Influence of SiMe3 substituents on structures and hydrosilylation activities of ((SiMe3)1 or 2-Indenyl)Ni(PPh3)Cl

Article abstract of DOI:10.1021/om0494420

This report examines the effect of substituents R on structures and reactivities of the complexes (R-Ind)Ni(PPh₃)Cl (R-Ind = 1-Me-indenyl, 1; 1-SiMe₃-indenyl, 2; 1,3-(SiMe₃) ₂-indenyl, 3). NMR studies indicate that a relatively facile dissociation of PPh₃ takes place in solutions of complex 3 (ΔG* ≈ 10 kcal/mol in C₆D₆) but not those of complexes 1 and 2, implying that the presence of Ind substituents at the 1- and 3-positions can influence the kinetic lability of PPh₃. X-ray analyses have also shown that the PPh₃ ligand and the SiMe ₃ group adjacent to it in complex 3 experience some steric repulsion, which is manifested in angular deformations (out-of-plane bending of the SiMe₃ group by about 0.56-0.65 A and 5-10° variations in the P-Ni-Cl and P-Ni-C3 angles) and a somewhat longer Ni-P bond (ca. 2.19 A). Reactivity studies have shown that complexes 1-3 are effective precatalysts for the addition of PhSiH₃ to styrene in the presence of the cationic initiator NaBPh₄; α-addition of the silyl moiety takes place regioselectively to give PhCH(Me)(SiPhH₂). The catalytic activities depend on the styrene:PhSiH₃ ratio but not the Ind substituents; thus, catalytic turnover numbers increase from ca. 75 with a 1:1 ratio to ca. 95 with a 1:1.5 ratio for all three precursors. The hydrosilylation can also proceed in the absence of initiator, but in this case the activities are strongly dependent on Ind substituents, increasing in the order 1-Me-Ind < 1-SiMe₃-Ind < 1,3-(SiMe₃) ₂-Ind.

Full text of DOI:10.1021/om0494420

Organometallics 2005, 24, 149-155
149
Influence of SiMe3 Substituents on Structures and
Hydrosilylation Activities of
((SiMe3)1 or 2-Indenyl)Ni(PPh3)Cl
Yaofeng Chen, Christine Sui-Seng, Sylvain Boucher, and Davit Zargarian*
De´partement de Chimie, Universite´ de Montre´al, Montre´al, Que´bec, Canada H3C 3J7
Received July 22, 2004
This report examines the effect of substituents R on structures and reactivities of the
complexes (R-Ind)Ni(PPh3)Cl (R-Ind ) 1-Me-indenyl, 1; 1-SiMe3-indenyl, 2; 1,3-(SiMe3)2-
indenyl, 3). NMR studies indicate that a relatively facile dissociation of PPh3 takes place in
solutions of complex 3 (∆Gq ≈ 10 kcal/mol in C6D6) but not those of complexes 1 and 2,
implying that the presence of Ind substituents at the 1- and 3-positions can influence the
kinetic lability of PPh3. X-ray analyses have also shown that the PPh3 ligand and the SiMe3
group adjacent to it in complex 3 experience some steric repulsion, which is manifested in
angular deformations (out-of-plane bending of the SiMe3 group by about 0.56-0.65 Å and
5-10° variations in the P-Ni-Cl and P-Ni-C3 angles) and a somewhat longer Ni-P bond
(ca. 2.19 Å). Reactivity studies have shown that complexes 1-3 are effective precatalysts
for the addition of PhSiH3 to styrene in the presence of the cationic initiator NaBPh4;
R-addition of the silyl moiety takes place regioselectively to give PhCH(Me)(SiPhH2). The
catalytic activities depend on the styrene:PhSiH3 ratio but not the Ind substituents; thus,
catalytic turnover numbers increase from ca. 75 with a 1:1 ratio to ca. 95 with a 1:1.5 ratio
for all three precursors. The hydrosilylation can also proceed in the absence of initiator, but
in this case the activities are strongly dependent on Ind substituents, increasing in the order
1-Me-Ind , 1-SiMe3-Ind < 1,3-(SiMe3)2-Ind.
Introduction
lylation of olefins and ketones.7 Cationic species can also
be generated in the absence of initiators by using the
precursors (i-Pr-Ind)Ni(PPh3)(OSO2CF3)8 or [(η5,η1-
Ind∧NR2)Ni(PR3)]+ (∧ ) various side chains tethering
the amine moiety to the Ind ligand)9 or by heating the
complexes [IndNi(PR3)2]+ bearing bulky phosphine
ligands.10
The available mechanistic information indicates that
among the reactions promoted by IndNi(PR3)X, only the
hydrosilylation of olefins involves phosphine dissocia-
tion. Consistent with this assertion, the addition of
PhSiH3 to styrene gives a higher yield with the pre-
catalyst (1-Me-Ind)Ni(PPh3)Cl, 1, relative to its PMe3
analogue (69% vs 36%),7 whereas the opposite is true
for the polymerization reactions.2a It seemed reasonable,
therefore, to suppose that the presence of sterically
bulky substituents on the Ind ligand should favor the
hydrosilylation reaction by inducing the dissociation of
PPh3. However, initial tests did not show any advantage
in using bulkier Ind substituents; for instance, the
complex (1-(i-Pr)-Ind)Ni(PPh3)Cl catalyzed the hydrosi-
lylation reaction no more effectively than its 1-Me-Ind
Recent reports have shown that a number of interest-
ing reactions can be catalyzed by species generated from
the in-situ activation of the complexes IndNi(L)X (Ind
) indenyl and its substituted derivatives; L ) neutral
ligands such as phosphines or heterocarbenes; X )
anionic ligands such as halides, alkyls, triflate, etc.).1
For instance, combining the Ni-Cl precursors with
methylaluminoxanes (MAO) generates species that
promote the polymerization of ethylene,2 alkynes,3 and
PhSiH3;4 on the other hand, using cationic initiators
such as AgBF4, NaBPh4, or AlCl3 instead of MAO
generates5 the electronically unsaturated and highly
electrophilic cations [IndNi(PR3)]+, which promote the
oligomerization of some olefins6 as well as the hydrosi-
(1) For a review on the structures, characterization, and reactivities
of group 10 metal indenyl complexes see: Zargarian, D. Coord. Chem.
Rev. 2002, 233-234, 157.
(2) (a) Dubois, M.-A.; Wang, R.; Zargarian, D.; Tian, J.; Vollmerhaus,
R.; Li, Z.; Collins, S. Organometallics 2001, 20, 663. (b) Groux, L. F.;
Zargarian, D.; Simon, L. C.; Soares, J. B. P. J. Mol. Catal. A: Chem.
2003, 193, 51.
(3) (a) Wang, R.; Be´langer-Garie´py, F.; Zargarian, D. Organometal-
lics 1999, 18, 5548. (b) Wang, R.; Groux, L. F.; Zargarian, D. J.
Organomet. Chem. 2002, 660, 98. (c) Rivera, E.; Wang, R.; Zhu, X. X.;
Zargarian, D.; Giasson, R. J. Mol. Catal. A 2003, 204-205, 325.
(4) Fontaine, F. G.; Kadkhodazadeh, T.; Zargarian, D. Chem.
Commun. 1998, 1253.
(7) Fontaine, F.-G.; Nguyen, R.-V.; Zargarian, D. Can. J. Chem.
2003, 81, 1299.
(8) Wang, R.; Groux, L. F.; Zargarian, D. Organometallics 2002, 21,
5531.
(9) (a) Groux, L. F.; Be´langer-Garie´py, F.; Zargarian, D.; Vollmer-
haus, R. Organometallics 2000, 19, 1507. (b) Groux, L. F.; Zargarian
D. Organometallics 2001, 20, 3811. (c) Groux, L. F.; Zargarian D.
Organometallics 2003, 22, 3124. (d) Groux, L. F.; Zargarian D.
Organometallics 2003, 22, 4759.
(10) Jime´nez-Tenorio, M.; Puerta, M. C.; Salcedo, I.; Valerga, P.;
Costa, S. I.; Silva, L. C.; Gomes, P. T. Organometallics 2004, 23, 3139.
(5) Vollmerhaus, R.; Be´langer-Garie´py, F.; Zargarian, D. Organo-
metallics 1997, 16, 4762.
(6) (a) Dubois, M.-A. M. Sc. Thesis, Universite´ de Montre´al, 2000.
(b) Sun, H.-M.; Li, W.-F.; Han, X.; Shen, Q.; Zhang, Y. J. Organomet.
Chem. 2003, 688, 132. (c) Li, W.-F.; Sun, H.-M.; Shen, Q.; Zhang, Y.;
Yu, K.-B. Polyhedron 2004, 23, 1473.
10.1021/om0494420 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 12/09/2004

150 Organometallics, Vol. 24, No. 1, 2005
Chen et al.
Scheme 1
two halves of the Ind ligand equivalent; in other words,
the C1 symmetry dictated by the solid state structure
of this complex (vide infra) is converted to a Cs sym-
metry in the solution. On the other hand, the absence
of any shielding effects for H4/H5 implies little or no
interaction between these protons and the phenyl
groups of PPh3. These phenomena can occur as a result
of two possible processes: a rapid rotation of the Ind
ligand, which would create the requisite mirror plane,
or a rapid dissociation/reassociation of PPh3, which
would render the two halves of the Ind ligand equivalent
and minimize the above-discussed shielding effect.
Consistent with the latter possibility, the ambient-
temperature 31P{1H} NMR spectrum of 3 exhibits a very
broad signal for the PPh3 ligand coordinated to Ni (ca.
28 ppm in C6D6, width at half-height ∼60-70 Hz)14 and
a less intense signal for free PPh3 (ca. -5 ppm in C6D6).
The nature of this dynamic process was further probed
by variable-temperature (VT) NMR studies, as described
below.
The VT NMR spectra of complex 3 showed that the
broad 31P{1H} signal sharpened gradually upon lower-
ing the temperature of the NMR probe, reaching a width
at half-height of ∼10 Hz at -70 °C; on the other hand,
the 1H singlet due to the SiMe3 groups broadened upon
lowering the temperature until it split into two broad
singlets (0.64 and -0.19 ppm) at -70 °C (Figure 1). The
coalescence temperature (ca. 223 K) and the ∆δ for the
individual 1H NMR resonances due to SiMe3 groups (ca.
330 Hz) have been used to estimate a ∆Gq value of ca.
10 kcal/mol.15 This energy barrier is smaller than the
∆Gq values found for the rotation of the Ind ligands in
the related complexes IndNiPPh3Cl (16.0 kcal/mol), (2-
Me-Ind)Ni(PPh3)Cl (15.6 kcal/mol), and (1,3-Me2-Ind)-
Ni(PPh3)Cl (15.5 kcal/mol). We conclude, therefore, that
the NMR features of complex 3 are more consistent with
a dissociation/reassociation of PPh3 as opposed to an Ind
rotation. The kinetic lability of PPh3 in 3 must be
induced by the steric repulsion between the PPh3 ligand
and the SiMe3 group adjacent to it; the effects of steric
repulsion on the solid state structures of these com-
plexes have been examined by X-ray crystallography,
as described below.
analogue (61% vs 69%). On the other hand, since the
complexes (1-R-Ind)Ni(PPh3)X always adopt a configu-
ration that places the PPh3 ligand away from the Ind
substituent to avoid steric congestion,1 we reasoned that
a more reliable way to evaluate the influence of ligand
sterics on the dissociation of PPh3 would require study-
ing both 1-R-Ind and the 1,3-R2-Ind analogues of these
complexes. Therefore, we are examining the kinetic
lability of the PPh3 ligand in the complexes (1-R-Ind)-
Ni(PPh3)Cl and (1,3-R2-Ind)Ni(PPh3)Cl and evaluating
their reactivities. The results of our studies on the first
series of these complexes (R ) SiMe3) are presented
herein.
Results and Discussion
Synthesis and Characterization of (1-SiMe3-
Ind)Ni(PPh3)Cl, 2, and (1,3-(SiMe3)2-Ind)Ni(PPh3)-
Cl, 3. The ligands SiMe3-IndH and 1,3-(SiMe3)2-IndH
can be prepared by reacting Cl-SiMe3 with LiInd or Li-
[1-(SiMe3)-Ind],11 respectively, whereas the target com-
plexes 2 and 3 were prepared by reacting (PPh3)2NiCl2
with Li[1-(SiMe3)-Ind] and Li[1,3-(SiMe3)2-Ind], respec-
tively (Scheme 1).12 The full characterization of these
complexes by NMR spectroscopy and X-ray analysis is
described below.
1
The H NMR spectrum of 2 displayed well-resolved
signals for all Ind protons; the multiplicities and relative
chemical shifts of these signals follow a pattern that is
commonly observed for the previously studied 1-R-Ind
analogues. For instance, the signals for H4 (d, 6.39 ppm)
and H5 (t, 6.93 ppm) were strongly shielded in com-
parison to those for H6 (t, 7.20 ppm) and H7 (d, 7.59
ppm), and the signal for H3 was also very upfield (m,
3.54 ppm). The shielding of the signals for H3, H4, and
H5 is caused by their proximity to the phenyl rings of
the PPh3 ligand.1,13
Solid State Structures of 2 and 3. Two crystallo-
graphically independent molecules were found in the
unit cells of both compounds. Complex 2 contains
disordered Ph and Cl groups, as follows: there are two
Ph groups disordered over two positions in molecule 1;
in molecule 2, two Ph groups are disordered over two
positions, the third Ph group is disordered over three
positions, and the Cl is disordered over two positions.
Despite these disorders, the structure was refined to a
good degree of precision (R ) 4.54%). Complex 3 was
free of disorder and refined to a very good degree of
precision (R ) 3.63%). The ORTEP drawings for 2 and
3 (molecule no. 1 in both cases) are shown in Figures 2
and 3, respectively, the crystal data and refinement
1
On the other hand, the H NMR spectrum of 3 was
quite different in that it showed only an unresolved
multiplet for H4-H7 signals at ca. 7.0-7.2 ppm;
moreover, only one signal, a sharp singlet at 0.19 ppm,
was observed for the two, ostensibly inequivalent, SiMe3
groups present in this complex. The unexpected equiva-
lence of the symmetry-related signals in 3 hints at the
existence, in solution, of a mirror plane that renders the
(11) Ready, T. E.; Chien, J. C. W.; Rausch, M. D. J. Organomet.
Chem. 1996, 519, 21.
(14) In comparison, the width at half-height for 1 and (1,3-Me2-Ind)-
Ni(PPh3)Cl (ref 6a) are 2 and 6 Hz, respectively.
(12) The preparation of complex 2 has been described previously
(ref 6a).
(15) The Holmes-Gutowski equation, ∆Gq ) RTc{22.96 + ln(Tc/∆δ)},
wherein R is the gas constant (1.987 cal/K‚mol), Tc (K) is the
coalescence temperature, and ∆δ (Hz) is the difference in the frequen-
cies of the coalescing signals, can be used for this purpose: Abraham,
R. J.; Loftus, P. Proton and Carbon-13 NMR Spectroscopy; Wiley: New
York, 1985; Chapter 7, pp 165-168, eq 7.11.
(13) (a) Huber, T. A.; Be´langer-Garie´py, F.; Zargarian, D. Organo-
metallics 1995, 14, 4997. (b) Huber, T. A.; Bayrakdarian, M.; Dion, S.;
Dubuc, I.; Be´langer-Garie´py, F.; Zargarian, D. Organometallics 1997,
16, 5811.

((SiMe3)1 or 2-Indenyl)Ni(PPh3)Cl
Organometallics, Vol. 24, No. 1, 2005 151
1
Figure 1. Variable-temperature H NMR spectra for 3 (toluene-d8, 400 MHz).
Table 1. Crystal Data, Data Collection, and
Structure Refinement Parameters for 2 and 3
2
3
formula
mol wt
C
30H30ClNiPSi
C33H38ClNiPSi2
615.94
543.76
cryst color, habit
cryst dimens (mm)
symmetry
space group
a (Å)
red, plate
orange, plate
0.26 × 0.24 × 0.10 0.50 × 0.50 × 0.07
triclinic
monoclinic
P21/c
18.1219(2)
23.2566(2)
15.8556(2)
90
103.0050(10)
90
6511.00(12)
8
1.257
Bruker AXS
SMART 2K
220(2)
1.54178
2.926
ω scan
2592
P1h
9.90640(10)
16.09400(10)
18.94740(10)
114.60(1)
90.32(1)
92.57(1)
2742.99(4)
4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
D(calcd) (g cm-1
)
1.317
diffractometer
Bruker AXS
SMART 2K
223(2)
temp (K)
Figure 2. ORTEP diagram for complex 2 (molecule no.
1). Thermal ellipsoids are shown at 30% probability, and
hydrogen atoms are omitted for clarity.
wavelength, λ (Å)
absorp coeff, µ (mm-1
scan type
1.54178
)
2.999
ω scan
F(000)
1136
θmin - θmax (deg)
h,k,l range
2.57-72.98
-11 e h e 12
-19 e k e 19
-23 e l e 23
10 438
2.50-72.99
-22 e h e 22
-28 e k e 28
-19 e l e 18
12 907
indep reflns used
(I > 2σ(I))
absorp corr
correction
multiscan
multiscan
SADABS
SADABS
transmn (min., max.)
0.5550, 0.8050
0.41, 0.86
0.0363, 0.1020
1.028
R [F2 > 2σ(F2)], wR(F2) 0.0454, 0.1246
goodness of fit on F2
largest diff peak and
hole (e/Å3)
1.060
0.918, -0.681
0.428, -0.326
with the largest distortion arising from the small C1-
Ni-C3 angles (ca. 66-68°). As commonly observed in
this family of complexes,1 the Ind-Ni interaction in 2
and 3 is primarily through the allylic carbons, while the
Ni-C bond distances for the benzo carbons are signifi-
cantly longer. This “slippage” away from an ideal η5
hapticity is attributed to the tendency of Ni(II) to form
16-electron complexes.
Another common type of slippage in this family of
complexes is the so-called “sideways slippage”, which
is reflected in the unsymmetrical Ni-C bonds involving
the allylic carbons (Ni-C1 > Ni-C3); this distortion is
caused by the unequal trans influences of the PR3 and
X ligands (X ) halides, phthalimidato, thiolato, triflato,
etc.). Both molecules of complex 2 exhibit this type of
Figure 3. ORTEP diagram for complex 3 (molecule no.
1). Thermal ellipsoids are shown at 30% probability, and
hydrogen atoms are omitted for clarity.
parameters are given in Table 1, and a selection of
structural parameters is listed in Table 2.
In both compounds, the coordination geometry around
the Ni atom can be described as distorted square planar,

152 Organometallics, Vol. 24, No. 1, 2005
Table 2. Selected Bond Distances (Å) and Angels (deg) for Complexes 2 and 3
Chen et al.
2 (molec. 1, X ) 1)
2 (molec. 2, X ) 2)
3 (molec. 1, X ) 1)
3 (molec. 2, X ) 2)
Ni(X)-P(X)
2.1886(7)
2.1828(7)
2.128(2)
2.070(2)
2.052(3)
2.323(3)
2.335(2)
1.423(3)
1.402(4)
1.451(5)
1.434(3)
1.471(3)
1.877(2)
2.1819(8)
2.188(av.)
2.135(2)
2.060(3)
2.038(3)
2.339(3)
2.374(3)
1.415(4)
1.410(5)
1.449(5)
1.430(4)
1.466(5)
1.871(3)
2.1841(5)
2.1959(5)
2.0946(16)
2.0577(17)
2.1208(16)
2.3369(16)
2.3194(17)
1.417(2)
1.432(2)
1.478(2)
1.430(2)
1.473(2)
1.8838(17)
1.8760(18)
87.985(18)
177.56(5)
110.15(5)
94.07(5)
161.71(5)
67.85(7)
0.22
2.1984(5)
2.1865(5)
2.1543(17)
2.0422(17)
2.0831(16)
2.3764(17)
2.4219(18)
1.409(2)
1.426(2)
1.470(2)
1.434(2)
1.471(2)
1.8795(18)
1.8715(17)
91.172(18)
169.44(5)
106.63(5)
95.68(5)
162.08(5)
67.02(7)
0.28
Ni(X)-Cl(X)
Ni(X)-C(X1)
Ni(X)-C(X2)
Ni(X)-C(X3)
Ni(X)-C(X3a)
Ni(X)-C(X7a)
C(X1)-C(X2)
C(X2)-C(X3)
C(X3)-C(X3a)
C(X3a)-C(X7a)
C(X7a)-C(X1)
C(X1)-Si(X1)
C(X3)-Si(X2)
P(X)-Ni(X)-Cl(X)
P(X)-Ni(X)-C(X1)
P(X)-Ni(X)-C(X3)
C(X1)-Ni(X)-Cl(X)
C(X3)-Ni(X)-Cl(X)
C(X3)-Ni(X)-C(X1)
∆M-Ca (Å)
96.61(3)
166.65(7)
100.38(8)
96.23(7)
162.96(8)
66.9(1)
0.24
95.26(6)
165.40(8)
99.14(9)
99.32(9)
163.87(11)
66.49(11)
0.26
HAb (deg)
11.10
10.19
11.19
10.30
9.57
10.24
FAc (deg)
7.90
9.41
a ∆(M-C) ) 0.5{(M-C3a + M-C7a)} - 0.5{(M-C1 + M-C3)}. b HA is the angle formed between the planes defined by C1/C2/C3 and
C1/C3/C3a/C7a. c FA is the angle formed between the planes defined by C1/C2/C3 and C3a/C4/C5/C6/C7/C7a.
“sideways slippage”: Ni1-C11 ) 2.128(2) Å > Ni1-C13
) 2.052(3) Å; Ni2-C21 ) 2.135(2) Å > Ni1-C23 )
2.038(3) Å. In the case of complex 3, however, one of
the two independent molecules shows the opposite
trend: Ni1-C11 ) 2.0946(16) Å < Ni1-C13 ) 2.1208-
(16) Å. This unusually longer Ni-C13 distance is
presumably caused by the steric repulsion between PPh3
and its neighboring SiMe3 group; we suspect that the
reason why a similar elongation is not observed for the
corresponding bond in molecule 2 (Ni2-C23) is related
to the greater out-of-plane bending of Si22 in this
molecule, which tends to minimize steric repulsions
between the adjacent SiMe3 and PPh3 groups (vide
infra).
CH2NMe29b), but the Ni-P distance in molecule 2 of 3
is somewhat longer (Ni2-P2 ) 2.1984(5) Å).
Altogether, the above findings show that the proxim-
ity of the SiMe3 and PPh3 groups in 3 affects the solid
state structure primarily through angular deformations,
whereas in solution it increases the kinetic lability of
PPh3. The influence of Ind substituents on the catalytic
activities of 2 and 3 is described in the following section.
Catalytic Reactivities of 2 and 3. We have reported
previously that combining (1-Me-Ind)Ni(PPh3)Cl (1) and
NaBPh4 produces an active catalyst for the addition of
PhSiH3 to a number of olefins and ketones. With
styrene, for instance, this system gives PhCH(Me)-
(SiPhH2) in up to 80 catalytic turnovers (eq 1).7 We have
The effect of the aforementioned steric repulsion is
most evident in the out-of-plane bending of the SiMe3
group adjacent to PPh3 in 3. Thus, Si12 and Si22 atoms
are bent out of the plane of Ind16 (away from PPh3) by
0.56 and 0.65 Å, respectively; in comparison, the out-
of-plane bending of the SiMe3 group adjacent to Cl is
much smaller (0.10 and 0.23 Å in 3 and 0.15 and 0.16
Å in 2). The steric repulsion between PPh3 and the
adjacent SiMe3 group is also manifested in the relative
sizes of the P-Ni-C3 and P-Ni-Cl angles: the former
is larger in 3 (ca. 110° and 107°) relative to 2 (ca. 100°
and 99°), while the latter is smaller in 3 (ca. 88° and
91°) relative to 2 (ca. 97° and 95°). The Ni-C5 ring
distances in 2 (average ca. 1.82 Å) and 3 (average ca.
1.84 Å) are also somewhat longer than the correspond-
ing distance of ca. 1.81 Å in IndNi(PPh3)Cl13a and (1-
Me-Ind)Ni(PPh3)Cl.13b On the other hand, the effect of
steric factors on the Ni-P bond distances is less clear-
cut. Thus, the Ni-P bond distances in both molecules
of 2 (2.182-2.189 Å) and in molecule 1 of 3 (Ni1-P1)
2.1841(5)) are quite similar to the corresponding dis-
tances in the complexes R-IndNi(PPh3)Cl (ca. 2.180-
2.186 Å for R ) H,13a Me,13b (CH2)3N(t-Bu)H,9a CH2-
examined the activities of complexes 2 and 3 for
catalyzing this reaction as a means for evaluating the
influence of Ind substituents on reactivities. Initial tests
were conducted under the same conditions that were
used in our previous studies, i.e., a Ni:NaBPh4:PhSiH3:
styrene ratio of 1:10:100:100 and a reaction time of 16-
24 h at room temperature. The results of these tests
showed that complexes 2 and 3 give the same product
as 1, with virtually none of the other regioisomer being
detected by NMR. The final yields (69-77%) were
similar for all three precatalysts when the reaction was
run over 5-21 h (Table 3; compare runs 1a-c, 2a-c,
and 3a-c), which implies that all three complexes have
comparable reactivities for the addition of PhSiH3 to
styrene.
Next, we examined the catalytic activities of the
precatalysts in the presence of excess PhSiH3, for the
following reason. An important side-reaction that occurs
to different degrees during these Ni-catalyzed hydrosi-
lylation reactions is the dehydrogenative coupling of
(16) The central C atom (C2) was not included in the definition of
this plane, because it is often out-of-plane and puckered.

((SiMe3)1 or 2-Indenyl)Ni(PPh3)Cl
Organometallics, Vol. 24, No. 1, 2005 153
Table 3. Addition of PhSiH3 to Styrene Catalyzed
by (Rn-Ind)Ni(PPh3)Cl
tivity of the cationic intermediates with PhSiH3. On the
other hand, phosphine dissociation should occur to a
greater extent from the neutral precursor, so that the
precursor that most readily forms the coordinatively
unsaturated intermediate (R-Ind)Ni(Cl) in the absence
of cationic initiators should promote the catalysis more
effectively.
time yield
run Ni:NaBPh4:PhSiH3:styrene
R-Ind
1-Me-Ind
(h)
(%)
1a
1b
1c
2a
2b
2c
3a
3b
3c
4
1:10:100:100
1:10:100:100
1:10:100:100
2
5
16
2
5
18
2
5
66
69
73
49
75
77
71
74
76
>95
>95
92
8
1-SiMe3-Ind
To test the above hypothesis, we carried out the
hydrosilylation reaction in the absence of NaBPh4 and
found that the catalysis does indeed proceed with the
unactivated neutral precursors. Thus, complex 3 was
found to give the same product in almost the same yield
whether or not NaBPh4 was present in the reaction; on
the other hand, complexes 1 and 2 gave much lower
yields in the absence of the initiator (compare runs 1b,
2b, and 3b to runs 7-9). Using excess PhSiH3 improved
the yields of the hydrosilylation reactions catalyzed by
2 and 3 in the absence of initiator, but the catalysis by
1 was not affected (runs 10-12). These results show
that complexes 2 and 3 are effective, single-component
precatalysts for the addition of PhSiH3 to styrene; the
order of catalytic activities observed in the uninitiated
reactions (3 > 2 . 1) appears to reflect the greater PPh3
dissociation occurring with 3, which is presumably a
function of the steric congestion on Ind.20
Proposed Mechanisms. The above findings have a
number of mechanistic implications. First, the fact that
both the uninitiated and initiated reactions give the
same final product implies a common intermediate in
these two catalytic systems. We propose that the
catalytically active intermediate common to both cata-
lytic systems is the species IndNi(H)L wherein L is
either PPh3 or one of the substrates (Scheme 2). This
species can form via two different paths, depending on
whether the cationic initiator is used: (a) in the pres-
ence of NaBPh4, the in-situ generated cationic interme-
diate can abstract a hydride from PhSiH3 to give the
Ni-H species, in addition to a silylium ion;21 (b) in the
absence of initiator, the phosphine-dissociated species
IndNi(Cl) can undergo a concerted σ-bond metathesis
reaction with PhSiH3 to form the putative Ni-H inter-
mediate.22
1,3-(SiMe3)2-Ind
21
5
1:10:150:100
1:10:150:100
1:10:150:100
1:0:100:100
1:0:100:100
1:0:100:100
1:0:150:100
1:0:150:100
1:0:150:100
1-Me-Ind
5
1-SiMe3-Ind
1,3-(SiMe3)2-Ind
1-Me-Ind
5
6
5
7
5
8
1-SiMe3-Ind
1,3-(SiMe3)2-Ind
1-Me-Ind
1-SiMe3-Ind
1,3-(SiMe3)2-Ind
5
23
69
7
9
5
10
11
12
5
5
56
82
5
PhSiH3 (eq 2).17 Since this side-reaction depletes the
amount of silane available for the hydrosilylation reac-
tion, we reasoned that using an excess of PhSiH3 should
help improve the yields of the hydrosilylation reaction.
As an approximate measure of the extent to which this
side reaction is promoted by each of the complexes under
study, we reacted PhSiH3 alone with the Ni precursors
and NaBPh4. Monitoring the evolution of gas18 from
these reactions showed that the rate of PhSiH3 oligo-
merization follows the order 3 > 2 > 1; therefore, we
expected that using excess silane should have a greater
influence on the hydrosilylation activities of 3 and 2.
Interestingly, however, tests showed that the presence
of excess silane improved the hydrosilylation activities
of all three complexes more or less equally (runs 4-6).
It is not clear why the presence of excess silane improves
the reaction of 1 to the same extent as those of 2 and 3,
since the above-mentioned side-reaction does not take
place to a significant extent with 1. Nevertheless, the
comparable catalytic activities of complexes 1-3 show
that the increased steric congestion on the Ind ligand
does not have a favorable effect on the catalytic hy-
drosilylation reaction under these conditions.
The absence of a strong correlation between the steric
congestion on Ind and the outcome of the hydrosilylation
catalysis in the presence of NaBPh4 prompted us to
consider whether Ind substituents might have a greater
influence on the reactivities in the absence of initiator.
In principle, the highly electrophilic, coordinatively
unsaturated Ni center in the cationic intermediates [(R-
Ind)Ni(PPh3)]+ generated from 1-3 would be unlikely
to undergo PPh3 dissociation; moreover, these species
should be much more reactive toward PhSiH3 than the
neutral precursors.19 Thus, the presence of bulky Ind
substituents might exert little influence over the reac-
(19) It should be noted that the cationic intermediates can also react
with styrene, but this reaction is much more sluggish than that with
PhSiH3; thus, heating mixtures of styrene and the in-situ-generated
cations over several hours gives poly(styrene), but the presence of
PhSiH3 in the reaction mixture suppresses the polymerization in favor
of the hydrosilylation.
(20) Throughout this discussion, we have assumed that the steric
effects of the SiMe3 groups are much more important than their
inductive effects. In principle, this assumption is tentative because we
have not made systematic measurements on the inductive effects of
Ind substituents in these complexes. However, previous studies of the
reduction potentials of these complexes have indicated that the
electronics of the Ni center is primarily affected by the ligands X and
PR3 (e.g., Me . Cl; PMe3 > PCy3 > PPh3), while Ind substituents seem
to have little influence over reduction potentials.
(21) In our original report on the Ni-catalyzed hydrosilylation of
olefins (ref 7) we have presented some indirect evidence for the
likelihood that the coordinatively unsaturated Ni cations under
discussion are sufficiently electrophilic to abstract H- from silanes.
The fate of the silylium ion is not known yet, but on the basis of the
31P NMR spectrum of a catalytic reaction mixture we have proposed
that they might give rise to phosphonium species such as [Ph3P-
(SiPhH2)][BPh4].
(22) We cannot rule out the possibility of a stepwise addition/
elimination pathway between PhSiH3 and the phosphine-dissociated
species IndNi(Cl), but the requirement in these reactions for Ni(IV)
intermediates makes this alternative less likely than the proposed
concerted pathway.
(17) Previous studies have shown that combining (1-Me-Ind)Ni-
(PPh3)Cl with cationic initiators such as AlCl3 generates species that
homologate PhSiH3 to (PhSiH)n (Mw < 1000): ref 4.
(18) The identity of the gas evolved from the reaction of PhSiH3 with
our complexes has been confirmed to be H2 (using both GC and Raman
spectroscopy) on several occasions during our studies on the oligomer-
ization and hydrosilylation reactions. In the latter reactions, the
evolution of gas subsides partially when the olefin is added. It is
important to note that we have never detected the presence of SiH4,
the only other gas that is likely to evolve in the reactions of PhSiH3;
this is consistent with our findings that silane redistribution reactions
do not occur to any appreciable extent in our systems.

154 Organometallics, Vol. 24, No. 1, 2005
Chen et al.
Scheme 2
influence of the R-substituent is likely due to its role in
inducing the dissociation of the PPh3 ligand, a step that
was found to be rather facile for complex 3. The direct
reaction of PhSiH3 with 3 is reminiscent of the reaction
of (1-Me-Ind)Ni(PPh3)Me with PhSiH3 to give CH4 and
(by inference) the reactive Ni-SiH2Ph derivative.25
Interestingly, while the nature of the Ni-X moiety is
important for the relative rate of the direct metathetic
reaction between IndNi(PPh)3X and PhSiH3, the Ni-Me
derivative being much more reactive than the Ni-Cl
derivative, the more important factor seems to be the
lability of the PPh3 ligand, which is significantly de-
pendent on the Ind-substituent. As a result, the steri-
cally bulky Ni-Cl derivatives such as 3 appear to be
more reactive toward PhSiH3 than their less bulky Ni-
Me counterparts such as (1-Me-Ind)Ni(PPh)Me.
The discovery that bulky Ind ligands can preclude the
need for initiators simplifies the protocol for the catalytic
reactions and might facilitate other reactions. As men-
tioned earlier, complex 3 catalyzes the oligomerization
of PhSiH3 to (PhSiH)n in the absence of any initiators/
activators; we are currently investigating this reactivity.
The M-Cl/Si-H exchange proposed above is well-
precedented in the reactivities of precursors such as
platinic acid or Wilkinson’s catalyst and forms the basis
of the well-developed catalytic chemistry of these com-
plexes (hydrosilylation, Si-Si bond formation, etc.).
More pertinent precedents involving Ni-Cl precursors
also exist in the early studies of Kumada and co-
workers,23 which showed that reacting a number of bis-
(phosphine)NiCl2 complexes with HSiMenCl3-n (n ) 0,
1, 2) leads to Ni(0) species, presumably via Ni-H
intermediates. Therefore, we believe that the Ni-Cl
precursors under discussion, and in particular the in-
situ-generated phosphine-dissociated intermediates, re-
Experimental Section
General Procedures. All manipulations were performed
under a nitrogen atmosphere using standard Schlenk tech-
niques and a glovebox. Dry, oxygen-free solvents were em-
ployed throughout. Ni(PPh3)2Cl2 was prepared from NiCl2‚
6H2O and PPh3. PhSiH3 was prepared from PhSiCl3 and
LiAlH4 according to a published procedure.26 The preparation
of Li[(SiMe3)-Ind] has been reported previously (ref 11); the
same procedure was used for the preparation of Li[1,3-
(SiMe3)2-Ind]. Styrene was purchased from Aldrich, passed
through an alumina column, dried over CaH2, and distilled
under vacuum prior to use. All other chemicals used in the
experiments were obtained from commercial sources and used
as received. A Bruker ARX 400 spectrometer was used for
act directly with PhSiH3 to give the analogous Ni-H
24
complexes and PhSiHnCl3-n
.
1
recording H (400 MHz), 13C{1H} (100.56 MHz), and 31P{1H}
The proposed common intermediate, IndNi(H)L, can
then promote either the hydrosilylation reaction (L )
styrene) or the silane oligomerization (L ) PhSiH3), as
illustrated in Scheme 2. An alternative pathway, not
shown in Scheme 2, would involve a reductive elimina-
tion of Ind-H from the Ni-H intermediate to generate
an Ind-free Ni(0) species that could promote both
catalytic reactions. This scenario would help rationalize
the independence of the hydrosilylation activities from
the Ind substituent and is consistent with our prelimi-
nary findings that Ni(PPh3)4 can catalyze these reac-
tions, albeit less efficiently than the indenyl nickel
precursors.7
NMR (161.92 MHz). The elemental analyses were performed
by the Laboratoire d’Analyse EÄ le´mentaire (Universite´ de
Montre´al).
1-(SiMe3)-IndNi(PPh3)Cl (2). An Et2O solution (80 mL)
of Li[(SiMe3)-Ind] (690 mg, 3.55 mmol) was added dropwise
to a stirring suspension of Ni(PPh3)2Cl2 (2.575 g, 3.93 mmol)
in Et2O (30 mL) at rt. The reaction mixture was stirred for 30
min after the addition. Filtration and evaporation under
vacuum gave a residual solid, which was washed with hexane
(2 × 20 mL) and then extracted four times with a 1:5 mixture
of ether/hexane (total volume of extracts 120 mL). Evaporation
1
of this solution gave the final product (1.49 g, 77% yield). H
NMR (C6D6): 7.75 (m, PPh3), 7.59 (d, 3JH-H ) 8, H7), 7.21 and
7.03 (m, PPh3), 7.20 (t, 3JH-H ) 8, H6), 6.93 (t, 3JH-H ) 8, H5),
6.65 (d, 3JH-H ) 2, H2), 6.39 (d, 3JH-H ) 8, H4), 3.54 (m, H3),
0.66 (s, Si(CH3)3). 13C{1H} NMR (CDCl3, 100.56 MHz): 134.30
Conclusion
2
1
The results presented in this report demonstrate that
the complexes (R-Ind)Ni(PPh3)Cl can catalyze the hy-
drosilylation of styrene in the absence of a cationic
initiator and that the steric bulk of the Ind substituent
affects the catalytic activities in these reactions. The
(d, JC-P ) 11.1 Hz, Cortho), 132.00 (d, JC-P ) 43.7 Hz, Cipso),
3
130.53 (s, Cpara), 129.08 (s, C7a), 128.50 (d, JC-P ) 10.4 Hz,
Cmeta), 127.31 (s, C6), 126.75 (s, C3a), 125.82 (s, C5), 120.91
(s, C7), 117.73 (s, C4), 109.18 (s, C2), 95.8 (d, 2JC-P ) 13.9 Hz,
C1), 72.74 (s, C3), -0.61 (s, (CH3)3Si). 31P{1H} NMR (C6D6):
28.60 (br). Anal. Calcd for C30H30Cl1Ni1P1Si1: C, 66.26; H, 5.56.
Found: C, 66.06; H, 5.54.
1,3-(SiMe3)2-IndNi(PPh3)Cl (3). An Et2O solution (100
mL) of Li[1,3-(SiMe3)2-Ind] (1.07 g, 4.01 mmol) was added
dropwise to a stirring suspension of Ni(PPh3)2Cl2 (3.42 g, 5.22
(23) (a) Kiso, Y.; Kumada, M.; Tamao, K.; Umeno, M. J. Organomet.
Chem. 1973, 50, 297. (b) Kiso, Y.; Kumada, M.; Maeda, K.; Sumitani,
K.; Tamao, K. J. Organomet. Chem. 1973, 50, 311.
(24) It is worth noting that the silane-induced reductions of the bis-
(phosphine)NiCl2 complexes studied by Kumada (ref 23) require high
temperatures (90-120 °C) and long induction periods (15-20 h), in
contrast to the relatively facile catalysis promoted by complex 3; this
difference is presumably related to the more facile phosphine dissocia-
tion from the latter.
(25) Fontaine, F.-G.; Zargarian, D. Organometallics 2002, 21, 401.
(26) Benkeser, R. A.; Landesman, H.; Foster, D. J. J. Am. Chem.
Soc. 1952, 74, 648.

((SiMe3)1 or 2-Indenyl)Ni(PPh3)Cl
Organometallics, Vol. 24, No. 1, 2005 155
mmol) in Et2O (30 mL) at rt. The reaction mixture was stirred
for half an hour after the addition and filtered, and the filtrate
was evaporated under vacuum. The resulting solid was
extracted with a 1:5 mixture of ether/hexane (200 mL), and
the extracts were concentrated to approximately 10 mL; this
led to the precipitation of a dark red powder, which was
isolated by filtration and dried under vacuum (1.48 g, 60%
yield). 1H NMR (C6D6): 7.78 (br, PPh3), 7.19-7.16 (m, aromatic
protons of Ind), 6.99-6.95 (m, aromatic protons of Ind and
solution (for 3). The crystallographic data were collected on a
Bruker AXS SMART 2K diffractometer with graphite-mono-
chromated Cu KR radiation (λ ) 1.54178 Å) at 220(2) K, using
SMART.27 Cell refinement and data reduction were done using
SAINT.28 A SADABS29 absorption correction was applied. The
structures were solved by direct methods using SHELXS9730
and difmap synthesis using SHELXL97;31 the refinements
were done on F2 by full-matrix least squares. The PPh3 and
Cl groups in 2 are disordered. Details of data collection and
refinement are listed in Table 1, while a selection of structural
parameters is listed in Table 2. Complete crystallographic data
for these structures are included in the Supporting Informa-
tion.
PPh3), 0.19 (s, Si(CH3)3). 13C{1H} (CDCl3): 134.44 (d, 2JP-C
)
11.3 Hz, Cortho), 129.86 (Cpara), 127.82 (Cmeta), 125.81 (C3a and
C7a), 120.59 and 120.03 (C5, C6, C4, and C7), 115.91 (C1 and
C3), 88.18 (C2), -0.71 (-SiMe3). 31P{1H} NMR (C6D6): 27.84
(br). Anal. Calcd for C33H38Cl1Ni1P1Si2: C, 64.35; H, 6.22.
Found: C, 63.45; H, 6.01.
Acknowledgment. This work was made possible
thanks to the financial support provided by the Natural
Sciences and Engineering Research Council of Canada
(operating grants to D.Z. and graduate scholarships to
S.B.) and Universite´ de Montre´al (scholarships to C.S.-
S.).
General Procedure for Ni-Catalyzed Hydrosilylation
of Styrene. C6D6 mixtures of the Ni complex (5 µmol), styrene
(500 µmol, ca. 1.0-1.5 M), PhSiH3 (500 or 750 µmol), and
NaBPh4 (50 µmol) were agitated in an ultrasonic bath through-
1
out the reaction time and analyzed by H NMR spectroscopy
over various time intervals. The yields were determined from
a calibration curve prepared as follows. Pure samples of the
hydrosilylation product were obtained from large-scale reac-
tions, purified by distillation, and used for making mixtures
with styrene and PhSiH3 in proportions corresponding to
5-95% yields. The 1H NMR spectra of these mixtures were
then recorded, and the integrations of the appropriate signals
for each component (PhC(CH3)H(SiH2Ph), PhCHdCH2, and
PhSiH3) were plotted against the concentration ratios. The
resulting plot was linear in the range corresponding to yields
below 70-80%, while the higher yield values seemed to follow
a logarithmic function. Fortunately, the entire data set could
be fitted to a Lorentzian function that allowed accurate
determination of yields ranging from 5 to 95% from NMR
integration ratios. The yields obtained from this calibration
curve should be considered accurate to (5%.
Supporting Information Available: Complete details of
the X-ray analysis of 2 and 3, including tables of crystal data,
collection and refinement parameters, bond distances and
angles, anisotropic thermal parameters, and hydrogen atoms.
This information is available free of charge via the Internet
at http://acs.pubs.org.
OM0494420
(27) SMART, Release 5.059, Bruker Molecular Analysis Research
Tool; Bruker AXS Inc.: Madison, WI 53719-1173, 1999.
(28) SAINT, Release 6.06, Integration Software for Single Crystal
Data; Bruker AXS Inc.: Madison, WI 53719-1173, 1999.
(29) Sheldrick, G. M. SADABS, Bruker Area Detector Absorption
Corrections; Bruker AXS Inc.: Madison, WI 53719-1173, 1997.
(30) Sheldrick, G. M. SHELXS, Program for the Solution of Crystal
Structures; University of Goettingen: Germany, 1997.
(31) Sheldrick, G. M. SHELXL, Program for the Refinement of
Crystal Structures; University of Goettingen: Germany, 1997.
X-ray Crystallographic Studies. Crystals suitable for
X-ray diffraction were obtained by recrystallization from an
ether/hexane solution (for 2) or by slow evaporation of a hexane