohle, D. S.; Li, C.-J. Org. Lett. 2005, 7, 673.
(e) Yang, C.-G.; He, C. J. Am. Chem. Soc. 2005, 127, 6966. (f) Li, Z.; Shi,
Z.; He, C. J. Organomet. Chem. 2005, 690, 5049. (g) Luo, Y.; Li, C.-J.
Chem. Commun. 2004, 1930. (h) Yao, X.; Li, C.-J. J. Am. Chem. Soc. 2004,
126, 6884. (i) Shi, Z.; He, C. J. Org. Chem. 2004, 69, 3669. (j) Casado, R.;
Contel, M.; Laguna, M.; Romero, P.; Sanz, S. J. Am. Chem. Soc. 2003,
125, 11925. (k) Reetz, M. T.; Sommer, K. Eur. J. Org. Chem. 2003, 3485.
(l) Mizushima, E.; Sato, K.; Hayashi, T.; Tanaka, M. Angew. Chem., Int.
Ed. 2002, 41, 4563. (m) Mu¨ller, T. E.; Grosche, M.; Herdtweck, E.; Pleier,
A.-K.; Walter, E.; Yan, Y.-K. Organometallics 2000, 19, 170. (n) Teles, J.
H.; Brode, S.; Chabanas, M. Angew. Chem., Int. Ed. 1998, 37, 1415. (o)
Fukuda, Y.; Utimoto, K. Synthesis 1991, 975. (p) Fukuda, Y.; Utimoto, K.
J. Org. Chem. 1991, 56, 3729. (q) References within refs 4a,j,q.
(8) (a) Ito, H.; Yajima, T.; Tateiwa, J.-I; Hosomi, A. Chem. Commun.
2000, 981. (b) For the hydrosilylation of alkynes catalyzed by Au
nanoparticles supported on carbon or alumina, see: Caporusso, A. M.;
Aronica, L. A.; Schiavi, E.; Martra, G.; Vitulli, G.; Salvadori, P. J.
Organomet. Chem. 2005, 690, 1063. (c) For the hydrosilylation of alkenes
catalyzed by Pt/Au bimetallic colloids, see: Schmid, G.; West, H.; Mehles,
H.; Lehnert, A. Inorg. Chem. 1997, 36, 891.
The utility of P,N ligands in supporting catalytically active
platinum-group complexes is well-established.11 In this regard,
we have demonstrated previously that such metal complexes
featuring 1c and related P,N-substituted indenes can participate
(10) Angermaier, K.; Zellar, E.; Schmidbaur, H. J. Organomet. Chem.
1994, 472, 371.
(11) For selected reviews, see: (a) Ka¨llstro¨m, K.; Munslow, I.; Ander-
sson, P. G. Chem.sEur. J. 2006, 12, 3194. (b) Guiry, P. J.; Saunders, C.
P. AdV. Synth. Catal. 2004, 346, 497. (c) Chelucci, G.; Orru`, G.; Pinna, G.
A. Tetrahedron 2003, 59, 9471. (d) Helmchen, G.; Pfaltz, A. Acc. Chem.
Res. 2000, 33, 336. (e) Gavrilov, K. N.; Polosukhin, A. I. Russ. Chem.
ReV. 2000, 69, 661.
(9) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

Au-Catalyzed Hydrosilylation
Organometallics, Vol. 26, No. 4, 2007 1071
Table 1. Crystallographic Data
4
2
6
[7]+OTf-
empirical formula
Fw
C15H21AuClP
464.70
C17H26AuClNP
507.77
C30H42AuClP2
696.99
C31H42AuF3O3P2 S
810.61
cryst size
cryst syst
space group
a (Å)
0.43 × 0.42 × 0.06
monoclinic
P21/c (No. 14)
15.625 (2)
7.3752 (10)
15.269 (2)
90
118.454 (2)
90
1546.9 (4)
4
0.30 × 0.22 × 0.14
0.39 × 0.32 × 0.22
monoclinic
P21/c (No. 14)
9.0257 (5)
20.3683 (11)
16.1902 (9)
90
94.9747 (8)
90
2965.2 (3)
4
0.23 × 0.22 × 0.15
orthorhombic
Pna21 (No. 33)
26.567 (2)
9.2095 (8)
13.1111 (12)
90
triclinic
P1h(No. 2)
9.3708 (10)
10.1136 (10)
10.3753 (11)
88.223 (2)
84.120 (2)
68.059 (2)
907.25 (16)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
90
90
3207.9 (5)
4
1.678
4.799
52.78
Z
F
calcd (g cm-3
)
)
1.995
9.767
52.76
1.859
8.337
52.74
1.561
5.176
52.80
µ (mm-1
2θ limit (deg)
-19 e h e 19
-9 e k e 9
-19 e l e 19
11475
-11 e h e 11
-12 e k e 12
-12 e l e 12
6848
-11 e h e 11
-25 e k e 25
-20 e l e 20
23284
-33 e h e 33
-11 e k e 11
-16 e l e 16
24364
total data collected
ind reflns
3156
3671
6071
6566
Rint
0.0313
0.0278
0.0219
0.0376
obsd reflns
3005
3452
5602
5666
abs correction
range of transmission
data/restraints/params
Gaussian integration (face-indexed)
Gaussian integration (face-indexed)
multiscan (SADABS)
0.3955-0.2374
6071/0/307
0.0160
0.0405
1.049
multiscan (SADABS)
0.5330-0.4049
6566/0/416
0.0268
0.0600
1.074
0.5918-0.1020
3156/0/163
0.0218
0.0564
1.117
0.3882-0.1888
3671/0/190
0.0444
0.1373
1.222
2
R1 [Fo2 g 2σ(Fo )]
2
wR2 [Fo2 g -3σ(Fo )]
GOF
largest peak, hole (eÅ-3
)
0.907, -1.549
5.825, -1.278
0.768, -0.382
2.780, -0.433
in a range of stoichiometric and/or catalytic transformations
involving E-H bond activation.6 In the pursuit of related Au-
(I) coordination complexes, 1c was treated with Me2SAuCl,
affording (κ1-P,N-1c)AuCl (4) in 67% isolated yield (eq 2). Data
obtained from solution NMR spectroscopic studies supported
the structure proposed for 4, which was confirmed on the basis
of data obtained from a single-crystal X-ray diffraction experi-
ment. An ORTEP9 diagram of 4 is presented in Figure 2. The
nearly linear geometry at Au (177.60(8)°) as well as the Au-P
(2.247(2) Å) and Au-Cl (2.294(2) Å) distances in 4 are
indistinguishable from those in 2 (vide supra) and can be
compared with other structurally related Au(I) complexes.12 The
Au‚‚‚N separation (3.67 Å) lies outside the sum of the van der
Waals radii for these elements (3.25 Å),13 thereby confirming
the κ1-P,N binding mode of 1c in 4; similar (κ1-P,N)AuCl
coordination complexes of potentially bidentate P,N ligands have
been reported.12 While this monodentate coordination motif for
1c is also observed in (κ1-P,N-1c)Rh(COD)Cl,6e,f the ability of
1c to function as a bidentate κ2-P,N ligand has been demon-
strated for both Pt and Ru.6b,d
inseparable 2:3 isomeric mixture of (κ1-P,N-1d)AuCl (5a) and
(κ1-3-R2P-2-Me2N-indene)AuCl (5b), which was isolated as an
analytically pure solid in 56% yield and characterized by use
of 1-D and 2-D NMR techniques (eq 3). Whereas in solution
i
the 1-R2P-indenes (R ) Pr,6e Ph14) are converted readily into
1a and 1b either with heating or upon treatment with NEt3, we
have shown previously that both 1c and 1d evolve slowly to an
equilibrium mixture of 1c,d and the corresponding 3-R2P-2-
Me2N-indene isomer, with the resultant isomeric mixture being
retained under the conditions that resulted in the quantitative
isomerization of the aforementioned 1-R2P-indenes.6e Consistent
with these observations, and in keeping with (κ1-P,N-1c)Rh-
(COD)Cl, which also resists rearranging to (κ1-3-R2P-2-Me2N-
indene)Rh(COD)Cl,6e,f neither 5a nor 5b could be converted to
its isomer, either with heating (50 °C, 6 days) or upon exposure
to NEt3, iPrOH, or H2O in THF solution. Notably, under similar
conditions, Ru and Pt (κ2-P,N-1c)MLn species have been
observed to isomerize cleanly to the corresponding κ2-3-R2P-
2-Me2N-indene complexes.6b,d
In contrast to the preparation of 4, during which products
derived from the isomerization of the ancillary ligand 1c were
not detected by use of NMR spectroscopic methods, treatment
of 1d with Me2SAuCl generated cleanly (1H and 31P NMR) an
In the pursuit of an L2AuCl species, complex 2 was treated
with 1 equiv of 1a, thereby allowing for the isolation of (κ1-
P-1a)2AuCl (6) as an analytically pure light brown crystalline
solid in 69% yield (Scheme 1). An ORTEP9 diagram of 6 is
(12) For selected examples, see: (a) Kreiter, R.; Firet, J. J.; Ruts, M. J.
J.; Lutz, M.; Spek, A. L.; Gebbink, R. J. M. K.; van Koten, G. J. Organomet.
Chem. 2006, 691, 422. (b) Bowen, R. J.; Fernandes, M. A.; Gitari, P. W.;
Layh, M.; Moutloali, R. M. Eur. J. Inorg. Chem. 2005, 1955. (c)
Papathanasiou, P.; Salem, G.; Waring, P.; Willis, A. C. J. Chem. Soc., Dalton
Trans. 1997, 3435. (d) Assmann, B.; Angermaier, K.; Paul, M.; Riede, J.;
Schmidbaur, H. Chem. Ber. 1995, 128, 891.
(14) Fallis, K. A.; Anderson, G. K.; Rath, N. P. Organometallics 1992,
11, 885.
(13) Bondi, A. J. Phys. Chem. 1964, 68, 441.

1072 Organometallics, Vol. 26, No. 4, 2007
Wile et al.
Scheme 1
presented in Figure 3, which highlights a distorted trigonal planar
coordination geometry at Au (Σangles at Au ≈ 360°) that is also
evident in some other crystallographically characterized (R3P)2-
AuCl complexes.4q,15 Notably, the Au-P (2.3181(5) and 2.3050-
(5) Å) and Au-Cl (2.6577(6) Å) distances in 6 are lengthened
significantly relative to those found in both 2 and 4. In contrast
to the dissimilar Au-P distances in 6 that may arise due to
Figure 3. ORTEP diagram for 6 shown with 50% displacement
ellipsoids and with the atomic numbering scheme depicted; selected
hydrogen atoms have been omitted for clarity. Selected interatomic
distances (Å) and angles (deg) for 6: Au-P1 2.3181(5); Au-P2
2.3050(5); Au-Cl 2.6577(6); P1-C13 1.814(2); P2-C23 1.816-
(2); C11-C12 1.500(3); C12-C13 1.344(3); C21-C22 1.504(3);
C22-C23 1.341(3); Cl-Au-P1 102.23(2); Cl-Au-P2 112.34-
(2); and Pl-Au-P2 145.26(2).
1
crystal packing effects, both H and 13C NMR data for this
complex are consistent with an effective C2V symmetric solution
structure for 6.
The preparation of (κ1-P,N-1c)2AuCl complexes proved to
be less straightforward. Following the addition of 1 equiv of
1c to 4 in THF, the 31P{1H} NMR spectrum of the reaction
mixture revealed multiple broad resonances centered around 62
and -5 ppm. Upon cooling from 300 to 170 K, several de-
coalescence events were noted, eventually resulting in a
complicated spectrum that could not be unambiguously assigned.
In addition to the spectral complexities arising from the
anticipated presence of isomeric meso- and rac-(κ1-P,N-
1c)2AuCl and/or [(κ1-P,N-1c)2Au]+Cl- products in this reaction,
it is possible that oligomeric Au complexes, in which 1c serves
to bridge metal centers, are also formed.4q,10,16,17 All efforts to
isolate pure materials from such reactions were unsuccessful.
In exploring the synthetic viability of [(κ1-P-1a)2Au]+X-
species, complex 6 was treated with 1 equiv of AgOTf (Scheme
1). Subsequent examination of the reaction mixture by use of
31P{1H} NMR methods revealed the consumption of 6, along
with the clean formation of a single phosphorus-containing
product ([(κ1-P-1a)2Au]+OTf-, [7]+OTf-), giving rise to a sharp
singlet at 53 ppm (300 K). Complex [7]+OTf- was isolated in
72% yield and characterized by the use of NMR spectroscopic
and X-ray crystallographic methods. An ORTEP9 diagram of
[7]+OTf- is presented in Figure 4. The linear Au coordination
environment in [7]+OTf- (179.26(4)°) is found commonly in
[L2Au]+X- complexes.12d,17d,18 No close Au‚‚‚OTf or Au‚‚‚Au
contacts were found in the crystal structure of [7]+OTf-, and
the Au-P distances in this complex (2.310(1) and 2.315(1) Å)
Figure 4. ORTEP diagram for [7]+OTf- shown with 50%
displacement ellipsoids and with the atomic numbering scheme
depicted; selected hydrogen atoms and the triflate counterion have
been omitted for clarity. Selected interatomic distances (Å) and
angles (deg) for [7]+OTf-: Au-P1 2.310(1); Au-P2 2.315(1); P1-
C13 1.800(4); P2-C23 1.804(4); C11-C12 1.507(7); C12-C13
1.326(7); C21-C22 1.483(7); C22-C23 1.333(7); and Pl-Au-
P2 179.26(4).
differ only modestly from those found in 6. The solution
characterization of [7]+OTf- is consistent with the solid-state
structure of this complex. Interestingly, virtual coupling to
phosphorus is observed in the 1H and 13C{1H} NMR spectra of
[7]+OTf-.19 For example, whereas the 1H NMR signal for each
of the diastereotopic methyl groups within the iPr2P fragments
of 1a, 2, and 6 appears as a doublet of doublets, similar signals
in [7]+OTf- appear as a virtual doublet of tripletssa result of
coupling to both P atoms that presumably is enabled by the
linearity of the P-Au-P unit in [7]+OTf-.
(15) (a) Viotte, M.; Gautheron, B.; Kubicki, M. M.; Mugnier, Y.; Parish,
R. V. Inorg. Chem. 1995, 34, 3465. (b) Phang, L.-T.; Hor, T. S. A.; Zhou,
Z.-Y.; Mak, T. C. W. J. Organomet. Chem. 1994, 469, 253. (c) Houlton,
A.; Mingos, D. M. P.; Murphy, D. M.; Williams, D. J.; Phang, L.-T.; Hor,
T. S. A. J. Chem. Soc., Dalton Trans. 1993, 3629.
(16) For an example of dimeric Au(I) complexes supported by bridging
P,N ligands, see: Crespo, O.; Ferna´ndez, E. J.; Gil, M.; Gimeno, M. C.;
Jones, P. G.; Laguna, A.; Lo´pez-de-Luzuriaga, J. M.; Olmos, M. E. J. Chem.
Soc., Dalton Trans. 2002, 1319.
(17) For selected examples of oligomeric Au coordination complexes,
see: (a) Mohr, F.; Jennings, M. C.; Puddephatt, R. J. Angew. Chem., Int.
Ed. 2004, 43, 969. (b) Burchell, T. J.; Eisler, D. J.; Jennings, M. C.;
Puddephatt, R. J. Chem. Commun. 2003, 2228. (c) Wilton-Ely, J. D. E. T.;
Schier, A.; Mitzel, N. W.; Nogai, S.; Schmidbaur, H. J. Organomet. Chem.
2002, 643-644, 313. (d) Puddephatt, R. J. Coord. Chem. ReV. 2001, 216,
313. (e) Brandys, C.-M.; Puddephatt, R. J. J. Am. Chem. Soc. 2001, 123,
4839. (f) Khan, M. N. I.; Staples, R. J.; King, C.; Fackler, J. P., Jr.;
Winpenny, R. E. P. Inorg. Chem. 1993, 32, 5800.
Au-Catalyzed Hydrosilylation of Aldehydes. The addition
of Si-H bonds to carbonyl compounds provides a direct and
(18) (a) Bardaj´ı, M.; Jones, P. G.; Laguna, A.; Villacampa, M. D.;
Villaverde, N. Dalton Trans. 2003, 4529. (b) Brandys, C.-M.; Puddephatt,
R. J. Chem. Commun. 2001, 1280. (c) Ro¨mbke, P.; Schier, A.; Schmidbaur,
H. J. Chem. Soc., Dalton Trans. 2001, 2482. (d) Bowmaker, G. A.;
Schmidbaur, H.; Kru¨ger, S.; Ro¨sch, N. Inorg. Chem. 1997, 36, 1754. (e)
Guy, J. J.; Jones, P. G.; Sheldrick, G. M. Acta Crystallogr., Sect. B 1976,
32, 1937.
(19) For a discussion of virtual coupling in transition metal phosphine
complexes, see: Crabtree, R. H. The Organometallic Chemistry of the
Transition Metals, 4th ed.; Wiley: New York, 2005; Ch. 10.

Au-Catalyzed Hydrosilylation
Scheme 2
Organometallics, Vol. 26, No. 4, 2007 1073
Table 2. Au(I)-Catalyzed Addition of Me2PhSiH to
Benzaldehyde (8a) at 70 °Ca
time yield 9a yield other
entry
mol % catalyst
(h)
(%)b
(%)b
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
3% 2c
24
24
24
12
24
24
24
24
24
24
24
12
24
24
3
3
3
3
3
3
3
3
50
1
42
99
47
4
<1
7
5
31
42
99
<1
52
27
2
98
97
98
53
31
99
2
<1
<1
1
3% 2 + 6% Et3Nc
3% 2 + 3% 1ac
3% 2 + 20% 1ac
3% 3d
1
atom-economical route to synthetically useful O-protected silyl
alcohols.20 While a diversity of carbonyl hydrosilylation catalysts
have been identified,20 Cu complexes supported by phosphine
or N-heterocyclic carbene (NHC) ligands have proven particu-
larly effective, and the development of such catalysts continues
to attract attention.21 In contrast, only a single report for each
of Ag22 and Au8a documents the catalytic abilities of the heavier
group 11 elements in hydrosilylation chemistry. With regard to
the study of ligand effects in Au-catalyzed hydrosilylations,
Hosomi and co-workers noted that while catalysts comprised
of 3 mol % Ph3PAuCl and X mol % Ph3P (X ) 0 or 20) were
ineffective in mediating the addition of Me2PhSiH to benzal-
dehyde at 70 °C, a catalyst mixture comprised of 3 mol % Ph3-
3% 3 + 20% 1b
3% 4
3% 4 + 20% 1c
3% 5a/5b
<1
<1
4
<1
1
<1
1
<1
1
<1
<1
2
<1
1
2
1
<1
2-9
2-10
2-11
2-12
2-13
2-14
2-15
2-16
2-17
2-18
2-19
2-20
2-21
2-22
3% 5a/5b + 20% 1d
3% 6c
3% 6 + 20% 1a
3% [7]+OTf-
3% [7]+OTf- + 20% 1a
3% Me2SAuCl
3% Me2SAuCl + 20% Ph3Pc
3% Me2SAuCl + 20% nBu3Pc
3% Me2SAuCl + 20% Et3Pc,d
3% Me2SAuCl + 20% tBu3P
3% Me2SAuCl + 20% Cy3P
3% Me2SAuCl + 20% NHCe
3% Ph3PAuCl + 20% nBu3P
n
PAuCl and 20 mol % Bu3P proved capable of mediating the
hydrosilylation of various aldehyde substrates under similar
conditions.8a,23 Building upon these preliminary observations,
we sought to evaluate the catalytic abilities of the Au(I)
derivatives of 1a-d reported herein, as well as those of Me2-
SAuCl/L mixtures (L ) 1,3-diisopropyl-4,5-dimethylimidazol-
a Reactions conducted in THF at 70 °C with 2 equiv of Me2PhSiH relative
to benzaldehyde. b Yields quoted with respect to benzaldehyde consumed
at the time quoted based on GC-MS and GC-FID data (average of two
runs). c A precipitate of metallic gold was observed at the conclusion of
the reaction. d Under these conditions, Ph2SiH2 (86%, <3% double hy-
drosilylation product), Et3SiH (34%), and (EtO)3SiH (7%) all proved inferior
to Me2PhSiH. e NHC ) 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene.
t
2-ylidene or R3P, R ) Et, nBu, Bu, Cy, or Ph), in the
hydrosilylation of aldehydes at both 70 and 24 °C (Scheme 2).
catalytic abilities of 4 and 5a/5b were evaluated. Although the
1-R2P-2-Me2N-indene ligands in 4 and 5a/5b are bound
exclusively through phosphorus, we envisioned that the pendent
nitrogen fragment may help to temporarily stabilize coordina-
tively unsaturated reactive Au intermediates with respect to
bimolecular decomposition, thereby precluding the need for
excess phosphine. However, both 4 and 5a/5b performed poorly
as catalysts, even in the presence of excess 1c or 1d (entries
2-7 to 2-10).
As anticipated, the results of catalytic experiments conducted
using 3 mol % (κ1-P-1a)2AuCl (6) (entry 2-11) or 3 mol %
6/20 mol % 1a (entry 2-12) were indistinguishable from those
obtained when employing 3 mol % 2/3 mol % 1a (entry 2-3)
or 3 mol % 2/20 mol % 1a (entry 2-4), respectively. In an effort
to identify more active Au hydrosilylation catalysts, (κ1-P-
1a)2Au+ complexes were viewed as interesting targets. Given
the recently established activity of AgOTf in aldehyde hydrosi-
lylation,22 we opted to study the catalytic behavior of preformed
[7]+OTf-, rather than (κ1-P-1a)2AuCl/AgOTf mixtures. Unfor-
tunately, [7]+OTf- proved vastly inferior to 6 under similar
conditions (entries 2-13 and 2-14).
Our preliminary hydrosilylation survey was conducted using
benzaldehyde (8a) and Me2PhSiH, under conditions similar to
those employed by Hosomi and co-workers (70 °C, THF, 3 mol
% Au);8a the results of these experiments are summarized in
Table 2. Reactions employing 3 mol % 2 proceeded to a limited
extent, affording 9a in 50% yield after 24 h (entry 2-1). Given
the possibility that loss of HCl may play a role in the formation
of the active Au(I) catalyst, the catalytic abilities of a 3 mol %
2/6 mol % Et3N mixture were examined under similar condi-
tions, with disappointing results (entry 2-2). In light of the
observation by Hosomi and co-workers that the addition of 20
n
mol % Bu3P to 3 mol % Ph3PAuCl was required to generate
an active hydrosilylation catalyst,8a the use of 3 mol % 2 in
combination with added 3-iPr2P-indene (1a) was explored. While
no reactivity benefits were derived from the use of a 3 mol %
2/3 mol % 1a mixture (entry 2-3), nearly quantitative conversion
of 8a to 9a was achieved in 12 h by use of a catalyst mixture
comprised of 3 mol % 2/20 mol % 1a (entry 2-4). By
comparison, analogous Au catalysts based on 3-Ph2P-indene
performed poorly (entries 2-5 and 2-6). Encouraged by the
performance of Au(I) species supported by 1a, and in light of
the established reactivity benefits associated with the use of
bidentate P,N ligands in platinum-group metal catalysis,11 the
Having examined the utility of indenylphosphine ligands in
the Au-mediated hydrosilylation of benzaldehyde, we turned
our attention to the use of more conventional, commercially
available phosphines in this chemistry. Expanding on the
preliminary report by Hosomi and co-workers,8a in which the
divergent performance of catalysts derived 3 mol % Ph3PAuCl
(20) (a) Carpentier, J. F.; Bette, V. Curr. Org. Chem. 2002, 6, 913. (b)
Ojima, I.; Li, Z.; Zhu, J. In Chemistry of Organic Silicon Compounds, Vol.
2; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998; p 1687.
(21) For selected reports that document the Cu-mediated hydrosilylation
of carbonyl compounds, see: (a) Lipshutz, B. H.; Lower, A.; Kucejko, R.
J.; Noson, K. Org. Lett. 2006, 8, 2969. (b) D´ıez-Gonza´lez, S.; Scott, N.
M.; Nolan, S. P. Organometallics 2006, 25, 2355. (c) Yun, J.; Kim, D.;
Yun, H. Chem. Commun. 2005, 5181. (d) Jurkauskas, V.; Sadighi, J. P.;
Buchwald, S. L. Org. Lett. 2003, 5, 2417. (e) Sirol, S.; Courmarcel, J.;
Mostefai, N.; Riant, O. Org. Lett. 2001, 3, 4111. (f) Mahoney, W. S.;
Brestensky, D. M.; Stryker, J. M. J. Am. Chem. Soc. 1988, 110, 291.
(22) Wile, B. M.; Stradiotto, M. Chem. Commun. 2006, 4104.
n
and 20 mol % R3P (R ) Ph or Bu) at 70 °C is described, we
sought to evaluate more thoroughly the influence of phosphine
substitution, as well as NHC ligation, on Au-catalyzed hydrosi-
lylation under similar conditions. For convenience, Me2SAuCl
was employed in place of Ph3PAuCl as a source of AuCl. While
both Me2SAuCl alone (entry 2-15) and 3 mol % Me2SAuCl/20
mol % Ph3P (entry 2-16) exhibited poor catalytic properties,
mixtures of 3 mol % Me2SAuCl/20 mol % R3P (R ) nBu, entry
(23) It has been shown previously that 20 mol % R3P (R ) nBu8a or
Et22) alone is incapable of catalyzing the addition of Me2PhSiH to
benzaldehyde under these conditions.
t
2-17; R ) Et, entry 2-18; or R ) Bu, entry 2-19) were found

1074 Organometallics, Vol. 26, No. 4, 2007
Wile et al.
n
t
Table 3. Au(I) Catalyzed Addition of Me2PhSiH to
by use of either Bu3P or Bu3P. A similar ligand dependence
on conversion was also noted for the hydrosilylation of the
aliphatic aldehydes 8c and 8d (entries 3-8 to 3-10 and entries
3-11 to 3-13, respectively). While for substrates 8c and 8d, the
lower yields relative to those achieved in the reduction of 8a
or 8b were also accompanied by a loss in selectivity; the
aldehyde trimer was still not a significant contributor to the
product distribution. As well, the chemoselective hydrosilylation
of 4-acetylbenzaldehyde (8e) and trans-cinnamaldehyde (8f) was
achieved in high yield at 24 °C (entries 3-14 to 3-16 and entries
3-17 to 3-19, respectively).26
Aldehydes (8) at 24 °Ca
yield 9 yield other
entry
mol % catalyst
3% 2 + 20% 1a
aldehyde
(%)b
(%)b
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
8a
8a
8a
8a
8b
8b
8b
8c
8c
8c
8d
8d
8d
8e
8e
8e
8f
3
99
98
99
88
98
97
74
85
85
45
79
78
>99
98
98
97
97
90
1
<1
1
3% Me2SAuCl + 20% Et3P
3% Me2SAuCl + 20% nBu3P
3% Me2SAuCl + 20% tBu3P
3% Me2SAuCl + 20% Et3P
3% Me2SAuCl + 20% nBu3P
3% Me2SAuCl + 20% tBu3P
3% Me2SAuCl + 20% Et3P
3% Me2SAuCl + 20% nBu3P
1
1
2
2
4
7
5
3-10 3% Me2SAuCl + 20% tBu3P
3-11 3% Me2SAuCl + 20% Et3P
3-12 3% Me2SAuCl + 20% nBu3P
3-13 3% Me2SAuCl + 20% tBu3P
3-14 3% Me2SAuCl + 20% Et3P
3-15 3% Me2SAuCl + 20% nBu3P
3-16 3% Me2SAuCl + 20% tBu3P
3-17 3% Me2SAuCl + 20% Et3P
3-18 3% Me2SAuCl + 20% nBu3P
3-19 3% Me2SAuCl + 20% tBu3P
<1
Conclusion
3
2
In summary, a series of new Au(I) complexes featuring κ1-
3-R2P-indene (R ) iPr, 1a; R ) Ph, 1b) and κ1-1-R2P-2-Me2N-
indene (R ) Pr, 1a; R ) Ph, 1b) ligands have been prepared
<1
2
2
i
and structurally characterized. In studies exploring the utility
of these Au(I) species as catalysts for the hydrosilylation of
benzaldehyde at 70 °C, complexes supported by the P,N ligands
1c or 1d proved to be inferior to those featuring the inde-
nylphosphines 1a or 1b. While nearly quantitative conversion
was achieved by use of 3% (κ1-1a)AuCl/20% 1a at 70 °C, this
catalyst mixture performed poorly at 24 °C. In contrast, among
the other 3% Me2AuCl/20% L catalyst mixtures examined (L
) 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene or R3P, R )
Et, nBu, tBu, Cy, or Ph), those employing Et3P, nBu3P, or tBu3P
proved to be both active and selective for the hydrosilylation
of various aldehydes at 70 °C (3 h) or 24 °C (24 h). Notably,
this represents the first application of Au complexes as carbonyl
hydrosilylation catalysts at ambient temperatures and under-
scores the important influence of ancillary ligand structure on
such Au-mediated transformations. Although the specific role
that excess phosphine plays in generating an active Au hydro-
silylation catalyst in this context is not clear,23 it is plausible
that the shift of an equilibrium in the direction of what might
be more catalytically competent, higher coordination number
Au species may occur. As well, we are currently unable to
comment as to whether the active Au catalysts in these systems
are homogeneous or heterogeneous in nature, and as such,
catalysis by colloidal species resulting from the reduction of
Au(I) precursors cannot be ruled out on the basis of our findings.
However, the known instability of monomeric LnAuH species,27
in contrast to LnAuSiR3 complexes,28 suggests that the latter
may represent more viable intermediates in a homogeneous
catalytic cycle. Further studies directed toward identifying the
nature of the active catalyst involved in these transformations,
as well as developing a more thorough understanding of
ancillary ligand effects in Au-mediated E-H activation catalysis,
are underway and will be reported on in due course.
<1
8f
8f
2
3
a Reactions conducted in THF at 24 °C with 2 equiv. Me2PhSiH relative
to aldehyde. b Yields quoted with respect to aldehyde consumed at 24 h
based on GC-MS and GC-FID data (average of two runs).
n
to be as effective as the 3 mol % Ph3PAuCl/20 mol % Bu3P
catalyst system reported by Hosomi (entry 2-22) under similar
conditions,8a providing 9a in high yield after 3 h. Conversely,
catalysts comprised of 3 mol % Me2SAuCl/20 mol % L, where
L ) Cy3P (entry 2-20) or 1,3-diisopropyl-4,5-dimethylimidazol-
2-ylidene (entry 2-21), proved inferior under such experimental
conditions. These preliminary findings appear to suggest that
Au-catalyzed benzaldehyde hydrosilylation is enabled by a
strongly donating trialkylphosphine, although the poor perfor-
mance of the catalyst system employing Cy3P (∼170°) versus
t
those based on Et3P (∼130°) or Bu3P (∼180°) suggests that
there is no simple correlation between catalytic performance
and phosphine cone angle.24 Moreover, the lackluster conversion
achieved by use of the NHC ligand in this chemistry is also
surprising, given the utility of such ligands in carbonyl hydrosi-
lylation catalysis involving either Cu25 or Ag.22 Notably, the
benzaldehyde trimer was not detected as a side product in these
Au-mediated reactions, in contrast to our observations made
when employing related Ag-based hydrosilylation catalysts.22
n
Whereas the ability of 3 mol % Ph3PAuCl/20 mol % Bu3P
to mediate the hydrosilylation of various aldehydes at 70 °C
has been demonstrated,8a studies examining the utility of Au-
based hydrosilylation catalysts at ambient temperatures have
not been reported. In an effort to evaluate further the scope of
Au-mediated aldehyde hydrosilylation, the previously surveyed
catalyst systems that afforded >95% benzaldehyde conversion
at 70 °C (i.e., 3% 2 + 20% 1a; 3% Me2SAuCl + 20% R3P, R
n
t
) Et, Bu, or Bu) were examined for catalytic activity at 24
°C (Table 3). Although negligible conversion was achieved with
3% 2/20% 1a (entry 3-1), the trialkylphosphine-based Au
catalysts provided 9a in nearly quantitative yield (entries 3-2
to 3-4). In light of these results, the hydrosilylation of some
alternative aldehyde substrates at 24 °C was studied. Although
the high yield reduction of 2,6-dimethylbenzaldehyde (8b) was
achieved when employing 3 mol % Me2SAuCl/20 mol % R3P
(R ) Et, entry 3-5; R ) nBu, entry 3-6; or R ) tBu, entry 3-7),
the conversions achieved with Et3P were less than those obtained
Experimental Procedures
General Considerations. Except where noted, all manipulations
were conducted in the absence of oxygen and water under an
atmosphere of dinitrogen, either by use of standard Schlenk methods
or within an mBraun glovebox apparatus, utilizing glassware that
was oven-dried (130 °C) and evacuated while hot prior to use. Celite
(Aldrich) and Al2O3 (Fisher, neutral, Brockman Activity I, 60-
325 mesh) were oven-dried (130 °C) for 5 days and then evacuated
1
(26) The identities of 9e and 9f were confirmed on the basis of H and
(24) Tolman, C. A. Chem. ReV. 1977, 77, 313.
(25) For example: (a) D´ıez-Gonza´lez, S.; Kaur, H.; Zinn, F. K.; Stevens,
E. D.; Nolan, S. P. J. Org. Chem. 2005, 70, 4784. (b) References within
ref 21.
13C NMR data.
(27) Khairallah, G. N.; O’Hair, R. A. J.; Bruce, M. I. Dalton Trans. 2006,
3699 and references cited therein.
(28) Meyer, J.; Willnecker, J.; Schubert, U. Chem. Ber. 1989, 122, 223.

Au-Catalyzed Hydrosilylation
Organometallics, Vol. 26, No. 4, 2007 1075
for 24 h prior to use. Non-deuterated solvents tetrahydrofuran, dichlo-
romethane, toluene, benzene, and pentane were deoxygenated and
dried by sparging with dinitrogen gas, followed by passage through
a double-column solvent purification system purchased from mBraun
Inc. Tetrahydrofuran and dichloromethane were purified over two
alumina-packed columns, while toluene, benzene, and pentane were
purified over one alumina-packed column and one column packed
with copper-Q5 reactant. The solvents used within the glovebox
were stored over activated 4 Å molecular sieves. All liquid reagents,
including the deuterated solvents C6D6 (Aldrich), CD2Cl2 (Cam-
bridge Isotope Laboratories), CDCl3 (CIL), and all silanes (Aldrich)
were degassed using three repeated freeze-pump-thaw cycles and
stored over 4 Å molecular sieves for a minimum of 24 h prior to
use, unless otherwise noted. Compounds 1a,6e 1b,14 1c,6f 1d,6e 1,3-
diisopropyl-4,5-dimethylimidazol-2-ylidene,29 and Me2SAuCl30 were
prepared employing reported methods. Benzaldehyde (ACP) was
washed with 10% aqueous sodium bicarbonate until no further CO2
was evolved, followed by saturated aqueous sodium sulfite, then
dried over magnesium sulfate and distilled under reduced pressure.
With the exception of the phosphines, which were obtained from
either Alfa (Et3P) or Strem (all others), all other chemicals were
obtained from Aldrich in high purity. AgOTf (Aldrich) was dried
g, 1.1 mmol) in CH2Cl2 (8 mL) was added a suspension of Me2-
SAuCl (0.31 g, 1.1 mmol) in CH2Cl2 (4 mL). The reactant mixture
was noted to clear almost immediately, and after 0.25 h at 24 °C,
stirring was arrested, and residual solvent along with other volatiles
was removed in vacuo. The residue was washed with pentane (2
× 3 mL), and solvent and other volatile materials were removed
in vacuo to yield 3 as a white solid (0.42 g, 0.79 mmol, 75%).
Melting point 155-157 °C. Anal. (%) Calcd for C21H17AuClP: C,
1
47.34; H, 3.22. Found: C, 47.44; H, 3.54. H NMR (C6D6): δ
7.34 (m, 1H, C7-H), 7.28-7.19 (m, 4H, ortho Ph-H), 7.16 (m, 1H,
C4-H), 7.02-6.96 (m, 2H, para Ph-H), 6.93 (m, 1H, C5-H), 6.88-
6.81 (m, 4H, meta Ph-H), 6.76 (m, 1H, C6-H), 5.96 (d, 1H,3JPH
)
8.0 Hz, C2-H), 2.93 (s, 2H, CH2); 13C{1H} NMR (C6D6): δ 148.2
(d,2JPC ) 7 Hz, C2), 143.7 (d,3JPC ) 9 Hz, C7a), 142.2 (d,2JPC
15 Hz, C3a), 133.9 (d,2JPC ) 14 Hz, ortho Ph-C), 133.8 (d,1JPC
)
)
61 Hz, ipso Ph-C), 133.2 (d,1JPC ) 15 Hz, C3), 131.6 (para Ph-C),
129.0 (d,3JPC ) 12 Hz, meta Ph-C), 126.9 (C6), 126.0 (C5), 124.0
(C4), 121.5 (C7), 39.9 (d,3JPC ) 12 Hz, CH2); 31P{1H} NMR
(C6D6): δ 15.2.
Preparation of 4. To a magnetically stirred solution of Me2-
SAuCl (1.1 g, 3.5 mmol) in CH2Cl2 (10 mL) was added a solution
of 1c (1.0 g, 3.5 mmol) in CH2Cl2 (10 mL). After 0.25 h at 24 °C,
stirring was arrested, and residual solvent along with other volatiles
was removed in vacuo. The solid material was recrystallized from
CH2Cl2 to yield 4 as a light gray powder (1.2 g, 2.3 mmol, 67%).
Crystals suitable for X-ray diffraction were grown from a concen-
trated toluene solution at 24 °C. Melting point 194-195 °C. Anal.
1
in vacuo for a minimum of 48 h prior to use. All H, 13C, and 31P
NMR characterization data were collected at 300 K on a Bruker
AV-500 spectrometer operating at 500.1, 125.8, and 202.5 MHz
(respectively) with chemical shifts reported in parts per million
1
downfield of SiMe4 (for H and 13C) or 85% H3PO4 in D2O (for
1
31P). In some cases, slightly fewer than expected independent H
(%) Calcd for C17H26AuClNP: C, 40.21; H, 5.16; N, 2.76. Found:
or 13C NMR resonances were observed, despite prolonged data
acquisition times. 1H and 13C NMR chemical shift assignments were
based on data obtained from 1H-1H COSY, 1H-13C HSQC, 1H-13C
HMBC, and DEPT NMR experiments. GC-MS and GC-FID were
performed on a Perkin-Elmer AutoSystem XL gas chromatograph
equipped with a TurboMass mass spectrometer. GC-MS analyses
were performed using a Supelco 30 m × 0.25 mm MDN-5S 5%
phenyl methylsiloxane, film thickness 0.50 µm, temperature
programmed: 60 °C, 1 min; 20 °C/min to 200 °C, 7 min; and 45
°C/min to 280 °C, 7 min. GC-FID analyses were done in a similar
way except on a Supelco DB200 column. Melting points were
obtained on an electrothermal apparatus using samples sealed in
capillaries under dinitrogen. Elemental analyses for all compounds
were performed by Canadian Microanalytical Service Ltd., with
the exception of 4, which was performed by Desert Analytics.
Preparation of 2. To a magnetically stirred solution of 1a (0.077
g, 0.33 mmol) in CH2Cl2 (3 mL) was added a suspension of Me2-
SAuCl (0.097 g, 0.33 mmol) in CH2Cl2 (2 mL). After 0.25 h at
24 °C, stirring was arrested, and residual solvent along with other
volatiles was removed in vacuo. The residue was washed with
pentane (2 × 3 mL) and recrystallized from CH2Cl2/EtOH to yield
2 as a white solid (0.014 g, 0.29 mmol, 88%). Crystals suitable for
X-ray diffraction were grown from a diffusion of pentane into a
CH2Cl2 solution at room temperature. Melting point 160-163 °C.
Anal. (%) Calcd for C15H21AuClP: C, 38.77; H, 4.55. Found: C,
1
C, 40.17; H, 5.23; N, 2.39. H NMR (CDCl3): δ 7.29 (d,3JHH
)
7.5 Hz, 1H, C7-H), 7.23 (t,3JHH ) 7.5 Hz, 1H, C6-H), 7.14 (d,3JHH
) 7.5 Hz, 1H, C4-H), 6.96 (t,3JHH ) 7.5 Hz, 1H, C5-H), 5.72 (s,
1H, C3-H), 4.30 (d,2JPH ) 10.0 Hz, 1H, C1-H), 2.90 (s, 6H,
N(CH3)2), 2.59 (m, 1H, P(CHCH3aCH3b)), 1.88 (m, 1H, P(CHCH3-
cCH3d)), 1.54 (dd, 3H,3JPH ) 18.0 Hz,3JHH ) 6.5 Hz, P(CHCH3-
aCH3b)), 1.30 (dd, 3H,3JPH ) 18.5 Hz,3JHH ) 6.0 Hz, P(CHCH3-
aCH3b)), 0.98 (dd, 3H,3JPH ) 19.5 Hz,3JHH ) 7.5 Hz, P(CHCH3-
cCH3d)), 0.72 (dd, 3H,3JPH ) 15.0 Hz,3JHH ) 7.0 Hz, P(CHCH3-
cCH3d)); 13C{1H} NMR (CDCl3): δ 157.8 (d,2JPC ) 3 Hz, C2),
145.6 (d,2JPC ) 2 Hz, C7a), 135.5 (d,3JPC ) 7 Hz, C3a), 128.4
(C6), 123.5 (C7), 122.0 (C5), 119.4 (C4), 106.6 (C3), 44.5 (d,1JPC
) 21 Hz, C1), 43.8 (N(CH3)2), 23.4 (d,1JPC ) 20 Hz, P(CHCH3-
cCH3d)), 22.9 (d,1JPC ) 20 Hz, P(CHCH3aCH3b)), 22.8 (d,2JPC
)
5 Hz, P(CHCH3cCH3d)), 20.7 (d,2JPC ) 5 Hz, P(CHCH3aCH3b)),
20.0 (d,2JPC ) 3 Hz, P(CHCH3aCH3b)), 18.3 (d,2JPC ) 2 Hz,
P(CHCH3cCH3d)); 31P{1H} NMR (CDCl3): δ 62.3.
Preparation of 5a/5b. To a magnetically stirred suspension of
Me2SAuCl (0.11 g, 0.36 mmol) in toluene (2 mL) was added a
solution of 1d (0.12 g, 0.35 mmol) in toluene (3 mL). After 2 h at
24 °C, stirring was arrested, and residual solvent along with other
volatiles was removed in vacuo. The residue was dissolved in
minimal THF (2-3 mL) and filtered through Celite to remove the
black solid material that had formed in the reaction. THF and other
volatiles were removed in vacuo, and the resulting solid was washed
with pentane (2 × 3 mL). Solvent and other volatiles were removed
in vacuo, yielding 5a/5b as a yellow/brown solid (0.11 g, 0.20
mmol, 56%). Anal. (%) Calcd for C23H22AuClNP: C, 47.97; H,
3.85; N, 2.43. Found: C, 47.72; H, 3.76; N, 2.39. 1H NMR (CD2-
Cl2): δ 7.81-7.44 (m, 20H, 5a and 5b, Ph-H), 7.30 (d,3JHH ) 7.5
Hz, 1H, 5b, C4-H or C7-H), 7.18 (t,3JHH ) 7.5 Hz, 1H, 5a, C5-H
1
38.79; H, 4.66. H NMR (C6D6): δ 7.64 (d,3JHH ) 7.4 Hz, 1H,
C7-H), 7.10 (t,3JHH ) 8.8 Hz, 1H, C5-H), 7.06 (t,3JHH ) 8.8 Hz,
1H, C6-H), 6.63 (d,2JPH ) 10.2 Hz, 1H, C2-H), 2.90 (s, 2H, CH2),
1.91 (m, 2H, P(CHCH3CH3)2), 0.86 (dd, 6H,3JPH ) 19.1 Hz,3JHH
) 6.9 Hz, P(CHCH3CH3)2), 0.64 (dd, 6H,3JPH ) 17.4 Hz,3JHH
)
7.1 Hz, P(CHCH3CH3)2); 13C{1H} NMR (C6D6): δ 151.4 (d,2JPC
) 11 Hz, C2), 144.0 (d, JPC ) 7 Hz, C7a or C3a), 142.9 (d, JPC
)
or C6-H), 7.04 (d,3JHH ) 7.5 Hz, 1H, 5a, C7-H), 6.89 (t,3JHH
7.5 Hz, 1H, 5b, C5-H or C6-H), 6.78 (t,3JHH ) 7.5 Hz, 1H, 5b, C5
)
9 Hz, C3a or C7a), 131.0 (d,1JPC ) 50 Hz, C3), 126.6 (C5), 125.7
(C6), 124.1 (C4), 121.5 (C7), 39.5 (d,3JPC ) 12 Hz, CH2), 24.6
(d,1JPC ) 36 Hz, P(CHCH3CH3)2), 19.6 (d,2JPC ) 5 Hz, P(CHCH3-
CH3)2), 18.4 (P(CHCH3CH3)2); 31P{1H} NMR (C6D6): δ 44.4.
Preparation of 3. To a magnetically stirred solution of 1b (0.31
or C6), 6.72 (t,3JHH ) 7.5 Hz, 1H, 5a, C5 or C6), 6.51 (d,3JHH
)
7.5 Hz, 1H, 5a, C4-H), 6.21 (d,3JHH ) 7.5 Hz, 1H, 5b, C4-H or
C7-H), 5.60 (s, 1H, 5a, C3-H), 4.85 (d,2JPH ) 11.5 Hz, 1H, 5a,
C1-H), 3.79 (s, 2H, 5b, CH2), 3.08 (s, 6H, 5b, N(CH3)2), 2.62 (s,
6H, 5a, N(CH3)2); 13C{1H} NMR (CD2Cl2): δ 173.2 (5b, C2), 157.0
(5a, C2), 146.5 (5a, C3a or C7a), 135.4 (d, JPC ) 14 Hz, aryl C-H),
(29) Kuhn, N.; Kratz, T. Synthesis 1993, 561.
(30) Uson, R.; Laguna, A. Organomet. Synth. 1986, 3, 322.

1076 Organometallics, Vol. 26, No. 4, 2007
Wile et al.
134.8 (quaternary-C), 133.8 (d, JPC ) 13 Hz, aryl C-H), 133.3 (d,
JPC ) 14 Hz, aryl C-H), 132.5 (aryl C-H), 131.3 (aryl C-H), 129.0
(d, JPC ) 12 Hz, aryl C-H), 128.6 (d, JPC ) 21 Hz, aryl C-H),
128.5 (JPC ) 22 Hz, aryl C-H), 128.3 (5a, C5 or C6), 126.0 (5b,
C5 or C6), 124.0 (d,4JPC ) 4 Hz, 5a, C4), 122.7 (5b, C4 or C7),
121.4 (2 overlapping s, 5a, C5 or C6, and 5b, C5 or C6), 119.1
(5b, C4 or C7), 118.8 (5a, C7), 106.0 (5a, C3), 47.5 (d,1JPC ) 25
Hz, 5a, C1), 45.2 (5b, N(CH3)2), 42.1 (5a, N(CH3)2), 40.7 (d,3JPC
) 9 Hz, 5b, CH2); 31P{1H} NMR (CD2Cl2): δ 47.9 (5a), 14.8 (5b).
Preparation of 6. To a magnetically stirred solution of 2 (0.12
g, 0.26 mmol) in THF (2 mL) was added a solution of 1a (0.062
g, 0.27 mmol) in THF (1.5 mL). After stirring 0.1 h at 24 °C, the
yellow solution was filtered through Celite, pentane (10 mL) was
added, and the solution was placed in a -35 °C freezer. After
several days, the supernatant was decanted, and the resulting crystals
were washed with pentane (2 × 3 mL), then solvent and other
volatiles were removed in vacuo to yield light brown crystals, 6
(0.13 g, 0.18 mmol, 69%). Crystals suitable for X-ray diffraction
were grown from a concentrated sample of 6 in THF at -35 °C.
Melting point 160-161 °C. Anal. (%) Calcd for C30H42AuClP2:
SMART 1000 CCD diffractometer using graphite-monochromated
Mo KR (λ ) 0.71073 Å) radiation, employing samples that were
mounted in inert oil and transferred to a cold gas stream on the
diffractometer. Programs for diffractometer operation, data collec-
tion, data reduction, and multiscan absorption correction (including
SAINT and SADABS) were supplied by Bruker. The structures
were solved by use of direct methods in the case of 2 and 6, or
Patterson search/structure expansion in the case of 4 and [7]+OTf-,
and refined by use of full-matrix least-squares procedures (on F2)
2
2
2
with R1 based on Fo g 2σ(Fo ) and wR2 based on Fo g -3σ-
2
(Fo ). Anisotropic displacement parameters were employed through-
out for the non-hydrogen atoms, and all hydrogen atoms were added
at calculated positions and refined by use of a riding model
employing isotropic displacement parameters based on the isotropic
displacement parameter of the attached atom. For [7]+OTf-, the
final refined value of the absolute structure parameter (0.183(6))
supported that the correct absolute structure had been correctly
chosen.31 Further details are provided in the Supporting Information.
General Protocol for the Hydrosilylation of Aldehydes. The
protocol used for the hydrosilylation of benzaldehyde with dim-
ethylphenylsilane, employing 3 mol % Me2SAuCl and 20 mol %
Et3P in THF, is provided as a representative procedure. To a
suspension of Me2SAuCl in THF (0.022 g, 0.072 mmol in 1.6 mL
of THF) was added Et3P (0.071 mL, 0.057 g, 0.48 mmol). The
clear, colorless solution was allowed to equilibrate for 5 min under
the influence of magnetic stirring, at which point benzaldehyde (0.25
mL, 2.4 mmol) was added by use of an Eppendorf pipet. The
resultant solution was stirred for an additional 5 min to ensure
equilibration of the benzaldehyde with the catalyst, after which
dimethylphenylsilane (0.73 mL, 0.65 g, 4.8 mmol) was added.
Subsequently, 0.7 mL aliquots were placed in 13 × 100 mm
borosilicate tubes and sealed with a PTFE valve. Reactor cells were
immediately transferred to a temperature-controlled mineral oil bath.
Magnetic stirring of the solutions was initiated, and the headspace
vapor pressure was reduced to approximately 0.5 mmHg. Occasion-
ally, color changes and/or formation of metal precipitate were noted
during the course of the reaction, as indicated in the footnote of
Table 2 (see text). At the desired sampling time, the reactor cells
were opened and filtered through a short Al2O3 column (5 cm long
× 0.5 cm diameter) from which clear, colorless solutions eluted.
Benzene was passed through the column to increase the total eluted
volume to between 1.0 and 1.5 mL. These solutions were transferred
to GC vials and sealed. Products of each reaction were identified
by use of GC-MS, and quantitative data were obtained from GC-
FID analysis. Tabulated data represent the average of two runs.
1
C, 51.69; H, 6.07; N, 0. Found: C, 51.73; H, 6.11; N, <0.3. H
NMR (C6D6): δ 7.93 (d,3JHH ) 7.5 Hz, 2H, C4-H or C7-H), 7.19
(d,3JHH ) 7.5 Hz, 2H, C4-H or C7-H), 7.15 (t,3JHH ) 7.5 Hz, 2H,
C5-H or C6-H), 7.08 (t,3JHH ) 7.0 Hz, 2H, C5-H or C6-H), 6.97
(d,3JPH ) 7.0 Hz, 2H, C2-H), 3.01 (s, 4H, CH2), 2.42 (m, 4H,
P(CHCH3CH3)2), 1.24 (dd,3JPH ) 17.5 Hz,3JHH ) 10.0 Hz, 12H,
P(CHCH3CH3)2), 0.96 (dd,3JPH ) 15.5 Hz,3JHH ) 6.5 Hz, 12H,
P(CHCH3CH3)2); 13C{1H} NMR (C6D6): δ 147.9 (C2), 145.1 (d,
JPC ) 11 Hz, C3a or C7a), 144.1 (d, JPC ) 6 Hz, C3a or C7a),
134.4 (d, JPC ) 26 Hz, C3), 126.3 (aryl CH), 125.3 (aryl CH),
123.8 (aryl CH), 122.1 (aryl CH), 39.6 (d,3JPC ) 9 Hz, CH2), 24.4
(d,1JPC ) 21 Hz, P(CHCH3CH3)2), 19.8 (d,2JPC ) 8 Hz, P(CHCH3-
CH3)2), 18.8 (P(CHCH3CH3)2); 31P{1H} NMR (C6D6): δ 35.2 (∆ν1/2
) ∼950 Hz).
Preparation of [7]+OTf-. To a magnetically stirred solution of
6 (0.065 g, 0.093 mmol) in THF (3 mL) was added a solution of
AgOTf (0.024 g, 0.094 mmol) in THF. After 0.75 h at 24 °C,
stirring was arrested, and the light yellow solution was filtered
through Celite. The solution was placed in a -35 °C freezer, and
after 2 weeks, light yellow crystals formed, which proved to be
suitable for X-ray crystallographic studies. Crystals were isolated
and washed with pentane (2 × 3 mL), and residual solvent and
other volatiles were removed in vacuo to yield [7]+OTf- (0.054 g,
0.067 mmol, 72%). Melting point 142 °C. Anal. (%) Calcd for
C31H42AuF3O3P2S: C, 45.93; H, 5.52; N, 0. Found: C, 45.81; H,
5. 34; N, <0.3. 1H NMR (CD2Cl2): δ 7.85 (d,3JHH ) 7.5 Hz, 2H,
C4-H or C7-H), 7.62 (d,3JHH ) 7.5 Hz, 2H, C4-H or C7-H), 7.35
(m, 2H, C5-H or C6-H), 7.31 (t,3JHH ) 7.0 Hz, 2H, C5-H or C6-
Acknowledgment. Acknowledgment is made to the Natural
Sciences and Engineering Research Council (NSERC) of
Canada, the Canada Foundation for Innovation, the Nova Scotia
Research and Innovation 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 assistance in the acquisition of NMR data.
H), 7.26 (m, 2H, C2-H), 3.76 (s, 4H, CH2), 2.96 (virtual t of septets,
2/ 4
J
) 2.5 Hz,3JHH ) 7.0 Hz, 4H, P(CHCH3CH3)2), 1.43 (virtual
PH
3
3/5
d of t, JHH ) 7.0 Hz,
J
) 10.0 Hz, 12H, P(CHCH3CH3)2),
PH
3
3/5
1.28 (virtual d of t, JHH ) 7.0 Hz,
J
) 8.5 Hz, 12H,
PH
P(CHCH3CH3)2); 13C{1H} NMR (CD2Cl2): δ 150.8 (C2), 144.1
(C3a or C7a), 143.4 (C3a or C7a), 129.9 (m, C3), 126.7 (C5 or
C6), 126.5 (C5 or C6), 124.7 (C4 or C7), 121.1 (C4 or C7), 41.0
Supporting Information Available: Single-crystal X-ray dif-
fraction data in CIF format for 2, 4, 6, and [7]+OTf-. This material
is available free of charge via the Internet at http://pubs.acs.org.
3/5
1/3
(virtual t,
J
) 6 Hz, CH2), 25.2 (virtual t,
J
) 16 Hz,
PC
PC
P(CHCH3CH3)2), 20.0 (P(CHCH3CH3)2), 19.1 (P(CHCH3CH3)2);
31P{1H} NMR (CD2Cl2): δ 53.0.
OM060948N
Crystallographic Solution and Refinement Details. Crystal-
lographic data were obtained at 193((2) K on a Bruker PLATFORM/
(31) (a) Flack, H. D. Acta Crystallogr., Sect. A 1983, 39, 876. (b) Flack,
H. D.; Bernardinelli, G. Acta Crystallogr., Sect. A 1999, 55, 908.