Synthesis and structure of PNP-supported iridium silyl and silylene complexes: Catalytic hydrosilation of alkenes

Article abstract of DOI:10.1021/ja903737j

Oxidative addition of bulky primary, secondary, and tertiary silanes to PNP (PNP ) [N(2-PⁱPr₂-4-Me-C₆H₃) ₂]^-) iridium complexes (PNP)IrH₂ and (PNP)Ir(COE) (11) afforded iridium silyl hydride complexes (PNP)Ir(H) (SiRR′R″) (3-8). Addition of 2 equiv of PhSiH₃ or (3,5-Me₂C₆H₃)SiH₃ to (PNP)IrH ₂ or 11 yielded disilyl complexes (PNP)Ir(SiH₂R) ₂ (R ) Ph (9), 3,5-Me₂C₆H₃ (10)). Hydride abstraction from (PNP)Ir-(H)(SiH₂R) (R = Trip (5), Dmp (6)) by [Ph₃C][B(C₆F₅)₄] afforded iridium silylene complexes [(PNP)(H)Ir=SiR(H)][B(C₆F₅) ₄] (R ) Trip (12), Dmp (13)) exhibiting downfield ²⁹Si NMR resonances (234 ppm (12), 226 ppm (13)) and downfield 1H NMR resonances for the Si-H group (10.76 ppm (12), 9.76 ppm (13)). Thermally stable disubstituted silylene complexes [(PNP)(H)Ir=SiPh₂][A] (A = ^-B(C ₆F₅)₄ (14), ^-CB₁₁H ₆Br₆ (16)) were isolated via hydride abstraction from (PNP)Ir(H)(SiHPh₂). The X-ray structure of 16 confirmed sp ² hybridization at silicon and revealed a short Ir-Si bond of 2.210(2) A. Catalytic hydrosilation of alkenes by hydrogen-substituted silylene complexes [(PNP)(H)Ir=SiMes(H)][B(C₆F₅) ₄] (1) and 14 exhibited anti-Markovnikov regioselectivity with an array of alkene substrates. Addition of H₃SiMes to complex 1 afforded [(PNP)(SiH(Mes)(Hex))IrH(SiH₂Mes)][B(C₆F ₅)₄] (19), featuring a β-agostic interaction demonstrated by a J_SiH of 102 Hz for the N-SiH hydrogen. Similarly, addition of H₂SiPh₂ to 16 afforded the structurally characterized Ir(V) disilyl complex [(PNP)(SiPh₂)Ir(SiPh ₂H)(H)₂][CB₁₁H₆Br₆] (20). Complex 20 was found to be catalytically active for the hydrosilation of alkenes, which is consistent with its intermediacy in the catalytic cycle.

Full text of DOI:10.1021/ja903737j

Published on Web 07/15/2009
Synthesis and Structure of PNP-Supported Iridium Silyl and
Silylene Complexes: Catalytic Hydrosilation of Alkenes
Elisa Calimano and T. Don Tilley*
Department of Chemistry, UniVersity of California, Berkeley, California 94720
Received May 7, 2009; E-mail: tdtilley@berkeley.edu
Abstract: Oxidative addition of bulky primary, secondary, and tertiary silanes to PNP (PNP ) [N(2-PiPr2-
4-Me-C6H3)2]-) iridium complexes (PNP)IrH2 and (PNP)Ir(COE) (11) afforded iridium silyl hydride complexes
(PNP)Ir(H)(SiRR′R′′) (3-8). Addition of 2 equiv of PhSiH3 or (3,5-Me2C6H3)SiH3 to (PNP)IrH2 or 11 yielded
disilyl complexes (PNP)Ir(SiH2R)2 (R ) Ph (9), 3,5-Me2C6H3 (10)). Hydride abstraction from (PNP)Ir-
(H)(SiH2R) (R ) Trip (5), Dmp (6)) by [Ph3C][B(C6F5)4] afforded iridium silylene complexes [(PNP)(H)Ird
SiR(H)][B(C6F5)4] (R ) Trip (12), Dmp (13)) exhibiting downfield 29Si NMR resonances (234 ppm (12), 226
ppm (13)) and downfield 1H NMR resonances for the Si-H group (10.76 ppm (12), 9.76 ppm (13)). Thermally
stable disubstituted silylene complexes [(PNP)(H)IrdSiPh2][A] (A ) -B(C6F5)4 (14), -CB11H6Br6 (16)) were
isolated via hydride abstraction from (PNP)Ir(H)(SiHPh2). The X-ray structure of 16 confirmed sp2
hybridization at silicon and revealed a short Ir-Si bond of 2.210(2) Å. Catalytic hydrosilation of alkenes by
hydrogen-substituted silylene complexes [(PNP)(H)IrdSiMes(H)][B(C6F5)4] (1) and 14 exhibited anti-
Markovnikov regioselectivity with an array of alkene substrates. Addition of H3SiMes to complex 1 afforded
[(PNP)(SiH(Mes)(Hex))IrH(SiH2Mes)][B(C6F5)4] (19), featuring a ꢀ-agostic interaction demonstrated by a
JSiH of 102 Hz for the N-SiH hydrogen. Similarly, addition of H2SiPh2 to 16 afforded the structurally
characterized Ir(V) disilyl complex [(PNP)(SiPh2)Ir(SiPh2H)(H)2][CB11H6Br6] (20). Complex 20 was found to
be catalytically active for the hydrosilation of alkenes, which is consistent with its intermediacy in the catalytic
cycle.
unsaturated transition metal center.5 These synthetic routes have
provided a variety of transition metal silylene complexes,3,6 and
Introduction
Transition metal silylene complexes are of interest for their
potential role in catalytic transformations involving organosi-
lanes, such as the synthesis of chlorosilanes by the Direct
Process1 and the redistribution of organosilanes.2 Research on
transition metal silylene complexes has led to the development
of several synthetic strategies for accessing these previously
elusive species.3 Established, general synthetic strategies are
based on the chemical modification of silyl ligands by abstrac-
tion of an anionic substituent on the silyl ligand4 or by
R-hydrogen migration of a group from the silyl ligand to an
investigations on their stoichiometric reactivity have revealed
unusual transformations with small molecules such as chlori-
nated hydrocarbons,7 epoxides,8 nitriles,9 isocyanates,10 and
carbonyl compounds.5e,11
Thus, transition metal silylene complexes would seem to offer
the potential for a number of new, metal-mediated transforma-
tions of organosilicon compounds, but so far only a handful of
catalytic reactions have been shown to involve metal silylene
(5) Several examples of silylene complexes by R-migration chemistry: (a)
Rankin, M. A.; MacLean, D. F.; Schatte, G.; McDonald, R.; Stradiotto,
M. J. Am. Chem. Soc. 2007, 129, 15855–15864. (b) Peters, J. C.;
Feldman, J. D.; Tilley, T. D. J. Am. Chem. Soc. 1999, 121, 9871–
9872. (c) Mork, B. V.; Tilley, T. D. J. Am. Chem. Soc. 2004, 126,
4375–4385. (d) Mork, B. V.; Tilley, T. D.; Schultz, A. J.; Cowan,
J. A. J. Am. Chem. Soc. 2004, 126, 10428–10440. (e) Watanabe, T.;
Hashimoto, H.; Tobita, H. Angew. Chem., Int. Ed. 2004, 43, 218–
221. (f) Yoo, H.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 2006,
128, 6038–6039.
(1) (a) Walter, H.; Gerhard, R.; Bohmhammel, K. J. Chem. Soc., Faraday
Trans. 1996, 92, 4605–4608. (b) Acker, J.; Bohmhammel, K. J. Phys.
Chem. B 2002, 5105–5117. (c) Rochow, E. G.; Gilliam, W. F. J. Am.
Chem. Soc. 1941, 63, 798–800. (d) Seyferth, D. Organometallics 2001,
20, 4978–4992. (e) Okamoto, M.; Onodera, S.; Okano, T.; Suzuki,
E.; Ono, Y. J. Organomet. Chem. 1997, 531, 67–71.
(2) (a) Curtis, M. D.; Epstei, P. S. AdV. Organomet. Chem. 1981, 19,
213–255. (b) Kumaada, M. J. Organomet. Chem. 1975, 100, 127–
138. (c) Pestana, D. C.; Koloski, T. S.; Berry, D. H. Organometallics
1994, 13, 4173–4175. (d) Grumbine, S. K.; Tilley, T. D. J. Am. Chem.
Soc. 1994, 116, 6951–6952.
(6) Okazaki, M.; Tobita, H.; Ogino, H. Dalton Trans. 2003, 493–506.
(7) (a) Wanandi, P. W.; Glaser, P. B.; Tilley, T. D. J. Am. Chem. Soc.
2000, 122, 972–973. (b) Glaser, P. B.; Wanandi, P. W.; Tilley, T. D.
Organometallics 2004, 23, 693–704.
(3) Waterman, R.; Hayes, P. G.; Tilley, T. D. Acc. Chem. Res. 2007, 40,
712–719.
(8) Hashimoto, H.; Ochiai, M.; Tobita, H. J. Organomet. Chem. 2007,
692, 36–43.
(4) Several examples of silylene complexes by anion abstraction: (a)
Grumbine, S. K.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L. J. Am.
Chem. Soc. 1994, 116, 5495–5496. (b) Grumbine, S. K.; Mitchell,
G. P.; Straus, D. A.; Tilley, T. D. Organometallics 1998, 17, 5607–
5619. (c) Glaser, P. B.; Wanandi, P. W.; Tilley, T. D. Organometallics
2004, 23, 693–704. (d) Klei, S. R.; Tilley, T. D.; Bergman, R. G.
Organometallics 2002, 21, 3376–3387.
(9) Watanabe, T.; Hashimoto, H.; Tobita, H. J. Am. Chem. Soc. 2006,
128, 2176–2177.
(10) Mitchell, G. P.; Tilley, T. D. J. Am. Chem. Soc. 1997, 119, 11236–
11243.
(11) (a) Watanabe, T.; Hashimoto, H.; Tobita, H. J. Am. Chem. Soc. 2007,
129, 11338–11339. (b) Ochiai, M.; Hashimoto, H.; Tobita, H. Dalton
Trans. 2009, 1812–1814.
9
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J. AM. CHEM. SOC. 2009, 131, 11161–11173 11161

A R T I C L E S
Calimano and Tilley
Scheme 1
This complex has provided a second example of a silylene-
mediated, highly regioselective hydrosilation catalyst. In this
contribution, synthetic pathways to a variety of PNP-supported
iridium silyl and silylene complexes are presented, along with
detailed spectroscopic and structural characterizations of these
species. A more complete description of the hydrosilation
catalysis has been developed, and notably, complexes resulting
from addition of the silane substrate to a cationic iridium silylene
species have been characterized. These species appear to
represent the resting state of the hydrosilation catalyst and
provide insight into how the nitrogen donor atom of the PNP
ligand may play a role in bond activations and product formation
in (PNP)M complexes.
Results and Discussion
Synthesis and Characterization of (PNP)IrH(SiR3) Complexes
from (PNP)IrH2. Several synthetic routes to silylene complexes
are based on chemical transformations of transition metal silyl
precursors. A convenient route to silyl complexes utilizes the
oxidative addition of an Si-H bond to a transition metal.19,20
This approach permits access to a variety of substituents on
the resulting silyl ligands due to the commercial and synthetic
availability of a range of organosilane substrates. Previous
reports of bond activations by (PNP)IrH2 describe facile
oxidative additions of sp2 C-H bonds upon addition of
norbornene as a dihydrogen acceptor.21 Hence, (PNP)IrH2 was
envisioned as a good starting point for Si-H bond activation
routes to iridium silyl complexes, which might then serve as
precursors to cationic iridium silylene complexes.
The synthesis of (PNP)IrH(SiH2Mes) (2) from the reaction
of (PNP)IrH2 with MesSiH3 has been previously reported.17
Similarly, additions of silanes CySiH3, (C6F5)SiH3, TripSiH3
(Trip ) 2,4,6-iPr3C6H2), DmpSiH3 (Dmp ) 2,6-dimesitylphe-
nyl), Ph2SiH2, and Ph2SiHCl to (PNP)IrH2 in hexanes afforded
the iridium silyl hydride complexes 3-8, with the concomitant
evolution of dihydrogen gas (eq 1). The formation of these Ir(III)
silyl hydrides is quantitative by 1H NMR spectroscopy, and these
complexes can be crystallized from pentane or hexanes at -30
°C. In contrast to C-H activations, activations of Si-H bonds
by (PNP)IrH2 do not require a hydrogen acceptor.
complexes.12,13 A striking recent example involves the ruthe-
nium silylene complex [Cp*(PiPr3)(H)2RudSiH(Ph)][B(C6F5)4],
which is a catalyst for the regioselective hydrosilation of alkenes.
Notably, this catalysis proceeds by a previously unknown
mechanism and provides strictly anti-Markovnikov regioselec-
tivity for a variety of olefin substrates. This catalyst is also highly
selective for primary silane substrates and affords only secondary
silane products. Mechanistic investigations implicate a reaction
pathway involving the direct insertion of an alkene into the
Si-H bond of an H-substituted silylene complex,14 rather than
a more traditional Chalk-Harrod cycle (Scheme 1).15 Additional
experimental and computational studies suggest that this reactiv-
ity is strongly correlated with a positive charge on the silylene
complex, and in particular with a high degree of silylenium
character (resonance form B). Computational studies suggest
that electrophilicity at silicon promotes alkene binding to the
silylene ligand and subsequent insertion of the alkene into the
Si-H bond.16 This crucial Si-C bond-forming step produces
a new silylene ligand, and subsequent steps lead to release of
product and activation of the primary silane to produce another
H-substituted silylene ligand (Scheme 1). However, it should
be noted that, whereas the Si-H addition step has been
independently observed, little is known about the subsequent
steps in the catalytic cycle, and none have been observed.
To better understand this new type of hydrosilation reaction,
it is of interest to develop a variety of catalysts that function in
a similar manner, to further probe steric, electronic, and
mechanistic factors that are associated with this reactivity.
Recently, this effort has targeted cationic, H-substituted silylene
complexes such as the iridium silylene complex [(PNP)(H)Ird
SiMes(H)][B(C6F5)4]17 (1, PNP ) [-N(2-PiPr2-4-Me-C6H3)2],18
Mes ) 2,4,6-Me3C6H2), which was recently communicated.
Complexes 3-8 exhibit spectroscopic characteristics consis-
tent with the proposed structures in eq 1. The 1H NMR spectra
for 3-8 feature two methine resonances and four methyl
resonances for the isopropyl groups, indicating Cs symmetry.
(12) Klei, R. K.; Tilley, T. D.; Bergman, R. G. Organometallics 2002, 21,
4648–4661.
(13) Glaser, P. B.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 13640–
13641.
(14) (a) Beddie, C.; Hall, M. B. J. Am. Chem. Soc. 2004, 126, 13564–
13565. (b) Bo¨hme, U. J. Organomet. Chem. 2006, 691, 4400–4410.
(15) Chalk, A. J.; Harrod, J. F. J. Am. Chem. Soc. 1965, 87, 16–21.
(16) Hayes, P. G.; Beddie, C.; Hall, M. B.; Waterman, R.; Tilley, T. D.
J. Am. Chem. Soc. 2006, 128, 428–429.
(19) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175–292.
(20) (a) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rappoport,
Z., Eds.; Wiley: New York, 1991; Chapters 9, 10, pp 245-307, 309-
364. (b) Tilley, T. D. In The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24,
pp 1415-1477.
(17) Calimano, E.; Tilley, T. D. J. Am. Chem. Soc. 2008, 130, 9226–9227.
(18) Fan, L.; Yang, L.; Guo, C.; Foxman, B. M.; Ozerov, O. V.
Organometallics 2004, 23, 4778–4787.
(21) Fan, L.; Parkin, S.; Ozerov, O. V. J. Am. Chem. Soc. 2005, 127, 16772–
16773.
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Catalytic Hydrosilation of Alkenes
A R T I C L E S
Table 1. NMR Data for Complexes 3-8
the reaction of (PNP)IrH2 with an excess of the more sterically
encumbered H3SiMes exclusively afforded silyl hydride complex
2. Similarly, reaction of the primary silane H3SiPh produced
disilyl complex 9, whereas the disubstituted silane H2SiPh2
exclusively gave silyl hydride species 7, even in the presence
of excess silane.
complex
δ
1H (SiH)
δ
29Si (IrSi)
δ
1H (IrH)
(PNP)IrH(SiH2Cy) (3)
(PNP)IrH(SiH2(C6F5)) (4)
(PNP)IrH(SiH2Trip) (5)
(PNP)IrH(SiH2Dmp) (6)
(PNP)IrH(SiHPh2) (7)
(PNP)IrH(SiPh2Cl) (8)
4.07
4.60
5.02
4.39
6.28
N/A
–27.3
–79.0
–74.1
–50.9
–21.0
10.8
–20.76
–21.67
–21.24
–20.21
–19.83
–19.59
Synthesis of (PNP)IrH(SiR3) and (PNP)Ir(SiH2R)2 Complexes
from (PNP)IrCOE. Synthesis of an iridium(I) complex for use
in Si-H bond activations was achieved by addition of (PNP)Li24
to [(COE)2IrCl]2 in toluene, to produce the alkene complex
(PNP)IrCOE (11) in 64% yield (eq 3).
The 31P{1H} NMR spectra for these complexes reveal a single
resonance for the PNP ligand at 47-49 ppm. The 29Si NMR
shifts for 3-8 are indicative of the presence of a silyl ligand19
1
(Table 1). The H NMR shifts for the Si-H and Ir-H groups
are also tabulated in Table 1. Coupling between the iridium
hydride and the silicon atom was found to result in 2JSiH values
of less than 4 Hz for 4 and 8, and this is consistent with complete
oxidative addition of the Si-H bond.19
Single crystals of 6 were obtained by cooling a concentrated
hexanes solution to -30 °C. The X-ray structure of 6 reveals a
distorted trigonal bipyramid geometry about iridium with the
phosphorus atoms in the apical positions (Figure 1). The
P1-Ir1-P2 angle of 161.73(6)° is similar to those of other
iridium complexes with this rigid ligand framework.21 The Ir-Si
distance of 2.323(2) Å is comparable to the corresponding
distances in other structurally characterized iridium silyl com-
plexes.22 The hydride ligand was not located but is presumed
to occupy the remaining equatorial position of the trigonal
bipyramid. The N-Ir-Si angle of 140.1(2)° is wider than
expected for a trigonal bipyramid, as has been documented for
other PNP five-coordinate d6 complexes.23
At ambient temperature, the 1H NMR spectrum of 11 exhibits
two distinct resonances for the methyl substituents on the
aromatic rings of the ligand backbone, inequivalent aromatic
proton resonances for the ligand backbone, and broadened
resonances for the PCHMe2 groups. The 1H NMR spectrum of
11 at room temperature exhibits a resonance at 3.01 ppm,
identified as the alkene hydrogen of the cyclooctene ligand.
Variable-temperature NMR studies of 11 in toluene-d8 indicated
coalescence of these ligand resonances at 90 °C. The 31P{1H}
NMR spectrum of 11 gives rise to an AB quartet pattern, and
the observed JPP coupling constant of 351 Hz supports a trans
arrangement for the phosphorus nuclei. The 13C{1H} NMR shift
for the alkenyl carbon at 41.1 ppm is indicative of a π-basic
iridium center and a considerable amount of metallocyclopro-
pane character.25
Complex 11 crystallizes in the P21/n space group from a
concentrated pentane solution to -30 °C. The X-ray structure
depicts a slightly distorted square planar geometry about iridium
and a perpendicular binding of the cyclooctene ligand with
respect to the P-Ir-P-N plane (Figure 2). The distortion from
square planar geometry results from the rigidity of the coordina-
tion of the PNP ligand and leads to a P-Ir-P bond angle
(161.86(7)°) that is slightly reduced from linearity.
Synthesis and Characterization of (PNP)Ir(SiH2R)2 Complexes
from (PNP)IrH2. Addition of 2 equiv of PhSiH3 to (PNP)IrH2
in hexane led to the formation of disilyl iridium complex
(PNP)Ir(SiH2Ph)2 (9) as burgundy microcystals in 79% yield
(eq 2). The 1H NMR spectrum of 9 exhibits only one resonance
for the methine CH group and two resonances for the CHMe2
methyls, indicating the presence of two equivalent silyl groups
at iridium. The 29Si NMR spectrum features a single resonance
at -37.5 ppm for the silyl ligands. Similarly, (PNP)Ir-
H2 reacted with an excess of XylSiH3 (Xyl ) 3,5-Me2C6H3) to
give the disilyl iridium complex (PNP)Ir(SiH2Xyl)2 (10) in good
1
yield as a dark red solid (eq 2). H and 29Si NMR spectra for
10 reveal features similar to those of 9, including a 29Si NMR
resonance at -38.2 ppm for the silyl ligands.
Addition of H3SiMes and H2SiPh2 to 11 in hexanes at
ambient temperature resulted in the formation of 1 and 7,
respectively, and the release of cyclooctene. Similarly,
addition of 1 equiv of XylSiH3 to complex 11 in benzene-d6
afforded a mixture of the corresponding silyl hydride species
and disilyl complex 10. Thus, complex 11 is similar to
(PNP)IrH2 in its behavior as a precursor to a variety of
iridium silyl complexes. Furthermore, no hydrosilation of
(22) A search of the Cambridge Crystallographic Structure Database
revealed a range of 2.29-2.41 Å for Ir-Si bond lengths for iridium
silyl complexes.
The steric properties of the silane substrate dictate whether a
complex of the type (PNP)Ir(SiR3)2 or (PNP)IrH(SiR3) is
obtained from the reaction of excess silane with (PNP)IrH2 or
(PNP)IrCOE (Vide infra). The silyl hydride products are obtained
when the silane substrate used is di- or trisubstituted, or for
monosubstituted silanes containing a bulky substituent. Attempts
to isolate the silyl hydride complexes by dropwise addition of
1 equiv of PhSiH3 or XylSiH3 to (PNP)IrH2 in hexanes gave a
mixture of the disilyl and silyl hydride complexes. However,
(23) (a) Oliva´n, M.; Eisenstein, O.; Caulton, K. G. Organometallics 1997,
16, 2227–2229. (b) Riehl, J.-F.; Jean, Y.; Eisenstein, O.; Pe´lissier, M.
Organometallics 1992, 11, 729–737. (c) Lam, W. H.; Shimada, S.;
Batsanov, A. S.; Lin, Z.; Marder, T. B.; Cowan, J. A.; Howard,
J. A. K.; Mason, S. A.; McIntyre, G. J. Organometallics 2003, 22,
4557–4568.
(24) Weng, W.; Yang, L.; Foxman, B. C.; Ozerov, O. V. Organometallics
2004, 23, 4700–4705.
(25) Crabtree, R. H. The Organometallic Chemistry of Transition Metals,
4th ed.; Wiley-Interscience: New York, 2005.
9
J. AM. CHEM. SOC. VOL. 131, NO. 31, 2009 11163

A R T I C L E S
Calimano and Tilley
Table 2. NMR Data for Iridium Silylene Complexes 12-14
complex
δ
29Si (IrdSi)
δ
1H (SiH) 1H (IrH)
δ
[(PNP)(H)IrdSiH(Trip)][B(C6F5)4] (12)
[(PNP)(H)IrdSiH(Dmp)][B(C6F5)4] (13)
[(PNP)(H)IrdSiPh2][B(C6F5)4] (14)
233.9
226.6
264.8
10.76
9.75
N/A
-18.4
-20.4
-20.6
1
to the Si-H resonance via a 2D H,29Si HMBC NMR experi-
ment). Isolation of complex 12 was not successful due to its
rapid decomposition to a mixture of intractable products within
45 min at ambient temperature.
Figure 1. Molecular structure of 6 displaying thermal ellipsoids at the
50% probability level. H-atoms except for those attached to Si1 and
disordered hexanes have been omitted for clarity. Selected bond lengths
(Å): Ir1-Si1 ) 2.323(2), Ir1-N1 ) 2.060(6). Selected bond angles (deg):
N1-Ir1-Si1 ) 140.1(2), P1-Ir1-P2 ) 161.73(6).
Reaction of 6 with 1 equiv of [Ph3C][B(C6F5)4] in bromoben-
zene-d5 gave an intense blue-green solution, which contained
[(PNP)(H)IrdSiH(Dmp)][B(C6F5)4] (13) in 65% yield (by
1
integration of the Ir-H and Si-H signals in the H NMR
spectrum). Isolation of this compound was achieved by reaction
of 6 with 1 equiv of [Ph3C][B(C6F5)4] in fluorobenzene, and
the resulting blue-green solution was added to pentane at -30
°C to remove the triphenylmethane byproduct to give a blue
solid. Complex 13 is thermally sensitive and was observed to
undergo extensive decomposition over 19 h at -30 °C in
fluorobenzene. It is therefore difficult to isolate in pure form.
1
The H NMR spectrum of 13 exhibits complicated overlap-
ping signals with several diagnostic resonances that support the
formation of a hydrogen-substituted silylene complex. These
overlapping signals can be attributed to two rotamers of 13,
most likely arising from hindered rotation around the Ir-Si bond
due to steric constraints imposed by the bulky terphenyl
substituent. Two overlapping triplets at 9.75 ppm (1JSiH ) 206
Hz) are assigned to the Si-H group of 13 and correlate (by a
Figure 2. Molecular structure of 11 displaying thermal ellipsoids at the
50% probability level. H-atoms have been omitted for clarity. Selected bond
lengths (Å): C1-C2 ) 1.43(1), N1-Ir1 ) 2.067(5). Selected bond angles
(deg): P1-Ir1-P2 ) 161.86(7).
cyclooctene was observed at room temperature after forma-
tion of the silyl hydride or disilyl complexes.
1
2D H,29Si HMBC NMR experiment) to a broad 29Si NMR
Synthesis and Characterization of Iridium Silylene Complexes
[(PNP)(H)IrdSiRR′][B(C6F5)4]. Treatment of (PNP)IrH(SiH2Mes)
(2) with 1 equiv of [Ph3C][B(C6F5)4] afforded a cationic,
hydrogen-substituted silylene complex 1 via a hydride abstrac-
tion pathway, as previously communicated.17 Several attempts
to synthesize a larger family of PNP-supported iridium silylene
complexes via treatment of complexes 3 and 4 with [Ph3C]-
[B(C6F5)4] afforded intractable mixtures of products. For these
resonance at 226.6 ppm. The iridium hydrides give rise to a
1
second pair of overlapping peaks in the H NMR spectrum at
-20.49 and -20.43 ppm. The 31P{1H} NMR spectrum also
exhibits two overlapping signals at 54.6 and 54.4 ppm in a 2:1
ratio. Similarly, rotamers were observed for aryl complexes of
the type (PNP)IrH(Ar) (where Ar ) 2,5-Me2C6H3, 2-C6H4F,
and 2-C6H4Cl).21
Synthesis of a disubstituted iridium silylene complex was
achieved by a hydride abstraction from 7 by [Ph3C][B(C6F5)4]
to afford [(PNP)(H)IrdSiPh2][B(C6F5)4] (14) as a violet solid
in 97% yield after precipitation from pentane at -30 °C. The
1H NMR spectrum of 14 exhibits a hydride resonance at -20.6
ppm and no resonance for a Si-H group. The 29Si{1H} NMR
resonance at 264.8 ppm is indicative of a silylene ligand.
Furthermore, the coupling constant between the silicon center
and the iridium hydride ligand (∼10 Hz) is consistent with the
absence of a strong interaction between the hydride and silylene
ligands. Complex 14 is thermally stable in fluorobenzene at
ambient temperature for at least 3 weeks, unlike the hydrogen-
substituted analogues. The NMR data for complexes 12-14 are
summarized in Table 2.
1
mixtures, H NMR spectroscopy indicated the absence of the
characteristic downfield resonance associated with a hydrogen-
substituted silylene complex.26
Addition of [Ph3C][B(C6F5)4] to complex 5 in bromobenzene-
d5 initially produced a bright blue-green solution. Initial
decomposition was observed, as indicated by a color change to
brown within 10 min at ambient temperature. One of the species
in solution was identified by 1H and 29Si NMR spectroscopy as
the hydrogen-substituted silylene complex [(PNP)(H)IrdSiH-
(Trip)][B(C6F5)4] (12). The silylene ligand exhibits a 1H NMR
shift of 10.76 ppm (1JSiH ) 206.2 Hz) for the Si-H group and
a
29Si NMR resonance at 233.9 ppm (obtained by correlation
(26) (a) Mork, B. V.; Tilley, T. D. J. Am. Chem. Soc. 2004, 126, 4375–
4385. (b) Simons, R. S.; Gallucci, J. C.; Tessier, C. A.; Youngs, W. J.
J. Organomet. Chem. 2002, 654, 224–228.
A common synthetic route to cationic transition metal silylene
complexes involves the abstraction of an anionic substituent on
9
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Catalytic Hydrosilation of Alkenes
A R T I C L E S
a silyl ligand, such a chloride or triflate.3 However, treatment
of 8 with Li(Et2O)2B(C6F5)4 in bromobenzene-d5 at room
temperature gave no reaction, and heating to 75 °C gave an
intractable mixture of products rather than 14. Similarly, efforts
to facilitate anion exchange by treatment of 8 with AgOTf in
either dichloromethane-d2 or bromobenzene-d5 gave a complex
mixture of products, rather than the desired (PNP)IrH-
(SiPh2OTf). Thus, interestingly, the preferred method for
synthesis of [(PNP)(H)IrdSiRR′]+ silylene complexes involves
hydride abstraction. Hydride abstractions with [Ph3C][PF6] have
been employed for the synthesis of base-stabilized iron silylene
complexes Cp(CO)2FedSiMe(ArN) (ArN ) 2-(Me2NCH2)C6-
H4)27 and Cp(CO)2FedSiMe2 ·HMPA,28 but this synthetic route
has not been used to obtain base-free silylene complexes.
Previously reported examples of iridium silylene complexes
are limited to [Cp*(PMe3)(H)IrdSiR2][B(C6F5)4],29 [(PMe3)3(H)2
IrdSiMes2][MeB(C6F5)3],5b [(PEt3)3(H)2IrdSiH(Dmp)][B(C6-
F5)4],26b and [PhB(CH2PPh2)3](H)2IrdSiR2.5b Complexes 1, 12,
and 13 represent a significant contribution to the synthetic
accessibility of these rare hydrogen-substituted silylene com-
plexes, which include [Cp*(H)2Os)SiR(H)][B(C6F5)4] (R )
Trip,Dipp,Si(SiMe3)3,C6F5,H),30 [(PEt3)3(H)2IrdSiH(Dmp)][B(C6-
F5)4],26b Cp*(dmpe)(H)ModSiR(H) (R ) Ph, Mes, Bn),5d
[Cp*(dmpe)(H)2WdSiDipp(H)][B(C6F5)4],5c Cp*(CO)(H)Rud
SiH(C(SiMe3)3),31 and Cp*(CO)2(H)WdSiH(C(SiMe3)3).5e It is
apparent that the nature of the substituent on silicon has a large
effect on the stability of these complexes, and this is possibly
related to steric constraints imposed by the bulky PNP ligand.
Figure 3. Molecular structure of the cation in 16 displaying thermal
ellipsoids at the 50% probability level. H-atoms, carborane anion, and
fluorobenzene molecule have been omitted for clarity. Selected bond lengths
(Å): Ir1-Si1 ) 2.210(2), Ir1-N1 ) 2.022(5). Selected angles (deg):
Ir1-Si1-C1 ) 131.5(3), C1-Si1-C7 ) 108.3(3), C7-Si1-Ir1 )
120.2(2), N1-Ir1-Si1 ) 146.6(2).
X-ray-quality crystals of 16 were obtained from a concen-
trated solution of fluorobenzene via slow solvent evaporation
(Figure 3). Complex 16 cocrystallized with one disordered
molecule of fluorobenzene centered on an inversion center. The
crystal structure reveals no interaction between the CB11H6Br6
anion and the unsaturated silicon center. The Ir-Si bond
distance of 2.210(2) Å for 16 is very close to that observed for
structurally characterized silylene complexes of the type
[PhB(CH2PPh2)3](H)2IrdSiR2 (2.250(3) and 2.260(3) Å).5b The
sum of the bond angles about silicon is 360.0(8)°, a value that
is quite consistent with sp2 hybridization. The N-Ir-Si bond
angle of 146.6(4)° indicates a substantial distortion from a
trigonal bipyramidal coordination geometry, as observed for the
silyl hydride complex 6. Although the Ir-H hydrogen atom was
not located during the structure refinement, it would presumably
occupy the empty coordination site in the equatorial plane of
the distorted trigonal pyramid. In addition, the P2NIr and SiC2Ir
least-squares planes are nearly perpendicular; the angle between
these planes is 79.4°.
Stoichiometric and Catalytic Reactions of Alkenes with
Iridium Silylene Complexes. Addition of cyclooctene, 1-hexene,
or styrene to a solution of complex 1 resulted in rapid addition
of the alkene to the silylene ligand to produce disubstituted
silylene complexes [(PNP)(H)IrdSiMes(R)][B(C6F5)4] (R )
C8H15, (CH2)5CH3, CH2CH2Ph), with anti-Markovnikov regio-
chemistry.17 Furthermore, complex 1 serves as a catalyst for
the hydrosilation of alkenes with primary silane substrates, to
afford disubstituted silane products (RR′SiH2) with anti-Mark-
ovnikov selectivity. The disubstituted silane products are inactive
toward further hydrosilation.
Synthesis and Structure of [(PNP)(H)IrdSiRR′][CB11H6Br6]
Complexes. Attempts to crystallize iridium silylene complexes
1 and 14 from a variety of solvents were unsuccessful and led
to viscous oils instead of crystalline material. To improve the
crystallinity of these complexes, substitution of the tetrakis(pen-
tafluorophenyl)borate counteranion with other weakly coordinat-
ing anions was explored.32 The use of carborane anions was
encouraged by the reports of their utility in the crystallization
of silicon-based cations and their compatibility with cations
containing electrophilic silicon.33
Use of [Ph3C][CB11H6Br6] rather than [Ph3C][B(C6F5)4] in
the synthetic method of eq 4 allowed access to [(PNP)(H)Ird
SiH(Mes)][CB11H6Br6] (15) and [(PNP)(H)IrdSiPh2][CB11H6-
Br6] (16). The change in anion does not lead to significant
differences in the NMR spectroscopy of the complexes. Notably,
no significant shift was observed in the 29Si NMR resonances
of the silylene ligands for 15 and 16 versus 1 and 14, indicating
that in both cases there is little interaction between the anion
and the silicon center in solution. Furthermore, these compounds
are readily isolated as solids after multiple pentane washes,
whereas the analogous B(C6F5)4- salts gave foams after similar
procedures.
In addition to hydrosilation, complex 1 was found to promote
redistribution of both silane substrates and hydrosilation prod-
ucts. For example, heating a bromobenzene-d5 solution of
MesSiH3 with 2 mol % of 1 to 60 °C for 18 h resulted in
formation of Mes2SiH2 (6%), as determined by 1H NMR
spectroscopy. Under the same conditions, Hex2SiH2 was formed
in 20% yield from the redistribution of HexSiH3. Furthermore,
addition of PhSiH3 to a solution of 1 (2 mol %) in bromoben-
zene-d5 afforded Ph2SiH2 (17%) after 18 h at ambient temper-
ature. Due to this competitive redistribution, a mixture of silanes
(27) Kobayashi, H.; Ueno, K.; Ogino, H. Organometallics 1995, 14, 5490–
5492.
(28) Kobayashi, H.; Ueno, K.; Ogino, H. Chem. Lett. 1999, 239–240.
(29) Klei, S. R.; Tilley, T. D.; Bergman, R. G. Organometallics 2002, 21,
3376–3387.
(30) Glaser, P. B.; Tilley, T. D. Organometallics 2004, 23, 5799–5812.
(31) Ochiai, M.; Hashimoto, H.; Tobita, H. Angew. Chem., Int. Ed. 2007,
46, 8192–8194.
(32) For weakly coordinating anions, see review and references within:
Krossing, I.; Raabe, I. Angew. Chem., Int. Ed. 2004, 43, 2066–
2090.
(33) (a) Reed, C. A. Acc. Chem. Res. 1998, 31, 133–139. (b) Kim, K.-C.;
Reed, C. A.; Elliott, D. W.; Mueller, L. J.; Tham, F.; Lin, L.; Lambert,
J. B. Science 2002, 297, 825–827.
(34) Brown, H. C.; Sharp, R. L. J. Am. Chem. Soc. 1966, 88, 5851–5854.
9
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A R T I C L E S
Calimano and Tilley
is generally obtained from catalytic hydrosilation reactions by
1, and for this reason reduced yields of the hydrosilation
products were sometimes observed.
ligand at the iridium center. A similar dependence of the regiose-
lectivity of hydroboration on the steric properties of the borane
has been reported, with increasing steric crowding at the boron
center resulting in higher anti-Markovnikov selectivity.35,37 For
example, the regioselectivity for hydroboration of styrene by
dicyclohexylborane is 99% for the anti-Markovnikov product,
compared to 89% selectivity with diborane as the reagent.37b
This regioselectivity for stoichiometric Si-H addition to
alkenes is also observed in hydrosilation catalysis with the same
alkene substrates. Hydrosilations employing vinyltrimethylsilane
or p-chlorostyrene substrates were conducted using a 5 mol %
loading of 1 in bromobenzene-d5 at 50 or 60 °C (Table 3, entries
a and b). Exclusive formation of anti-Markovnikov products
was observed in these catalytic reactions, as with styrene as
the substrate. High yields were observed for these reactions
involving H3SiMes as the substrate, as the concurrent redistribu-
tion of this silane is relatively slow.
The catalytic hydrosilation reactions previously reported
involved a 5 mol % loading of catalyst 1. A lower catalyst
loading (1 mol %) was investigated for the hydrosilation of
MesSiH3 with 1-hexene in bromobenzene-d5 (Table 3, entry c).
This hydrosilation catalysis is slower but is complete after 18 h,
and the hydrosilation products are obtained in comparable yield.
In order to test for the activity of the catalyst after one catalytic
run, another 100 equiv of MesSiH3 and 1-hexene were added
to the reaction mixture, and this resulted in further formation
of product in 84% yield after 20 h at 60 °C (Table 3, entry d).
It should be noted, however, that the stability of the catalyst is
dependent on the nature of the silane substrate. For example, it
was found that use of PhSiH3 as a substrate with a 1 mol %
catalyst loading limited the recyclability of the catalyst, which
lost activity after one catalytic run, presumably due to decom-
position of the active catalyst under these conditions (Table 3,
entries e and f).
The disubstituted silylene complex 14 was investigated as a
catalyst for olefin hydrosilation, since it is easier than 1 to
prepare and store, given its greater thermal stability. Hydrosi-
lation runs were conducted using a 5 mol % loading of 14 with
equimolar amounts of silane and alkene in bromobenzene-d5
(Table 3, entries g and h). As shown in Table 3, complexes 14
and 1 catalyze alkene hydrosilation with comparable yields and
selectivities.
Mechanistic Investigations of Alkene Hydrosilation by
Iridium Silylene Complexes. The first step of alkene hydrosi-
lation catalysis by 1 is thought to involve formation of a
disubstituted silylene complex (such as 17 and 18) via reaction
of an H-substituted iridium silylene complex with an alkene.
Two possible mechanisms for the formation of the disubstituted
iridium silylene complexes from the reaction of alkenes might
be envisioned (Scheme 2): one involves direct insertion of the
alkene into the Si-H bond (path A), and a second possibility
involves insertion of the alkene into the Ir-H bond, followed
by migration of the resulting alkyl group to the unsaturated
silylene ligand and then R-hydrogen migration to regenerate a
silylene ligand (path B). The former mechanism is favored, as
it would explain the observed high selectivity for primary silane
substrates in hydrosilation catalysis by 1.
Previous mechanistic investigations for hydrosilation by
[Cp*(PiPr3)(H)2RudSiH(Ph)][B(C6F5)4] suggested that the reac-
tion with alkenes proceeds via direct insertion of the alkene
into the Si-H bond, analogous to the insertion of alkenes into
a B-H bond in hydroboration. The regioselectivity for hy-
droboration with simple boranes is dependent on the alkene
substrate. For example, hydroboration of styrene by diborane
produces a 81:19 ratio of anti-Markovnikov to Markovnikov
hydroboration products.34 In contrast, hydrogen-substituted
silylene complex 1 reacts with styrene in fluorobenzene at
ambient temperature to give [(PNP)(H)IrdSiMes(CH2CH2Ph)]-
[B(C6F5)4], isolated in quantitative yield as the only regioisomer
(by NMR spectroscopy). In addition, catalytic hydrosilation of
styrene with primary silanes (RSiH3, 5 mol % 1, bromobenzene-
d5, 16-46 h at 60 °C) afforded H2SiR(CH2CH2Ph) (34-77%)
as the only regioisomer.17 Similarly, [Cp*(PiPr3)(H)2RudSiH-
(Ph)][B(C6F5)4] catalyzes the hydrosilation of styrene with
PhSiH3 to produce H2SiPh(CH2CH2Ph) in >99% yield by NMR
spectroscopy.13
To further probe electronic factors that might influence the
regioselectivity of this hydrosilation, alkene substrates that have
been observed to afford a higher percentage of Markovnikov
borane additions were examined.35 For example, the hydrobo-
ration of trimethylvinylsilane with trimethylamineborane in
diethylene glycol at 80 °C is reported to give a 66:34 ratio of
ꢀ-trimethylsilylethanol to R-trimethylsilylethanol after oxidation
of the boranes to alcohols.36 Similarly, the hydroboration of
p-chlorostyrene by diborane afforded a 73:25 ratio of ꢀ- to
R-alcohol after oxidation.34 Addition of a slight excess of
vinyltrimethylsilane to 1 in C6H5F at room temperature afforded
the disubstituted silylene complex [(PNP)(H)IrdSi(Mes)(CH2CH2-
1
SiMe3)][B(C6F5)4] (17), isolated in 85% yield (eq 5). The H
NMR spectrum of 17 exhibits a hydride resonance at -18.63
ppm, and the 31P{1H} NMR spectrum contains a broad singlet
at 60.7 ppm. Two 29Si NMR resonances are observed for 17, at
-3.1 and 301.1 ppm, corresponding to the SiMe3 and the
silylene ligand, respectively. Similarly, addition of p-chlorosty-
rene to
1 in C6H5F at ambient temperature afforded
[(PNP)(H)IrdSi(Mes)(CH2CH2PhCl)][B(C6F5)4] (18) (PhCl
)
p-C6H4Cl), isolated in 82% yield (eq 5). Complex 18 exhibits
1
NMR resonances similar to those of 17, including a H NMR
resonance at -19.05 ppm for the hydride ligand, a broad
31P{1H} NMR resonance at 60.9 ppm, and a 29Si NMR
resonance at 293.3 ppm for the silylene ligand. The products
resulting from anti-Markovnikov addition for these alkene
subtrates are the only observed isomers for 17 and 18 by
2
multinuclear NMR spectroscopy. The JSiH coupling constants
associated with the silylene ligand and the Ir hydride for 17
and 18 are less than 10 Hz.
(35) Brown, H. C. Boranes in Organic Chemistry; Cornell University Press:
Ithaca, NY, 1972.
(36) Seyferth, D. J. Inorg. Nucl. Chem. 1958, 7, 152–153.
(37) (a) Vishwakarma, L. C.; Fry, A. J. Org. Chem. 1980, 45, 5306–5308.
(b) Zweifel, G.; Ayyangar, N. R.; Brown, H. C. J. Am. Chem. Soc.
1963, 85, 2072–2075. (c) Brown, H. C.; Zweifel, G. J. Am. Chem.
Soc. 1961, 83, 1241–1246.
The very high anti-Markovnikov regioselectivity for catalysis
by 1 may result from the steric crowding provided by the PNP
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Catalytic Hydrosilation of Alkenes
A R T I C L E S
Table 3. Results of Catalytic Trials for Alkene Hydrosilation
entry
silane
alkene
catalyst (mol %)
time (h)
product
yield (%)
a
b
c
d
e
f
g
h
i
H3SiMes
H3SiMes
H3SiMes
H3SiMes
H3SiPh
p-chlorostyrene
vinyltrimethylsilane
1-hexene
1-hexene
styrene
styrene
1-hexene
1-hexene
1-hexene
1 (5)
1 (5)
20
24a
20
19
20
38
16
3.5
3
H2SiMes(CH2CH2PhCl)
H2SiMes(CH2CH2SiMe3)
H2SiMes(Hex)
73
66
78
84
30
11
74
52
81
1 (1)
1 (1)b
1 (1)
H2SiMes(Hex)
H2SiPh(CH2CH2Ph)
H2SiPh(CH2CH2Ph)
H2SiMes(Hex)
H2Si(Hex)2
H2SiMes(Hex)
H3SiPh
1 (1)b
14 (5)
14 (5)
20 (5)
H3SiMes
H3SiHex
H3SiMes
a Catalysis conducted at 50 °C. b After addition of second substrate.
Scheme 2
Addition of 1 equiv of H3SiMes to [(PNP)(H)IrdSi(Mes)Hex]-
[B(C6F5)4] in fluorobenzene at ambient temperature produced
a color change to light blue. The reaction mixture was then
added to pentane at -30 °C, and a light blue oil settled out
after 1 h at -30 °C. The solvent was decanted to remove the
organic components, and the remaining oil was dried under
vacuum to give a light blue solid. Multinuclear NMR spectros-
copy of this mixture led to the proposed structure for the major
1
organometallic species (19) depicted in eq 6. The H NMR
spectrum of 19 exhibits two resonances at 4.78 and 4.68 ppm
assigned to diasterotopic Si-H hydrogens of an Ir-SiH2Mes
group, as indicated by a large one-bond JSiH coupling constant
In subsequent steps of the catalytic cycle, product release and
regeneration of an H-substituted silylene ligand would involve
reactions with the incoming silane substrate. Computational
studies on the hydrosilation of alkenes by [Cp*(PiPr3)(H)2-
RudSiH(Ph)][B(C6F5)4] suggest that, after addition of the alkene
CH2dCHR to form [Cp*(PiPr3)(H)2RudSi(CH2CH2R)-
(Ph)][B(C6F5)4], the catalytic cycle proceeds via migration of a
hydride ligand to silicon, followed by binding of the silane
substrate to the ruthenium center.14 These studies also suggest
that product release and regeneration of the silylene ligand occur
by low-barrier rearrangements involving several intermediates
that contain silyl and hydride groups and exhibit nonclassical
Si· · ·H interactions. Experimentally, the reaction of a silylene
complex with a hydrosilane has been characterized for the
reaction of PhSiH3 with Cp*(dmpe)(H)ModSiH(Ph), to afford
the disilyl complex Cp*(dmpe)Mo(H)(SiH2Ph)2 via initial
R-hydrogen migration to the silylene ligand followed by Si-H
activation of the free silane.5d
1
of ca. 180 Hz. The H NMR spectrum of 19 also exhibits two
upfield resonances at -5.81 and -11.94 ppm. The resonance
at -5.81 ppm is assigned to a ꢀ-agostic Si-H group on the
basis of observable silicon satellites (JSiH ) 102 Hz) in
conjunction with the unusual, relative downfield shift for a
hydride resonance in this system.38 The resonance at -11.94
ppm is identified as an iridium hydride ligand with a small 2JSiH
coupling constant of 8 Hz, indicating little to no interaction
1
between this hydride and silicon atom. A 2D H,29Si HMBC
experiment revealed a resonance at -78.1 ppm attributed to
the Ir-SiH2Mes group, via correlation with the diasterotopic
Si-H signals, and a resonance at 0.83 ppm attributed to the
nitrogen-bound silyl group, via a correlation with the ꢀ-agostic
Si-H signal. In addition, the 31P{1H} NMR spectrum of 19
displays two doublets at 39.8 and 9.9 ppm for inequivalent
phosphorus atoms. The JPP coupling constant of 244.6 Hz is
slightly decreased from that observed for 11, implying a small
deviation from a trans arrangement of the phosphorus atoms.
Some of the unidentified organometallic species are likely
isomers of complex 19, as these give rise to similar features in
the hydride region of the 1H NMR spectrum. Thus, 19 appears
to result from migration of a silylene group to the nitrogen atom
of the PNP ligand. A similar migratory insertion, of a carbene
into the Ir-N bond of an iridium PNP complex, was previously
documented by Grubbs and co-workers as resulting from
reaction of carbon monoxide with (PNP)IrdCH(OtBu).39
To gain insight into the nature of silane activation by a
PNP-iridium silylene complex, a slight excess of H3SiMes was
added to a bromobenzene-d5 solution of [(PNP)(H)IrdSi(Mes)-
Hex][B(C6F5)4] (obtained from the reaction of 1-hexene with
1), and the resulting reaction was monitored by multinuclear
NMR spectroscopy at ambient temperature. Upon addition of
the silane, a color change from intense to pale blue was
observed. 1H and 31P{1H} NMR spectroscopy revealed forma-
tion of one major organometallic product (19, 33-43%),
H2SiMes(Hex) (39%), and several unidentified organometallic
species. In a related experiment, 1-hexene and H3SiMes were
added to a 5 mol % loading of 1 in bromobenzene-d5 at room
temperature, and the resulting solution was monitored over 3
days by NMR spectroscopy. After 4 h, the formation of
H2SiMes(Hex) (19%) was observed, and the 31P{1H} spectrum
revealed the presence of 19 in solution as the major iridium-
containing species. Over the course of 72 h, all of the silane
substrate was consumed, and the major Ir-based species remain-
ing was 19 (by 31P{1H} NMR spectroscopy). Notably, complex
1 was not observed during the catalytic reaction, and 19 appears
to be the resting state in the catalytic mixture.
Attempts to crystallize 19 gave oils instead of crystalline
material, even when employing CB11H6Br6 as the anion. For
this reason, an analogue to 19 was synthesized by reaction of
an excess of H2SiPh2 with 16 in C6H5F to afford
[(PNP)(SiPh2)Ir(SiPh2H)(H)2][CB11H6Br6] (20) in 86% yield as
9
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A R T I C L E S
Calimano and Tilley
off-white crystals from vapor diffusion of hexanes into an
1
o-C6H4Cl2 solution. The H NMR spectrum for 20 at ambient
temperature contains broadened signals for the PNP, silyl, and
1
hydride ligands, suggesting a dynamic process. The H NMR
spectrum at low temperature (-70 °C) contains sharp signals
for the Si-H hydrogen and for the iridium hydrides, although
there are several broad resonances in the aromatic region. The
Si-H resonance at -70 °C appears at 5.56 ppm as a doublet
of doublets due to couplings to phosphorus (JPH ) 21.6 Hz)
and one of the hydride ligands (JHH ) 2.9 Hz). The inequivalent
iridium hydride ligands give rise to resonances at -11.31 ppm
(1JPH ) 111.7 Hz, indicating a trans arrangement with a
phosphorus atom) and -11.95 ppm (as a broad singlet). In
contrast to 19, both Ir-H resonances of 20 appear upfield of
-10 ppm and exhibit small JSiH values (e10 Hz), suggesting
full Si-H oxidative addition to the iridium center. The 29Si
NMR spectrum for 20 exhibits resonances at 6.1 and -37.3
ppm, for the nitrogen-bound silylene group (N-SiPh2) and the
silyl ligand (SiPh2H), respectively. Thus, the NMR data for 20
indicate that this compound is better described as an Ir(V) disilyl
dihydride complex. The 31P{1H} NMR spectrum for 20 contains
two doublets with a small JPP coupling constant of 17.1 Hz,
indicating a cis relationship between the phosphorus atoms, in
contrast to complex 19, where a trans geometry is indicated. A
small impurity (∼10%) gives rise to a second set of SiH (1H)
and IrH (2H) signals, suggesting the presence of a second
regioisomer (20b), and this is consistent with an occupational
disorder observed in the crystal structure (Vide infra).
Figure 4. Molecular structure of the cation in 20, displaying thermal
ellipsoids at the 50% probability level. H-atoms, the carborane anion, and
Si2B have been omitted for clarity. Selected bond lengths (Å): Ir1-Si1 )
2.318(2), Ir1-Si2A ) 2.365(2), Ir1-N1 ) 2.294(4), N1-Si1 ) 1.795(5).
Selected angles (deg): P1-Ir1-P2 ) 102.39(5), Si1-Ir1-Si2A ) 121.01(6),
N1-Ir1-Si1 ) 45.8(1).
Scheme 3
The structure of 20 was confirmed by single-crystal X-ray
crystallography; however, the hydride ligands were not located
from the difference Fourier map (Figure 4). The X-ray structure
confirms N-Si bond formation, consistent with the NMR
assignments for complexes 19 and 20. The Ir1-Si1 distance of
2.318(2) Å and the Ir1-Si2A distance of 2.365(2) Å are within
the expected range for iridium silyl Ir-Si bond lengths.22 The
Ir1-N1 distance at 2.294(4) Å is elongated with respect to that
observed for 16 but still within bonding distance of the iridium
center. The PNP ligand is bound in a facial manner to the iridium
center, with the phosphorus donors in a cis arrangement. The
silyl group on iridium is disordered such that it occupies two
positions in an 85:15 ratio. This disorder is likely due to the
cocrystallization of both regioisomers of 20.
The results presented above suggest that the N donor atom
of PNP complexes may play an important role in substrate
activation. In particular, the migration of hydride or silyl ligands
to the N atom may provide lower energy pathways for bond
activations, which avoid high coordination numbers and high
valence states for iridium. A possible mechanism that illustrates
the potential role of the PNP amido group in alkene hydrosilation
is shown in Scheme 3. The involvement of the amido group of
a PNP ligand in bond activations by transition metal complexes
has been proposed for dihydrogen activation,40 intramolecular
CH activation,41 hydrogenation of ketones,42 and migratory
insertions of carbonyl,43 vinylidene,44 and carbene ligands.39
As a first step in the proposed mechanism of Scheme 3,
reaction of an alkene with the hydrogen-substituted silylene
complex generates the disubstituted silylene complex. This step
has been observed in stoichiometric reactions for this system
and in related reactions of [Cp*(PiPr3)(H)2RudSiH(Ph)]-
[B(C6F5)4],13 [Cp*(PiPr3)(H)2Os)SiH(Trip)][B(C6F5)4],13 and
[PhB(CH2PPh2)3](H)2IrdSiH(Mes).5b The disubstituted silylene
could be in equilibrium with a cationic silyl intermediate A via
an R-migration step.3 This equilibrium would strongly favor
the silylene isomer, as A was not observed in solution by NMR
spectroscopy. For the next step, involving activation of the silane
substrate, two possibilities are illustrated. One involves oxidative
The catalytic competence of 20 in alkene hydrosilation was
examined by subjecting it to the same catalytic conditions
employed for 1. Thus, H3SiMes and 1-hexene were combined
with a 5 mol % loading of 20 in bromobenzene-d5 (Table 3,
entry i). After 3 h at 60 °C, complete conversion of the substrates
to H2SiMes(Hex) was observed, with high yields similar to those
observed with 1 and 14 as catalysts. Therefore, complex 20 is
an efficient precatalyst for alkene hydrosilation. Furthermore,
addition of 2 equiv of (p-tolyl)2SiH2 to 20 in bromobenzene-d5
followed by heating at 60 °C for 19 h gave a mixture of silane
products including H2SiPh2 and H2SiPh(p-tolyl) (26 and 30%
1
yield vs 20, respectively) as determined by H NMR spectros-
copy and GC/MS, revealing the ability of 20 to promote silane
redistribution.
9
11168 J. AM. CHEM. SOC. VOL. 131, NO. 31, 2009

Catalytic Hydrosilation of Alkenes
A R T I C L E S
addition of the silane to produce an Ir(V) disilyl hydride species
B. A second pathway involves binding of the silane substrate,
accompanied by migration of the silyl ligand to the amido
nitrogen to create an open coordination site. This could produce
a σ-complex such as C, which would proceed to oxidative
addition product D. Structure D might be stabilized by a
secondary interaction of the Si-H bond of the silyl amido ligand
with the iridium center, as observed in complexes 19 and 20
(depicted in Scheme 3 in a simplified form without this
interaction). Elimination of the silane product may proceed
directly from D via a concerted transition state (E) or from the
disilyl hydride complex B by reductive elimination. Eliminations
of the type shown for E have been proposed for early transition
metal complexes.45 Regeneration of the H-substituted silylene
could proceed by a second R-migration from coordinatively
unsaturated silyl intermediate F. Note that a competitive reaction
of the hydrogen-substituted silylene complex with more silane,
prior to reaction with the alkene, could also be operative and
could result in catalyst inhibition and/or unproductive side
reactions.
Iridium silylene complexes 1 and 14 catalyze the regiose-
lective hydrosilation of alkenes, thus providing a second example
of silylene complexes acting as catalysts for this reaction. Similar
to catalysis with [Cp*(PiPr3)(H)2RudSiH(Ph)][B(C6F5)4], the
only other known silylene catalyst for this reaction, hydrosila-
tions mediated by 1 and 14 feature selectivity for primary silane
substrates and exclusive anti-Markovnikov selectivity. Previous
studies of hydrosilation mediated by [Cp*(PiPr3)(H)2RudSiH-
(Ph)][B(C6F5)4] suggest a mechanism in which the alkene inserts
into the Si-H bond in a manner analogous to that in hydrobo-
ration. This is consistent with the presence of a cationic silylene
complex that possesses significant silylenium character and an
empty orbital at silicon that allows interaction with an alkene
as an incoming nucleophile. Similarly, investigations on the
regioselectivity of hydrosilations catalyzed by 1 demonstrate
strict anti-Markovnikov selectivity, even with vinyltrimethyl-
silane and p-chlorostyrene. The observed regioselectivity is
similar to that of hydroboration with sterically hindered borane
reagents, suggesting that the sterics at the transition metal
fragment might contribute to the observed regioselectivity.
Investigations of stoichiometric reactions between silane
substrates and iridium silylene complexes indicate that the
catalytic reaction involves interesting silyl complexes of iridium
that possess Si-N bonds. These complexes are catalytically
competent and appear to represent the resting state for the
catalyst. Thus, it is of interest to design related catalysts based
on pincer ligands that do not contain a donor amido group.
Especially since structural variations in pincer ligands of this
type should influence the behavior of related hydrosilation
catalysts, research along such directions is ongoing.
Concluding Remarks
Suitable silyl hydride precursors for the synthesis of iridium
silylene complexes are readily accessed via Si-H activations
by (PNP)IrH2 or (PNP)IrCOE. There is a limitation in the
availability of silyl hydride precursors to silylene complexes
with this system, as small monosubstituted silanes give disilyl
species from the reaction of 2 equiv of silanes with (PNP)Ir
starting materials. Hydride abstractions from the silyl hydride
precursors afford cationic iridium silylene complexes, and the
substitution pattern at the silylene ligand is important in
determining the thermal stability of the complex.
Experimental Section
General Considerations. All experiments were carried out under
a nitrogen atmosphere using standard Schlenk techniques or an inert
atmosphere (N2) glovebox. Olefin impurities were removed from
pentane by treatment with concentrated H2SO4, 0.5 N KMnO4 in 3
M H2SO4, and NaHCO3. Pentane was then dried over MgSO4,
stored over activated 4 Å molecular sieves, and dried over alumina.
Thiophene impurities were removed from benzene and toluene by
treatment with H2SO4 and saturated NaHCO3. Benzene and toluene
were then dried over CaCl2 and further dried over alumina.
Tetrahydrofuran, diethyl ether, dichloromethane, and hexanes were
dried over alumina. Fluorobenzene was dried over P2O5, degassed,
and distilled under N2. Benzene-d6 was dried by vacuum distillation
from Na/K alloy. C6D5Br was refluxed over CaH2 for 20 h and
then distilled under nitrogen. Methylene chloride-d2 was dried by
vacuum distillation from CaH2. (PNP)IrH2,21 H3SiMes,46
H3SiTrip,47 H3SiDmp,48 [Ph3C][B(C6F5)4],49 and [Ph3C][CB11H6-
Br6]50 were prepared according to literature methods. Hydrosilanes
were prepared via lithium aluminum hydride reduction of the
corresponding chlorosilane. All other chemicals were purchased
from commercial sources and used without further purification.
NMR spectra were recorded using Bruker DRX-500, AV-500,
(38) For examples of Si-H ꢀ-agostic interactions, see: (a) Peulecke, N.;
Ohff, A.; Kosse, P.; Tillack, A.; Spannenberg, A.; Kempe, R.;
Baumann, W.; Burlakov, V. V.; Rosenthal, U. Chem. Eur. J. 1998, 4,
1852–1861. (b) Delpech, F.; Sabo-Etienne, S.; Donnadieu, B.; Chau-
dret, B. Organometallics 1998, 17, 4926–4928. (c) Dioumaev, V. K.;
Carroll, P. J.; Berry, D. H. Angew. Chem., Int. Ed. 2003, 42, 3947–
3949. (d) Nikonov, G. I.; Mountford, P.; Green, J. C.; Cooke, P. A.;
Leech, M. A.; Blake, A. J.; Howard, J. A. K.; Lemenovskii, D. A.
Eur. J. Inorg. Chem. 2000, 1917–1921. (e) Nikonov, G. I.; Mountford,
P.; Kuzmina, L. G.; Howard, J. A. K.; Lemenovskii, D. A.; Roiter-
shtein, D. M. J. Organomet. Chem. 2001, 628, 25–29. (f) Nikonov,
G. I.; Mountford, P.; Ignatov, S. K.; Green, J. C.; Leech, M. A.;
Kuzmina, L. G.; Razuvaev, A. G.; Rees, N. H.; Blake, A. J.; Howard,
J. A. K.; Lemenovskii, D. A. J. Chem. Soc., Dalton Trans. 2001, 2903–
2915. (g) Ignatov, S. K.; Rees, N. H.; Dubberley, S. R.; Razuvaev,
A. G.; Mountford, P.; Nikonov, G. I. Chem. Commun. 2004, 952–
953. (h) Khalimon, A. Y.; Simionescu, R.; Kuzmina, L. G.; Howard,
J. A. K.; Nikonov, G. I. Angew. Chem., Int. Ed. 2008, 47, 7701–
7704.
(39) Whited, M. T.; Grubbs, R. H. Organometallics 2008, 27, 5737–5740.
(40) (a) Fryzuk, M. D.; MacNeil, P. A. Organometallics 1983, 2, 682–
684. (b) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. Organometallics
1985, 4, 1145–1147. (c) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J.
J. Am. Chem. Soc. 1987, 109, 2803–2812. (d) Fryzuk, M. D.;
Montgomery, C. D.; Rettig, S. J. Organometallics 1991, 10, 467–
473. (e) Ozerov, O. V.; Huffman, J. C.; Watson, L. A.; Caulton, K. G.
Organometallics 2003, 2539–2541.
1
AVB-400, and AVQ-400 spectrometers. H NMR spectra were
referenced internally by the residual solvent proton signal relative
to tetramethylsilane. 13C{1H} NMR spectra were referenced inter-
nally relative to the 13C signal of the NMR solvent relative to
(41) Fryzuk, M. D.; Huang, L.; McManus, N. T.; Paglia, P.; Rettig, S. J.;
White, G. S. Organometallics 1992, 11, 2979–2990.
(42) (a) Clarke, Z. E.; Maragh, P. T.; Dasgupta, T. P.; Gusev, D. G.; Lough,
A. J.; Abdur-Rashid, K. Organometallics 2006, 25, 4113–4117. (b)
Bi, S.; Xie, Q.; Zhao, X.; Zhao, Y.; Kong, X. J. Organomet. Chem.
2008, 693, 633–638.
(46) Soldner, M.; Sandor, M.; Schier, A.; Schmidbaur, H. Chem. Ber. 1997,
130, 1671–1676.
(47) Smit, C. N.; Bickelhaupt, F. Organometallics 1987, 6, 1156–1163.
(48) Simons, R. S.; Haubrich, S. T.; Mork, B. V.; Niemeyer, M.; Power,
P. P. Main Group Chem. 1998, 2, 275–283.
(43) Fryzuk, M. D.; MacNeil, P. A. Organometallics 1982, 1, 1540–1541.
(44) Walstrom, A. N.; Watson, L. A.; Pink, M.; Caulton, K. G. Organo-
metallics 2004, 23, 4814–4816.
(49) Scott, V. J.; Celenligil-Cetin, R.; Ozerov, O. V. J. Am. Chem. Soc.
2005, 127, 2852–2853.
(45) (a) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9–16. (b) Gountchev,
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116, 1907–1913.
9
J. AM. CHEM. SOC. VOL. 131, NO. 31, 2009 11169

A R T I C L E S
Calimano and Tilley
tetramethylsilane. 19F{1H} spectra were referenced relative to a C6F6
external standard. 31P{1H} spectra were referenced relative to an
85% H3PO4 external standard. 29Si NMR spectra were referenced
relative to a tetramethylsilane standard and obtained via 2D 1H 29Si
HMBC unless specified otherwise. All spectra were recorded at
room temperature unless otherwise noted. Virtual quartets are
denoted as “vq”, complex multiplets as “m”, and broad resonances
as “br”. In 13C{1H} NMR spectra, resonances obscured by the
solvent signal are omitted. Elemental analyses were performed at
the College of Chemistry Microanalytical Laboratory, University
of California, Berkeley.
CHMe2), 2.62 (2H, br m, CHMe2), 2.19 (6H, s, ArMe), 2.18 (2H,
br, CHMe2), 1.45 (12H, d, J ) 6.6 Hz, Trip CHMe2), 1.30 (6H, d,
J ) 6.9 Hz, Trip CHMe2), 1.20 (6H, vq, CHMe2), 1.10 (6H, vq,
CHMe2), 0.97 (12H, br m, CHMe2), -21.24 (1H, t, 2JPH ) 9.2 Hz,
IrH). 13C{1H} NMR (C6D6, 125.8 MHz): δ 163.6 (t, JCP ) 10.5
Hz), 155.2, 149.2, 135.7, 132.5, 131.8, 128.8, 126.9 (t, JCP ) 3.4
Hz), 124.4 (t, JCP ) 20.8 Hz), 120.4, 115.6 (t, JCP ) 4.8 Hz), 34.9
(s, Trip CHMe2), 33.3 (s, Trip CHMe2), 25.8 (br m, CHMe2), 24.9
(s, Trip CHMe2), 24.4 (s, Trip CHMe2), 23.5 (br m, CHMe2), 20.4
(s, ArMe), 19.0 (br, CHMe2), 18.4 (br, CHMe2), 18.2 (br, CHMe2),
16.9 (br, CHMe2). 31P{1H} NMR (C6D6, 202.5 MHz): δ 47.2 (s).
29Si NMR (C6D6, 99.4 MHz): δ -74.1. Anal. Calcd for
C41H66NIrP2Si: C, 57.58; H, 7.78; N, 1.64. Found: C, 57.79; H,
7.63; N, 1.82.
(PNP)IrH(SiH2Dmp) (6). A solution of (Dmp)SiH3 (0.143 g, 0.42
mmol) in 3 mL of hexanes was added to a solution of (PNP)IrH2
(0.259 g, 0.42 mmol) in 10 mL of hexanes. Upon addition of the
silane, rapid evolution of dihydrogen gas was observed. After
standing at ambient temperature for 30 min, the solution was
concentrated (ca. 3 mL) until initial crystal formation was observed
and then placed in a -30 °C freezer over 18 h to afford bright
orange crystals. Yield: 0.320 g (80%). 1H NMR (C6D6, 500 MHz):
δ 7.60 (2H, d, J ) 8.4 Hz, ArH), 7.20 (1H, t, J ) 7.6 Hz, ArH),
6.99 (4H, overlapping signals, ArH), 6.88 (4H, s, ArH), 6.78 (2H,
d, J ) 8.3 Hz), 4.39 (2H, t, 3JPH ) 4.4 Hz, 1JSiH ) 185.6 Hz, SiH),
2.36 (12H, s, ArMe), 2.22 (6H, s, ArMe), 2.20 (6H, s, ArMe), 2.15
(2H, m, CHMe2), 2.01 (2H, m, CHMe), 1.12 (6H, vq, CHMe2),
1.02-0.9 (18H, overlapping signals, CHMe2), -20.21 (1H, t, 2JPH
) 8.7 Hz, Ir-H). 13C{1H} NMR (C6D6, 125.8 MHz): δ 163.6 (t,
JCP ) 10.2 Hz, ArC), 149.0 (s, ArC), 142.0 (s, ArC), 141.7 (s,
ArC), 136.7 (s, ArC), 135.7 (s, ArC), 133.0 (s, ArC), 131.6 (s,
ArC), 129.6 (s, ArC), 128.5 (s, ArC), 126.4 (t, JCP ) 3.3 Hz, ArC),
124.3 (t, JCP ) 21.2 Hz, CHMe2), 22.2 (s, ArMe), 21.1 (s, ArMe),
20.6 (s, CHMe2), 20.4 (s, ArMe), 19.3 (s, CHMe2), 18.6 (s, CHMe2),
17.5 (s, CHMe2). 31P{1H} NMR (C6D6, 163.0 MHz): δ 47.3 (s).
29Si (C6D6, 99.4 MHz) NMR: δ -50.9. Anal. Calcd for
C50H68NIrP2Si: C, 62.21; H, 7.10; N, 1.45. Found: C, 62.37; H,
7.27; N, 1.83.
(PNP)IrH(SiH2Cy) (3). A solution of CySiH3 (0.018 g, 0.16
mmol) in 1 mL of hexanes was added dropwise to (PNP)IrH2 (0.100
g, 0.16 mol) in 4 mL of hexanes. Upon addition of the silane, rapid
evolution of dihydrogen gas was observed. After 30 min at ambient
temperature, the reaction mixture was filtered, evaporated to
dryness, and lyophilized in 2 mL of benzene to give a dark orange
powder. Yield: 0.094 g (85%). 1H NMR (C6D6, 500 MHz): δ 7.76
(2H, d, J ) 8.5 Hz, ArH), 7.01 (2H, br s, ArH), 6.86 (2H, d, J )
1
8.4 Hz, ArH), 4.07 (2H, br m, JSiH ) 168.4 Hz, SiH), 2.71 (2H,
m, CHMe2), 2.35 (2H, br d, J ) 12.8 Hz, CH2), 2.20 (6H, s, ArMe),
2.20 (2H, ov m, CHMe2), 1.94 (2H, br d, J ) 11.1 Hz, CH2), 1.82
(1H, br m, CH2), 1.54-1.43 (5H, ov m, CH2), 1.25 (6H, vq,
CHMe2), 1.19 (6H, vq, CHMe2), 1.11 (6H, vq, CHMe2), 1.05 (1H,
2
m, CH), 0.95 (6H, vq, CHMe2), -20.76 (t, JPH ) 9.2 Hz, IrH).
13C{1H} NMR (C6D6, 125.8 MHz): δ 163.8 (t, JCP ) 10.8 Hz),
132.8, 131.9, 126.7 (t, JCP ) 3.4 Hz), 124.2 (t, JCP ) 21.0 Hz),
115.6 (t, JCP ) 5.1 Hz) (ArC), 32.3 (s, CH2), 29.6 (s, CH), 29.3
(CH2), 27.6 (CH2), 25.6 (t, JCP ) 15.7 Hz, CHMe2), 23.6 (t, JCP
)
14.6 Hz, CHMe2), 20.4 (s, ArMe), 19.7 (s, CHMe2), 19.0 (s,
CHMe2), 18.4 (s, CHMe2), 16.8 (s, CHMe2). 31P{1H} NMR (C6D6,
202.5 MHz): δ 49.0 (s). 29Si NMR (C6D6, 99.4 MHz): δ -27.3.
Anal. Calcd for C32H54NIrP2Si: C, 52.29; H, 7.40; N, 1.91. Found:
C, 53.71; H, 7.68; N, 1.76. Despite recrystallizations, compound 3
did not provide consistent and reliable combustion data. However,
the compound is pure by NMR spectroscopy.
(PNP)IrH(SiH2C6F5) (4). A solution of (C6F5)SiH3 (0.032 g, 0.16
mmol) in 1 mL of hexanes was added dropwise to (PNP)IrH2 (0.100
g, 0.16 mol) in 4 mL of hexanes. Upon addition of the silane, rapid
evolution of dihydrogen gas and a color change to red were
observed. After standing at ambient temperature for 45 min, the
solution was filtered, concentrated to ca. 1 mL, and cooled at -30
°C until red crystals formed. The dark red crystals were collected
(PNP)IrH(SiHPh2) (7). A solution of Ph2SiH2 (0.039 g, 0.21
mmol) in 2 mL of hexanes was added to a solution of (PNP)IrH2
(0.130 g, 0.21 mmol) in 10 mL of hexanes. Upon addition of the
silane, rapid evolution of dihydrogen gas was observed. After
standing at ambient temperature for 30 min, some initial crystal
nucleation occurred and the reaction mixture was placed in a -30
°C freezer for 18 h to afford red-orange crystals. The resulting solid
can be recrystallized via a toluene/hexanes layer diffusion at -30
°C. Yield: 0.115 g (68%). 1H NMR (C6D6, 500 MHz): δ 7.94 (4H,
d, J ) 6.8 Hz, ArH), 7.73 (2H, d, J ) 8.5 Hz, ArH), 7.16 (4H, s,
ArH), 7.10 (2H, t, J ) 7.3 Hz, ArH), 6.95 (2H, s, ArH), 6.87(2H,
1
and dried under vacuum. Yield: 0.100 g (76%). H NMR (C6D6,
500 MHz): δ 7.71 (2H, J ) 8.5 Hz, ArH), 6.95 (2H, br, ArH),
6.83 (2H, d, J ) 8.0 Hz, ArH), 4.60 (2H, br t, J ) 5.0 Hz, 1JSiH
)
189.0 Hz, SiH), 2.59 (2H, m, CHMe2), 2.17 (6H, s, ArMe), 2.10
(2H, m, CHMe2), 1.14 (6H, vq, CHMe2), 1.02 (12H, ov m, CHMe2),
0.84 (6H, vq, CHMe2), -21.67 (t, JPH ) 9.1 Hz, IrH). 13C{1H}
NMR (C6D6, 125.8 MHz): δ163.8 (t, JCP ) 10.5 Hz), 132.8, 132.1,
123.7 (t, JCP ) 21.3 Hz), 115.8 (t, JCP ) 5.5 Hz) (ArC), 25.7 (t,
JCP ) 16.5 Hz, CHMe2), 23.4 (t, JCP ) 14.7 Hz, CHMe2), 20.3 (s,
ArMe), 18.7 (s, CHMe2), 18.7 (s, CHMe2), 18.1 (s, CHMe2), 16.7
(s, CHMe2). 19F{1H} NMR (C6D6, 376.5 MHz): δ -125.3 (m),
-154.2 (t, J ) 20.3 Hz), -161.7 (m). 31P{1H} NMR (C6D6, 202.5
MHz): δ 48.8 (s). 29Si NMR (C6D6, 99.4 MHz): δ -79.0. Anal.
Calcd for C32H43NF5IrP2Si: C, 46.93; H, 5.29; N, 1.71. Found: C,
47.20; H, 5.50; N, 1.67.
3
d, J ) 8.5 Hz, ArH), 6.28 (1H, td, JPH ) 8.6 Hz, JH ) 4.6 Hz,
1JSiH ) 179.6 Hz, SiH), 2.16 (6H, s, ArCH3), 2.15 (2H, m, CHMe2),
2.09 (2H, m, CHMe2), 1.27 (6H, vq, CHMe2), 1.01 (6H, vq,
CHMe2), 0.88 (6H, vq, CHMe2), 0.78 (6H, vq, CHMe2), -19.83
(1H, td, 2JPH ) 9.5 Hz, JH ) 4.6 Hz). 13C{1H} NMR (C6D6, 125.8
MHz): δ 163.1 (t, JCP ) 10.1 Hz, ArC), 142.0 (s, ArC), 136.9 (s,
ArC), 132.6 (s, ArC), 132.0 (s, ArC), 127.2 (s, ArC), 126.8 (t, JCP
) 3.3 Hz, ArC), 125.0 (t, JCP ) 20.9 Hz, ArC), 115.5 (t, JCP ) 4.7
Hz, ArC), 27.1 (t, JCP ) 16.0 Hz, CHMe2), 22.4 (t, JCP ) 14.5 Hz,
CHMe2), 20.4 (s, ArMe), 20.4 (s, CHMe2), 19.06 (s, CHMe2), 17.68
(s, CHMe2), 17.25 (s, CHMe2). 31P{1H} NMR (C6D6, 202.5 MHz):
δ 46.8. 29Si NMR (C6D6, 99.4 MHz): δ -21.0. Anal. Calcd for
C38H52NIrP2Si: C, 56.69; H, 6.51; N, 1.74. Found: C, 57.00; H,
6.76; N, 2.03.
(PNP)IrH(SiH2Trip) (5). A solution of TripSiH3 (0.041 g, 0.18
mmol) in 1 mL of hexanes was added dropwise to (PNP)IrH2 (0.109
g, 0.18 mmol) in 4 mL of hexanes. Upon addition of the silane,
rapid evolution of dihydrogen gas and a color change to bright
orange were observed. After standing for 1 h, the solution was
filtered, evaporated to dryness, and lyophilized in ca. 2 mL of
benzene to afford 5 as an orange powder. Yield: 0.110 g (73%).
1H NMR (C6D6, 500 MHz): δ 7.73 (2H, d, J ) 8.5 Hz, ArH), 7.16
(under solvent signal, TripH), 6.99 (2H, br s, ArH), 6.85 (2H, d, J
(PNP)IrH(SiClPh2) (8). A solution of Ph2SiHCl (0.035 g, 0.16
mmol) in 2 mL of hexanes was added to a solution of (PNP)IrH2
(0.100 g, 0.16 mmol) in 5 mL of hexanes. Upon addition of the
chlorosilane, rapid evolution of dihydrogen gas was observed. After
standing at ambient temperature for 45 min, the solution was placed
in a -30 °C freezer for 18 h to afford red crystals. Yield: 0.104 g
1
) 8.0 Hz, ArH), 5.02 (2H, br, JSiH ) 173.1 Hz, SiH), 4.19 (2H,
sept, J ) 6.6 Hz, Trip CHMe2), 2.89 (1H, sept, J ) 6.9 Hz, Trip
9
11170 J. AM. CHEM. SOC. VOL. 131, NO. 31, 2009

Catalytic Hydrosilation of Alkenes
A R T I C L E S
1
(77%). H NMR (C6D6, 500 MHz): δ 8.11 (4H, d, J ) 7.1 Hz,
m, CH2), 1.61 (2H, m, CH2), 1.51 (4H, br m, CH2), 1.37 (6H, br
m, CHMe2), 1.19 (6H, br m, CHMe2), 1.04 (12H, ov m, CHMe2).
1H NMR (toluene-d8, 500 MHz, 90 °C): δ 7.50 (2H, d, J ) 7.9
Hz, ArH), 6.92 (2H, s, ArH), 6.75 (2H, d, J ) 7.7 Hz, ArH), 3.01
(2H, br s, CH ) CH), 2.41 (4H, br s, CHMe), 2.30 (2H, d, J )
11.2 Hz, CH2), 2.20 (6H, s, ArMe), 1.78 (2H, m, CH2), 1.70 (2H,
m, CH2), 1.51-1.47 (6H, ov m, CH2), 1.33 (12H, br s, CHMe2),
1.06 (12H, br m, CHMe2). 13C{1H} NMR (C6D6, 125.8 MHz): δ
ArH), 7.69 (2H, d, J ) 8.5 Hz, ArH), 7.12 (4H, t, J ) 7.3 Hz,
ArH), 7.06 (2H, t, J ) 7.3 Hz, ArH), 7.01 (2H, brs, ArH), 6.85
(2H, d, J ) 8.4 Hz, ArH), 2.16 (4H, CHMe2 under methyl signal),
2.14 (6H, s, ArCH3), 1.37 (6H, vq, CHMe2), 1.02 (6H, vq, CHMe2),
0.92 (6H, vq, CHMe2), 0.78 (6H, vq, CHMe2), -19.59 (1H, t, 2JPH
) 9.2 Hz, 2JSiH ) 2.7 Hz, Ir-H). 13C{1H} NMR (benzene-d6, 125.8
MHz): δ 163.1 (t, JCP ) 10.1 Hz, ArC), 143.5 (s, ArC), 136.2 (s,
ArC), 132.6 (s, ArC), 131.9 (s, ArC), 128.8 (s, ArC), 127.5 (s,
ArC), 127.1 (s, ArC), 125.0 (t, JCP ) 21.4 Hz, ArC), 115.9 (s, ArC),
28.0 (t, JCP ) 15.1 Hz, CHMe2), 23.2 (t, JCP ) 13.8 Hz, CHMe2),
21.3 (s, CHMe2), 20.4 (s, ArMe), 19.4 (s, CHMe2), 18.48 (s,
CHMe2), 17.4 (s, CHMe2). 31P{1H} NMR (C6D6, 163.0 MHz): δ
45.9 (s). 29Si NMR (C6D6, 99.4 MHz): δ 10.8. Anal. Calcd for
C38H51NClIrP2Si: C, 54.37; H, 6.12; N, 1.67. Found: C, 54.70; H,
6.37; N, 1.96.
165.3 (m), 164.5 (m), 132.2 (d, JCP ) 22.2 Hz), 131.8 (d, JCP
)
20.9 Hz), 128.9 (s), 125.9 (br m), 125.1 (d, JCP ) 40.2 Hz), 123.1
(d, JCP ) 45.7 Hz), 116.2 (m), 116.1 (m) (ArC), 41.1 (s, CHdCH),
36.2 (br, CHMe2), 33.4 (s, CH2), 27.7 (s, CH2), 21.1 (s, ArMe),
20.9 (s, ArMe), 17.6 (s, CHMe2), 17.3 (s, CHMe2). 31P{1H} NMR
2
(C6D6, 202.5 MHz): δ 29.4, 27.7, 26.2, 24.5 (AB quartet, JPP
)
351 Hz). Anal. Calcd for C34H54NIrP2: C, 55.87; H, 7.45; N, 1.92.
Found: C, 55.56; H, 7.26; N, 2.16.
(PNP)Ir(SiH2Ph)2 (9). A solution of PhSiH3 (0.018 g, 0.16 mmol)
in 1 mL of pentane was added to a solution of (PNP)IrH2 (0.050 g,
0.08 mmol) in 5 mL of pentane. Upon addition of the silane, rapid
evolution of dihydrogen gas and a color change to dark red were
observed. After 15 min, the solution was decanted to leave a
[(PNP)(H)IrdSiH(Trip)][B(C6F5)4] (12). A solution of [Ph3C]-
[B(C6F5)4] (0.011 g, 0.01 mmol) in 0.5 mL of C6D5Br was added
to 5 (0.010 g, 0.01 mmol). The solution turned bright green. The
resulting solution was immediately analyzed by NMR spectroscopy.
Complex 12 decomposed after 45 min at ambient temperature. 1H
1
1
burgundy microcrystalline solid. Yield: 0.053 g (79%). H NMR
NMR (C6D5Br, 500 MHz): δ 10.76 (1H, vq, JSiH ) 206.2 Hz,
(C6D6, 500 MHz): δ 7.93 (4H, d, J ) 6.6 Hz, ArH), 7.69 (2H, d,
J ) 8.5 Hz, ArH), 7.12-7.02 (6H, ov m, ArH), 6.84 (2H, d, J )
8.5 Hz, ArH), 6.72 (2H, brs, ArH), 5.21 (4H, t, JPH ) 5.8 Hz, 1JSiH
) 177.6 Hz, SiH2Ph), 2.49 (4H, m, CHMe2), 2.14 (6H, s, ArMe),
1.09 (12H, vq, CHMe2), 0.84 (12H, vq, CHMe2). 13C{1H} NMR
(C6D6, 125.8 MHz): δ 162.6 (t, JCP ) 9.4 Hz, ArC), 140.1 (s, ArC),
137.2 (s, ArC), 132.6 (s, ArC), 132.4 (s, ArC), 128.9 (s, ArC),
127.9 (t, JCP ) 3.5 Hz, ArC), 127.8 (s, ArC), 123.4 (t, JCP ) 21.6
Hz, ArC), 116.1 (t, JCP ) 5.2 Hz, ArC), 26.0 (t, JCP ) 15.4 Hz,
CHMe2), 20.8 (s, ArMe), 18.4 (s, CHMe2), 17.9 (s, CHMe2). 31P{1H}
NMR (C6D6, 202.5 MHz): δ 35.2 (s). 29Si NMR (C6D6, 99.4 MHz):
δ -37.5. Anal. Calcd for C38H54NIrP2Si2: C, 54.65; H, 6.52; N,
1.68. Found: C, 54.53; H, 6.60; N, 1.78.
SiH), -18.37 (1H, vq, IrH). 29Si NMR (C6D5Br, 99.4 MHz): δ
233.9.
[(PNP)(H)IrdSiH(Dmp)][B(C6F5)4] (13). A solution of [Ph3C]-
[B(C6F5)4] (0.066 g, 0.07 mmol) in 0.5 mL of C6H5F was added to
a solution of 6 (0.070 g, 0.07 mmol) in 1 mL of C6H5F. Upon
addition, a color change from orange to an intense blue occurred.
The resulting C6H5F solution was added to 15 mL of cold pentane
and placed in the -30 °C freezer. After 2 h, a blue oil settled out.
The solution was carefully decanted (the washing procedure can
be repeated to remove any persistent triphenylmethane impurities).
The resulting blue oil was dried under vacuum for 1 h. Yield: 0.119
g (65% yield of 13 by integration of Ir-H and Si-H groups). The
resulting solid can be stored at -30 °C for approximately 2 weeks
before significant decomposition. The 1H NMR indicates the
presence of two diasteromers of 13 in a 2:1 ratio. Due the
complexity of the resulting spectra, only the Si-H and Ir-H data
are given. The 29Si NMR resonance was obtained via a 2D
1H,29Si{1H} HMBC experiment as a crosspeak with the downfield
SiH resonance. No other 29Si resonances were found via this
experiment. 1H NMR (C6D5Br, 500 MHz): for 13a, δ 9.75 (t, SiH,
1JSiH ) 206 Hz), -20.49 (t, IrH); for 13b, δ 9.73 (t, SiH) -20.43
(t, IrH). 31P{1H} NMR (C6D5Br, 202.5 MHz): for 13a, δ 54.6 (br
s); 13b, δ 54.4 (br s). 29Si NMR (C6D5Br, 99.4 MHz): δ 226.6.
19F{1H} NMR (C6D5Br, 376.5 MHz): δ -130.8 (br s), -161.3 (t,
J ) 20.7 Hz), -165.1 (br t, J ) 19.3 Hz). Anal. Calcd for
C74H67NBF20IrP2Si: C, 54.08; H, 4.11; N, 0.85. Found: C, 53.77;
H, 4.01; N, 1.20.
(PNP)Ir(SiH2(m-Xylyl))2 (10). A solution of XylSiH3 (0.022 g,
0.16 mmol) in 1 mL of hexanes was added to a solution of
(PNP)IrH2 (0.050 g, 0.08 mmol) in 5 mL of hexanes. Upon addition
of the silane, rapid evolution of dihydrogen gas and a color change
to dark red were observed. After 15 min, the solution was
concentrated (ca. 2 mL) and cooled to -30 °C to afford dark red
1
microcrystals. Yield: 0.040 g (56%). H NMR (C6D6, 500 MHz):
δ 7.72 (2H, d, J ) 8.4 Hz, ArH), 2.63 (4H, s, ArH), 6.90 (2H, d,
J ) 8.2 Hz, ArH), 6.77 (4H, two overlapping s, ArH), 5.23 (t, 3JPH
) 5.9 Hz, 1JSiH ) 177 Hz, SiH), 2.56 (4H, m, CHMe2), 2.14 (6H,
s, ArMe), 2.12 (12H, s, ArMe), 1.18 (12H, vq, CHMe2), 0.85 (12H,
vq, CHMe2). 13C{1H} NMR (C6D6, 125.7 MHz): δ 162.4 (t, JCP
)
9.7 Hz, ArC), 139.7 (s, ArC), 136.4 (s, ArC), 135.3 (s, ArC), 132.5
(s, ArC), 132.3 (s, ArC), 130.3 (s, ArC), 127.6 (t, JCP ) 3.4 Hz,
ArC), 123.8 (t, JCP ) 21.2 Hz, ArC), 116.1 (t, JCP ) 4.8 Hz, ArC),
25.9 (t, JCP ) 15.3 Hz, CHMe2), 21.8 (s, ArMe), 20.8 (s, ArMe),
18.5 (s, CHMe2), 18.1 (s, CHMe2). 31P{1H} NMR (C6D6, 202.5
MHz): δ 35.2 (s). 29Si NMR (C6D6, 99.4 MHz): δ -38.2. Anal.
Calcd for C42H62NIrP2Si2: C, 56.60; H, 7.01; N, 1.57. Found: C,
56.39; H, 7.03; N, 1.78.
[(PNP)(H)IrdSiPh2][B(C6F5)4] (14). A solution of [Ph3C]-
[B(C6F5)4] (0.192 g, 0.21 mmol) in 0.5 mL of C6H5F was added to
a solution of 7 (0.168 g, 0.21 mmol) in 1 mL of C6H5F. Upon
addition, a color change from red-orange to a purple occurred. The
resulting C6H5F solution was added to 15 mL of cold pentane and
placed in the -30 °C freezer. After 2 h, a purple oil settled to the
bottom of the vial. The solution was carefully decanted (the washing
procedure can be repeated to remove any persistent triphenyl-
methane impurities). The resulting violet oil was dried under
vacuum for 1 h to afford 14 as a purple foam. Yield: 0.300 g (97%).
1H NMR (C6D5Br, 500 MHz): δ 7.76 (4H, br, ArH), 7.50 (2H, d,
J ) 8.2 Hz, ArH), 7.43 (2H, br, ArH), 7.30 (4H, br, under solvent
signal, ArH), 7.01 (2H, d, J ) 8.3 Hz, ArH), 6.90 (2H, s, ArH),
2.25 (6H, s, ArMe), 2.24 (2H, br, CHMe2, under methyl signal),
2.01 (2H, br, CHMe2), 0.96 (6H, vq, CHMe2), 0.84 (6H, vq,
(PNP)Ir(C8H14) (11). A solution of (PNP)Li (0.26 g, 0.59 mmol)
in toluene (5 mL) was added dropwise to a solution of [(COE)2IrCl]2
(0.26 g, 0.29 mmol) in toluene (5 mL). Upon addition, the solution
turned dark orange-red and a fine precipitate formed. After standing
for 30 min at ambient temperature, the solution was evacuated to
dryness, extracted into pentane (10 mL), and filtered through Celite
to remove the LiCl precipitate. The clear red solution was
concentrated to approximately 1 mL of pentane and cooled to -30
°C to afford bright orange crystals. Yield (combined first and second
crops): 0.28 g (64%). 1H NMR (C6D6, 500 MHz, ambient
2
CHMe2), 0.61 (12H, overlapping m, CHMe2), -20.6 (1H, t, JPH
2
temperature): δ 7.69 (2H, d, J ) 7.9 Hz, ArH), 7.00 (1H, d, JPH
)
) 8.9 Hz, JSiH ) 10 Hz, Ir-H). 13C{1H} NMR (C6D5Br, 125.8
6.1 Hz, ArH), 6.90 (1H, d, JPH ) 6.2 Hz, ArH), 6.81 (2H, vt, ArH),
3.04 (2H, br, CH ) CH), 2.38 (6H, ov, CH2 and CHMe2), 2.25
(3H, s, ArMe), 2.21 (3H, s, ArMe), 1.86 (2H, m, CH2), 1.76 (2H,
MHz): δ 162.2 (t, JCP ) 10.0 Hz, ArC), 150.1 (br m, ArC), 148.1
(br m, ArC), 139.9 (br m, ArC), 138.0 (br m, ArC), 137.3 (s, ArC),
136.0 (br m, ArC), 135.2 (br s, ArC), 134.1 (s, ArC), 132.7 (s,
9
J. AM. CHEM. SOC. VOL. 131, NO. 31, 2009 11171

A R T I C L E S
Calimano and Tilley
ArC), 128.3 (t, JCP ) 23.3 Hz, ArC), 120.3 (t, JCP ) 23.9 Hz, ArC),
116.3 (t, JCP ) 4.9 Hz, ArC), 27.0 (t, JCP ) 16.5 Hz, CHMe2),
25.2 (t, JCP ) 16.3 Hz, CHMe2), 20.8 (s, ArMe), 19.9 (s, CHMe2),
18.7 (s, CHMe2), 18.5 (s, CHMe2), 18.2 (s, CHMe2). 31P{1H} NMR
(C6D5Br, 163.0 MHz): δ 66.0. 19F{1H} NMR (C6D5Br, 376.5 MHz):
δ -130.8 (br s), -161.3 (t, J ) 20.7 Hz), -165.1 (br t, J ) 19.3
Hz). 29Si NMR (C6D5Br, 99.4 MHz): δ 264.8. Anal. Calcd for
C62H50NBF20IrP2Si: C, 50.24; H, 3.40; N, 0.95. Found: C, 49.90;
H, 3.28; N, 1.02.
125.8 MHz): δ 161.4 (t, JCP ) 9.3 Hz), 150.1 (br m), 148.2 (br m),
143.8 (s), 140.0 (br m), 138.0 (br m), 136.1 (br m), 134.0 (s), 132.3
(s), 120.2 (t, JCP ) 24.5 Hz), 116.5 (br m) (ArC), 34.4 (CH2), 25.9
(br m, CHMe2), 24.8 (s, ArMe), 24.6 (br m, CHMe2), 21.6 (s,
ArMe), 20.8 (s, ArMe), 20.6 (s, CHMe2), 18.5 (s, CHMe2), 17.9 (s,
CHMe2), 17.5 (s, CHMe2), -2.0 (s, SiMe3). 31P{1H} NMR (C6D5Br,
202.5 MHz): δ 60.7 (br s). 29Si NMR (C6D5Br, 99.4 MHz): δ 3.1
(SiMe3), 301.1 (IrdSi). 19F{1H} NMR (C6D5Br, 376.5 MHz): δ
-130.8 (br s), -161.3 (t, J ) 20.7 Hz), -165.1 (br t, J ) 19.3
Hz). Anal. Calcd for C64H65NBF20IrP2Si2: C, 49.61; H, 4.23; N,
0.90. Found: C, 49.47; H, 4.34; N, 1.08.
[(PNP)(H)IrdSiH(Mes)][CB11H6Br6] (15). A solution of [Ph3C]-
[CB11H6Br6] (0.044 g, 0.05 mmol) in 1 mL of C6H5F was added to
a solution of 2 (0.040 g, 0.05 mmol) in 1 mL of C6H5F. The reaction
solution was stirred for 10 min giving an intense blue solution.
The resulting C6H5F solution was added to 10 mL of cold hexanes
and placed in the -30 °C freezer. After 1 h, the blue solid was
collected via filtration. The solid was redissolved in C6H5F, and
the washing procedure was repeated to ensure removal of the
triphenylmethane byproduct. The collected solid was washed with
[(PNP)(H)IrdSiMes(CH2CH2(C6H4Cl)][B(C6F5)4] (18). An ex-
cess of p-chlorostyrene (0.008 g, 0.06 mmol) was added to a
solution of 1 (0.080 g, 0.06 mmol) in 3 mL of C6H5F to give a
dark blue solution. After 10 min, the reaction mixture was added
to cold pentane (5 mL) and placed in the -30 °C freezer for 1 h.
The resulting dark blue oil was collected by decantation of the
supernatant and dried under vacuum to give a dark blue solid. Yield:
1
1
hexanes and dried. Yield: 0.068 g (94%). H NMR (C6D5Br, 400
0.072 g (82%). H NMR (C6D5Br, 500 MHz): δ 7.30 (2H, under
MHz): δ 10.69 (1H, br, 1JSiH ) 208 Hz, SiH), 7.43 (2H, d, J ) 8.4
Hz, ArH), 6.65 7.02 (2H, s, ArH), 6.88 (2H, d, J ) 8.3 Hz, ArH),
(2H, s, ArH), 3.5-2.5 (6H, br, carborane), 2.4-2.2 (8H, overlapping
br m, CHMe2 + ArMe), 2.28 (6H, s, ArMe), 2.12 (3H, s, ArMe),
2.11 (2H, under methyl resonance, br m, CHMe2,), 1.07 (6H, vq,
CHMe2), 0.95-079 (18H, ov m, CHMe2), -18.83 (1H, br H, IrH).
31P{1H} NMR (C6D5Br, 202.5 MHz): δ 58.3 (s). 29Si NMR (C6D5Br,
99.4 MHz): δ 244.7. Anal. Calcd for C36H59NB11Br6IrP2Si2: C,
31.19; H, 4.29; N, 1.01. Found: C, 31.06; H, 4.16; N, 1.08.
[(PNP)(H)IrdSiPh2)][CB11H6Br6] (16). A solution of [Ph3C]-
[CB11H6Br6] (0.106 g, 12.4 mmol) in 1 mL of C6H5F was added to
a solution of 7 (0.100 g, 12.4 mmol) in 1 mL of C6H5F. The reaction
solution was stirred for 10 min to give an intense violet solution.
The resulting C6H5F solution was added to 10 mL of cold hexanes
and placed in the -30 °C freezer. After 1 h, the purple solid was
collected via filtration. The solid was redissolved in C6H5F, and
the washing procedure was repeated to ensure removal of the
triphenylmethane byproduct. The collected solid was washed with
solvent signal, ArH), 7.15 (2H, d, J ) 8.3 Hz, ArH), 6.95 (4H, ov
m, ArH), 6.74 (2H, d, J ) 8.3 Hz), 6.65 (2H, s, ArH), 2.65 (2H,
t, J ) 7.7 Hz, CH2), 2.32 (2H, m, CHMe2), 2.23 (6H, s, ArMe),
2.14 (3H, s, ArMe), 2.13 (6H, s, ArMe), 2.04 (2H, m, CHMe2),
1.58 (2H, br t, CH2), 1.07 (6H, vq, CHMe2), 0.89 (6H, vq, CHMe2),
0.80 (6H, vq, CHMe2), 0.71 (6H, vq, CHMe2), -19.05 (1H, t, 2JPH
2
) 9.0 Hz, JSiH ) 10 Hz, IrH). 13C{1H} NMR (C6D5Br, 125.8
MHz): δ 161.4 (t, JCP ) 8.2 Hz), 150.0 (br m), 148.1 (br m), 144.2
(s), 139.9 (br m), 139.7 (s), 138.0 (s), 136.0 (br m), 135.4 (s), 134.0
(s), 133.2 (s), 132.8 (s), 129.5 (s), 120.2 (t, JCP ) 23.1 Hz), 116.6
(br m) (ArC), 43.7 (s, CH2), 31.0 (s, CH2), 26.5 (br m, CHMe2),
25.1 (br m, CHMe2), 24.6 (s, ArMe), 21.7 (s, ArMe), 20.8 (s, ArMe),
20.6 (s, CHMe2), 18.6 (s, CHMe2), 17.7 (s, CHMe2), 17.4 (s,
CHMe2). 31P{1H} NMR (C6D5Br, 202.5 MHz): δ 60.9 (br s). 29Si
NMR (C6D5Br, 99.4 MHz): δ 293.3. 19F{1H} NMR (C6D5Br, 376.5
MHz): δ -130.8 (br s), -161.3 (t, J ) 20.7 Hz), -165.1 (br t, J
) 19.3 Hz). Anal. Calcd for C67H60NBClF20IrP2Si: C, 50.69; H,
3.81; N, 0.88. Found: C, 50.91; H, 4.02; N, 0.90.
[(PNP)(SiH(Mes)(Hex))IrH(SiH2Mes)][B(C6F5)4] (19). Determi-
nation of a yield by NMR spectroscopy: A solution of H3SiMes
(0.0016 g, 0.01 mmol) and bis(p-fluorophenyl)methane (0.0021 g,
0.01 mmol) in bromobenzene-d5 (0.5 mL) was added to [(PNP)-
(H)IrdSiMes(Hex)][B(C6F5)4] (0.016 g, 0.01 mmol), and the
reaction mixture was analyzed by NMR spectroscopy. Yield:
33-43% for 19, 39% for H2SiMes(Hex). The mixture of iridium-
containing products can be separated from organic impurities by
washing with pentane and drying under vacuum to afford a light
1
hexanes and dried. Yield: 0.145 g (82%). H NMR (C6D5Br, 500
MHz): δ 7.79 (4H, br, ArH), 7.50 (2H, d, J ) 8.5 Hz, ArH), 7.43
(4H, br, ArH), 7.01 (2H, d, J ) 8.6 Hz, ArH), 6.90 (2H, br, ArH),
3.5-2.5 (6H, br, carborane), 2.33 (2H, m, CHMe2), 2.29 (6H, s,
ArMe), 2.08 (2H, m, CHMe2), 0.99 (6H, vq, CHMe2), 0.88 (6H,
vq, CHMe2), 0.61 (12H, ov m, CHMe2), -20.42 (1H, t, 2JPH ) 9.2
Hz). 13C{1H} NMR (C6D5Br, 125.8 MHz): δ 162.3 (t, JCP ) 8.7
Hz), 137.4 (br s), 135.3 (br s), 134.0 (s), 132.9 (s), 128.6 (t, JCP
)
22.2 Hz), 120.6 (t, JCP ) 23.8 Hz), 116.3 (t, JCP ) 5.1 Hz) (ArC),
41.5 (br, carborane), 27.1 (t, JCP ) 16.5 Hz, CHMe2), 25.2 (t, JCP
) 17.6 Hz, CHMe2), 21.0 (s, ArMe), 20.3 (s, CHMe2), 19.0 (s,
CHMe2), 18.8 (s, CHMe2), 18.5 (s, CHMe2). 31P{1H} NMR (C6D5Br,
162.0 MHz): δ 67.5 (s). 29Si{1H} NMR (CD2Cl2, 99.4 MHz): δ
265.6 (br m). 11B{1H} NMR (C6D5Br, 128.4 MHz): δ -1.0 (s),
-9.4 (s), -20.3 (s). Anal. Calcd for C39H58NB11Br6IrP2Si: C, 32.95;
H, 4.11; N, 0.99. Found: C, 34.48; H, 4.25; N, 0.95. Partial
cocrystallization of fluorobenzene accounts for the discrepancy.
Anal. Calcd for C39H58NB11Br6IrP2Si·0.6(C6H5F): C, 34.59; H, 4.16;
N, 0.95.
1
1
blue foam. H NMR (C6D5Br, 500 MHz): δ 4.75 (1H, br m, JSiH
) 183.2 Hz, SiH2Mes), 4.67 (1H, br m, 1JSiH ) 179.8 Hz, SiH2Mes),
-5.81 (1H, br s, 1JSiH ) 101.9 Hz, η2SiH), -11.94 (1H, t, 2JPH
)
18.3 Hz, 2JSiH ) 8.5 Hz, IrH). 31P{1H} NMR (C6D5Br, 162.0 MHz):
δ 39.8 (d), 9.9 (d, JPP ) 244.6 Hz). 29Si NMR (C6D5Br, 99.4 MHz):
δ 0.83 (NSiMes(Hex)(H)), -78.1 (IrSiH2Mes).
[(PNP)(SiPh2)Ir(SiPh2H)(H)2][CB11H6Br6] (20). An excess of
H2SiPh2 (0.030 g, 0.16 mmol) was added to a solution of 16 (0.078
g, 0.05 mmol) in 7 mL of C6H5F. The reaction mixture was stirred
for 18 h at ambient temperature to give a colorless solution. The
reaction mixture was dried under vacuum, giving a light blue foam.
Off-white crystals of 20 were obtained by the vapor diffusion of
hexanes into a o-C6H4Cl2 solution of the complex. Yield: 0.076 g
(86%). 1H NMR (CD2Cl2, 500 MHz, 203 K): δ 8.41 (1H, br, ArH),
7.98 (d, J ) 7.2 Hz, ArH), 7.60 (1H, br, ArH), 7.52 (1H, br, ArH),
7.39 (5H, m, ArH), 7.23 (3H, m, ArH), 7.25-7.07 (9H, ov m, ArH),
6.99-6.89 (7H, ov m, ArH), 6.79 (2H, ov m, ArH), 6.12 (1H, br
d, J ) 7.2 Hz, ArH), 5.56 (1H, dd, JPH ) 21.6 Hz, JHH ) 2.9 Hz,
[(PNP)(H)IrdSiMes(CH2CH2SiMe3)][B(C6F5)4] (17). An excess
of vinyltrimethylsilane (0.006 g, 0.06 mmol) was added to a solution
of 1 (0.070 g, 0.05 mmol) in 3 mL of C6H5F to give a dark blue
solution. After 10 min, the reaction mixture was added to cold
pentane and placed in the -30 °C freezer for 1 h. A dark blue oil
was collected by decanting the supernatant and dried under vacuum
to give a dark blue solid. Yield: 0.063 g (85%). 1H NMR (C6D5Br,
500 MHz): δ 7.33 (2H, under solvent signal, ArH), 6.95 (4H, ov
m, ArH), 6.63 (s, ArH), 2.32 (2H, br m, CHMe2), 2.23 (6H, s,
ArMe), 2.18 (6H, s, ArMe), 2.10 (3H, s, ArMe), 2.08 (2H, br m,
CHMe2), 1.36 (2H, br m, CH2), 1.05 (6H, vq, CHMe2), 0.98 (6H,
vq, CHMe2), 0.80 (12H, ov m, CHMe2), 0.02 (9H, s, SiMe3), -18.63
(1H, t, 2JPH ) 9.0 Hz, 2JSiH ) 10 Hz, IrH). 13C{1H} NMR (C6D5Br,
3
1JSiH ) 170.2 Hz, JSiH ) 5.9 Hz, SiH), 2.73 (1H, m, CHMe2),
2.68 (1H, br s, carborane), 2.6-1.8 (5H, br, carborane), 2.30 (3H,
s, ArMe), 2.24 (3H, s, ArMe), 2.30-2.22 (2H, under methyl
resonance, CHMe2), 1.69 (1H, m, CHMe2), 1.51-1.39 (9H, ov m,
CHMe2), 1.26 (3H, vq, CHMe2), 0.29 (3H, dd, JPH ) 23.8 Hz, JHH
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11172 J. AM. CHEM. SOC. VOL. 131, NO. 31, 2009

Catalytic Hydrosilation of Alkenes
A R T I C L E S
) 6.0 Hz, CHMe2), 0.18 (6H, ov m, CHMe2), -0.10 (3H, dd, JPH
) 17.5 Hz, JHH ) 6.3 Hz, CHMe2), -11.31 (1H, ddd, JPH ) 111.7
followed by the alkene (0.14 mmol) and the silane (0.14 mmol).
The solution was transferred to a Teflon-capped J. Young NMR
tube and heated to 60 °C in an oil bath with a temperature-controlled
hot plate for 3-46 h (see Table 3). The progress of the reaction
was monitored by 1H NMR spectroscopy, and yields were obtained
by integration against a standard. The reaction solution was then
opened to air, diluted with 2 mL of hexanes, filtered through silica
gel to remove any metal species, and analyzed by GC/MS.
X-ray Crystallography. General Considerations. The single-
crystal X-ray analyses of compounds 6, 11, 16, and 20 were carried
out at the UC Berkeley CHEXRAY crystallographic facility. All
measurements were made on a Bruker SMART or APEX CCD
area detector with graphite-monochromated Mo KR radiation (λ
) 0.71069 Å). Data were integrated by the program SAINT and
analyzed for agreement using XPREP. Empirical absorption cor-
rections were made using SADABS. Structures were solved by
direct methods or Patterson methods using the SHELX program
package. For 6, the checkcif report featured alert level “A”
associated with disordered hexanes in the unit cell, but this does
not affect the crystallographic data associated with 6. For 20,
PLATON SQUEEZE51 was used to treat disordered hexanes (see
Supporting Information). Crystallographic data are summarized in
the Supporting Information, and CIF files for all structures are also
included.
Hz, JPH ) 18.0 Hz, JHH ) 4.5 Hz, IrH), -11.95 (1H, br s, 2JSiH
)
)
1
10.3 Hz); for 20b (13%), δ 5.72 (1H, t, JPH ) 7.3 Hz, JSiH
184.6 Hz, SiH), -10.23 (2H, dd, JPH ) 80.8 Hz, JPH ) 17.1 Hz,
IrH). 13C{1H} NMR (CD2Cl2, 125.8 MHz, 203 K): δ 153.7 (d, JPC
) 16.8 Hz), 152.2 (d, JPC ) 15.2 Hz), 141.2 (d, JPC ) 4.2 Hz),
139.6 (d, JPC ) 6.2 Hz), 139.4 (br m), 138.9 (s), 136.4 (ov m),
135.9 (s), 135.3 (ov m), 134.9 (s), 133.7 (s), 132.6 (s), 132.2 (s),
132.2 (s), 132.1 (s), 131.9 (s), 131.8 (s), 131.1 (s), 130.8 (d, JCP
)
7.8 Hz), 130.5 (s), 130.3 (s), 129.7 (s), 128.3 (s), 128.0 (s), 127.1
(s), 126.3 (s), 125.1 (br m), 122.9 (d, JCP ) 9.0 Hz, ArC), 41.4 (s,
carborane), 34.1 (d, JCP ) 28.0 Hz, CHMe2), 30.8 (d, JCP ) 21.7
Hz, CHMe2), 26.2 (d, JCP ) 13.5 Hz, CHMe2), 25.1 (d, JCP ) 8.4
Hz, CHMe2), 23.0 (d, JCP ) 34.1 Hz, CHMe2), 21.9 (br m, CHMe2),
20.7 (s, ArMe), 20.4 (s, ArMe), 18.6 (ov s, CHMe2), 18.2 (ov s,
CHMe2), 17.0 (s, CHMe2), 16.5 (s, CHMe2). 31P{1H} NMR (CD2Cl2,
99.4 MHz, 203 K): δ 38.8 (d), 19.9 (d, JPP ) 17.1 Hz). 29Si NMR
(CD2Cl2, 99.4 MHz, 203 K): δ 6.1 (NSiPh2), -37.3 (IrSiPh2H).
Anal. Calcd for C51H69NB11Br6IrP2Si2: C, 38.17; H, 4.33; N, 0.87.
Found: C, 38.55; H, 4.31; N, 1.17.
Detailed Procedure for Small-Scale Catalytic Redistribution
Reactions. Catalytic runs for silane redistribution were performed
in Teflon-capped J. Young NMR tubes. In a representative catalytic
run, 1 (0.007 g, 0.005 mmol, 2 mol %) was dissolved in 0.6 mL of
bromobenzene-d5, and the resulting solution was added to bis(p-
fluorophenyl)methane (0.0099 g, 0.05 mmol) (as a standard)
followed by the silane (0.24 mmol). The solution was transferred
to a Teflon-capped J. Young NMR tube. For PhSiH3 substrate, the
solution was left at ambient temperature for 18 h. For the remaining
silane substrates, the reaction mixture was heated to 60 °C in an
oil bath with a temperature-controlled hot plate for 18 h (see Table
Acknowledgment. This work was supported by the National
Science Foundation under Grant No. CHE-0649583. The authors
thank Drs. Fred Hollander and Antonio Di Pasquale of the UC
Berkeley CHEXRAY facility for assistance with X-ray crystal-
lography and Rudi Nunlist for assistance with NMR spectroscopy.
Supporting Information Available: Tables of atomic coor-
dinates, thermal displacement parameters, selected bond lengths
and angles, and crystallographic information files for 6, 11, 16,
and 20; GC/MS and NMR spectroscopy for hydrosilation
products. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
3). The progress of the reaction was then monitored via H NMR
spectroscopy, and yields were obtained by integration against a
standard. The reaction solution was then opened to air, diluted with
2 mL of hexanes, filtered through silica gel to remove any metal
species, and analyzed by GC/MS.
Detailed Procedure for Small-Scale Catalytic Hydrosilation
Reactions. Hydrosilation catalytic runs were performed in Teflon-
capped J. Young NMR tubes. In a representative catalytic run, 1
(0.010 g, 0.007 mmol, 5 mol %) was dissolved in 0.6 mL of
bromobenzene-d5, and the resulting solution was added to bis(p-
fluorophenyl)methane (0.0143 mg, 0.14 mmol) (as a standard),
JA903737J
(51) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht
University: Utrecht, The Netherlands, 2008.
9
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