Cationic iridium(I) complexes as catalysts for the alcoholysis of silanes

Article abstract of DOI:10.1021/om020938w

The syntheses of five cationic iridium(I) complexes, containing the bidentate ligands bis-(1-pyrazolyl)methane (BPM) and bis(3,5-dimethyl-1-pyrazolyl)methane (dmBPM), {[Ir(BPM)-(COD)]⁺(BPh₄)^-} (1), {[Ir(dmBPM)(COD)]⁺(BPh₄)^-} (2), {[Ir(BPM)(COD)]^-[Ir(COD)Cl₂]^-} (4), {[Ir(BPM)(CO)₂]⁺(BPh₄)^-} (3), and {[Ir(dmBPM)(CO)₂]⁺(BPh₄)^-} (5), are reported. The complexes were characterized by NMR spectroscopy, and the solid-state structure of {[Ir(BPM)(CO)₂]⁺(BPh₄)^-} (3) was determined by single-crystal X-ray crystallographic analysis. The complexes {[Ir(BPM)(CO)₂]⁺(BPh₄)^-} (3) and {[Ir(dmBPM)(CO)₂]^- (BPh₄)^-} (5) are effective catalysts for the alcoholysis of a range of alcohols and hydrosilanes, including secondary and tertiary hydrosilanes, under mild conditions.

Full text of DOI:10.1021/om020938w

Organometallics 2003, 22, 2387-2395
2387
Ca tion ic Ir id iu m (I) Com p lexes a s Ca ta lysts for th e
Alcoh olysis of Sila n es
Leslie D. Field,*,† Barbara A. Messerle,*,‡ Manuela Rehr,‡ Linnea P. Soler,† and
Trevor W. Hambley†
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia, and School of
Chemical Sciences, University of New South Wales, Sydney, NSW 2052, Australia
Received November 13, 2002
The syntheses of five cationic iridium(I) complexes, containing the bidentate ligands bis-
(1-pyrazolyl)methane (BPM) and bis(3,5-dimethyl-1-pyrazolyl)methane (dmBPM), {[Ir(BPM)-
(COD)]+(BPh4)-} (1), {[Ir(dmBPM)(COD)]+(BPh4)-} (2), {[Ir(BPM)(COD)]+[Ir(COD)Cl2]-} (4),
{[Ir(BPM)(CO)2]+(BPh4)-} (3), and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5), are reported. The com-
plexes were characterized by NMR spectroscopy, and the solid-state structure of {[Ir-
(BPM)(CO)2]+(BPh4)-} (3) was determined by single-crystal X-ray crystallographic analysis.
The complexes {[Ir(BPM)(CO)2]+(BPh4)-} (3) and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) are
effective catalysts for the alcoholysis of a range of alcohols and hydrosilanes, including
secondary and tertiary hydrosilanes, under mild conditions.
Sch em e 1
In tr od u ction
Silyl ethers are among the most widely used protect-
ing groups for the hydroxyl functionality in organic syn-
thesis.1 They also play an important role in inorganic
synthesis as precursors in the preparation of sol-gels
and other condensed siloxane materials.2 Silyl ethers
are most commonly prepared from chlorosilanes (R4-xSi-
Clx) by reaction with alcohols or alkoxides, under acidic
or basic reaction conditions.3 The addition of hydrosi-
lanes to alcohols is, however, also an attractive route
to silyl ethers because the only side-product formed is
hydrogen gas (Scheme 1).
The alcoholysis of hydrosilanes requires a catalyst
because alcohols are not generally sufficiently nucleo-
philic to attack hydrosilanes. Strongly nucleophilic or
electrophilic catalysts can be used to promote the
alcoholysis of silanes,2 and a limited number of transi-
tion metal complexes have also been reported as
catalysts.2-18 Few metal catalysts are active at room
temperature2,12,13-17 and most are unreactive with the
bulkier trialkylhydrosilanes (R3SiH).3 Wilkinson’s cata-
lyst, [Rh(PPh3)3Cl], only catalyzes the alcoholysis of
triethylsilane when refluxed in benzene.6,9-11 [Cp2TiCl2/
n-BuLi] is one of the more active catalysts, where the
primary (RSiH3) and secondary (R2SiH2) hydrosilanes
are generally more reactive than tertiary hydrosilanes.16
One of the most efficient transition metal catalysts for
silane alcoholysis reported to date is the copper(I)
hydride cluster, [Ph3PCuH]6, which is an active catalyst
under mild conditions and has proved successful in
alcoholysis of secondary and tertiary hydrosilanes.2 Only
a few iridium complexes have been reported to catalyze
the alcoholysis of hydrosilanes.8,12,14
There have been a number of mechanistic studies
on the transition-metal-mediated alcoholysis of si-
lanes.8-10,12,14,15,19 All involve the initial activation of the
silane by the metal center either by oxidative addition
of the silicon hydride or by binding of the silane to the
metal center in an η2 fashion, followed by reaction with
the alcohol. All of the proposals involve no specific acti-
vation of the alcohol, and the driving force in the reac-
tion is the formation of the strong silicon-oxygen bond.
In this paper we report a series of novel cationic
iridium(I) complexes containing the bidentate ligands
† University of Sydney.
‡ University of New South Wales.
* Corresponding author.
(11) Corriu, R. J . P.; Moreau, J . J . E. J . Organomet. Chem. 1977,
127, 7-17.
(1) Kocienski, P. J . Protecting Groups; Thieme: Stuttgart, 1994; pp
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315-333;
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Catal. 1981, 10, 171.
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Chem. 1992, 31, 4709-4711.
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228, 191-201.
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3045-3051.
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120, 337-346.
(19) Patai, S.; Rappoport, Z. The Chemistry of Organic Silicon
Compounds; J . Wiley and Sons: Chinchester, 1989; Vol. 1, pp 317-
318.
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114, 135.
10.1021/om020938w CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/07/2003

2388 Organometallics, Vol. 22, No. 12, 2003
Field et al.
Sch em e 2
Sch em e 3
The dicarbonyl complexes 3 and 5 were also synthesized
directly by reaction of 2 equiv of the bispyrazolyl ligand,
BPM or dmBPM, with 1 equiv of {[Ir(COD)Cl]2} and 2
equiv of NaBPh4 under an atmosphere of carbon mon-
oxide.
Both 3 and 5 were isotopically labeled with 13C at the
carbonyl positions by placing the reactants under an
atmosphere of 13C-carbon monoxide (99.4 atom %) to
yield either {[Ir(BPM)(13CO)2]+(BPh4)-} (3-13CO) or
{[Ir(dmBPM)(13CO)2]+(BPh4)-} (5-13CO).
bis(1-pyrazolyl)methane (BPM) and bis(3,5-dimethyl-1-
pyrazolyl)methane (dmBPM): {[Ir(BPM)(COD)]+(BPh4)-}
(1), {[Ir(dmBPM)(COD)]+(BPh4)-} (2), {[Ir(BPM)(CO)2]+-
(BPh4)-} (3), {[Ir(BPM)(COD)]+[Ir(COD)Cl2]-} (4),
and {[Ir(dmBP-M)(CO)2]+(BPh4)-} (5). The complexes
3 and 5 catalyze the alcoholysis of hydrosilanes under
mild conditions, in both the absence and presence
of air. The catalysts are effective for the alcoholysis
of a range of alcohols and hydrosilanes, including
secondary and tertiary hydrosilanes. The solid-state
structure of 3 was determined by single-crystal X-ray
crystallographic analysis.
The dicarbonyl complexes {[Ir(BPM)(CO)2]+(BPh4)-}
(3) and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) and the COD
complexes {[Ir(BPM)(COD)]+(BPh4)-} (1) and {[Ir(dm-
BPM)(COD)]+(BPh4)-} (2) were fully characterized by
NMR spectroscopy. The complexes 1, 2, 3, and 5 possess
C2 symmetry, with a plane of symmetry bisecting the
bidentate pyrazolyl ligands such that the 1H and 13C
resonances due to the two pyrazolyl rings of the bound
ligands’ NMR spectra are equivalent. The COD com-
plexes 1 and 2 also have two perpendicular planes of
symmetry within the bound COD ligand. The two
carbonyl groups in each of 3 and 5 are equivalent by
13C NMR spectroscopy.
Although the six-membered iridium metallacycle is
undoubtedly not planar in solution, the resonances due
to the bridging methylene protons of the BPM ligands
of {[Ir(BPM)(CO)2]+(BPh4)-} (3) and {[Ir(BPM)(COD)]+-
Resu lts a n d Discu ssion
1
(BPh4)-} (1) appear as a singlet in the H NMR spectra
at room temperature,29 probably as a result of averaging
arising from rapid ring inversion. The corresponding
resonances due to the methylene backbone protons of
the dmBPM ligands in {[Ir(dmBPM)(COD)]+(BPh4)-}
(2) and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) are cleanly
split into an AB system at room temperature. This
indicates that the Ir(dmBPM) metallacycle in 5 and 2
adopts a more rigid conformation, where inversion is
Syn th esis of Ir id iu m Com p lexes. Where a large
number of metal complexes containing polypyrazolylbo-
rate ligands have been previously described,20-25 only
a limited number of iridium and rhodium complexes
containing the related poly(1-pyrazolyl)methane ligands
have been reported.26-28
The complexes {[Ir(BPM)(COD)]+(BPh4)-} (1) and
{[Ir(dmBPM)(COD)]+(BPh4)-} (2) were obtained by the
reaction of the ligands BPM or dmBPM, respectively,
in a 2:1 molar ratio with {[Ir(COD)Cl]2} in the presence
of 2 equiv of NaBPh4 (Scheme 2). Complex 1 was
isolated as an air-stable, bright yellow powder, and 2
was obtained as a mildly air-sensitive bright orange
powder. Both complexes are cationic and four-coordinate
and have essentially square-planar geometry about the
metal center.
(20) Lees, A. J .; Purwoko, A. A.; Tibensky, S. D. Inorg. Chem. 1996,
35, 7049-7055.
(21) Lees, A. J .; Purwoko, A. A. Inorg. Chem. 1996, 35, 675-682.
(22) Graham, W. A.; Ghosh, C. K.; Rodgers, D. P. J . Chem. Soc.,
Chem. Commun. 1988, 1511-1512.
(23) Crabtree, R. H.; Tanke, R. S. Inorg. Chem. 1989, 28, 3444-
3447.
(24) Poveda, M. L.; Carmona, E.; Boutry, O. J . Organomet. Chem.
1997, 528, 143-150.
(25) Graham, W. A. G.; Ghosh, C. K.; Hoyano, J . K.; Krentz, R. J .
Am. Chem. Soc. 1989, 111, 5480-5481.
In the absence of NaBPh4, reaction of equimolar
amounts of BPM with {[Ir(COD)Cl]2} afforded the air-
sensitive bright orange microcrystalline solid {[Ir(BPM)-
(COD)]+[Ir(COD)Cl2]-} (4).
(26) Peterson, L. K.; Leung, P. Y. J . Organomet. Chem. 1981, 219,
409-420.
(27) Ballesteros, P.; Lopez, C.; Lopez, C.; Claramunt, R. M.; J imenez,
J . A.; Cano, M.; Heras, J . V.; Pinilla, E.; Monge, A. Organometallics
1994, 13, 289-297.
Iridium(I) dicarbonyl complexes {[Ir(BPM)(CO)2]+(B-
Ph4)-} (3) and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5), con-
taining the bidentate N-donor ligands BPM or dmBPM
(Scheme 2), were synthesized via the displacement of
COD from the iridium(I) COD complexes 1 and 2,
respectively, under an atmosphere of carbon monoxide.
(28) Oro, L. A.; Esteban, M.; Claramunt, R. M.; Elguero, L.; Foces-
Foces, C.; Cano, F. H. J . Organomet. Chem. 1984, 276, 79-97.
(29) In a freshly prepared solution of {[Ir(BPM)(COD)]+(BPh4)-} (1)
in deuterated acetone, the methylene protons slowly exchange for
deuterons. The equivalent exchange process was not observed for
{[Ir(dmBPM)(COD)]+(BPh4)-} (2), {[Ir(BPM)(CO)2]+(BPh4)-} (3), or
{[Ir(dmBPM)(CO)2]+(BPh4)-} (5).

Cationic Ir(I) Complexes as Catalysts
Organometallics, Vol. 22, No. 12, 2003 2389
Ta ble 1. Cr ysta llogr a p h ic Da ta for
{[Ir (BP M)(CO)2]+(BP h 4)-} (3)
empirical formula
fw
cryst dimens
V
IrC33H28N4O2B
715.64 g mol-1
0.32 × 0.125 × 0.10 mm
1469.6 Å3
cryst syst
2θ range
space group
Z value
monoclinic
1 < θ < 25
P21
2
Dcalc
1.617 gcm-3
F000
704
cryst color
cryst habit
lattice params
pale yellow
prism
a ) 10.516(1) Å
b ) 13.342(4) Å
c ) 10.762(1) Å
â ) 103.293(9)°
Mo KR (λ ) 0.71073 Å)
graphite monochromated
273.2K
-12 f 12, 0 f 15, 0 f 12
total: 2833 unique: 2780;
N0 ) 2534
radiation
temperature
hkl range
no. of reflns measd
corrections
Lorentz-polarization absorption
(transmn factors: 0.679-0.588,
analytical)
structure solution
function minimized
direct methods with SHELXS-86
1/2
R ) ∑(||Fo| - |Fc||)/∑|Fo|
Rw ) (∑w(|Fo| - |Fc|)2/
2 1/2
∑w|Fo
|
least squares weights
no. variables
w ) 1/(σ2(Fo))
370
residuals: R; Rw
0.021; 0.017
max. shift/error in final cycle 0.042
max. peak in final diff map
min. peak in final diff map
0.56 e-/Å3
-0.47 e-/Å3
inhibited by the added steric bulk of the methyl sub-
stituents on the bispyrazolyl ligand.30
The complexes 1, 2, 3, and 5 all catalyze a degree of
H/D exchange with deuterated solvents (d6-acetone, d8-
THF, and d4-methanol) on standing, and this can be
rationalized by the propensity of these complexes for
C-H activation.
F igu r e 1. ORTEP (30% thermal ellipsoids) plots and
crystal structure numbering of the cation fragment of
{[Ir(BPM)(CO)2]+(BPh4)-} (3) (a) as viewed from above the
coordination plane showing the puckering of the two
pyrazolyl rings up into the plane and the puckering of the
geminal atoms down into the plane; (b) as viewed from the
side of the coordination plane showing the pseudo-boat
conformation of the [Ir(NN)2C] metallocycle and the pla-
narity about the iridium atom.
X-r a y Cr yst a l St r u ct u r e of {[Ir (BP M)(CO)2]+-
(BP h 4)-} (3). The solid-state structure of {[Ir(BPM)-
(CO)2]+(BPh4)-} (3) was determined by single-crystal
X-ray crystallographic analysis (Table 1). Pale yellow
prismatic crystals suitable for X-ray crystal analysis
were obtained by the addition of hexane to a concen-
trated solution of 3 in THF. ORTEP31 plots, including
the atom-numbering scheme, of the cation 3 are shown
in Figure 1. The bond lengths and bond angles for the
inner coordination sphere of 3 are listed in Table 2.
The iridium atom is essentially contained within the
coordination plane defined by C(8), C(9), N(1), and N(3),
as it is situated only 0.0091 Å from this plane. Distortion
of the geometry from the idealized square-planar coor-
dination is due to the bite angle (85.9(2)°) of the BPM
ligand. Although the angle between the carbonyl ligands
is nearly 90° (89.6(3)°), the N-Ir-C(O) angles (91.9(3)°,
92.6(2)°) compensate the reduced angle produced by
BPM. The two trans bond angles through the iridium
center of 3 approach linearity and measure 178.5° and
177.7°.
Ta ble 2. Bon d Len gth s a n d An glesa of th e In n er
Coor d in a tion Sp h er e of {[Ir (BP M)(CO)2]+(BP h 4)-}
(3)
atoms
bond lengths (Å)
atoms
bond angles (deg)
Ir-N(1)
Ir-N(3)
Ir-C(8)
Ir-C(9)
2.057(5)
2.059(4)
1.827(7)
1.853(7)
N(1)-Ir-N(3)
C(8)-Ir-C(9)
N(1)-Ir-C(9)
N(3)-Ir-C(8)
N(1)-Ir-C(8)
N(3)-Ir-C(9)
85.9(2)
89.6(3)
91.9(3)
92.6(2)
178.5(2)
177.7(2)
a
Estimated standard deviations in the least significant figure
are given in parentheses.
A plane of symmetry bisects {[Ir(BPM)(CO)2]+(BPh4)-}
(3) through the [Ir(NN)2C] metallacycle and through the
C(O)-Ir-C(O) bond angle. The six-membered iridium
chelate ring, defined by Ir(1), N(1), N(2), C(7), N(4), and
N(3), has a boat conformation but is distorted to-
ward an envelope conformation because the Ir(1) flap
is bent less (dihedral angle: 154.9°) than the C(7) flap
(dihedral angle: 127.6°) with respect to the plane of the
(30) Rodriguez-Ubis, J . C.; J uanes, O.; de Mendoza, J . J . Organomet.
Chem. 1989, 363, 393-399.
(31) (a) J ohnson, C. K. ORTEP, A Thermal Ellipsoid Plotting
Program; Oak Ridge National Labs: Oak Ridge, TN, 1965. (b) J ohnson,
C. K. ORTEPII, Report ORNL-5138; Oak Ridge National Laborato-
ries: Oak Ridge, TN, 1976.

2390 Organometallics, Vol. 22, No. 12, 2003
Field et al.
Ta ble 3. Silyl Eth er s P r od u ced a fr om th e Ca ta lytic Alcoh olysis of Hyd r osila n es Usin g
{[Ir (BP M)(CO)2]+(BP h 4)-} (3)
MeOH
Et3SiOMe
EtOH
iPrOH
Et3SiOiPr
Et3SiH
Et3SiOEtb
22 min, 306, 65%
Me2PhSiOMe
9 min, 747, 81%
Ph3SiOMe
26 min, 118, 80%
Et2Si(OMe)2
27 min, 249, 93%
Me2PhSiOEt
10 min, 673, 82%
Ph3SiOEt
47 min, 65, 87%
Et2Si(OEt)2
50 min, 135, 72%
Me2PhSiHc
Ph3SiHd
Et2SiH2
Ph2SiH2
Me2PhSiOiPr
7 min, 961, 87%
Ph3SiOiPr
31 min, 99, 88%
Et2Si(OiPr)2
14 min, 487, 80%
Ph2Si(OMe)2
<5 min, >1362, 61%
Ph2Si(OEt)2
6 min, 1135, 76%
Ph2Si(OiPr)2
8 min, 961, 82%
8 min, 841, 89%
<15 min, >448, 93%
a
Time for 50% conversion (min). Turn-over number (moles of product per mole of catalyst per hour) calculated at 50% conversion.
b
Isolated yields with 0.45 mol % catalyst in air at 40 °C in THF solution. At 25 °C and 1% catalyst loading, T50% ) 120 min, 25 t.o./h.
c Also reacted with tBuOH to form PhMe2SiOtBu, T50% ) 21 min, 320 t.o./h, 82% yield (isolated). Catalyst loading 0.98 mol % for all
d
reactions involving Ph3SiH.
metallacycle defined by the four nitrogen atoms. This
is most likely a result of the different coordination
geometry of iridium compared to that of carbon32 and
is not uncommon in metal complexes containing BPM.
The structure of the complex {[Ir(BPM)(CO)2]+(BPh4)-}
(3) is the first reported crystal structure of an iridium
complex containing the BPM ligand. There are very few
crystal structures reported for iridium complexes that
contain two N-donor ligands, and specifically few that
contain a bidentate N-donor ligand. The structures of a
number of related rhodium complexes containing bi-
dentate N-donor ligands, including rhodium BPM com-
plexes, have been reported, and these include {[Rh(BPM)-
(COD)]+(ClO4)-},28 {[Rh(Ph-BPM)(NBD)]+(PF6)-},27 {[Rh-
((mim)2CH2)(CO)2]+(BPh4)-}33 {((mim)2CH2) ) bis(N-
methylimidazol-2-yl)methane}, and {[Rh((mBnzmim)2-
CH2)(CO)2]+(BPh4)-}33 {((mBnzmim)2CH2) ) bis(N-
methylbenzimidazol-2-yl)methane}.
Alcoh olysis of Hyd r osila n es Ca ta lyzed by {[Ir -
(BP M)(CO)2]+-(BP h 4)-} (3). A range of monofunctional
alcohols (methanol, ethanol, and 2-propanol) was re-
acted with a series of tertiary hydrosilanes, R3SiH (Et3-
SiH, Me2PhSiH, and Ph3SiH), and secondary hydrosi-
lanes, R2SiH2 (Et2SiH2 and Ph2SiH2), in the presence
of {[Ir(BPM)(CO)2]+(BPh4)-} (3) in air. The trialkylsilyl
ether (R3SiOR′) and dialkylsilyl ether (R2Si(OR′)2) prod-
ucts (Scheme 1) were produced in good yields at high
turnover rates (Table 3). The reactions were catalyzed
at a loading of approximately 0.45 mol % of catalyst 3,
with the exception that the reactions with Ph3SiH
required a higher catalyst loading.
In these reactions, the hydrosilane substrate was
added to a solution of the alcohol and catalyst in THF
solution containing a small quantity of n-octane as an
internal standard for GC analysis. The reaction mixture
was heated to 40 °C in air. No significant induction
period was observed for the reactions, and each of the
reactions proceeded to completion with 100% conversion
of the hydrosilane to silyl ether. The formation of the
silyl ether products was monitored by GC and proceeded
in an exponential manner. The time taken for the
reaction to be 50% complete (T50%) was used to estimate
the number of turnovers per hour for each reaction
(Table 3). 29Si{1H} NMR spectroscopy was also used in
the characterization of the silicon products. The 29Si
chemical shifts of the five hydrosilanes used in this work
and their silyl ether derivatives from methanol, ethanol,
and 2-propanol are tabulated in the Supporting Infor-
mation.
For the alcoholysis of silanes catalyzed by {[Ir(BPM)-
(CO)2]+(BPh4)-} (3), the reactivities of the hydrosilanes,
in order of decreasing activity are
MeOH: Ph2SiH2 > Me2PhSiH > Et2SiH2 > Et3SiH
> Ph3SiH
EtOH: Et2SiH2 > Ph2SiH2 > Me2PhSiH > Et3SiH >
Ph3SiH
iPrOH: Et2SiH2 > Me2PhSiH > Ph2SiH2 > Et3SiH >
Ph3SiH
The least reactive hydrosilanes for all three of the
alcohols tested are Et3SiH and Ph3SiH, with Ph3SiH
being consistently the least reactive of the hydrosilanes.
The reactions with Me2PhSiH were also notably exo-
thermic. Reactions of alcohols with secondary silanes
proceeded at a significantly higher rate than the analo-
gous reactions with tertiary silanes; however, complete
conversion to the dialkyl silyl ether occurred in all cases.
Most reported alcoholysis reactions promoted by
transition metal catalysts have been carried out under
inert atmospheres, such as argon or nitrogen9-17 since
the catalysts tend to be highly air-sensitive. However,
a number of catalysts have now been reported, e.g., the
copper(I) hydride cluster [Ph3PCuH]6 (6), that are more
active under an atmosphere of air than an inert atmos-
phere.2 To assess the effect of an atmosphere of argon
on the catalytic efficiency of {[Ir(BPM)(CO)2]+(BPh4)-}
(3), the ethanolysis of Et3SiH was followed by GC under
reaction conditions identical to those used for the
analogous reaction conducted under an atmosphere of
air. The presence of air (249 t.o./h, T50% ) 27 min) or
the absence of air (269 t.o./h, T50% ) 25 min) had no
significant effect on the catalytic activity of 3.
Alcoh olysis of Dih yd r osila n es Ca t a lyzed b y
{[Ir (BP M)(CO)2]+(BP h 4)-} (3). On the addition of
diphenylsilane to ethanol in the presence of 3, at 25 °C,
rapid conversion to the final product Ph2Si(OEt)2 was
observed by NMR, with 50% conversion to Ph2Si(OEt)2
after 10 min. In addition, some initial conversion to the
monohydrosilane Ph2SiH(OEt) was observed (Figure 2).
A maximum conversion to Ph2SiH(OEt) (approximately
20%) occurred after 10 min, after which time the
quantity of Ph2SiH(OEt) decreased along with the
increase in conversion to the final product Ph2Si(OEt)2
(32) Rendle, D. F.; Storr, A.; Trotter, J . Can. J . Chem. 1975, 53,
2944.
(33) Elgafi, S.; Field, L. D.; Messerle, B. A.; Hambley, T. W.; Turner,
P. J . Organomet. Chem. 1999, 588, 69-77.

Cationic Ir(I) Complexes as Catalysts
Organometallics, Vol. 22, No. 12, 2003 2391
Ta ble 5. Com p a r ison of Ra tes of Alcoh olysis of
Hyd r osila n es Ca ta lyzed by a Ra n ge of Tr a n sition
Meta l Ca ta lysts: {[Ir (BP M)(CO)2]+(BP h 4)-} (3),
{[Ir (d m BP M)(CO)2]+(BP h 4)-} (5), [P h 3P Cu H]6 (6),2
{[Ir H2S2(P P h 3)2]+(SbF 6)-} (S ) THF ) (7),14
[Ru (P Me3)2(CO)2Cl2] (8),13 a n d [Cp 2TiCl2/n -Bu Li]
(9)16
catalyst
turnover numbera
Et3SiH
Et3SiOMe
306
Et3SiOEt
249
348
>8
47,000
1500
Et3SiOiPr
135
3b
5b
6c,d,e >8
7
7f
530,000
2500
130,000
580
8g
Me2PhSiH
Me2PhSiOMe Me2PhSiOEt Me2PhSiOiPr
3b
747
673
824
961
F igu r e 2. Stepwise conversion of Ph2SiH2 to Ph2SiH(OEt)
and Ph2Si(OEt)2 as catalyzed by {[Ir(BPM)(CO)2]+(BPh4)-}
(3). The reaction was monitored by NMR spectroscopy: 2
) Ph2SiH(OEt) and 9 Ph2Si(OEt)2.
5b
6c,e
9h
>213
>160
>79
1.1i
no reactionj
Ph3SiOiPr
99
Ph3SiH
Ph3SiOMe
118
Ph3SiOEt
65
120
3b
Ta ble 4. Efficien cy of {[Ir (d m BP M)(CO)2]+(BP h 4)-}
5b
(5) for th e Eth a n olysis of Hyd r osila n esa
6c,e
>36
>33
>29
Ph2Si(OMe)2 Ph2Si(OEt)2 Ph2Si(OiPr)2
product
T
50%,b t.o./hc
Ph2SiH2
3b
961
841
324
>64
45h
448
Et3SiOEt
Me2PhSiOEt
Ph3SiOEt
Et2Si(OEt)2
Ph2Si(OEt)2
26 min, 348
11 min, 824
38 min, 120
301 min, 31
28 min, 324
5b
6c,e
9h
>126
>74
d
4i
a
Turn-over number (moles of product per pole of catalyst per
b
hour) calculated at 50% conversion. In THF solution under air
a
b
Catalyst loading 0.33 mol %, in air at 40 °C. Time for 50%
at 40 °C; the rates of reaction were determined by GC. c In benzene
conversion (min). c Turn-over number (moles of product per mole
of catalyst per hour) calculated at 50% conversion. Catalyst
d
under air at room temperature. Reactions with Et3SiH were
d
incomplete at 48 h. e Estimated using the isolated yield, the
reaction time, and ratio of catalyst to reactants. The real reaction
rate could be significantly higher. f In DCM solution under N2 at
25 °C; the rate of reaction was determined by monitoring hydrogen
loading 0.66 mol %.
(Figure 2). The addition of ethanol to the dihydrosilane
occurs in a stepwise fashion, with initial formation of
the mono silyl ether Ph2SiH(OEt), followed by a second
slower addition to form Ph2Si(OEt)2.
g
gas evolution. In THF solution at 18 °C under argon; the rate of
reaction was determined by GC.
estimated using GC. In THF solution, under N2 initially at 0 °C
then raised to room temperature. In THF solution, under N2
h
The rate of reaction was
i
j
Alcoh olysis of Hyd r osila n es Ca ta lyzed by {[Ir -
(d m BP M)(CO)2]+(BP h 4)-} (5). The dicarbonyl iridium
complex {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) was also cata-
lytically active for the alcoholysis of hydrosilanes and
was reactive under both aerobic and anaerobic condi-
tions. The catalytic efficiency of 5 in air was assessed
in the reaction of ethanol with a range of hydrosilanes
(Table 4) under conditions similar to those used for
{[Ir(BPM)(CO)2]+(BPh4)-} (3). All of the reactions pro-
ceeded to completion with 100% conversion of the
hydrosilane to silyl ether.
initially at 0 °C then brought to reflux.
reactive with both dialkyl- and trialkylhydrosilanes in
the alcoholysis of hydrosilanes, including reactions with
the less reactive Et3SiH. While the complexes {[IrH2S2-
(PPh3)2]+(SbF6)-} (S ) solvent) (7) and [Ru(PMe3)2(CO)2-
Cl2] (8) are significantly more effective catalysts than 3
and 5 in the alcoholysis of Et3SiH, the complexes 3 and
5 are more effective for the synthesis of silyl ethers from
aromatic silanes such as Me2PhSiH, Ph3SiH, and Ph2-
SiH2.
The rates of silane ethanolysis catalyzed by {[Ir(dm-
BPM)(CO)2]+(BPh4)-} (5) were comparable to those
catalyzed by {[Ir(BPM)(CO)2]+(BPh4)-} (3) for the range
of tertiary silanes studied. However, for the two-stage
double ethanolysis reaction of dihydrosilanes, catalysis
by 5 proceeded at a significantly slower rate, and this
must be attributed to the influence of the methyl
substituents on the pyrazolyl backbone of 5.
Com p a r ison of O-Silyla tion Ca ta lytic Activities
of {[Ir (BP M)(CO)2]+(BP h 4)-} (3) a n d {[Ir (d m BP M)-
(CO)2]+(BP h 4)-} (5) w ith Oth er Ca ta lysts. The ma-
jority of the transition metal catalysts that are known
to catalyze the alcoholysis of silanes either are inactive
with tertiary hydrosilanes or show diminished reactivity
in the alcoholysis of trialkylhydrosilanes.3 Table 5
compares the catalytic efficiency of {[Ir(BPM)(CO)2]+-
(BPh4)-} (3) and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) with
other known O-silylation catalysts. Of those catalysts
that are reactive with tertiary hydrosilanes, few catalyze
the alcoholysis of Et3SiH. The complexes 3 and 5 are
Scop e of Alcoh olysis w ith Et3SiH Ca ta lyzed by
{[Ir (BP M)(CO)2]+(BP h 4)-} (3). The scope of the cata-
lytic activity of {[Ir(BPM)(CO)2]+(BPh4)-} (3) with Et3-
SiH was assessed with a series of alcohols that varied
in terms of alkyl chain length, branching, and complex-
ity (Table 6). The influence of multiple hydroxyl func-
tionalities, ether functionalities, and chloro substituents
was also examined, as well as the catalyzed reaction of
water with Et3SiH. In all cases, the time at which the
reactions were stopped was noted, although this only
serves to indicate an upper limit to the reaction time
and not to provide quantitative catalytic rates.
Complex 3 catalyzes the alcoholysis of Et3SiH with
all of the alcohol substrates tested, including primary,
secondary, tertiary, aromatic, and bulky alcohols as well
as diols, a triol, and alcohols containing multiple-ether
functionalities and a chloro substituent.
The reaction of Et3SiH with primary alcohols cata-
lyzed by {[Ir(BPM)(CO)2]+(BPh4)-} (3) proceeded in near
quantitative yields for most of the alcohols. The catalytic

2392 Organometallics, Vol. 22, No. 12, 2003
Field et al.
Ta ble 6. Alcoh olysisa of Et3SiH Ca ta lyzed by
produce, exclusively, triethylsilanol, Et3SiOH, which
then reacts with another equivalent of Et3SiH, over a
period of several hours, to generate the silyl ether,
hexaethyldisiloxane, Et3SiOSiEt3. The silanol, Et3SiOH,
and silyl ether, Et3SiOSiEt3, products were observed as
side-products in several of the O-silylation reactions
when the reactants or solvents were not scrupulously
dry.
{[Ir (BP M)(CO)2]+(BP h 4)-} (3)
The reaction of 1,3-propanediol with 2 equiv of Et3-
SiH in the presence of 3 led to the exclusive formation
of the bis-silylated product. The reaction proceeded
quickly, and the product was isolated in high yield (94%,
109 t.o.). The reaction of pinacol, a bis-tertiary diol, with
2 equiv of Et3SiH catalyzed by 3, led to the formation
of a mixture of the mono- and the bis-silylated pinacol
compounds. Of the few catalysts that have been reported
to date that promote the alcoholysis of diols with
trialkylsilanes, [Ph3PCuH]6 (6) is the only one to
produce the fully bis-silylated species from pinacol.2 The
reaction of the triol glycerol with 3 equiv of Et3SiH in
the presence of 3 led to exclusive production (79%) of
the tris-silylated product.
The presence of multiple ether groups on the reac-
tants appeared to have little effect on the catalytic
capability of {[Ir(BPM)(CO)2]+(BPh4)-} (3). The com-
pound 3 was catalytically active in the reaction of Et3-
SiH with benzyl tetraethyleneglycol to produce the
expected silyl ether. The substitution of a chloro group
for a proton on the methyl end of a polyether alcohol,
2-[2-(2-chloroethoxy)ethoxy]ethanol, also did not inhibit
the alcoholysis of Et3SiH catalyzed by 3. In contrast,
ether groups with the oxygen atom â to the hydroxyl
group and the presence of a chloro group on the methyl
group of ethanol both have been reported to inhibit the
catalytic activity of both {[IrH2S2(PPh3)2]+(SbF6)-} (S
) solvent) (7)14 and [Ru(PMe3)2(CO)2Cl2] (8)13 in the
alcoholysis of Et3SiH.
Ca ta lytic Activity of {[Ir (BP M)(COD)]+(BP h 4)-}
(1) in th e Alcoh olysis of Et3SiH. The iridium 1,5-
cyclooctadiene (COD) complex, {[Ir(BPM)(COD)]+(B-
Ph4)-} (1), was significantly less effective as a catalyst
for the alcoholysis of hydrosilanes. In the reaction
between Et3SiH and 1-phenylethanol in CDCl3, only a
yield of 10% was observed after 24 h.
a
Typically 3.1 mmol of Et3SiH and an equimolar ratio of alcohol
(in terms of OH groups available) in 3 mL of THF was stirred in
the presence of 0.4 mol % of catalyst at room temperature under
argon. Characterization data including 1H, 13C, and 29Si NMR
b
chemical shifts of the triethylsilyl ethers are listed in the Sup-
porting Information. c Time (hours) elapsed before the isolation
of the silyl ether from the reaction mixture. The reaction may have
d
been complete in significantly less time. Products not isolated.
The % conversion was determined by integration of the 1H NMR
spectrum.
Con clu sion s
Iridium(I) complexes containing the bidentate pyra-
zolylmethane ligands BPM and dmBPM were prepared
readily and in high yield from the iridium precursor {[Ir-
(COD)Cl]2}. The complexes {[Ir(BPM)(COD)]+(BPh4)-}
(1), {[Ir(dmBPM)(COD)]+(BPh4)-} (2), {[Ir(BPM)(CO)2]+-
(BPh4)-} (3), and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) are
cationic, square-planar, and air-stable. If BPM is reacted
with {[Ir(COD)Cl]2} in the absence of NaBPh4, the
complex {[Ir(BPM)(COD)]+[Ir(COD)Cl2]-} (4) is formed.
The compounds {[Ir(BPM)(CO)2]+(BPh4)-} (3) and
{[Ir(dmBPM)(CO)2]+(BPh4)-} (5) were effective catalysts
for the alcoholysis of hydrosilanes with a range of
hydrosilanes and alcohols. The turn-over frequency of
3 with secondary (dihydrosilane) substrates was sig-
nificantly greater than with tertiary (hydrosilane) sub-
strates. Complex 5 was more effective as a catalyst for
the alcoholysis of tertiary silanes than the reactions
with secondary hydrosilanes. Both 3 and 5 are effective
activity of 3 does not diminish with elongation and
branching of the alkyl group on the alcohols. As the bulk
of the secondary alcohols was increased, the isolated
yields decreased, suggesting that the increased steric
bulk around the hydroxyl functionality influences the
catalytic activity of 3. The reaction of (-)-menthol with
Et3SiH catalyzed by 3 proceeded very slowly with a low
product yield.
Other transition metal complexes that have been
reported to catalyze the alcoholysis of triethylsilane, e.g.,
{[IrH2S2(PPh3)2]+(SbF6)-} (S ) solvent) (7)14 and [Ru-
(PMe3)2(CO)2Cl2] (8),13 show significantly lessened activ-
ity with the elongation and branching of the alkyl group
of the alcohol and are more sensitive to the steric bulk
near the hydroxyl group.
Complex 3 efficiently catalyzed the O-silylation of the
OH groups of water. The reaction proceeds stepwise
with the rapid initial reaction of H2O and Et3SiH to

Cationic Ir(I) Complexes as Catalysts
Organometallics, Vol. 22, No. 12, 2003 2393
butanol and (-)-menthol, which were dried under vacuum
prior to use, and 1-pentanol, 1-hexanol, 1-heptanol, 3,3-
dimethyl-2-butanol, and ClCH2CH2(OCH2CH2)2OH, which were
obtained from Aldrich and were used without further purifica-
tion. Iridium trichloride trihydrate was obtained as a generous
loan from J ohnson Matthey & Co. {[Ir(COD)Cl]2} was synthe-
sized using the method of Herde et al.34 C6H5CH2(OCH2CH2)4-
OH was synthesized using the method of Burns et al.35
NMR spectra were recorded on Bruker DRX NMR spec-
trometers at 300.1 (1H) MHz, 400.1 (1H) MHz, and 500.1 (1H)
MHz, or with a Bruker AMX600 NMR spectrometer at 600.1
(1H) MHz. 1H NMR and 13C NMR chemical shifts were
referenced internally to residual solvent resonances. Unless
otherwise stated, spectra were acquired at 300 K and the
temperatures quoted for acquisition of NMR spectra are
approximate ((2 K).
catalysts for the alcoholysis of silanes and have different
reactivity profiles, and this probably reflects the differ-
ences in the steric environment at the metal center as
a result of the different ligand structures. The fact that
the reaction displays some sensitivity to variations in
the ligand structure may well provide an avenue for
engineering greater substrate selectivity into catalytic
silane alcoholysis. The presence, or absence, of air had
little effect on the turn-over frequency of the alcoholysis
of hydrosilane reactions.
The complex {[Ir(BPM)(CO)2]+(BPh4)-} (3) catalyzed
the O-silylation of a range of complex alcohols with Et3-
SiH. The catalytic activity of 3 did not diminish signifi-
cantly with elongation and branching of the alkyl chain
on the alcohol. With bulky secondary alcohols, tertiary
alcohols, and aromatic alcohols, the rate of reaction with
Et3SiH was slowed. The O-silylation of the polyols, 1,3-
propanediol and pinacol, and glycerol with Et3SiH was
cleanly catalyzed by 3. The presence of chloro and/or
ether functionalities in the alcohol substrate has little
effect on the catalytic activity of 3. Water was also
catalytically O-silylated by 3 with Et3SiH to give the
products Et3SiOH and/or Et3SiOSiEt3 in high yield.
For a range of alcoholysis reactions, 3 and 5 are
significantly more effective catalysts than other cata-
lysts previously reported. The turn-over frequencies
reported for the same reactions that were catalyzed by
previously reported transition metal catalysts showed
that the iridium complexes 3 and 5 display a competitive
level of reactivity, especially with the traditionally more
unreactive tertiary hydrosilanes. Furthermore, hydrosi-
lation reactions catalyzed by 3 and 5 may be readily
carried out under relatively simple and mild reaction
conditions, under an atmosphere of air and at room
temperature.
GC analyses were performed using a Hewlett-Packard 5890
Series II gas chromatograph. Microanalyses were performed
by the Chemical Microanalytical Services Pty. Ltd, Melbourne,
Australia, and the Campbell Microanalytical Laboratory, The
University of Otago, New Zealand.
Syn th esis of P oly(1-p yr a zolyl)m eth a n e Liga n d s. Syn -
th esis of Bis(1-p yr a zolyl)m eth a n e (BP M). Bis(1-pyrazolyl)-
methane (BPM) was synthesized using a modification of the
procedure developed by Elguero et al. for the synthesis of rela-
ted bis(1-pyrazolyl)methane ligands.36 Dichloromethane (CH2-
Cl2) (50 mL) was added to a mixture of pyrazole (6.13 g, 90.0
mmol), tetrabutylammonium hydrogen sulfate {[N(C4H9)4]+-
(HSO4)-) (2.5 g, 7.36 mmol), powdered potassium hydroxide
(85%) (8.2 g, 6.8 mol), and potassium carbonate (K2CO3) (20.3
g, 147 mmol). The reaction mixture was stirred vigorously and
heated under reflux for 36 h. After filtration, the residue was
washed with hot CH2Cl2 (3 × 10 mL) and the organic portions
were combined. The solvent was removed from the organic
portions under reduced pressure to give the crude product as
white crystals. The crude product was recrystallized from
heptane to give bis(1-pyrazolyl)methane (BPM) as white
needlelike crystals (6.53 g, 98%). Mp: 111-114 °C (lit.37 111-
112 °C; lit.38,39 108 °C). Complete NMR data are reported in
the Supporting Information.
Exp er im en ta l Section
Syn t h esis of Bis(3,5-d im et h yl-1-p yr a zolyl)m et h a n e
(d m BP M). Bis(3,5-dimethyl-1-pyrazolyl)methane (dmBPM)
was synthesized using a modification of the procedure devel-
oped by J ulia, del Mazo, Avila, and Elguero.36 Dichloromethane
(CH2Cl2) (30 mL) was added to a mixture of 3,5-dimethylpyra-
zole (3.00 g, 31.2 mmol), tetrabutylammonium hydrogen
sulfate {[N(C4H9)4]+(HSO4)-} (816 mg, 2.40 mmol), powdered
potassium hydroxide (85%) (2.70 g, 48.1 mmol), and potassium
carbonate (K2CO3) (6.64 g, 48.0 mmol). The reaction mixture
was stirred vigorously and heated under reflux for 36 h. After
filtration, the residue was washed with hot CH2Cl2 (3 × 10
mL), and the organic portions were combined. The solvent was
removed from the organic portions under reduced pressure to
give the crude product as white crystals. The crude product
was recrystallized from heptane to give bis(3,5-dimethyl-1-
pyrazolyl)methane (dmBPM) as white needlelike crystals (3.12
g, 98%). Mp: 107-110 °C (lit.37 83-84 °C; lit.39 105 °C).
Complete NMR data are reported in the Supporting Informa-
tion.
The synthesis and manipulation of all ligands and metal
complexes were performed under an inert atmosphere of argon
or nitrogen unless otherwise stated, either by performing
reactions in an inert atmosphere drybox or by employing
standard Schlenk and vacuum line techniques. Hexane, hep-
tane, and tetrahydrofuran (THF) were predried over sodium
wire and were distilled with benzophenone over sodium wire
immediately prior to use. Absolute ethanol and methanol were
distilled from diethoxymagnesium and dimethoxymagnesium,
respectively. Acetone was dried over P2O5 before distillation.
2-Propanol (AR grade) was used without further purification.
Light petroleum was stirred over H2SO4 for at least 24 h prior
to distillation. Dichloromethane (DCM) was washed sequen-
tially with H2SO4, H2O, aqueous K2CO3 (5%) solution, and H2O,
prior to distillation from CaCl2. Deuterated solvents were first
dried, as for their proteo-analogues, then were degassed via
three consecutive freeze/pump/thaw cycles, then vacuum
distilled and stored under vacuum. All solvents used in air-
sensitive reactions were deareated prior to use either by
saturation with nitrogen or via four to five freeze/pump/thaw
cycles.
(34) Herde, J . L.; Lambert, J . C.; Senaff, C. V. Inorg. Synth. 1974,
15, 18.
(35) Burns, C. J .; Field, L. D.; Morgan, J .; Petteys, B. J .; Prashar,
J .; Ridley, D. D.; Sandanayake, K. R. A. S.; Vignevich, V. Aust. J . Chem.
2001, 54, 431-438.
All compressed gases were obtained from B.O.C. Gases. The
following agents were used as received: tetraphenylborate
(Aldrich), pyrazole (Aldrich), 3,5-dimethylpyrazole (Aldrich),
sodium tetraphenylborate (Aldrich), 1,5-cyclooctadiene (Ald-
rich), Et3SiH (Aldrich), Me2PhSiH (Fluka), Ph3SiH (Aldrich),
Et2SiH2 (Fluka), and Ph2SiH2 (Aldrich). Ph3SiH was distilled
under vacuum to ensure it was completely dry. Alcohols were
dried and distilled prior to use, with the exception of tert-
(36) Elguero, J .; J ulia, S.; del Mazo, J . M.; Avila, L. Org. Prep. Proc.
Int. 1984, 16, 299-307.
(37) Trofimenko, S. J . Am. Chem. Soc. 1970, 92, 5118-5126.
(38) Claramunt, R. M.; Hernandez, H.; Elguero, J .; J ulia, S. Bull.
Soc. Chim. Fr. 1983, 2, 5-10.
(39) Elguero, J .; Ochoa, C.; Sebastian, J .; Sala, P.; del Mazo, J .;
Sanco, M.; Fayet, J . P.; Vertut, M. C. J . Heterocycl. Chem. 1982, 19,
1141-1145.

2394 Organometallics, Vol. 22, No. 12, 2003
Field et al.
Syn th esis of Ir id iu m Com p lexes. {[Ir (BP M)(COD)]+(B-
P h 4)-} (1). Methanol (20 mL) was added to a mixture of BPM
(124 mg, 0.835 mmol), {[Ir(COD)Cl]2} (216 mg, 0.322 mmol),
and NaBPh4 (290 mg, 0.847 mmol), and the solution was
stirred for 12 h at room temperature, during which time a
bright orange precipitate developed. The precipitate was
collected by filtration and washed with hexane (10 mL),
methanol (3 mL), and hexane (10 mL) and dried under vacuum
to give [bis(1-pyrazolyl)methane](1,5-cyclooctadiene)iridi-
um(I) tetraphenylborate, {[Ir(BPM)(COD)]+(BPh4)-} (1), as a
bright orange powder (247 mg, 50%). Mp: 184-185 °C.
Found: C, 60.85; H, 5.24; N, 7.25. C39H40N4IrB requires: C,
61.00; H, 5.24; N, 7.30. 1H NMR (400 MHz, acetone-d6, 300
C8H12Cl2Ir), 370 (100). Mass spectrum (CI, NH3, m/z (%)): 449
(100, M+, C15H20N4Ir), 447 (70).
Syn th esis of {[Ir (BP M)(CO)2]+(BP h 4)-} (3). F r om {[Ir -
(COD)Cl]2}. Methanol (25 mL) and hexane (7 mL) were added
to a mixture of BPM (228 mg, 1.54 mmol), {[Ir(COD)Cl]2} (398
mg, 0.593 mmol), and NaBPh4
(458.7 mg, 1.34 mmol). The
solution was stirred for 45 min at room temperature, then
degassed via three freeze/pump/thaw cycles. The reaction
mixture was stirred under an atmosphere of carbon monoxide
for 12 h at room temperature, during which time a pale yellow
precipitate developed. The precipitate was collected by filtra-
tion and washed with hexane (10 mL), methanol (3 mL), and
hexane (10 mL) and dried under vacuum to give [bis(1-
pyrazolyl)methane]dicarbonyliridium(I) tetraphenylborate,
{[Ir(BPM)(CO)2]+(BPh4)-} (3), as a pale yellow powder (765
mg, 90%). Found: C, 55.0; H, 3.7; N, 7.8. C33H28N4O2IrB
requires: C, 55.39; H, 3.94; N, 7.83. 1H NMR (600 MHz, THF-
d8, 303 K): δ 8.21 (s, 2H, H3), 7.44 (s, 2H, H5), 7.43 (br m,
8H, ortho-BPh4), 6.94 (t, 8H, meta-BPh4), 6.81 (t, 4H, para-
3
3
K): δ 8.36 (d, 2H, J H5-H4 ) 2.6 Hz, H5), 8.21 (d, 2H, J H3-H4
3
) 2.2 Hz, H3), 7.50 (br m, 8H, ortho-BPh4), 7.07 (t, 8H, J )
3
7.4 Hz, meta-BPh4), 7.01 (s, 2H, H1′), 6.94 (dd, 4H, J ) 6.6,
3
6.5 Hz, para-BPh4), 6.81 (dd, 2H, J H4-H3,
) 2.6, 2.5 Hz,
H4-H5
H4), 4.50 (br s, 4H, H2′), 2.53 (br m, 4H, H3′a), 2.04 (dd, 4H,
3J ) 15.7 Hz, H3′b) ppm. 13C{1H} NMR (100 MHz, acetone-
BPh4), 6.56 (s, 2H, H4), 5.42 (s, 2H, H1′) ppm. 13C{1H} NMR
1
d6, 300 K): δ 165.4 (q, J BC ) 49.6 Hz, ipso-BPh4), 144.4 (C3),
1
(100 MHz, THF-d8, 300 K): δ 172.5 (Ir-CO), 166.3 (q, J BC
)
137.4 (ortho-BPh4), 136.4 (C5), 126.4 (meta-BPh4), 122.6 (para-
BPh4), 109.6 (C4), 70.3 (C2′), 64.8 (C1′), 32.1 (C3′) ppm. IR
(KBr, cm-1): 2361 (s), 1684 (m), 1653 (s), 1559 (s), 1540 (m),
1507 (m), 1425 (m), 1284 (s), 1066 (m), 761 (s), 734 (vs), 707
(vs), 612 (m). Mass spectrum (CI, NH3, m/z (%)): 449 (100,
M+, C15H20N4Ir), 447 (72).
49.4 Hz, ipso-BPh4), 149.7 (C3), 138.3 (ortho-BPh4), 138.0 (C5),
127.4 (meta-BPh4), 123.6 (para-BPh4), 111.0 (C4), 64.4 (C1′)
ppm. IR (KBr, cm-1): 3141 (m), 3124 (m), 3157 (m), 3000 (m),
2081 (vs, Ir-CtO), 2065 (w, Ir-13CtO), 2015 (vs, Ir-CtO),
1983 (w, Ir-13CtO), 1480 (w), 1408 (m), 1280 (s), 1109 (w), 1075
(m), 781 (m), 739 (m), 732 (m), 713 (s), 706 (s), 612 (m), 536
(w). Mass spectrum (ESI, MeOH, m/z (%)): 397 (100, M+,
C9H8N4O2Ir), 395 (59). (CI, NH3, m/z (%)): 397 (100, M+,
C9H8N4O2Ir), 395 (55).
F r om {[Ir (BP M)(COD)]+(BP h 4)-} (1). {[Ir(BPM)(COD)]+-
(BPh4)-} (1) (825 mg, 1.07 mmol) was mixed with methanol
(15 mL) and hexane (4 mL), and the resulting cloudy bright
yellow solution was degassed via three freeze/pump/thaw
cycles. The solution was stirred under an atmosphere of carbon
monoxide at room temperature for 1 h. The solution became
clear immediately, and within 2-3 min a pale yellow precipi-
tate formed. The solid was collected by filtration and washed
with hexane (3 × 5 mL) to give [bis(1-pyrazolyl)methane]-
dicarbonyliridium(I) tetraphenylborate, {[Ir(BPM)(CO)2]+(B-
Ph4)-} (3), as a yellow powder (638 mg, 83%); mp 185-186
°C. The spectroscopic data were identical to the sample
produced from {[Ir(COD)Cl]2}.
{[Ir (dm BP M)(COD)]+(BP h 4)-} (2). NaBPh4 (100 mg, 0.292
mmol) was added to a solution of {[Ir(COD)Cl]2} (87.0 mg,
0.130 mmol) in EtOH (20 mL). A solution of dmBPM (80.0 mg,
0.392 mmol) in EtOH (5 mL) was added, and the reaction
mixture was stirred 2.5 h at room temperature, during which
time a bright orange precipitate formed. The solid was collected
by filtration and washed with EtOH (3 × 3 mL) to give the
product [bis(3,5-dimethyl-1-pyrazolyl)methane](1,5-cycloocta-
diene)iridium(I) tetraphenylborate, {[Ir(dmBPM)(COD)]+(B-
Ph4)-} (2), as a bright orange powder (191 mg, 89%); mp 168-
169 °C. 1H NMR (600 MHz, THF-d8, 303 K): δ 6.82 (br m,
3
8H, ortho-BPh4), 6.35 (t, 8H, J ) 7.4 Hz, meta-BPh4), 6.21 (t,
3
4H, 3J ) 6.8 Hz, para-BPh4), 6.17 (d, 1H, J H1′a-H1′b ) 15.3
3
Hz, H1′a), 5.51 (s, 2H, H4), 5.32 (d, 1H, J
) 15.3 Hz,
H1′a-H1′b
H1′b), 3.94 (br s, 4H, H2′), 1.85 (s, 6H, C3-CH3), 1.81 (m, 4H,
H3′a), 1.69 (s, 6H, C5-CH3), 1.22 (m, 4H, H3′b) ppm. 13C NMR
1
(150 MHz, THF-d8, 303 K): δ 166.6 (q, J BC ) 49.9 Hz, ipso-
Syn t h esis of {[Ir (d m BP M)(CO)2]+(BP h 4)-} (5). F r om
{[Ir (COD)Cl]2}. Methanol (25 mL) and hexane (7 mL) were
added to a mixture of dmBPM (110 mg, 0.54 mmol), {[Ir(COD)-
Cl]2} (180 mg, 0.27 mmol), and NaBPh4 (240 mg, 0.70 mmol).
The solution was stirred for 45 min at room temperature,
during which time the intermediate, {[Ir(dmBPM)(COD)]+(B-
Ph4)-} (2), formed as a bright orange powder. The solution was
degassed via three freeze/pump/thaw cycles and stirred under
an atmosphere of carbon monoxide at room temperature for
2 h. After 30 min, a yellow precipitate was formed. The
precipitate was collected by filtration and washed with hexane
(10 mL), methanol (3 mL), and hexane (10 mL) and dried
under vacuum to give [bis(3,5-dimethyl-1-pyrazolyl)methane]-
dicarbonyliridium(I) tetraphenylborate, {[Ir(dmBPM)(CO)2]+-
(BPh4)-} (5), as a pale yellow powder (385 mg, 93%). 1H NMR
(600 MHz, THF-d8, 303 K): δ 7.37 (br s, 8H, ortho-BPh4), 6.89
(t, 8H, 3J ) 7.5 Hz, meta-BPh4), 6.75 (t, 4H, 3J ) 7.2 Hz, para-
BPh4), 6.22 (s, 2H, H4), 5.80 (br s, 1H, H1′a or H1′b), 5.70 (br
s, 1H, H1′a or H1′b), 2.49 (s, 6H, C3-CH3), 2.27 (s, 6H, C5-
CH3) ppm.13C NMR (150 MHz, THF-d8, 303 K): δ 172.7 (Ir-
BPh4), 155.4 (C3 or C5), 145.7 (C3 or C5), 138.6 (ortho-BPh4),
127.2 (meta-BPh4), 123.3 (para-BPh4), 111.5 (C4), 68.9 (C2′),
61.3 (C1′), 33.2 (C3′), 15.6 (C3-CH3), 12.2 (C5-CH3) ppm. IR
(KBr, cm-1): 3053 (w), 1561 (m), 1467 (m), 1425 (m), 1411 (m),
1276 (m), 1031 (w), 828 (m), 799 (w), 739 (s), 732 (2), 705 (vs),
673 (w), 613 (s). Mass spectrum (ESI, MeOH, m/z (%)): 505
(100, M+, C19H28N4Ir), 503 (55), 431 (88), 291 (24), 259 (53).
Syn th esis of {[Ir (BP M)(COD)]+[Ir (COD)(Cl)2]-} (4). A
solution of BPM (59 mg, 0.400 mmol) in acetone (20 mL) was
added to a solution of {[Ir(COD)Cl]2} (125 mg, 0.186 mmol) in
acetone (10 mL). As the ligand was added, the solution changed
from a strong orange color to a strong yellow color. The reaction
mixture was stirred at room temperature for 2 h. The volume
was reduced to 5 mL to precipitate the product, which was
collected by filtration and washed with acetone to yield [bis-
(1-pyrazolyl)methane](1,5-cyclooctadiene)iridium(I) dichloro-
(1,5-cyclooctadiene)iridium(I), {[Ir(BPM)(COD)]+[Ir(COD)(Cl)2]-}
(4), as an air-sensitive yellow microcrystalline solid (70 mg,
1
46%). H NMR (400 MHz, acetone-d6, 300 K): δ 8.81 (s, 2H,
1
H
BPM), 8.16 (s, 2H, HBPM), 7.38 (s, 2H, HBPM), 6.79 (s, 2H, HBPM),
4.47 (s, 4H, HCOD-anion), 3.88 (s, 4H, HCOD-cation), 2.51 (s, 4H,
COD-anion), 2.16 (s, 4H, HCOD-cation), 1.99 (s, 4H, HCOD-cation),
CO), 166.5 (q, J BC ) 48.9 Hz, ipso-BPh4), 138.5 (ortho-BPh4),
125.2 (meta-BPh4), 123.4 (para-BPh4), 110.9 (C4), 59.1 (C1′),
16.3 (C3-CH3), 12.2 (C5-CH3) ppm.
H
1.39 (s, 4H, HCOD-anion) ppm. IR (KBr, cm-1): 2995 (w), 2881
(m), 2831 (w), 1468 (w), 1424 (s), 1282 (s), 1223 (w), 1109 (m),
1065 (m), 999 (m), 896 (w), 871 (w), 766 (vs), 601 (w). Mass
spectrum (MALDI (+), m/z (%)): 449 (100, M+, C15H20N4Ir),
447 (85). Mass spectrum (MALDI (-), m/z (%)): 371 (85, M-,
F r om {[Ir (d m BP M)(COD)]+(BP h 4)-} (2). {[Ir(dmBPM)-
(COD)]+(BPh4)-} (2) (113 mg, 0.137 mmol) was dissolved in a
mixture of methanol (15 mL) and hexane (4 mL), and the
resulting intense yellow-orange solution was degassed via
three freeze/pump/thaw cycles. The solution was stirred under

Cationic Ir(I) Complexes as Catalysts
Organometallics, Vol. 22, No. 12, 2003 2395
an atmosphere of carbon monoxide at room temperature for 2
h. After 0.5 h the solution became yellow and a yellow
precipitate formed. The solid was collected by filtration and
washed with hexane (3 × 5 mL) to give [bis(3,5-dimethyl-1-
pyrazolyl)methane]dicarbonyliridium(I) tetraphenylborate,
{[Ir(dmBPM)(CO)2]+(BPh4)-} (5) as a yellow powder (98 mg,
99%); mp decomposes at 190 °C, melts at 216-219 °C. The
spectroscopic data were identical to the sample produced from
{[Ir(COD)Cl]2}.
{[Ir (BP M)(CO)2]+(BP h 4)-} (3) Cr ysta l Str u ctu r e Da ta .
A crystal was mounted on a glass fiber with cyanoacrylate
resin, and cell constants were determined by least-squares fits
to the setting angles of 25 independent reflections collected
on an Enraf Nonius CAD-4F four-circle diffractometer employ-
ing graphite-monochromated Mo KR radiation.
Data reduction and application of Lorentz, polarization,
and analytical absorption corrections were carried out using
teXsan.40 The structure was solved by direct methods using
SHELXS-8641 and refined using full-matrix least-squares
methods with teXsan.40 Hydrogen atoms were included at
calculated sites with isotropic thermal parameters based on
that of the riding atom, and the non-hydrogen atoms were
refined anisotropically. Neutral atom scattering factors were
taken from International Tables.42 Anomalous dispersion
effects were included in Fc.43 The values for ∆f ′ and ∆f′′ were
those of Creagh and McAuley.44 The values for the mass
attenuation coefficients are those of Creagh and Hubbell.45 All
other calculations were performed using the teXsan40 crystal-
lographic software package of Molecular Structure Corpora-
tion. An ORTEP31 projection of the molecule is provided in
Figure 1.
room temperature, and the reaction mixture was heated at
40 °C. Aliquots of the reaction mixture were taken at regular
intervals, and the concentrations of starting materials and
products were monitored by calibrated gas chromatography.
For reactions with tertiary hydrosilanes (R3SiH), the ratio of
reactants, solvent, and standard was ROH: 2, R3SiH: 1, THF:
10, n-octane: 0.2, except for the reactions with Ph3SiH, where
4 equiv of alcohol was used. For reactions with secondary
hydrosilanes (R2SiH2), the ratio of reactants, solvent, and
standard was ROH: 4, R2SiH2: 1, THF: 10, n-octane: 0.2.
Reactions were catalyzed by approximately 0.45 mol % of the
{[Ir(BPM)(CO)2]+(BPh4)-} (3) catalyst or by approximately 0.33
mol % of the {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) catalyst, except
where otherwise noted.
Silyl ether products from the reaction mixtures were isolated
by careful removal of the THF solvent under reduced pressure.
Hexane was added to precipitate the iridium species, and the
reaction mixture was filtered through a plug of flash silica
using hexane as the eluent. The hexane solvent was removed
under reduced pressure and with the more volatile products,
the solvent was removed, and the product isolated by fractional
distillation.
1
The silyl ether products were characterized using H, 13C,
13C{1H}, and 29Si{1H} NMR spectroscopy. The assignments of
the spectra were based on the observed couplings as well as
comparison with literature reports.2,15,16 Complete 1H, 13C, and
29Si assignments are reported in the Supporting Information.
Ack n ow led gm en t. We gratefully acknowledge fi-
nancial support from the Australian Research Council
(ARC) and The University of Sydney for an H.B. and
F.M. Gritton Scholarship (L.P.S). We thank Sarah Wren
for assistance with microanalyses, J ohnson Matthey Pty
Ltd for the generous loan of iridium salts, and Kitty
Hashimoto for the synthesis of C6H5CH2(OCH2CH2)4-
OH.
Syn th esis of Silyl Eth er s via th e Alcoh olysis of Hy-
d r osila n es Ca ta lyzed by {[Ir (BP M)(CO)2]+(BP h 4)-} (3),
{[Ir (d m BP M)(CO)2]+(BP h 4)-} (5), or {[Ir (BP M)(COD)]+-
(BP h 4)-} (1). In a typical reaction, the hydrosilane substrate
was added to a stirred solution of the alcohol, n-octane
(internal standard), THF (solvent), and iridium catalyst at
(40) teXsan Crystal Structure Analysis Package; Molecular Structure
Corporation, 1985 & 1992.
(41) Sheldrick, G. M. SHELXS-86, A Program for X-ray Crystal
Structure Determination; Oxford University Press: 1985; p 175.
(42) Cromer, D. T.; Waber, J . T. Table 2.2.A; Kynoch Press: Bir-
mingham, 1974; Vol. 4.
(43) Ibers, J . A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.
(44) Creagh, D. C.; McAuley, W. J . Table 4.2.6.8; Kluwer Academic
Publishers: Boston, 1992; Vol. C, 219-222.
(45) Creagh, D. C.; Hubbell, J . H. ; Kluwer Academic Publishers:
Boston, 1992; Vol. C, Table 4.2.4.3, pp 200-206.
Su p p or tin g In for m a tion Ava ila ble: A listing of 1H, 13C
NMR data for silyl ethers; 29Si NMR data for hydrosilanes and
their respective methoxy, ethoxy, and isopropyloxy-silyl ethers;
additional spectroscopic data for selected compounds; and
X-ray crystallographic data for {[Ir(BPM)(CO)2]+(BPh4)-} (3).
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM020938W