Steric influence on the reactivity of silyl-o-carboranes: Oxidative-addition reactions involving Si-H and B-H activation

Article abstract of DOI:10.1021/om034194d

The reactivity of mono(silyl)- and bis(silyl)-o-carboranes (HSiR₂)_n(C₂B₁₀H_12-n) (n = 1, R = Me, 1a; n = 1, R = Et, 1b; n = 2, R = Me, 3a; n = 2, R = Et, 3b) toward six-coordinate iridium [(Cp*IrCl₂)₂] and nine-coordinate rhenium [ReH₇(PPh₃)₂] complexes has been investigated. Reactions between the mono(silyl)-o-carboranes (1a,b) and (Cp*IrCl₂)₂ resulted in the formation of four-membered, cyclic seven-coordinate iridium complexes Cp*IrH₂[η¹: η¹-(SiR₂)BC₂B₉H₁₀-Si, B] (R = Me, 2a; R = Et, 2b), where Si-H activation in the mono-(silyl)-o-carborane (1) is accompanied by the concomitant B-H activation of a neighboring boron hydride. The X-ray structure of 2a reveals that the iridium center is coordinated to both silicon and boron in a four-legged piano-stool arrangement. In the reaction between the bis(silyl)-o-carboranes (3a,b) and (Cp*IrCl₂)₂, silylation occurs at both Si-H sites, giving rise to the complexes Cp*IrH₂[η¹:η¹- (SiR₂)₂C₂B₁₀H₁₀- Si,Si′] (R = Me, 4a; R = Et, 4b), in which the metal center forms part of a five-membered metallacycle (Ir-Si-C-C-Si). Interestingly, the reaction of 3a with ReH₇(PPh₃)₂ afforded the kinetically stabilized intermediate (PPh₃)₂ReH₅[η¹-SiMe₂C ₂B₁₀H₁₀(SiMe₂H)-Si] (8), in which only one of the Si-H groups is coordinated, as determined by X-ray crystallography.

Full text of DOI:10.1021/om034194d

Organometallics 2004, 23, 135-143
135
Ster ic In flu en ce on th e Rea ctivity of Silyl-o-ca r bor a n es:
Oxid a tive-Ad d ition Rea ction s In volvin g Si-H a n d B-H
Activa tion
Young-J oo Lee,† J ong-Dae Lee,† Sung-J oon Kim,† J aejung Ko,*,† Il-Hwan Suh,†
Minserk Cheong,*,‡ and Sang Ook Kang*,†
Department of Chemistry, Korea University, 208 Seochang,
Chochiwon, Chung-nam 339-700, Korea, and Department of Chemistry and
Research Institute for Basic Sciences, Kyung Hee University, Seoul 130-701, Korea
Received September 25, 2003
The reactivity of mono(silyl)- and bis(silyl)-o-carboranes (HSiR2)n(C2B10H12-n) (n ) 1, R )
Me, 1a ; n ) 1, R ) Et, 1b; n ) 2, R ) Me, 3a ; n ) 2, R ) Et, 3b) toward six-coordinate
iridium [(Cp*IrCl2)2] and nine-coordinate rhenium [ReH7(PPh3)2] complexes has been
investigated. Reactions between the mono(silyl)-o-carboranes (1a ,b) and (Cp*IrCl2)2 resulted
in the formation of four-membered, cyclic seven-coordinate iridium complexes Cp*IrH2[η1:
η1-(SiR2)BC2B9H10-Si,B] (R ) Me, 2a ; R ) Et, 2b), where Si-H activation in the mono-
(silyl)-o-carborane (1) is accompanied by the concomitant B-H activation of a neighboring
boron hydride. The X-ray structure of 2a reveals that the iridium center is coordinated to
both silicon and boron in a four-legged piano-stool arrangement. In the reaction between
the bis(silyl)-o-carboranes (3a ,b) and (Cp*IrCl2)2, silylation occurs at both Si-H sites, giving
rise to the complexes Cp*IrH2[η1:η1-(SiR2)2C2B10H10-Si,Si′] (R ) Me, 4a ; R ) Et, 4b), in which
the metal center forms part of a five-membered metallacycle (Ir-Si-C-C-Si). Interestingly,
the reaction of 3a with ReH7(PPh3)2 afforded the kinetically stabilized intermediate (PPh3)2-
ReH5[η1-SiMe2C2B10H10(SiMe2H)-Si] (8), in which only one of the Si-H groups is coordinated,
as determined by X-ray crystallography.
In tr od u ction
In particular, the platinum complex (PPh3)2Pt[η1:η1-
(SiMe2)2C2B10H10-Si,Si′] exhibits an unusually high
kinetic stability, which has been attributed to the
unique electronic and steric effects of the o-carborane
moiety and the strengthening of the Pt-Si bond.
As a continuation of our work, we now describe the
oxidative addition reactions between the mono- and
disubstituted silyl-o-carboranes (1, 3) and six-coordinate
iridium [(Cp*IrCl2)2] and nine-coordinate rhenium
[ReH7(PPh3)2] metal complexes. We have been able to
demonstrate that the bulkiness of the ancillary o-
The synthesis and study of organometallic complexes
possessing ancillary silyl-o-carboranyl ligands has re-
ceived considerable attention in the chemistry of group
10 metals, due mainly to its ability to impart a high
degree of kinetic stability to its complexes.1 We have
previously reported that the bis(silyl)-o-carborane reacts
with group 10 metal compounds to yield stable cyclic
bis(silyl)metal complexes,2 which have been identified
as key intermediates in the metal-catalyzed double
silylation of alkynes,3 alkenes,4 nitriles,5 and aldehydes.6
carboranyl group in the silyl ligands (HSiR2)n(C2B10H12-n
)
* To whom correspondence should be addressed. Tel: +82-41-860-
1334. Fax: +82-41-867-5396. E-mail: sangok@korea.ac.kr.
† Korea University.
(1, 3) plays an important role in the Si-H and B-H
activation processes (Chart 1). In the reaction between
(Cp*IrCl2)2 and 1, Si-H activation results in the forma-
tion of a monosilylated complex, in which the ancillary
o-carboranyl group is drawn sufficiently close to the
iridium center to initiate B-H activation, affording the
corresponding cyclometalated species Cp*IrH2[η1:η1-
(SiR2)BC2B9H10-Si,B] (R ) Me, 2a ; R ) Et, 2b). Inter-
estingly, the analogous (bis)silyl compound 3 undergoes
double-silylation reactions at the iridium metal to afford
the chelated Cp*IrH2[η1:η1-(SiR2)2C2B10H10-Si,Si′] (R )
Me, 4a ; R ) Et, 4b) complex. In the reaction between
3a and ReH7(PPh3)2, oxidative addition affords an
intermediate complex, in which the potentially chelating
(bis)silyl compound is bound to the rhenium center
through just one silyl group, as confirmed by X-ray
crystallography. Thus, mono- and disubstituted silyls
comprising a bulky o-carborane backbone have been
‡ Kyung Hee University.
(1) Review: (a) Kang, S. O.; Ko, J . Adv. Organomet. Chem. 2001,
47, 66. (b) Kang, S. O.; Lee, J .; Ko, J . Coord. Chem. Rev. 2002, 231,
47.
(2) (a) Kang, Y.; Lee, J .; Kong, Y. K.; Kang, S. O.; Ko, J . Organo-
metallics 2000, 19, 1722. (b) Kang, Y.; Kang, S. O.; Ko, J . Organo-
metallics 2000, 19, 1216. (c) Kang, Y.; Kang, S. O.; Ko, J . Organo-
metallics 1999, 18, 1818. (d) Kang, Y.; Lee, J .; Kong, Y. K.; Kang, S.
O.; Ko, J . Chem. Commun. 1998, 2343.
(3) (a) Naka, A.; Okazaki, S.; Hayashi, M.; Ishikawa, M. J . Or-
ganomet. Chem. 1995, 499, 35. (b) Ishikawa, M.; Ohshita, J .; Ito, Y.
Organometallics 1986, 5, 1518. (c) Ishikawa, M.; Matsuzawa, S.;
Higuchi, T.; Kamitori, S.; Hirotsu, K. Organometallics 1985, 4, 2040.
(d) Ishikawa, M.; Matsuzawa, S.; Hirotsu, K.; Kamitori, S.; Higuchi,
T. Organometallics 1984, 3, 1930. (e) Kiso, Y.; Tamao, K.; Kumada,
M. J . Organomet. Chem. 1974, 76, 105.
(4) Ishikawa, M.; Okazaki, S.; Naka, A.; Tachibana, A.; Kawauchi,
S.; Yamabe, T. Organometallics 1995, 14, 114.
(5) Reddy, N. P.; Uchimaru, Y.; Lautenschlager, H.-J .; Tanaka, M.
Chem. Lett. 1992, 45.
(6) Uchimaru, Y.; Lautenschlager, H.-J .; Wynd, A. J .; Tanaka, M.;
Goto, M. Organometallics 1992, 11, 2639.
10.1021/om034194d CCC: $27.50 © 2004 American Chemical Society
Publication on Web 12/06/2003

136 Organometallics, Vol. 23, No. 1, 2004
Lee et al.
Ch a r t 1. Mon o- a n d Bis(silyl)m eta l Com p lexes
Dep ictin g both Si-H a n d B-H Activa tion
F igu r e 1. Molecular structure of 2a with thermal el-
lipsoids drawn at the 30% level.
1H, two singlets at δ 0.36 and 0.49 for 2a and a multiplet
at δ 0.86-0.99 for 2b; 13C{1H}, two singlets at δ 5.07
and 5.46 for 2a and four singlets at around δ 4.72-7.92
for 2b. To further corroborate the NMR spectral data,
the X-ray structural analysis of 2a proves beyond doubt
the existence of a cyclometalated silyl ligand.
Sch em e 1. F or m a tion of th e Cyclom eta la te 2
th r ou gh Si-H a n d B-H Activa tion of th e
Mon o(silyl)-o-ca r bor a n e 1a
The coordination geometry around the Ir center in 2a
(Figure 1; selected bond distances and angles are given
in Tables 2 and 3, respectively) is a distorted-square-
pyramidal arrangement, formed by the Cp* ring, the
silyl and boron groups of the metalated o-carboranyl
ligand, and the two hydrides. The positions of the
hydrides were determined from difference maps but
were not refined. The four-membered iridasilacycle of
2a shows a slight folding along the B(1)-Si(1) vector,
which is probably due to the greater steric crowding
around the iridium metal center. This steric crowding
is reflected in the dihedral angle (0.6(4)°) formed
between the [Ir(1), B(3), Si(1)] and [C(1), B(3), Si(1)]
planes. In addition, the iridacyclic ring [Ir(1), B(3), Si(1)]
is tilted by 52.4(2)° relative to the Cp* ring, which in
turn influences the positions of the two hydrides, which
most likely occupy the vacant locations opposite the
iridacycle in a cisoid fashion. The Ir-Si bond distance
is relatively long (2.380(2) Å) compared to the same bond
in the noncyclometalated complex 6 (2.357(1) Å). As in
similar cyclometalated o-carboranyl complexes,8 a cer-
tain amount of strain is evident within the four-
membered ring, such that the associated bond angles
are distorted from their ideal geometries: B(3)-Ir(1)-
Si(1) ) 68.0(2)° instead of 90°; Ir(1)-B(3)-C(1) )
110.4(4)° instead of 120°; B(3)-C(1)-Si(1) ) 87.1(3)°
instead of 120°; C(1)-Si(1)-Ir(1) ) 94.5(2)° rather than
the ideal tetrahedral angle.
a
1
Conditions: (i) /2 (Cp*IrCl2)2, NEt3, THF, 25 °C.
further exploited in chemical transformations such as
Si-H and B-H activation, as shown in Chart 1.
Resu lts a n d Discu ssion s
Rea ction of th e Mon o(silyl)-o-ca r bor a n e w ith
(Cp *Ir Cl2)2. When the mono(silyl) ligand 1 is stirred
with (Cp*IrCl2)2 at room temperature (2 h), the mutually
cis Si-H and B-H groups undergo consecutive activa-
tion to afford the corresponding cyclometalates 2, as
shown in Scheme 1. This reaction was found to occur
only in the presence of base (triethylamine), where a
series of color changes, from orange to yellow and finally
colorless, support the gradual formation of the cyclo-
metalate 2.
The first indication of successful cyclometalation in
2a ,b is the appearance of singlet resonances in the
11B{1H} NMR spectrum at -22.38 and -22.03 ppm,
respectively, which are characteristic of metal-bonded
borons.7 As expected, once the rigid iridasilacycle is
formed, the individual borons of the o-carborane ligand
become chemically and magnetically inequivalent, giv-
ing rise to 10 distinct signals in the 11B{1H} NMR
spectrum. Importantly, this alteration in the stereo-
chemistry also causes the silicon-bound alkyl groups to
become nonequivalent, as confirmed by the occurrence
of the following signals in the relevant NMR spectra:
We postulate that the formation of 2 probably in-
volves the initial oxidative addition of HSiR2(C2B10H11
)
(1) to (Cp*IrCl2)2, followed by the subsequent release
of the ClSiR2(C2B10H11) byproduct and hydride inter-
mediates of the type (Cp*Ir)2HnCl4-n. Successive addi-
tion of 1 to these intermediate hydrides eventually leads
(8) Bae, J .-Y.; Lee, Y.-J .; Kim, S.-J .; Ko, J .; Cho, S.; Kang, S. O.
Organometallics 2000, 19, 1514.
(7) Hoel, E. L.; Hawthorne, M. F. J . Am. Chem. Soc. 1974, 96, 6770.

Addition Reactions Involving Si-H and B-H Activation
Organometallics, Vol. 23, No. 1, 2004 137
Ta ble 1. X-r a y Cr ysta llogr a p h ic Da ta a n d P r ocessin g P a r a m eter s for Com p ou n d s 2a , 6, 8, a n d 9‚2C7H8
2a
6
8
9‚2C7H8
formula
fw
cryst class
space group
Z
B
10C14H33SiIr
C20H33Si2Ir
521.84
triclinic
P1h
B10C42H59Si2P2Re
B10C56H73Si2P2Re
529.79
orthorhombic
Pbca
8
976.31
triclinic
P1h
1158.61
monoclinic
C2/c
2
2
8
cell constants
a, Å
b, Å
19.223(1)
16.73780(9)
13.7827(9)
9.205(1)
11.3828(9)
14.350(2)
16.218(2)
66.73(1)
82.686(9)
71.599(8)
2309.3(5)
2.782
33.296(2)
12.581(2)
27.983(1)
10.5230(6)
12.7868(8)
107.819(5)
91.172(7)
109.873(7)
1098.2(2)
6.187
c, Å
R, deg
â, deg
94.285(4)
γ, deg
V, Å3
4434.5(4)
6.072
11689(2)
2.210
µ, mm-1
cryst size, mm
0.4 × 0.4 × 0.5
0.5 × 0.55 × 0.55
0.3 × 0.4 × 0.4
0.30 × 0.30 × 0.30
d
calcd, g/cm3
1.587
1.578
1.404
1.311
F(000)
2064
516
988
4696
radiation
θ range, deg
h, k, l collected
Mo KR (λ ) 0.7107)
2.12-25.96
1.69-25.97
0-11, -12 to +12,
-15 to +15
4616
1.37-25.97
0-14, -17 to +17,
-19 to +19
9553
1.23-25.97
-40 to +40, -15 to +7,
-34 to +34
23 011
11 454
5743
572
0.0619
0.2208
0.962
0-23, 0-20, 0-16
no. of rflns measd
no. of unique rflns
no. of rflns used in refinement (I > 2σ(I))
no. of params
4385
4348
3040
254
0.0318
0.0747
1.072
4295
3890
223
0.0225
0.0562
1.093
9035
3840
535
0.1141
0.3477
0.974
R1a (I > 2σ(I))
wR2a (all data)
GOF
R1 ) ∑||Fo| - |Fc|| (based on reflections with Fo > 2σF2). wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2; w ) 1/[σ2(Fo2) + (0.095P)2]; P )
a
2
2
[max(Fo2, 0) + 2Fc2]/3 (also with Fo > 2σF2).
2
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) for Com p ou n d s 2a , 6, 8, a n d 9‚2C7H8
Compound 2a
Ir(1)-Si(1)
Ir(1)-C(7)
2.380(2)
2.251(5)
Ir(1)-B(3)
Ir(1)-C(8)
2.109(6)
2.265(6)
Si(1)-C(1)
Ir(1)-C(9)
1.915(6)
2.270(7)
Ir(1)-C(5)
Si(1)-C(3)
2.269(7)
1.864(6)
Ir(1)-C(6)
Si(1)-C(4)
2.267(6)
1.863(6)
Compound 6
Ir(1)-Si(1)
Ir(1)-C(12)
Si(1)-C(7)
2.359(1)
2.252(4)
1.875(4)
Ir(1)-Si(2)
Ir(1)-C(13)
Si(1)-C(8)
2.355(1)
2.253(4)
1.877(4)
Si(1)-C(2)
Ir(1)-C(14)
Si(2)-C(9)
1.896(4)
2.291(4)
1.892(4)
Si(2)-C(1)
Ir(1)-C(15)
1.890(5)
2.265(4)
Ir(1)-C(11)
Si(2)-C(10)
2.261(4)
1.892(5)
Compound 8
Re(1)-Si(1)
P(1)-C(7)
P(2)-C(37)
2.449(5)
1.86(2)
1.83(3)
Re(1)-P(1)
P(1)-C(13)
Si(1)-C(3)
2.438(6)
1.83(2)
1.86(2)
Re(1)-P(2)
P(1)-C(19)
Si(1)-C(4)
2.463(6)
1.83(2)
1.80(3)
Si(1)-C(1)
P(2)-C(25)
Si(2)-C(5)
2.01(2)
1.82(3)
2.01(7)
Si(2)-C(2)
P(2)-C(31)
Si(2)-C(6)
1.86(3)
1.81(2)
1.83(4)
Compound 9‚2C7H8
Re(1)-P(2)
Re(1)-Si(1)
P(1)-C(19)
2.464(3)
2.477(3)
1.85(1)
Re(1)-P(1)
P(1)-C(7)
P(2)-C(31)
2.466(3)
1.81(1)
1.81(1)
Re(1)-Si(2)
P(1)-C(13)
P(2)-C(37)
2.475(3)
P(2)-C(25)
Si(1)-C(1)
Si(2)-C(2)
1.852(1)
1.94(1)
1.95(1)
Si(1)-C(4)
Si(2)-C(6)
Si(1)-C(3)
1.85(1)
1.87(1)
1.86(1)
1.83(1)
1.83(1)
to the formation of 2. A similar mechanism has previ-
ously been proposed for the formation of (Cp*Ir)2H2-
(SiR3)2.9
lographic methods. From the DFT calculations, we can
confirm that the structure of 2a fits quite neatly with
the pseudo-square-pyramidal geometry of the model
ML5 complex. The calculated H-H distance (1.745 Å)
between the two hydrides of complex 2a , coupled with
the H-Si (2.296 Å) and H-B (2.114 Å) distances, all
suggest that complete oxidative addition of the Si-H
and B-H units to the iridium center has occurred.
To our knowledge, complexes 2a ,b are the first
examples of metallacyclobutanes formed through cyclo-
metalation with one of the B-H units of a mono(silyl)-
o-carborane. The use of a base in the cyclometalation
of 2 is noteworthy, since it clearly indicates that its
presence is necessary to initiate intramolecular B-H
activation in o-carboranes. Similarly, it has been noted
that metalation (proceeded by a series of rearrange-
ments) of the analogous o-carboranedithiolate Cp*Ir-
[η1:η1-S2C2B10H10-S,S′] via B-H activation, was found
to proceed at ambient temperatures and below, in the
presence of activated acetylenes.8
Theoretical studies involving geometry optimization
have proven to be efficient in locating hydride positions
in transition-metal complexes.10 Here, we have assigned
the hydride positions in complex 2a using density
functional theory (DFT) calculations, where those oc-
cupying a cisoid disposition are calculated to be more
stable than those with a transoid disposition, by 3.7
kcal/mol. The optimized cisoid structure of 2a is pre-
sented in Figure 2, along with a summary of the most
significant geometrical parameters. The main structural
features of the calculated geometry of 2a are in good
agreement with those determined by X-ray crystal-
(9) (a) Fernandez, M.-J .; Bailey, P. M.; Bentz, P. O.; Ricci, J . S.;
Koetzle, T. F.; Maitlis, P. M. J . Am. Chem. Soc. 1984, 106, 5458. (b)
Fernandez, M.-J .; Bailey, P. M.; Fernandez, M.-J .; Maitlis, P. M.
Organometallics 1983, 2, 164.
(10) Lin, Z.; Hall, M. B. Coord. Chem. Rev. 1994, 135/ 136, 845 and
references therein.

138 Organometallics, Vol. 23, No. 1, 2004
Lee et al.
Ta ble 3. Selected In ter a tom ic An gles (d eg) for Com p ou n d s 2a , 6, 8, a n d 9‚2C7H8
Compound 2a
Si(1)-Ir(1)-B(3)
C(3)-Si(1)-C(4)
Ir(1)-B(3)-B(4)
68.0(2)
106.3(3)
120.5(4)
Ir(1)-B(3)-C(1)
Ir(1)-Si(1)-C(3)
Ir(1)-B(3)-C(2)
110.4(4)
119.5(2)
119.6(4)
B(3)-C(1)-Si(1)
Ir(1)-Si(1)-C(4)
87.1(3)
119.4(2)
C(1)-Si(1)-Ir(1)
Ir(1)-B(3)-B(8)
94.5(2)
137.9(4)
Compound 6
Si(1)-Ir(1)-Si(2)
C(1)-Si(2)-Ir(1)
Ir(1)-Si(2)-C(10)
88.44(4)
106.4(1)
114.1(2)
Ir(1)-Si(1)-C(2)
Ir(1)-Si(1)-C(7)
105.8(1)
115.5(2)
Si(1)-C(2)-C(1)
Ir(1)-Si(1)-C(8)
120.0(3)
115.6(2)
C(2)-C(1)-Si(2)
Ir(1)-Si(2)-C(9)
119.4(3)
114.8(2)
Compound 8
P(1)-Re(1)-P(2)
Re(1)-Si(1)-C(3)
Re(1)-P(1)-C(19)
Si(1)-C(1)-C(2)
105.9(2)
114.4(7)
117.7(9)
124(2)
P(1)-Re(1)-Si(1)
Re(1)-Si(1)-C(4)
Re(1)-P(2)-C(25)
C(1)-C(2)-Si(2)
128.1(2)
116.1(9)
113.9(8)
125(2)
P(2)-Re(1)-Si(1)
Re(1)-P(1)-C(7)
Re(1)-P(2)-C(31)
125.8(2)
117.1(8)
119.5(8)
Re(1)-Si(1)-C(1)
Re(1)-P(1)-C(13)
Re(1)-P(2)-C(37)
116.0(7)
112.1(8)
116.2(9)
Compound 9‚2C7H8
P(2)-Re(1)-P(1)
P(2)-Re(1)-Si(1)
C(7)-P(1)-Re(1)
C(31)-P(2)-Re(1)
C(1)-Si(1)-Re(1)
98.8(1)
126.9(1)
111.6(4)
116.4(4)
109.3(4)
P(2)-Re(1)-Si(2)
P(1)-Re(1)-Si(1)
C(13)-P(1)-Re(1)
C(37)-P(2)-Re(1)
C(2)-Si(2)-Re(1)
117.0(1)
115.8(1)
118.8(5)
118.1(4)
109.6(3)
P(1)-Re(1)-Si(2)
110.9(1)
87.8(1)
118.6(4)
113.4(4)
C(4)-Si(1)-Re(1)
C(3)-Si(1)-Re(1)
C(5)-Si(2)-Re(1)
C(6)-Si(2)-Re(1)
116.3(5)
116.8(5)
116.5(5)
116.9(5)
Si(2)-Re(1)-Si(1)
C(19)-P(1)-Re(1)
C(25)-P(2)-Re(1)
F igu r e 2. DFT optimized structure of 2a with important
structural parameters.
Sch em e 2. F or m a tion of th e Sta ble
Bis(silyl)ir id iu m Com p lex 4a
F igu r e 3. DFT optimized structure of 4a with important
structural parameters.
to that reported for the formation of [Cp*Ir(H)2(SiEt3)2]
from HSiEt3 and (Cp*IrCl2)2.9
The 1H NMR spectra of complexes 3a ,b exhibit signals
confirming the presence of η5-C5Me5, alkylsilyl, and
hydride groups. The corresponding signal integrals,
together with elemental analysis results, suggest the
formation of a complex of formula Cp*IrH2[η2-(SiR2)2-
C2B10H10-Si,Si′]. An FT-IR study of complex 4 reveals
weak ν(Ir-H) bands at 2166 cm-1 with peak intensities
similar to those observed for Cp*IrH2(SiEt3)2 (2135
cm-1).11 To examine the stabilizing influence of the
chelating bis-silylated carboranyl on 4, we performed a
series of density functional calculations on the model
complex 4a , the optimized structure of which is shown,
along with some of its important structural parameters,
in Figure 3. Notably, the DFT calculations reveal that
the transoid disposition of hydride ligands is more stable
a
1
Conditions: (i) /2 (Cp*IrCl2)2, NEt3, THF, 25 °C.
Syn th esis of th e Disila cycloir id iu m Com p lex 4.
The disilacycloiridium complexes 4 were conveniently
prepared (44-62%) by reacting (Cp*IrCl2)2 with bis-
(silyl)-o-carborane (3) in THF, in the presence of tri-
ethylamine at 25 °C (2 h) (Scheme 2). Chromatographic
separation of the crude product afforded large, colorless
plates, which are freely soluble in hydrocarbon solvents
and stable to air. We believe that 4 arises from the
reaction between 3 and (Cp*IrCl2)2 in a manner similar
(11) Fernandez, M.-J .; Maitlis, P. M. J . Chem. Soc., Dalton Trans.
1984, 2063.

Addition Reactions Involving Si-H and B-H Activation
Organometallics, Vol. 23, No. 1, 2004 139
F igu r e 5. DFT optimized structure of 6 with important
structural parameters.
F igu r e 4. Molecular structure of 6 with thermal ellipsoids
drawn at the 30% level.
The structural analysis of the η5-bonded C5Me5 ring
(average Ir-C ) 2.264(4) Å) reveals a uniformity within
the ring carbon-carbon bonds (average C-C ) 1.428(7)
Å), implying it has an undistorted conformation. The
ring is bisected by a mirror plane containing the
hydrides (average Ir-H ) 1.649 Å), in which the two
dimethylsilyl ligands are reflected (Ir-Si ) 2.357(1) Å).
The Ir-Si bond length is comparable with the same
bond lengths reported for the octahedral and penta-
coordinate Ir(III) complexes, as well as the Ir-Si bond
distance reported for the seven-coordinate Ir(V) si-
lyls.11,14 The complexes may therefore be defined as
possessing a total of five formally uninegative ligands
about the iridium center, giving the metal a formal +5
oxidation state. Using DFT calculations, we observed
that complex 6 is more stable in the transoid rather
than cisoid disposition of hydrides, by 5.8 kcal/mol (see
the Supporting Information). The optimized structure
of 6 is shown along with some of its major structural
parameters in Figure 5.
than the cisoid structure by 9.2 kcal/mol (see the
Supporting Information).
To verify the significance of the bis-silylated o-
carboranyl ligand, we performed a similar reaction
between (Cp*IrCl2)2 and the analogous bis(silyl)benzene
5, as shown in eq 1.
For unequivocal characterization, we also attempted
the X-ray structural determination of 7. However, poorly
diffracting crystals precluded a satisfactory analysis (see
the Supporting Information). Nevertheless, the struc-
tural data were sufficient to establish that the iridium
metal adopts the expected “four-legged piano stool”
geometry, as defined by the two silyl groups of the
chelated bis(silyl)-o-carborane (3), a single hydride, and
the appearance of a chloride ligand. It is worthy of note
that the ligand arrangement in complex 7 is similar to
that found in the dihydride complex 6. Interestingly, the
difference between complexes 4 and 7 is even more
In addition to the expected bis-silylated product 6, we
observed the second bis-silylated species 7, toward the
end of the reaction, which was isolated in a ca. 1:1.5
ratio with 6. The X-ray crystallographic determination
of 6 at room temperature (Figure 4) revealed a four-
legged piano-stool geometry, in which the silyl and
hydride ligands are transoid. The positions of the
hydrides were determined from difference maps. The
metal-silicon and metal-hydrogen bond lengths and
angles are similar to the values reported for the corre-
sponding Cp*MH2(SiEt3)2 (M ) Rh, Ir) complexes.12,13
(13) (a) Schubert, U.; Mu¨ller, J .; Alt, H. G. Organometallics 1987,
6, 469. (b) Matarossa-Tchiroukhine, E.; J aouen, G. Can. J . Chem. 1988,
66, 2157.
(14) (a) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S.,
Rappoport, Z., Eds.; Wiley: New York, 1991; pp 264, 343. (b) Goikh-
man, R.; Aizenberg, M.; Kraatz, H.-B.; Milstein, D. J . Am. Chem. Soc.
1995, 117, 5865. (c) Aizenberg, M.; Milstein, D. J . Am. Chem. Soc. 1995,
117, 6456. (d) Tanke, R. S.; Crabtree, R. H. Organometallics 1991, 10,
415. (e) Loza, M.; Faller, J . W.; Crabtree, R. H. Inorg. Chem. 1995, 34,
2937. (f) Esteruelas, M. A.; Lahoz, F. J .; Onˇate, E.; Oro, L. A.;
Rodriguez, L. Organometallics 1996, 15, 823.
(12) (a) Fernandez, M.-J .; Bailey, P. M.; Bentz, P. O.; Ricci, J . S.;
Koetzle, T. F.; Maitlis, P. M. J . Am. Chem. Soc. 1984, 106, 5458. (b)
Ricci, J . S.; Koetzle, T. F.; Fernandez, M.-J .; Maitlis, P. M.; Green, J .
C. J . Organomet. Chem. 1986, 299, 383.

140 Organometallics, Vol. 23, No. 1, 2004
Lee et al.
Sch em e 3. Sequ en tia l Silyla tion Rea ction s
fascinating, since in the latter only the planar phenylene
unit is involved in metalation. From the evidence to
date, we can infer that 6 and 7 (as well as their
precursor 5) are less sterically congested than their
o-carborane counterpart 4, since their planar five-
membered rings take up smaller volume, resulting in
less strain on the bis(silyl)iridium center. Consequently,
the coordination of a chloride ligand in 7 might be the
result of the steric constraints imposed by the planar
phenylene backbone. It was noted that a decrease in the
steric bulk at the bis(silyl)iridium center allows a
greater number of chlorides access to the coordination
sites. By comparison with the parent ligands 3a and 5,
the values derived from DFT calculations suggest the
structure of 4a is preferred to 6 by some 7.9 kJ /mol (see
the Supporting Information). From a qualitative stand-
point, computational calculations derived for complex
4a are consistent with the corresponding experimental
results in that the o-carboranyl derivative 4 has been
readily prepared without the formation of side products.
Isola tion of a Kin etica lly Sta bilized Mon o-Silyl-
a ted Rh en iu m Hyd r id e (9). The oxidative addition
of Si-H to transition-metal polyhydrides is a well-
established area of study,15 particularly when chelating
bis-silylated compounds are involved.16 In the case of
the reaction between the chelating bis(silyl)benzene (5)
and ReH7(PPh3)2, an intermediate complex was isolated
in which only one Re-Si bond was evident. While the
structural details of this species have so far remained
elusive, we propose that, by replacement of the phenyl
group in 5 with the more bulky o-carboranyl unit, it
might be possible to produce an intermediate analogue
that would be sufficiently more stable to allow a more
definitive structural analysis. We feel the bis(silyl)-o-
carborane 3 is a most promising candidate for this
purpose, on the grounds that 3 is sterically more
protecting than the corresponding arylsilane 5. In fact,
3 has been successfully employed in the isolation of
several key intermediates obtained from double-silyl-
a
betw een 3a a n d ReH7(P P h 3)2
a
Conditions: (i) ReH7(PPh3)2, THF, 25 °C; (ii) toluene,
reflux.
ation reactions, such as L2M [η1:η1-(SiR2)2C2B10H10
-
Si,Si] (M ) Pt, L ) PPh3; M ) Ni, L ) PEt3).2
Indeed, the analogous reaction between 3a and
ReH7(PPh3)2 at room temperature generated an air-
stable, microcrystalline solid identical with the inter-
mediate species isolated in the reaction between 5 and
ReH7(PPh3)2, (Scheme 3).
F igu r e 6. Molecular structure of 8 with thermal ellipsoids
drawn at the 30% level.
nation. From the molecular structure of 8 shown in
Figure 6, we observe the expected tricapped-trigonal-
prismatic structure in which only one of the silyl groups
is bound by the metal, confirming the bis(silyl)-o-
carborane ligand to be essentially monodentate. The
precise location of the six hydrides in 8 could not be
confirmed by X-ray crystallographic means; however, we
propose they are positioned in the axial positions of a
tricapped trigonal prism, in accordance with similar
structural determinations on ReH6(SiPh3)(PPh3)2.15d
The 1H/13C NMR results of the mono(silyl)rhenium
complex are in complete agreement with the crystal
structure of 8 (Figure 6).
The 1H NMR spectrum of compound 8 exhibits
resonances which confirm the presence of triphenylphos-
phine (7.14-7.70 ppm), two nonequivalent dimethylsilyl
groups (0.38 and 0.83 ppm), and two nonequivalent
metal hydride protons (-5.62 and -5.28 ppm (2J H-H
)
19 Hz)). Recrystallization of the crude intermediate
(PPh3)2ReH6[η1-(SiMe2)C2B10H10(SiMe2H)-Si] (8) af-
forded crystals suitable for X-ray structural determi-
(15) (a) Delpech, F.; Sabo-Etienne, S.; Donnadieu, B.; Chaudret, B.
Organometallics 1998, 17, 4926. (b) Buil, M.; Espinet, P.; Esteruelas,
M. A.; Lahoz, F. J .; Lledo´s, A.; Mart´ınez-Ilarduya, J . M.; Maseras, F.;
Modrego, J .; Onˇate, E.; Oro, L. A.; Sola, E.; Valero, C. Inorg. Chem.
1996, 35, 1250. (c) Takao, T.; Suzuki, H.; Tanaka, M. Organometallics
1994, 13, 2554. (d) Luo, X.-L.; Baudry, D.; Boydell, P.; Charpin, P.;
Nierlich, M.; Ephritikhine, M.; Crabtree, R. H. Inorg. Chem. 1990, 29,
1511.
(16) (a) Fan, M.-F.; Lin, Z. Organometallics 1999, 18, 286. (b)
Delpech, F.; Sabo-Etienne, S.; Chaudret, B.; Daran, J .-C. J . Am. Chem.
Soc. 1997, 119, 3167. (c) Loza, M.; Faller, J . W.; Crabtree, R. H. Inorg.
Chem. 1995, 34, 2937. (d) Loza, M. L.; de Gala, S. R.; Crabtree, R. H.
Inorg. Chem. 1994, 33, 5073.
In an attempt to oxidatively add the remaining Si-H
to the rhenium center, a toluene solution of 8 was
refluxed for 1 h. Recrystallization of the crude material
from toluene afforded the expected cyclic bis(silyl)-
rhenium hydride (PPh3)2ReH5[η1:η1-(SiMe2)2C2B10H10
-
(SiMe2H)-Si,Si] (9). The composition and stereochem-
1
istry of 9 were elucidated from 11B, H, and 13C NMR

Addition Reactions Involving Si-H and B-H Activation
Organometallics, Vol. 23, No. 1, 2004 141
used without purification. (Cp*IrCl2)217 and ReH7(PPh3)218 were
prepared according to the literature procedures. All 1H (300.1
MHz, measured in CDCl3), 13C (75.4 MHz, measured in CDCl3),
31P (121.4 MHz, measured in CDCl3), and 29Si (59.60 MHz,
measured in CDCl3) NMR spectra were recorded on a Varian
Mercury-300BB spectrometer unless otherwise stated. 1H and
13C NMR chemical shifts are reported relative to Me4Si and
were determined by reference to the residual 1H or 13C solvent
peaks. Elemental analyses were performed with a Carlo Erba
Instruments CHNS-O EA1108 analyzer.
Syn th esis of Mon o(silyl)-o-ca r bor a n e 1. A representa-
tive procedure is as follows: to a solution of 0.72 g (5.0 mmol)
of o-carborane in 80 mL of THF, precooled to -78 °C, was
added 3.13 mL of n-butyllithium (1.6 M in hexanes). The
reaction mixture was warmed to room temperature and stirred
for 2 h, whereupon it was transferred, via cannula, to a
suspension of 5.5 mmol (1.1 equiv) of dimethylchlorosilane in
20 mL of Et2O that was cooled to -78 °C. The resultant yellow
mixture was warmed to room temperature and stirred for 2
h. The volatiles were then removed under reduced pressure;
the crude mixture was taken up in a minimal amount of Et2O
and filtered through a 1 × 5 cm pad of silica gel on a glass
frit. Removal of the volatiles provided the final crude product,
which was further purified from toluene at -5 °C to provide
pure dimethylsilyl-o-carborane 1a as a colorless oil. Yield: 87%
F igu r e 7. Molecular structure of 9 with thermal ellipsoids
drawn at the 30% level.
spectra and elemental analysis data. The multinuclear
NMR results of the bis(silyl)rhenium complex are in
complete agreement with the crystal structure of 9
(Figure 7). Furthermore, the structure of 9 shows a
strong resemblance to that of the previously reported
silyl hydride (PPh3)2ReH5[η1:η1-(SiMe2)2C6H4-Si,Si′],16d
which adopts a dodecahedral conformation with a tran-
soid disposition of silyls and hydrides.
1
3
(0.88 g, 4.35 mmol). H NMR: δ 4.10 (m, 1H, SiH, J H-H ) 4
3
Hz), 3.38 (br, 1H, Ccab-H), 0.33 (d, 6H, SiMe2, J H-H ) 4 Hz).
13C{1H} NMR: δ -3.94 (SiMe2). IR (KBr, cm-1): 2983 w, 2977
w (νCH), 2610 w, 2582 s (νBH), 2156 w (νSiH). Anal. Calcd for
B
10C4H18Si: C, 23.51; H, 8.88. Found: C, 23.43; H, 8.91.
1b. A procedure analogous to the preparation of 1a was
used, but starting from diethylchlorosilane (0.68 g, 5.5 mmol)
in benzene. Thus, 1b was purified from toluene at -5 °C.
Yield: 81% (0.93 g, 4.05 mmol). 1H NMR: δ 3.89 (m, 1H, SiH,
3J H-H ) 3 Hz), 3.38 (br, 1H, Ccab-H), 1.06 (t, 6H, SiCH2Me,
3J H-H ) 8 Hz), 0.84 (m, 4H, SiCH2Me). 13C{1H} NMR: δ 7.69,
3.22 (SiEt2). IR (KBr, cm-1): 2983 w, 2971 w (νCH), 2587 s (νBH),
2143 w (νSiH). Anal. Calcd for B10C6H22Si: C, 13.03; H, 12.03.
Found: C, 13.07; H, 12.07.
Su m m a r y
The present work reports a series of novel addition
reactions via Si-H and B-H activation. Thus, silyl
compounds comprising a bulky ancillary o-carboranyl
backbone have been further exploited in chemical
transformations involving Si-H and B-H activation.
Because of the presence of a bulky o-carboranyl unit,
the mono(silyl)-o-carborane (1) exhibits unusual reac-
tivities which have not been observed in the related
complex 5. For example, the reaction of 1 with six-
coordinate (Cp*IrCl2)2 affords the cyclometalated prod-
ucts of a coordinated silyl-o-carboranyl ligand. The
reaction of the bis(silyl)-o-carborane 3 with “half-
sandwich” six-coordinate iridium complexes produced
seven-coordinate iridium hydrides with a four-legged
“piano-stool” geometry. The reaction of ReH7(PPh3)2
with the chelating bis(silyl)-o-carborane (3a ) also affords
an unusual nine-coordinate rhenium product which
contains a single silyl group tether.
Syn th esis of Bis(silyl)-o-ca r bor a n e 3. A representative
procedure is as follows: to a solution of 0.72 g (5.0 mmol) of
o-carborane in 80 mL of THF, precooled to -78 °C, was added
6.90 mL of n-butyllithium (1.6 M in hexanes). The reaction
mixture was warmed to room temperature and stirred for 2
h, whereupon it was transferred, via cannula, to a suspension
of 11.0 mmol (2.2 equiv) of dimethylchlorosilane in 20 mL of
Et2O that was cooled to -78 °C. The resultant yellow mixture
was warmed to room temperature and stirred for 2 h. The
solution was reduced in vacuo to about half its orginal volume,
and some insoluble material was removed by filtration. The
crude residue was purified from toluene at -5 °C to provide
pure bis(dimethylsilyl)-o-carborane 3a as
a colorless oil.
Yield: 89% (1.15 g, 4.45 mmol). 1H NMR (C6D6): δ 4.01 (m,
3
3
2H, SiH, J H-H ) 4 Hz), -0.03 (d. 12H, SiMe2, J H-H ) 4 Hz).
13C{1H} NMR (C6D6): δ -2.31 (SiMe2). IR (KBr, cm-1): 2981
w (νCH), 2572 s (νBH) 2554 (νSiH). Anal. Calcd for C6H24B10Si2:
C, 27.46; H, 9.22. Found: C, 27.55; H, 9.19.
3b. A procedure analogous to the preparation of 3a was
used, but starting from diethylchlorosilane (1.35 g, 5.5 mmol)
in benzene. Thus, 3b was crystallized from toluene at -5 °C.
Yield: 83% (1.31 g, 4.15 mmol). 1H NMR: δ 3.98 (m, 1H, SiH,
3J H-H ) 3 Hz), 1.06 (t, 12H, SiCH2Me, 3J H-H ) 7 Hz), 0.89 (m,
8H, SiCH2Me). 13C{1H} NMR: δ 7.83, 4.11 (SiEt2). IR (KBr,
cm-1): 2993 w, 2975 w (νCH), 2581 s (νBH), 2152 w (νSiH). Anal.
Calcd for B10C10H32Si2: C, 37.70; H, 10.13. Found: C, 37.84;
H, 10.16.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under a dry, oxygen-free nitrogen or argon atmosphere using
standard Schlenk techniques or in a Vacuum Atmospheres
HE-493 drybox. Diethyl ether, toluene, hexane, and pentane
were distilled under nitrogen from sodium/benzophenone.
Dichloromethane was dried with CaH2. Benzene-d6 was dis-
tilled under nitrogen from sodium and stored in a Schlenk
storage flask until needed. CDCl3 was predried under CaH2
and vacuum-transferred. n-BuLi (1.6 M in hexanes) and
1,2-dichlorotetramethyldisilane were used as received from
Aldrich. o-Carborane was purchased from KATCHEM Ltd. and
(17) Kong, J . W.; Moseley, K.; Maitlis, P. M. J . Am. Chem. Soc. 1969,
91, 5970.
(18) Baudry, D.; Ephritikhine, M.; Felkin, H. J . Organomet. Chem.
1982, 224, 363.

142 Organometallics, Vol. 23, No. 1, 2004
Lee et al.
Rea ction of th e Mon o- or Bis(silyl)-o-ca r bor a n e w ith
(Cp *Ir Cl2)2. A representative procedure is as follows: a 3.0
mmol solution of 1a in THF (20 mL) was added to a stirred
solution of (Cp*IrCl2)2 (0.40 g, 0.5 mmol) in THF (30 mL) cooled
to -78 °C. A 0.25 g portion of NEt3 (2.5 mmol) was added with
stirring over 30 min. The reaction mixture was then allowed
to react at 0 °C for 1 h, and the solution was stirred for another
2 h at room temperature. The solution gradually turned yellow,
suggesting the formation of a metal silyl complex. The solution
was reduced in vacuo to about half its original volume, and
some insoluble material was removed by filtration. The solu-
tion was removed under vacuum, and the resulting residue
was taken up in a minimum of methylene chloride and then
transferred to a column of silica gel. The crude residue was
purified by column chromatography, affording >98% pure
complex as colorless crystals of 2a . Yield: 60% (0.079 g, 0.15
mixture was then allowed to react at 0 °C for 1 h, and the
solution was stirred for another 2 h at room temperature. The
orange solution turned yellow as the solution warmed. The
solution was filtered in air, and the solvent was removed under
reduced pressure. The resultant residue was extracted with
60 mL of hexane and reduced to 10 mL. Cooling at -30 °C
overnight gave a yellow solid which was dried under vacuum,
recrystallized from cold hexane, and characterized as 6 (0.038
1
g, 0.072 mmol, 29%). Mp: 165-167 °C dec. H NMR: δ 7.55
(m, 2H, C6H4), 7.18 (m, 2H, C6H4), 2.18 (s, 15H, C5Me5), 0.53
(s, 12H, SiMe2), -16.30 (s, 2H, Ir-H2). 13C{1H} NMR: δ 131.21,
126.83 (Ph), 97.54 (C5Me5), 10.69 (C5Me5), 6.19 (SiMe2). 29Si
NMR: δ 1.05 (SiMe2). IR (KBr, cm-1): 3040 w, 2980 w, 2963
m, 2937 w (νCH), 2164 w (νIrH). Anal. Calcd for C20H33Si2Ir: C,
45.96; H, 6.37. Found: C, 45.80; H, 6.35.
The remaining solid was passed through a short column of
silica gel with hexane/CHCl3 (90/10) as the eluent. A 0.060 g
(0.011 mmol, 43% yield) amount of 7 was obtained after
removal of the solvent. Mp: 172-173 °C dec. 1H NMR: δ 7.52
(m, 2H, C6H4), 7.21 (m, 2H, C6H4), 1.95 (s, 15H, C5Me5), 0.58
(s, 6H, SiMe2), 0.55 (s, 6H, SiMe2), -16.06 (s, 1H, Ir-H).
13C{1H} NMR: δ 131.94, 127.39 (Ph), 102.29 (C5Me5), 9.72
(C5Me5), 7.85 (SiMe2), -0.42 (SiMe2). 29Si NMR: δ 5.25 (SiMe2).
IR (KBr, cm-1): 3044 w, 2968 m, 2887 w (νCH), 2039 w (νIrH).
Anal. Calcd for C20H32Si2ClIr: C, 43.15; H, 5.80. Found: C,
43.29; H, 5.82.
1
mmol). Mp: 163-165 °C dec. H NMR: δ 2.91 (br, 1H, Ccab-
H), 2.13 (s, 15H, C5Me5), 0.49 (s, 3H, SiMe2), 0.36 (s, 3H, SiMe2),
-14.88 (br, 1H, Ir-H), -14.99 (br, 1H, Ir-H). 13C{1H} NMR:
δ 98.84 (C5Me5), 10.33 (C5Me5), 5.46 (SiMe2), 5.07 (SiMe2). 11B
1
1
NMR: δ -0.86 (d, 2B, J B-H ) 150 Hz), -2.62 (d, 2B, J B-H
)
1
1
160 Hz), -8.76 (d, 3B, J B-H ) 150 Hz), -12.08 (d, 2B, J B-H
) 150 Hz), -22.38 (s, 1B). 29Si NMR: δ -31.92 (SiMe2). IR
(KBr, cm-1): 3047 w, 2983 w, 2962 w, 2935 w, 2910 w (νCH),
2596 s, 2565 s (νBH), 2187 w, 2165 w (νIrH). Anal. Calcd for
B
10C14H33SiIr: C, 31.56; H, 6.25. Found: C, 31.67; H, 6.27.
2b. A procedure analogous to the preparation of 2a was
Rea ction of 1,2-Bis(d im eth ylsilyl)-o-ca r bor a n e (3a )
w ith ReH7(P P h 3)2. Under argon, ReH7(PPh3)2 (0.14 g, 0.2
mmol) was added to a stirred solution of complex 3a (0.052 g,
0.2 mmol) in THF (10 mL) cooled to 0 °C. The pale yellow
solution slowly turned dark yellow. After it was stirred for 30
min, the solution was evaporated to dryness. The crude residue
was purified from toluene at -5 °C to provide pure silyl-
tethered product 8 as yellow crystals. Yield: 0.15 g (0.15 mmol,
used, but starting from 3.0 mmol of 1b. After flash chroma-
tography on silica gel with hexane/CHCl3 (90/10), 2b was
isolated as colorless solids. Yield: 53% (0.074 g, 0.13 mmol).
1
Mp: 169-170 °C dec. H NMR: δ 2.97 (br, 1H, Ccab-H), 2.14
(s, 15H, C5Me5), 0.86-0.99 (m, 10H, SiEt2), -15.04 (br, 1H,
Ir-H2), -15.37 (br, 1H, Ir-H2). 13C{1H} NMR: δ 98.85
(C5Me5), 10.43 (C5Me5), 7.92 (SiCH2Me), 7.53 (SiCH2Me), 5.57
1
(SiCH2Me), 4.72 (SiCH2Me). 11B NMR: δ -0.68 (d, 2B, J B-H
1
75%). Mp: 153-155 °C dec. H NMR: δ 7.14-7.70 (m, 30H,
1
1
) 140 Hz), -2.82 (d, 2B, J B-H ) 140 Hz), -8.50 (d, 3B, J B-H
PPh3), 4.10 (m, 1H, SiH), 0.83 (s, 6H, SiMe2), 0.38 (d, 6H, SiMe2,
1
2
3J H-H ) 7 Hz), -5.28 (t, 6H, Re-H, J H-H ) 19 Hz). 13C{1H}
) 130 Hz), -12.32 (d, 2B, J B-H ) 130 Hz), -21.99 (s, 1B).
29Si NMR: δ -21.65 (SiEt2). IR (KBr, cm-1): 3045 w, 2991 w,
2959 w, 2943 w, 2910 w (νCH), 2613 s, 2590 s (νBH), 2195 w,
2162 w (νIrH). Anal. Calcd for B10C16H37SiIr: C, 34.27; H, 6.66.
Found: C, 34.14; H, 6.64.
2
NMR: δ 127.82-134.01 (PPh3), 20.85 (SiMe2H), -2.35 (SiMe ).
31P{1H} NMR: δ 9.95, 23.30 (PPh3). IR (KBr, cm-1): 3053 w,
2978 w (νCH), 2583 s (νBH) 1983 w, 1865 w (νReH). Anal. Calcd
for B10C42H59Si2P2Re: C, 51.51; H, 6.08. Found: C, 51.70; H,
6.06.
4a . A procedure analogous to the preparation of 2a was
used, but starting from 3.0 mmol of 3a . After flash chroma-
tography on silica gel with hexane/CHCl3 (90/10), 4a was
isolated as colorless solids. Yield: 62% (0.091 g, 0.16 mmol).
9. A solution of 8 (0.098 g, 0.1 mmol) in toluene (20 mL)
was heated for 1 h at 110 °C; conversion into 9, as monitored
1
by H NMR spectroscopy, was quantitative. The solvent was
1
Mp: 181-183 °C dec. H NMR: δ 2.10 (s, 15H, C5Me5), 0.46
removed in vacuo and the resulting solid crystallized from
toluene to give 0.066 g (0.068 mmol) of colorless microcrystals
(s, 12H, SiMe2), -16.15 (s, 2H, Ir-H2). 13C{1H} NMR: δ 98.73
(C5Me5), 10.45 (C5Me5), 5.40 (SiMe2). 11B NMR: δ -0.86 (d,
1
(68% yield). Mp: 166-168 °C dec. H NMR: δ 7.08-7.30 (m,
1
1
2
2B, J B-H ) 140 Hz), -5.37 (d, 2B, J B-H ) 145 Hz), -10.15
30H, PPh3), 0.35 (s, 12H, SiMe2), -6.75 (t, 5H, Re-H, J H-H
)
(d, 4B, J B-H ) 160 Hz), -12.96 (d, 2B, J B-H ) 140 Hz). 29Si
NMR: δ 14.01 (SiMe2). IR (KBr, cm-1): 2961 w (νCH), 2583 s
(νBH), 2166 w (νIrH). Anal. Calcd for B10C16H39Si2Ir: C, 32.53;
H, 6.66. Found: C, 32.43; H, 6.63.
1
1
19 Hz). 13C{1H} NMR: δ 133.66, 133.60, 130.05, 128.02 (PPh3),
13.97 (SiMe2). 31P{1H} NMR: δ 23.34 (PPh3). IR (KBr, cm-1):
3057 w, 2957 m (νCH), 2590 (νBH), 1981 w, 1867 w (νReH). Anal.
Calcd for B10C42H57Si2P2Re: C, 51.62; H, 5.88. Found: C, 51.43;
H, 5.86.
4b. A procedure analogous to the preparation of 2a was
used, but starting from 3.0 mmol of 3b. After flash chroma-
tography on silica gel with hexane/CHCl3 (90/10), 4b was
isolated as colorless solids. Yield: 44% (0.071 g, 0.11 mmol).
Cr ysta l Str u ctu r e Deter m in a tion . Crystals of 2a , 6, 8,
and 9 were obtained from toluene at -10 °C, sealed in glass
capillaries under argon, and mounted on the diffractometer.
Data were collected and corrected for Lorentz and polarization
effects. Each structure was solved by the application of direct
methods using the SHELXS-96 program19a and least-squares
refinement using SHELXL-97.19b After anisotropic refinement
of all non-H atoms several H atom positions could be located
in difference Fourier maps. These were refined isotropically,
while the remaining H atoms were calculated in idealized
positions and included into the refinement with fixed atomic
contributions. Further detailed information is listed in Table
1.
1
Mp: 185-186 °C dec. H NMR: δ 2.13 (s, 15H, C5Me5), 0.96,
-1.17 (m, 20H, SiEt2), -15.86 (s, 2H, Ir-H2). 13C{1H} NMR:
δ 98.14 (C5Me5), 11.51 (C5Me5), 7.83 (SiCH2Me), 5.24 (SiCH2Me).
11B NMR: δ -2.12 (d, 2B, 1J B-H ) 150 Hz), -8.99 (d, 2B, 1J B-H
1
) 150 Hz), -13.60 (d, 4B, J B-H ) 160 Hz), -14.91 (d, 2B,
1J B-H ) 140 Hz). 29Si NMR: δ 30.10 (SiEt2). IR (KBr, cm-1):
3069 s, 2963 m, 2874 m (νCH), 2606 s (νBH), 2166 w (νIrH). Anal.
Calcd for B10C20H47Si2Ir: C, 37.13; H, 7.33. Found: C, 37.27;
H, 7.31.
R ea ct ion of 1,2-Bis(d im et h ylsilyl)b en zen e (5) w it h
(Cp *Ir Cl2)2. A 3.0 mmol solution of 5 in THF (20 mL) was
added to a stirred solution of (Cp*IrCl2)2 (0.40 g, 0.5 mmol) in
THF (30 mL) cooled to -78 °C. A 0.253 g portion of NEt3 (2.5
mmol) was added with stirring over 30 min. The reaction
(19) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, A46, 467.
(b) Sheldrick, G. M. SHELXL, Program for Crystal Structure Refine-
ment; University of Go¨ttingen, Go¨ttingen, Germany, 1997.

Addition Reactions Involving Si-H and B-H Activation
Organometallics, Vol. 23, No. 1, 2004 143
Com p u ta tion a l Deta ils. Stationary points on the potential
energy surface were calculated using the Amsterdam Density
Functional (ADF) program, developed by Baerends et al.20,21and
vectorized by Ravenek.22 The numerical integration scheme
applied for the calculations was developed by te Velde et al.23,24
The geometry optimization procedure was based on the method
due to Versluis and Ziegler.25 The electronic configurations of
the molecular systems were described by double-ú STO basis
sets with polarization functions for the H, B, and C atoms,
while triple-ú Slater type basis sets were employed for the Si
and Ir atoms.26,27 The 1s electrons of B and C, the 1s-2p
electrons of Si, and the 1s-4d electrons of Ir were treated as
frozen cores. A set of auxiliary28 s, p, d, f, and g STO functions,
centered on all nuclei, was used in order to fit the molecular
density and the Coulomb and exchange potentials in each SCF
cycle. Energy differences were calculated by augmenting the
local exchange-correlation potential by Vosko et al.29 with
Becke’s30 nonlocal exchange corrections and Perdew’s31 non-
local correlation corrections (BP86). Geometries were opti-
mized including nonlocal corrections at this level of theory.
First-order Pauli scalar relativistic corrections32,33 were added
variationally to the total energy for all systems. In view of the
fact that all systems investigated in this work show a large
HOMO-LUMO gap, a spin-restricted formalism was used for
all calculations. No symmetry constraints were used.
Ack n ow led gm en t. We are grateful to the Korea
Research Foundation (Grant No. KRF-2002-015-CP0200)
for their financial support.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data (excluding structure factors) for the structures 2a , 6, 8,
and 9‚2C7H8 reported in this paper and listings giving opti-
mized geometries of the crucial structures reported (Cartesian
coordinates, in Å); crystallographic data are also available in
electronic form as CIF files. This material is available free of
charge via the Internet at http://pubs.acs.org.
(20) Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41.
(21) Baerends, E. J .; Ros, P. Chem. Phys. 1973, 2, 52.
(22) Ravenek, W. In Algorithms and Applications on Vector and
Parallel Computers; te Riele, H. J . J ., Dekker, T. J ., van de Horst, H.
A., Eds.; Elsevier: Amsterdam, The Netherlands, 1987.
(23) te Velde, G.; Baerends, E. J . J . Comput. Chem. 1992, 99, 84.
(24) Boerrigter, P. M.; te Velde, G.; Baerends, E. J . Int. J . Quantum
Chem. 1988, 33, 87.
(25) Versluis, L.; Ziegler, T. J . Chem. Phys. 1988, 88, 322.
(26) Snijders, J . G.; Baerends, E. J .; Vernoijs, P. At. Nucl. Data
Tables 1982, 26, 483.
OM034194D
(27) Vernoijis, P.; Snijders, J . G.; Baerends, E. J . Slater Type Basis
Functions for the Whole Periodic System; Internal Report (in Dutch);
Department of Theoretical Chemistry, Free University: Amsterdam,
The Netherlands, 1981.
(28) Krijn, J .; Baerends, E. J . Fit Functions in the HFS Method;
Internal Report (in Dutch); Department of Theoretical Chemistry, Free
University: Amsterdam, The Netherlands, 1984.
(29) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200.
(30) Becke, A. Phys. Rev. A 1988, 38, 3098.
(31) (a) Perdew, J . P. Phys. Rev. B 1986, 34, 7406. (b) Perdew, J . P.
Phys. Rev. B 1986, 33, 8822.
(32) Snijders, J . G.; Baerends, E. J . Mol. Phys. 1978, 36, 1789.
(33) Snijders, J . G.; Baerends, E. J .; Ros, P. Mol. Phys. 1979, 38,
1909.