Reactions of Cp*(PMe3)Ir(Me)OTf with silanes: Role of base-free silylene complexes in rearrangements of the resulting silicon-based ligands

Article abstract of DOI:10.1021/om020191+

The mechanisms of silicon-hydrogen activation by Cp*(PMe₃)Ir(Me)OTf (Cp* = η⁵-C₅-Me₅, OTf = OSO₂CF₃; 1) and rearrangements of the resulting silyliridium complexes were investigated. The scope of this reaction has been studied for silanes with a variety of substituents. Silylene complexes of the type [Cp*(PMe₃)Ir(SiR₂)(H)] [X] (X = OTf, R = Mes, 6; X = B(C₆F₅)₄, R = Ph, 16) have been isolated, and the likelihood of their involvement in the rearrangements is discussed. The kinetics of the isomerization reaction of the cyclometalated iridium(V) complex {Cp*(PMe₃)Ir(H)[κ²-SiH(Mes)(2-CH₂-4 ,6-Me₂C₆H₂)]}[OTf] (5) to the iridium silylene [Cp*(PMe₃)Ir(SiMes₂)(H)] [OTf] (6) were examined using NMR spectroscopic techniques. The primary kinetic isotope effect (Si-H vs Si-D bond) for this process was determined to be 1.4 ± 0.1, implying a rate-limiting hydride migration from silicon to iridium. The activation parameters for this isomerization have also been measured: ΔH^? = 23 ± 2 kcal/mol and ΔS^? = 0.1 ± 0.01 eu. Slow hydride migration to produce a silylene complex from either Cp*(PMe₃)Ir(Me)OTf (1) or [Cp*(PMe₃Ir(Me)(CH₂Cl₂)][BC₆F ₅)₄] (17) is observed for large substituents on silicon. However, production of the sterically less crowded complex [Cp*(PMe₃)Ir(SiPh₂)(H)] [B(C₆F₅)₄] (16) is extremely rapid upon reaction of 17 with H₂SiPh₂. This argues for the intermediacy of a three-coordinate silicon species.

Full text of DOI:10.1021/om020191+

3376
Organometallics 2002, 21, 3376-3387
Rea ction s of Cp *(P Me3)Ir (Me)OTf w ith Sila n es: Role of
Ba se-F r ee Silylen e Com p lexes in Rea r r a n gem en ts of th e
Resu ltin g Silicon -Ba sed Liga n d s
Steven R. Klei, T. Don Tilley,* and Robert G. Bergman*
Department of Chemistry, University of California, and Chemical Sciences Division,
Lawrence Berkeley National Laboratory, Berkeley, California 94720
Received March 7, 2002
The mechanisms of silicon-hydrogen activation by Cp*(PMe3)Ir(Me)OTf (Cp* ) η5-C5-
Me5, OTf ) OSO2CF3; 1) and rearrangements of the resulting silyliridium complexes were
investigated. The scope of this reaction has been studied for silanes with a variety of
substituents. Silylene complexes of the type [Cp*(PMe3)Ir(SiR2)(H)][X] (X ) OTf, R ) Mes,
6; X ) B(C6F5)4, R ) Ph, 16) have been isolated, and the likelihood of their involvement in
the rearrangements is discussed. The kinetics of the isomerization reaction of the cyclom-
etalated iridium(V) complex {Cp*(PMe3)Ir(H)[κ2-SiH(Mes)(2-CH2-4,6-Me2C6H2)]}[OTf] (5) to
the iridium silylene [Cp*(PMe3)Ir(SiMes2)(H)][OTf] (6) were examined using NMR spectro-
scopic techniques. The primary kinetic isotope effect (Si-H vs Si-D bond) for this process
was determined to be 1.4 ( 0.1, implying a rate-limiting hydride migration from silicon to
iridium. The activation parameters for this isomerization have also been measured: ∆Hq )
23 ( 2 kcal/mol and ∆Sq ) 0.1 ( 0.01 eu. Slow hydride migration to produce a silylene
complex from either Cp*(PMe3)Ir(Me)OTf (1) or [Cp*(PMe3)Ir(Me)(CH2Cl2)][B(C6F5)4] (17)
is observed for large substituents on silicon. However, production of the sterically less crowded
complex [Cp*(PMe3)Ir(SiPh2)(H)][B(C6F5)4] (16) is extremely rapid upon reaction of 17 with
H2SiPh2. This argues for the intermediacy of a three-coordinate silicon species.
In tr od u ction
has been studied recently.8 Relevant to these investiga-
tions is the reactivity of methyliridium salts with
silanes. The complex Cp*(PMe3)Ir(Me)OTf (Cp* ) η5-
C5Me5, OTf ) OSO2CF3; 1) is known to activate the
Si-H bonds of tertiary silanes (HSiR3) to liberate
methane and produce organometallic compounds of the
general formula Cp*(PMe3)Ir(SiR2OTf)(R), the result of
an apparent 1,2-shift of a group from silicon to the metal
center (eq 1).9 This 1,2-group migration models a
The phenomenon of substituent metathesis, or redis-
tribution, has been observed for many main-group and
transition-metal systems.1 Redistribution at silicon
centers occurs more easily than at carbon, yet not as
readily as at tin, and can be catalyzed by acids, bases,
and metals.2 Silicon redistribution reactions are utilized
industrially to convert unwanted byproducts from the
synthesis of functionalized silanes into useful materi-
als.1 The transition-metal-catalyzed pathway is believed
to involve 1,2-shifts of groups between the metal and
silicon and 1,3-shifts between metal-bound silicon cen-
ters. Evidence for intramolecular 1,3-shifts between
silicon atoms,3-5 and for an intermolecular exchange
between transition-metal silylene and silyl complexes,
has been documented.6 It was recently reported that a
silylene complex can be accessed by the 1,2-migration
of hydrogen from silicon to platinum.7
potential key step in metal-mediated redistribution
reactions. Moreover, the migration and cyclometalation
chemistry reported here adds to the growing number
of transformations observed after bond activation in the
Ir(III) system. Previously it has been reported that alkyl
and acyl complexes formed from C-H activation un-
dergo R- and â-elimination and decarbonylation reac-
tions, respectively.10,11
The reactivity of methyliridium(III) salts, including
stoichiometric and catalytic C-H activation reactions,
(1) Brook, M. A. Silicon in Organic, Organometallic, and Polymer
Chemistry; Wiley-Interscience: New York, 2000.
(2) Curtis, M. D.; Epstein, P. S. Adv. Organomet. Chem. 1981, 19,
213.
(3) Pannell, K. H.; Cervantes, J .; Hernandez, C.; Cassias, J .;
Vincenti, S. Organometallics 1986, 5, 1056.
(4) Tobita, H.; Ueno, K.; Ogino, H. Bull. Chem. Soc. J pn. 1988, 61,
2797.
(5) Haynes, A.; George, M. W.; Haward, M. T.; Poliakoff, M.; Turner,
J . J .; Boag, N. M.; Green, M. J . Am. Chem. Soc. 1991, 113, 2011.
(6) Grumbine, S. K.; Tilley, T. D. J . Am. Chem. Soc. 1994, 116, 6951.
(7) Mitchell, G. P.; Tilley, T. D. Angew. Chem., Int. Ed. 1998, 37,
2524.
(8) Klei, S. R.; Golden, J . T.; Burger, P.; Bergman, R. G. J . Mol.
Catal. A, in press.
(9) Burger, P.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 10462.
(10) Luecke, H. F.; Arndtsen, B. A.; Burger, P.; Bergman, R. G. J .
Am. Chem. Soc. 1996, 118, 2517.
(11) Alaimo, P. J .; Arndtsen, B. A.; Bergman, R. G. Organometallics
2000, 19, 2130.
10.1021/om020191+ CCC: $22.00 © 2002 American Chemical Society
Publication on Web 07/10/2002

Reactions of Cp*(PMe3)Ir(Me)OTf with Silanes
Organometallics, Vol. 21, No. 16, 2002 3377
Sch em e 1
We wished to ascertain whether base-free silylene
intermediates are formed in the 1,2-shift, or if the
rearrangement proceeds instead via a triflate-assisted
pathway involving a pentacoordinate silicon species
(Scheme 1). Although a number of base-stabilized si-
lylene complexes are known,12-14 base-free silylene
complexes are rare.7,15-19 We reported in preliminary
form the isolation of a rare iridium-silylene complex
kinetically stabilized by incorporation of bulky groups
on the silicon center.20 Although H2SiMes2 underwent
Si-H activation and migration of a substituent from
silicon to iridium upon treatment with 1, our inability
to access similar silylene complexes from anion metath-
esis reactions of Cp*(PMe3)Ir(SiPh2OTf)(Ph) (2) and
Cp*(PMe3)Ir(SiMe2OTf)Me21 (3) made us suspicious of
the generalization that silylene complexes were inter-
mediates in reactions of less hindered silanes. We now
report the full details of our investigation of 1,2-group
migrations resulting from a presumed 16-electron cat-
ionic iridium center. Reactions of Cp*(PMe3)Ir(Me)OTf
with a variety of silanes provided evidence for distin-
guishing between the two mechanisms illustrated in
Scheme 1.
F igu r e 1. ORTEP diagram of Cp*(PMe3)Ir(SiPh2OTf)(Ph)
(2). Thermal ellipsoids are shown at the 50% probability
level. Hydrogen atoms have been omitted for clarity.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 2
bond
distance
bond
angle
Ir-P
2.281(2)
2.317(2)
2.065(8)
1.9488(3)
1.819(5)
P-Ir-Si
90.95(8)
90.3(2)
92.5(2)
117.3(2)
125.86(6)
Ir-Si
P-Ir-C14
Si-Ir-C14
C14-Ir-C100
Si-Ir-C100
Ir-C14
Ir-C100
Si-O
performed. An ORTEP diagram of complex 2 is shown
in Figure 1. There are two crystallographically unique
but chemically identical molecules in the asymmetric
unit. The bond lengths of the two molecules are es-
sentially the same; representative bond lengths are
given in Table 1.22 Comparison to the data reported by
Oro and co-workers for IrH2(SiPh2OTf)(TFB)(PiPr3)
(TFB ) tetrafluorobenzobarrelene, Ir-Si ) 2.337(2) Å)
indicates that the Ir-Si bond length observed for 2 is
not unusual. Both the Oro compound and 2 are produced
by Si-H activation strategies, although the starting
material is Ir(I) for the former and Ir(III) for the latter.
F u r t h er R ea ct ivit y of Cp *(P Me3)Ir (Me)OTf (1)
tow a r d Sila n es. To probe the nature of steric and
electronic factors on migrations in [Cp*(PMe3)IrSiR3]+
systems, we examined the reactivity of 1 with a variety
of silanes. Addition of the bulky hydrosilane HSi(SiMe3)3
to Cp*(PMe3)Ir(Me)OTf (1) in CH2Cl2 affords Cp*-
(PMe3)Ir[Si(SiMe3)2Me](SiMe2OTf) (4; eq 2) in 82%
Resu lts
X-r ay Cr ystal Str u ctu r e ofCp*(P Me3)Ir (SiP h 2OTf)-
(P h ) (2). As reported by Burger et al., addition of
HSiPh3 to an orange solution of 1 affords Cp*(PMe3)Ir-
(SiPh2OTf)(Ph) (2) in 95% yield. Although this complex
had been fully characterized, a crystal structure had not
yet been obtained. Single crystals of 2 were grown by
slow evaporation of a CH2Cl2 solution into pentane at
room temperature, and an X-ray diffraction study was
(12) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rap-
poport, Z., Eds.; Wiley: New York, 1991; p 309.
(13) Zybill, C. Top. Curr. Chem. 1991, 160, 1.
(14) Corriu, R. J . P.; Chauhan, B. P. S.; Lanneau, G. F. Organome-
tallics 1995, 14, 1646.
(15) Mork, B. V.; Tilley, T. D. J . Am. Chem. Soc. 2001, 123, 9702.
(16) Peters, J . C.; Feldman, J . D.; Tilley, T. D. J . Am. Chem. Soc.
1999, 121, 9871.
(17) Wanandi, P. W.; Glaser, P. B.; Tilley, T. D. J . Am. Chem. Soc.
2000, 122, 972.
(18) Feldman, J . D.; Mitchell, G. P.; Nolte, J . O.; Tilley, T. D. J .
Am. Chem. Soc. 1998, 120, 11184.
(19) Straus, D. A.; Grumbine, S. D.; Tilley, T. D. J . Am. Chem. Soc.
1990, 112, 7801.
(20) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J . Am. Chem. Soc.
2000, 122, 1816.
isolated yield after 5 h at 25 °C. Diastereotopic trim-
ethylsilyl groups (δ 0.17 and 0.15) and three types of
Si-Me groups (δ 0.96, 0.78, and 0.44) are evident from
1
the H NMR spectrum. Cooling a concentrated CH2Cl2
solution of 4 to -35 °C for 2 weeks afforded X-ray-
(21) Klei, S. R.; Tilley, T. D.; Bergman, R. G. Organometallics 2001,
20, 3220.
(22) For complete details of this X-ray diffraction study, see the
Supporting Information.

3378 Organometallics, Vol. 21, No. 16, 2002
Klei et al.
NMR signal of 6 resonates at +301 ppm downfield of
SiMe4, clearly indicating that the silicon center is three-
coordinate.18 This is the first known example of a
silylene complex which does not coordinate triflate, and
we believe that steric congestion at the silicon center is
responsible for this observation.
F igu r e 2. ORTEP diagram of Cp*(PMe3)Ir(SiMe2OTf)(Si-
(SiMe3)2(Me) (4). Thermal ellipsoids are shown at the 50%
probability level. Hydrogen atoms have been omitted for
clarity.
Previous work has shown that heteroatom substitu-
ents have a stabilizing effect on metal silylene com-
plexes, on the basis of activation parameters for aceto-
nitrile exchange.23 With this in mind, the reactivity of
silanes of the type HSi(ER)3 (E ) S, O) with 1 was
examined with the hope that intermediate silyl or
silylene complexes would be sufficiently long-lived that
they could be observed.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 4
bond
distance
bond
angle
Ir-P
2.2532(18)
2.2987(18)
2.446(2)
1.9622(3)
1.837(5)
P-Ir-Si1
89.95(9)
94.85(7)
88.12(9)
123.49(6)
122.84(5)
Addition of 1 equiv of HSi(StBu)3 to a CH2Cl2 solution
Ir-Si1
Ir-Si2
Ir-C100
Si-O
P-Ir-Si2
Si1-Ir-Si2
Si1-Ir-C100
Si2-Ir-C100
of 1 produces [Cp*(PMe3)Ir(κ2-Si(StBu)2StBu)][OTf] (7)
in 88% isolated yield (eq 4). Unlike the reactions of
quality crystals. A crystallographic study confirmed the
structure, and an ORTEP diagram is shown in Figure
2. The Ir-Si bond length for the silicon bound to two
silyl groups and a methyl group is 2.446(2) Å, whereas
the Ir-Si bond length of the silicon bound to the triflate
is 2.2987(18) Å (Table 2). This comparison is informa-
tive, as it implies partial multiple-bond character in the
latter case. The 29Si NMR spectrum contains resonances
at 62.2 and -79.0 ppm for the two silicon atoms
attached to iridium, suggesting very different silicon
environments. Although the reaction takes 5 h to
proceed to completion, no intermediates were observed
by room-temperature 1H and 31P{1H} NMR spectros-
copy. Attempts to observe an iridium silylene complex
directly by the addition of either NaBArf (BArf ) B(3,5-
(CF3)2C6H3)4) or (Et2O)2LiB(C6F5)4 to the final product
4 led to intractable products.
Addition of a CD2Cl2 solution of Cp*(PMe3)Ir(Me)OTf
(1) to H2SiMes2 (Mes ) 2,4,6-Me3C6H2) results in rapid
evolution of CH4, and the solution adopts a pale yellow
color. This Si-H activation reaction, like all those
described subsequently except the reaction with HSi-
(SiMe3)3, occurs immediately at room temperature. The
presence of an iridium hydride was confirmed by 1H
NMR spectroscopy (δ -14.56, J P-H ) 24 Hz); the
diastereotopic protons of the iridium-methylene unit
resonate at 3.79 and 2.67 ppm. The combined spectro-
scopic data for this new material conclusively show that
it is a cyclometalated Ir(V) alkyl hydride, {Cp*(PMe3)-
alkyl- and aryl-substituted silanes, complete migration
of a thiolato group to iridium is not observed. The 31P-
{1H} NMR spectrum contains a broad resonance at δ
-45.4, and one of the 13C{1H} NMR spectral resonances
is broad (δ 40.1, SC(Me)3). The 1H NMR spectrum,
which contains three chemically inequivalent tert-butyl
thiolato groups, is consistent with the structure shown
in eq 4. However, it is also supportive both of an
unmigrated species in which hindered rotation renders
the thiolato groups inequivalent and also of a fully
migrated species. X-ray-quality crystals of 7 were grown
from CH2Cl2/pentane at -35 °C, and a structural study
was carried out. An ORTEP diagram of the cationic
portion of this compound is shown in Figure 3, and
representative bond lengths and angles for complex 7
are found in Table 3. The structure involves a dative
interaction between one of the tert-butyl thiolato groups
on silicon and the iridium center. Attempts to observe
equilibration of the thiolato groups by NMR spectros-
copy at elevated temperatures (60 °C) in ClCD2CD2Cl
led to decomposition.
Ir(H)[κ2-SiH(Mes)(2-CH2-4,6-Me2C6H2)]}[OTf] (5; eq 3),
formed apparently by intramolecular benzyl C-H bond
activation in the iridium silyl complex [Cp*(PMe3)Ir-
(SiHMes2)][OTf]. Complex 5 isomerizes to the bright
yellow base-free silylene complex [Cp*(PMe3)Ir(SiMes2)-
(H)][OTf] (6) over the course of 12 h, with no intermedi-
The bonding motif revealed by the crystal structure
of 7 suggests an “arrested” migration. We therefore
believed that it might be possible to complete the
migration if a suitable donor could be found to bind
(23) Grumbine, S. K.; Straus, D. A.; Tilley, T. D. Polyhedron 1995,
14, 127.
1
ates observed by H or 31P NMR spectroscopy. The 29Si

Reactions of Cp*(PMe3)Ir(Me)OTf with Silanes
Organometallics, Vol. 21, No. 16, 2002 3379
plished by treatment of 9 with CCl4. As expected, no
Ir-H resonances were observed for chloride complex 10
by 1H NMR spectroscopy; 1 equiv of chloroform was
detected by 1H NMR analysis of the crude reaction
mixture.
Reaction of 1 with HClSiPh2 gives an inseparable
mixture of two products by 1H and 31P{1H} NMR
spectroscopy. Treatment of this mixture with [PPN]Cl
led to the formation of Cp*(PMe3)Ir(SiPh2Cl)Cl (11) in
49% recrystallized yield (eq 6). Attempts to reduce this
species with common reducing agents (Na, Na(Hg), and
Riecke Mg), in hopes of accessing the neutral silylene
complex Cp*(PMe3)Ir(SiPh2), led to the formation of
multiple products. A similar route has provided the
silene complex Cp2W(η2-Me2SidCH2) by reduction of
Cp2W(Cl)(CH2SiMe2Cl) with Riecke Mg.24
An ion Meta th esis Rea ction s of th e Ir id iu m Silyl
Tr ifla te Com p lexes. The possibility of base-free sil-
ylene complex involvement in the rearrangement reac-
tions of iridium silyl complexes was probed using anion
metathesis reactions. The reaction of Cp*(PMe3)Ir(SiPh2-
OTf)(Ph) with (Et2O)2LiB(C6F5)4 yields the crystallo-
graphically characterized cyclometalated Ir(V) complex
[Cp*(PMe3)Ir(κ2-SiPh2(C6H4))(H)][B(C6F5)4] (12) (eq 7).20
F igu r e 3. ORTEP diagram of the cationic portion of [Cp*-
(PMe3)Ir(κ2-Si(StBu)2StBu)][OTf] (7). Thermal ellipsoids are
shown at the 50% probability level. Hydrogen atoms have
been omitted for clarity.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 7
bond
distance
bond
angle
Ir-P
2.3290(15)
2.3044(16)
2.4357(15)
2.219(2)
P-Ir-S1
P-Ir-Si
Si-Ir-S1
S2-Si-S1
S2-Si-S3
79.94(5)
100.66(6)
55.73(5)
115.20(9)
111.92(9)
Ir-Si
Ir-S1
Si-S1
Si-S2
2.124(2)
preferentially to silicon. Addition of acetonitrile to 7 led
to the liberation of isobutylene and formation of an
unidentified iridium complex. However, treatment of 7
with 1 equiv of a soluble fluoride source, TAS-F (tris-
(dimethylamino)sulfur (trimethylsilyl)difluoride)), pro-
duced [Cp*(PMe3)Ir[Si(StBu)2F](StBu)][OTf] (8) in 82%
isolated yield (eq 4). The 29Si NMR resonance (δ 9.1,
dd, J Si-F ) 400 Hz, J Si-P ) 25 Hz) is supportive of this
formulation, as is the detection of a stoichiometric
When Cp*(PMe3)Ir(SiPh2OTf)(Ph) is treated with 1
equiv of NaBArf (BArf ) 3,5-(CF3)2C6H3)4B), the reaction
mixture immediately adopts a dark blue-green color,
with one major product observed by 1H and 31P{1H}
NMR. This species decomposes over the course of hours
to multiple products. Only by using the soluble salt
(Et2O)2LiB(C6F5)4 was it possible to isolate an iridium-
containing product free of impurities; this was shown
to be [Cp*(PMe3Ir(H)(κ2-SiPh2(C6H4))][B(C6F5)4] (12),
which is pale yellow. This complex displays an Ir-H
NMR resonance at δ -12.7 (d, J P-H ) 20 Hz) and an
infrared νIr-H stretching frequency at 2084 cm-1. The
identity of the highly colored impurity present in the
reactions with NaBArf is currently unknown, as are the
identities of the decomposition products.
1
amount of Me3SiF by H NMR spectroscopy (δ 0.02, d,
J H-F ) 7.2 Hz). A driving force for this reaction is
presumed to be the formation of the strong Si-F bond.
The products formed when 1 was treated with 2 equiv
of HSi(OEt)3 in CH2Cl2 were identified as Cp*(PMe3)-
Ir[Si(OEt)2OTf](H) (9; 85% isolated yield) and Si(OEt)4
(eq 5). The presence of Si(OEt)4 was confirmed by
The novelty of this unprecedented Ir(III) to Ir(V) C-H
oxidative addition reaction led us to examine whether
the cyclometalation was limited to aryl substitution at
silicon. Specifically, metalation of the intermediate
trimethylsilyl-iridium complex “[Cp*(PMe3)Ir(SiMe3)-
(CH2Cl2)][B(C6F5)4]” would lead to a cationic iridium-
silene complex, a previously unknown structural type.
This expectation was confirmed on treatment of Cp*-
comparison of the volatile materials from the reaction
with an authentic sample using GC/MS and H NMR
1
spectroscopy. Using 1 equiv or less of HSi(OEt)3 did not
alter the course of the reaction; only the starting
material 1 and product 9 were observed by 1H NMR
spectroscopy under these conditions. Conversion of the
product to the corresponding chloride Cp*(PMe3)Ir[Si-
(OEt)2OTf](Cl) (10) in 80% isolated yield was accom-
(24) Koloski, T. S.; Carroll, P. J .; Berry, D. H. J . Am. Chem. Soc.
1990, 112, 6405.

3380 Organometallics, Vol. 21, No. 16, 2002
Klei et al.
(PMe3)Ir(SiMe2OTf)(Me) (3) with (Et2O)2LiB(C6F5)4,
which generated a mixture of [Cp*(PMe3)Ir(η2-CH2-
SiMe2)(H)][B(C6F5)4] (13) and [Cp*(PMe3)Ir(SiMe2(Et2O))-
(Me)][B(C6F5)4] (14) (eq 8).21 The silene complex 13 could
formation of the bright yellow silylene complex [Cp*-
(PMe3)Ir(SiPh2)(H)][B(C6F5)4] (16; eq 10). The H and
1
31P NMR resonances for the silylene complex 16 are
virtually identical with those of the iridium starting
material, but the 19F NMR spectrum indicates that a
metathesis reaction has taken place. Furthermore, the
29Si NMR spectrum contains a single resonance at 351.1
ppm. This remarkably downfield resonance for 16 is
diagnostic of a three-coordinate silicon center; the 29Si
NMR resonance for the iridium silyl triflate starting
material is 51.5 ppm. The lithium salts produced in the
metathesis may be partially removed by filtration.
However, samples isolated by this protocol typically
contain 0.2-0.5 equiv of lithium salts. It should be noted
that treating [Cp*(PMe3)Ir(Me)(CH2Cl2)][BArf] with
H2SiPh2 led to a complex mixture of products, as did
reaction of Cp*(PMe3)Ir(SiPh2OTf)(H) with NaBArf. We
suspect that undetectable impurities present from the
preparation of NaBArf are responsible for the latter
observation. No new resonances in the 19F NMR spec-
trum are observed, which would presumably result if
the weakly coordinating anion had been attacked in the
reaction.
Silylene complex 16 is very sensitive to adventitious
moisture. As a result, reactions performed with (Et2O)2-
LiB(C6F5)4 that has not been rigorously dried26 yield a
small amount of a hydrolysis product, which we specu-
late is [Cp*(PMe3)Ir(SiPh2OH)(H)2][B(C6F5)4]. 1H NMR
spectroscopy reveals that the hydrolysis product con-
tains an iridium-hydride resonance which gives an
integration of two protons (δ -14.67, d, J P-H ) 20 Hz).
However, evidence for the Si-OH functionality was not
found using NMR or IR spectroscopy. That this new
product is formed by hydrolysis was confirmed by
adding a substoichiometric amount of H2O to a sample
containing it and silylene complex 16. An increase in
the quantity of the hydrolysis product was observed by
integration of its resonance against those of an internal
standard.
be purified by crystallization from CH2Cl2/pentane at
-35 °C in 43% isolated yield. Campion and Tilley have
previously reported the synthesis and reactivity of the
charge-neutral analogue Cp*(PMe3)Ir(η2-CH2SiPh2) (15).25
An attempt was made to establish a synthetic link
between silene complexes 13 and 15. Reaction of HSi-
MePh2 with Cp*(PMe3)Ir(Me)OTf, followed by metath-
esis with (Et2O)2LiB(C6F5)4, should afford a protonated
derivative of the Campion silene complex 15. Deproto-
nation of 13 with a nonnucleophilic base should then
give Cp*(PMe3)Ir(η2-CH2SiPh2). However, while the
reaction of HSiMePh2 with 1 produced a mixture of Cp*-
(PMe3)Ir(SiMePhOTf)(Ph) diastereomers, the metath-
esis reaction of this mixture with (Et2O)2LiB(C6F5)4
resulted in the production of two major and two minor
products. The major products both exhibit iridium-
hydride resonances in their 1H NMR spectra (δ 12.85,
J H-H ) 20 Hz; δ 12.94, J H-H ) 20 Hz). Neither of these
products contains resonances in the expected chemical
shift range for a metalated methylene unit. These
combined data lead us to propose that the two major
anion metathesis products are the diastereomers of
[Cp*(PMe3)Ir(H)(η2-Si(Ph)(Me)(C6H4))][B(C6F5)4], result-
ing from cyclometalation of the phenyl group attached
to silicon (eq 9). Preferential attack on the C-H bond
Isotop e Effect a n d Ra te Stu d ies. Most of the silane
activation reactions are extremely rapid and no inter-
1
mediates were observed by H or 31P{1H} NMR spec-
troscopy, even at -80 °C. Nevertheless, information
concerning the activation/migration reaction mechanism
can be gained experimentally by measurement of isotope
effects and relative rates. The isotope effect for silane
oxidative addition was probed using a competition
experiment. Reaction of Cp*(PMe3)Ir(Me)OTf with a
mixture of 50 equiv of HSiPh3 and 50 equiv of DSiPh3
at 0 °C led to clean formation of Cp*(PMe3)Ir(SiPh2OTf)-
of the silicon-bound phenyl ring over attack on the
silicon-methyl group is believed to be a result of
thermodynamic considerations. Formation of a stronger
Ir-C(aryl) bond over a weaker Ir-C(alkyl) bond has
been considered as a driving force in the reaction of Cp*-
(PMe3)IrMeOTf with benzene to produce Cp*(PMe3)-
IrPhOTf.9
Access to complexes of the type [Cp*(PMe3)Ir(SiPh2)-
(H)][X] was straightforward. Reaction of (Et2O)2LiB-
(C6F5)4 with Cp*(PMe3)Ir(SiPh2OTf)(H) leads to the
1
(Ph). Using H NMR spectroscopy, the ratio of CH4 to
CH3D was measured to determine that the kinetic
(26) We have found that stirring a THF solution of (Et2O)2LiB(C6F5)4
over 4 Å molecular sieves for 2 days, followed by filtration and removal
of the solvent, is an effective way of producing the dry salt.
(25) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Am. Chem. Soc.
1990, 112, 4079.

Reactions of Cp*(PMe3)Ir(Me)OTf with Silanes
Organometallics, Vol. 21, No. 16, 2002 3381
Ta ble 4. Ra te Da ta for th e Con ver sion of 5 to 6
T (K)
rate constant (L mol-1
)
287.73
299.40
309.75
320.25
(2.43 ( 0.05) × 10-5
(9.00 ( 0.01) × 10-5
(3.85 ( 0.05) × 10-4
(1.60 ( 0.01) × 10-3
isotope effect for the silicon-hydrogen activation was
essentially unity (kH/kD ) 0.97 ( 0.08). It was then
desirable to compare this value to the intramolecular
kinetic isotope effect for the reaction of methyliridium
complex 1 with HDSiPh2. An attempt was made to
synthesize HDSiPh2 from HClSiPh2 and LiAlD4. How-
ever, a significant amount of redistribution to H2SiPh2
and D2SiPh2 was observed after workup. The redistri-
bution is presumably catalyzed by aluminum before or
during distillation of the product. This appears to
contradict an earlier reported synthesis of HDSiPh2.27
The isomerization reaction of cyclometalated complex
5 to iridium silylene 6 allows for a close examination of
1,2-hydride migration from silicon to iridium. To date,
there have been no detailed kinetic analyses of reactions
leading to base-free metal silylenes. Attempts were
made to prevent isomerization to the silylene complex
by trapping the cyclometalated iridium hydride complex
as the corresponding chloride; however, the presence of
CCl4 had no effect on the isomerization reaction. Kinetic
studies on the conversion of 5 to 6 revealed that the
isomerization exhibited clean first-order kinetics. A rate
constant of (9.00 ( 0.01) × 10-5 L mol-1 was measured
at 299.40 K in ClCD2CD2Cl. A similar protocol was
implemented for the study of deuterium migration in
F igu r e 4. Eyring plot for the conversion of 5 to 6.
lanes. For this reason, anion effects were examined. We
have previously reported that, in general, C-H activa-
tion processes are faster for [Cp*(PMe3)Ir(CH3)(CH2Cl2)]-
[B(C6F5)4] (17) relative to 1.28 Treatment of methyliri-
dium complex 17 with H2SiMes2 led to a rate that is
very similar to that observed for the reaction of H2SiMes
with complex 1 to form 5. It was found that the rate of
intramolecular rearrangement of complexes with smaller
substituents on silicon was very similar to the rate of
reaction between 1 and H2SiPh2. That is, reaction of 17
with H2SiPh2 leads to immediate production of silylene
complex 16.
{Cp*(PMe3)Ir(D)[κ2-SiH(Mes)(2-CH2-3,5-Me2C6H2)]}-
[OTf] (5-d), which was prepared by treating Cp*-
(PMe3)IrMeOTf with D2SiMes2. The first-order rate
constant for the isomerization of 5-d to 6-d is (6.54 (
0.01) × 10-5 L mol-1 at 299.25 K. Using an Eyring plot
(vide supra) to correct for the temperature difference
in the measured rate constants, the primary kinetic
isotope effect for this hydride/deuteride migration is 1.6
( 0.1. Addition of triflate ion (4 equiv), in the form of
[NHex4][OTf], had no effect on the first-order rate
constant for the isomerization. This implies that the
anion does not participate in the reaction.
The isomerization of 5 to silylene complex 6 was
further examined with regard to the temperature
dependence of the rate constant. The solvent chosen was
ClCD2CD2Cl, as the elevated temperatures necessary
for the study prevented the use of CD2Cl2. Although
CDCl3 was a potential solvent option, a small amount
of an unidentified product was evident when it was used
in the isomerization reaction. The rate constant for the
conversion of 5 to 6 was monitored between 290 and
320 K; measured values can be found in Table 4. A plot
of ln(k/T) vs 1/T fit well to a straight line, and the slope
and intercept were used to determine ∆Hq ) 23 ( 2 kcal/
mol and ∆Sq ) 0.1 ( 0.01 eu, respectively. The Eyring
plot can be found in Figure 4.
Discu ssion
The silyl complexes described here were obtained from
the corresponding alkyl derivatives. Although this
methodology is somewhat uncommon, related examples
are known for ruthenium,29 osmium,17 and rhodium,30
in addition to those for iridium.9,16 The circumstantial
evidence in every case supports a dissociative mecha-
nism in which a reactive 16-electron complex is involved.
The distinction of complex 1 is that it accesses the
coordinatively unsaturated intermediate via dissociation
of an anionic,31 rather than dative, ligand. Furthermore,
1 reacts with silanes under comparatively mild condi-
tions. The synthesis of cationic ruthenium-silyl com-
plexes has recently been effected under mild conditions
through phosphine removal by borane abstraction.32
The rearrangement products obtained in this work
could have the potential to serve as useful catalysts,
given the reactivity of structurally similar compounds.
For example, 16-electron silyl complexes of rhodium
have been shown to be effective catalysts for C-F
(28) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970.
(29) Straus, D. A.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J . J . Am.
Chem. Soc. 1987, 109, 5872.
(30) Aizenberg, M.; Milstein, D. Science 1994, 265, 359.
(31) A full paper concerning mechanistic aspects of the Ir(III) C-H
activation reaction has been written: Tellers, D. M.; Yung, C. M.;
Arndtsen, B. A.; Adamson, D. R.; Bergman, R. G. J . Am. Chem. Soc.,
in press.
Our ability to spectroscopically observe the formation
of the iridium silylene complex 6 questioned the rel-
evance of the reaction to the silyl migration behavior
observed in reactions of Cp*(PMe3)Ir(Me)OTf with si-
(27) Mayr, H.; Basso, N.; Hagen, G. J . Am. Chem. Soc. 1992, 114,
3060.
(32) Dioumaev, V. K.; Plossl, K.; Carroll, P. J .; Berry, D. H. J . Am.
Chem. Soc. 1999, 121, 8391.

3382 Organometallics, Vol. 21, No. 16, 2002
Klei et al.
Sch em e 2
Sch em e 3
activation of aromatic fluorocarbons.30 Brookhart and
co-workers have shown that the related cationic 16-
electron alkyl complexes of cobalt are useful for the
polymerization of ethylene.33 Also, cationic alkylrhodium
complexes have been used for catalytic tail-to-tail
dimerization of methyl acrylate,34 and cationic alkyl-
palladium complexes are active for living alternating
copolymerization of olefins and carbon monoxide.35,36
An interesting aspect of the silane activation products
formed from methyliridium complex 1 is their propen-
sity to undergo 1,2-rearrangement to form stable com-
plexes of the type Cp*(PMe3)Ir(SiR2OTf)(R), in prefer-
ence to structures of the form Cp*(PMe3)Ir(SiR3)(OTf).
These migration reactions are especially facile when a
comparison is made to the behavior of the corresponding
alkyl derivatives. For example, very little evidence has
been found for the interconversion of methyliridium
species with [Cp*(PMe3)Ir(dCH2)(H)][X] (X ) OTf,
BArf).8 This lower propensity for 1,2-migration may be
one of the factors responsible for the previously men-
tioned reluctance of carbon to undergo transition-metal-
catalyzed redistribution reactions.
All of our attempts to generate a complex of the type
“Cp*(PMe3)Ir(SiR3)(OTf)” have led to rearrangement to
other structures. For example, the reaction of Cp*-
(PMe3)Ir(Me)OTf with HSi(SiMe3)3 produces the more
extensively rearranged product Cp*(PMe3)Ir[Si(SiMe3)2-
Me](SiMe2OTf). This reaction requires 5 h for comple-
tion, quite a bit longer than that required for reactions
of Cp*(PMe3)Ir(Me)OTf with HSiPh3 and HSiMe3. An
apparent rate-determining Si-H activation step ac-
counts for the lack of observable intermediates. A
plausible mechanism for this apparent double migration
is shown in Scheme 2; this mechanism invokes base-
free iridium silylenes as key intermediates. Initial Si-H
bond activation undoubtedly produces [Cp*(PMe3)IrSi-
(SiMe3)3][OTf], which can then undergo 1,2-silyl migra-
tion to give [Cp*(PMe3)Ir[Si(SiMe3)2](SiMe3)][OTf],
followed by 1,3-methyl migration to [Cp*(PMe3)Ir-
[Si(SiMe3)2Me](SiMe2)][OTf], which is trapped by triflate
to give the observed products. The 1,3-methyl migration
in this mechanism implies that a silicon-supported
silylene complex is less stable than a silylene complex
which is bonded to carbon. An intramolecular 1,3-group
migration step involving silylene complexes has also
been suggested in recent work by Sakaba et al. to
explain redistribution reactions at a tungsten center.37
A similar mechanism has been suggested for a migra-
tion reaction stemming from “(PMe3)3RhSi(SiMe3)3”.38
The reaction of Cp*(PMe3)Ir(Me)OTf with HSi(OEt)3
also exhibits rearrangements that are more complicated
than simple 1,2-group migration. We have considered
two mechanisms to account for formation of Cp*-
(PMe3)Ir(H)[Si(OEt)2OTf] and Si(OEt)4; these are shown
in Scheme 3. Path A involves oxidative addition of a
Si-H bond to produce the presumed cationic silyl [Cp*-
(PMe3)IrSi(OEt)3][OTf], followed by oxidative addition
of HSi(OEt)3 to generate the Ir(V) complex [Cp*(PMe3)-
Ir(H)(Si(OEt)3)2][OTf], which extrudes Si(OEt)4 to give
[Cp*(PMe3)Ir(H)(Si(OEt)2)][OTf]. Charge neutralization
by triflate coordination affords the product (9). An
alternative explanation (path B) begins with a catalyzed
redistribution of HSi(OEt)3 to Si(OEt)4 and H2Si(OEt)2.
Reaction of the secondary silane with Cp*(PMe3)Ir(Me)-
OTf followed by 1,2-migration of hydride from silicon
to iridium and coordination of triflate would generate
the observed products. Experimental verification of this
latter hypothesis is hampered somewhat by the fact that
H2Si(OEt)2 is not commercially or synthetically avail-
able. It is reasonable to suggest, however, that Cp*-
(PMe3)Ir(Me)OTf is capable of mediating this redistri-
bution, given that similar reactions are catalyzed by
Lewis acids and bases and even proceed in the absence
of a catalyst.1,2 At this time there is no direct evidence
available to distinguish between the two mechanisms.
At the time we began studying the rearrangement
reactions in the Cp*(PMe3)Ir system, there were no
examples of base-free iridium silylene complexes. Since
that time the synthesis of [PhB(CH2PPh2)3]Ir(H)2-
(SiMes2) has been described.16 The methods by which
(33) Schmidt, G. F.; Brookhart, M. J . Am. Chem. Soc. 1985, 107,
1443.
(34) Brookhart, M.; Sabo-Etienne, S. J . Am. Chem. Soc. 1991, 113,
2777.
(35) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C. J .
Am. Chem. Soc. 1992, 114, 5894.
(36) Brookhart, M.; Wagner, M. I. J . Am. Chem. Soc. 1996, 118,
7219.
(37) Sakaba, H.; Tsukamoto, M.; Hirata, T.; Kabuto, C.; Horino, H.
J . Am. Chem. Soc. 2000, 122, 11511.
(38) Mitchell, G. P.; Tilley, T. D. Organometallics 1996, 15, 3477.

Reactions of Cp*(PMe3)Ir(Me)OTf with Silanes
Organometallics, Vol. 21, No. 16, 2002 3383
the silylene complexes are produced in these systems
share some similarities. In the Cp* system, one syn-
thetic approach involved anion metathesis with the
silyliridium triflate complexes to provide cationic sil-
ylene complexes. An alternative method requires treat-
ing the more reactive complex [Cp*(PMe3)Ir(CH3)(CH2-
Cl2)][B(C6F5)4] (17) with secondary silanes. The silylene
complex [PhB(CH2PPh2)3]Ir(H)2(SiMes2) is produced by
treating the π-cyclooctenyl complex [PhB(CH2PPh2)3]Ir-
(H)(η3-C8H13) with secondary silanes. Both the Cp* and
PhB(CH2PPh2)3 systems have the potential to undergo
the silane activation/1,2-migration transformation
through coordinatively unsaturated cationic alkyl spe-
cies. Olefin dissociation in the π-cyclooctenyl complex
[PhB(CH2PPh2)3]Ir(H)(η3-C8H13) would produce an open
coordination site, and CH2Cl2 dissociation is believed
to occur in [Cp*(PMe3)Ir(CH3)(CH2Cl2)][B(C6F5)4] (17).
Although the thermally sensitive methyliridium dichlo-
romethane-solvated complex [Cp*(PMe3)Ir(CH3)(CH2-
Cl2)][BArf] has been isolated successfully,28 the cationic
silyl complex [Cp*(PMe3)Ir(SiPh3)][B(C6F5)4] is appar-
ently not stabilized sufficiently by CH2Cl2 ligation.
Instead, activation of an ortho aryl C-H bond takes
place to yield {Cp*(PMe3)Ir(H)[η2-SiPh2(C6H4)]}[B(C6F5)4]
(12; eq 7). However, addition of the more strongly
coordinating solvent acetonitrile to 12 permits the
isolation of a cationic silyl complex, [Cp*(PMe3)Ir-
(SiPh3)(CH3CN)][B(C6F5)4], via a process which undoubt-
edly involves reductive elimination in 12. Given the fact
that reductive elimination is reversible, the cyclometa-
lated complex 12 can be viewed as a masked version of
the Ir(III) silyl complex [Cp*(PMe3)Ir(SiPh3)][B(C6F5)4].39
The cyclometalation reaction was extended to tertiary
silyliridium complexes which contain silicon-methyl
bonds, as Cp*(PMe3)Ir(SiMe2OTf)(Me) gave [Cp*(PMe3)-
Ir(H)(η2-SiMe2(CH2))][B(C6F5)4] (13) upon reaction with
(Et2O)2LiB(C6F5)4 (eq 8). In this case, the cyclometala-
tion event may also be viewed as a â-hydride elimina-
tion. A comparison between silene complex 13 and a
deprotonated analogue, the neutral iridium silene Cp*-
(PMe3)Ir(η2-CH2SiPh2) (15) prepared by Campion and
Tilley, is warranted. As a result of its “extra proton”,
silene complex 13 has C-H reductive elimination as an
accessible pathway. This reductive elimination is rapid
and reversible, such that addition of soft donor ligands
such as CO and ethylene to 13 traps the reductive
elimination product by coordination to the metal cen-
ter.21 The neutral silene complex 15 does not have access
to the reductive elimination pathway, however. As a
result, treatment of Cp*(PMe3)Ir(η2-CH2SiPh2) with
dative ligands such as PMe3, even at 140 °C, leads to
no observable reaction.40
tial relevance to the intermolecular C-H activation
reactions observed at cationic Ir(III) centers.9 Consistent
with our discovery of the cyclometalations reported here,
theoretical studies performed on model Ir(III) systems
supported the oxidative addition pathway.42,43
The ease with which the presumed 16-electron cat-
ionic silyliridium complexes underwent cyclometalation
to Ir(V) species leaves open to question whether our
ability to isolate the silylene complex [Cp*(PMe3)Ir-
(SiMes2)(H)][OTf] (6) was a result of steric effects or was
due to the use of a secondary silane in the synthesis.
The anion metathesis reaction of Cp*(PMe3)Ir(SiPh2-
OTf)(H) (the product of reaction of Cp*(PMe3)Ir(Me)OTf
with H2SiPh2) with (Et2O)2LiB(C6F5)4 was therefore
performed to distinguish these possibilities. The silylene
complex [Cp*(PMe3)Ir(SiPh2)(H)][B(C6F5)4] is formed in
this reaction, and the 29Si NMR signal of +351 ppm for
this species demonstrates that it is base-free. This
highlights the necessity of using secondary silanes in
the preparation of silylene complexes of this kind. The
possibility of interaction of the iridium-bound hydride
ligand with the silylene moiety is ruled out by the 29Si
NMR shift of the complex.
Isomerization of the cyclometalated iridium complex
5 to silylene complex 6 allows careful study of the 1,2-
migration from silicon to the metal center. In particular,
the steric environment provides a base-free silylene
complex with a triflate anion as the product. Therefore,
the large mesityl substituents on silicon enable the
study of an iridium silylene complex without salt
metathesis. The most interesting aspect of this process
is its long reaction time (12 h), compared to the
essentially instantaneous reactions of Cp*(PMe3)Ir(Me)-
OTf with HSiPh3 and HSiMe3. The slow isomerization
(eq 3) might be attibuted to a slow reductive elimination
step to produce [Cp*(PMe3)Ir(SiHMes2)][OTf] or a rate-
limiting migration step to yield the silylene complex.
The kinetic isotope effect of 1.6 ( 0.1 for Si-H vs
Si-D migration in 5 is believed to be a primary effect
and is relevant to determining the rate-limiting step of
the isomerization in eq 3. Isotope effects for other
reactions which produce base-free silylene complexes
have not yet been reported. A significant isotope effect
here indicates that the rate-limiting step is the hydride/
deuteride migration. Ruled out is the possibility of a
rate-limiting reductive elimination step, because no
isotope effect would be expected in that case. An
alternative hydride transfer mechanism in which the
silicon-bound hydride migrates directly to the metalated
carbon atom was ruled out by the following labeling
study. When Cp*(PMe3)Ir(Me)OTf was treated with D2-
SiMes2, clean formation of {Cp*(PMe3)Ir(D)[κ2-SiH-
The mechanism of C-H activation by Ir(III) com-
plexes has received much attention, with two mecha-
nistic postulates for the reaction being oxidative addi-
tion to an Ir(V) intermediate and a concerted σ-bond
metathesis.8,41 The reactions described here detail the
only observable C-H activation reactions of Ir(III)
materials to give stable Ir(V) aryl and alkyl hydride
complexes. As such, they are important in their poten-
(Mes)(2-CH2-4,6-Me2C6H2)]}[OTf] (5-d ) was observed.
2
Using H NMR spectroscopy, it was possible to observe
exclusive formation of [Cp*(PMe3)Ir(D)(dSiMes)2][OTf],
with no label incorporated into the mesityl methyl
groups. Since the rate-limiting step is group migration
in the conversion of 5 to 6, and this process necessarily
takes place without triflate assistance, the long reaction
time could indicate that triflate plays the role of
(39) A full account of the reactivity of the iridium silyl and silylene
complexes described here is in preparation.
(40) Campion, B. K. Ph.D. Thesis, University of California, San
Diego, 1990.
(41) Alaimo, P. J .; Bergman, R. G. Organometallics 1999, 18, 2707.
(42) Strout, D. L.; Zaric, S.; Niu, S. Q.; Hall, M. B. J . Am. Chem.
Soc. 1996, 118, 6068.
(43) Su, M. D.; Chu, S. Y. J . Am. Chem. Soc. 1997, 119, 5373.

3384 Organometallics, Vol. 21, No. 16, 2002
Klei et al.
accelerant in the other more rapid migration reactions.
Alternatively, the much larger silyl ligand in this case
may simply have difficulty achieving the proper orienta-
tion for hydride migration.
and Bergman reported that Fischer type cationic alky-
lidene hydride complexes can be synthesized through a
C-H bond activation/1,2-hydride migration strategy,
although isotope effects were not reported in that
work.10 The comparatively lower isotope effect in our
system suggests that there is less Si-H(D) bond break-
ing in the transition state for group migration.
To distinguish these possibilities, [Cp*(PMe3)Ir(Me)-
(CH2Cl2)][B(C6F5)4] (17) was treated with H2SiMes2. The
reaction rate was observed to be identical with that for
conversion of 5 to 6. This confirmed that the anion does
not affect this process. If the group migration takes
place with triflate assistance, it might then be expected
that generation of [Cp*(PMe3)Ir(SiPh2H)(CH2Cl2)]-
[B(C6F5)4] would result in a long-lived species that
gradually isomerized to [Cp*(PMe3)Ir(H)(SiPh2)][B(C6F5)4]
(16). However, treatment of methyliridium complex 17
with the sterically less demanding silane H2SiPh2
results in an immediate color change, and formation of
silylene complex 16 is observed spectroscopically within
10 min. This indicates that hydride migration from any
putative [Cp*(PMe3)Ir(SiPh2H)(CH2Cl2)][B(C6F5)4] in-
termediate is rapid. Therefore, the best explanation for
why the isomerization of 5 to 6 is slow is that the
required conformation for hydride migration in [Cp*-
(PMe3)Ir(SiMes2H)(CH2Cl2)][OTf] is difficult to achieve.
Unlike the isotope effect for group migration, the
isotope effect for silane oxidative addition is negligible
and consistent with earlier findings. A primary kinetic
isotope effect of 1.13 for the oxidative addition of Et3-
SiH to Cp2Ta(µ-CH2)2Ir(CO)2 to yield Cp2Ta(µ-CH2)2Ir-
(SiEt3)(H)(CO)2 has been reported previously.44 Expla-
nations offered for those results included a nonlinear
transition state (η2-bound Et3SiH) and a preequilibrium
involving a σ-complex (η1-bound Et3SiH). Graham and
co-workers similarly reported a small primary kinetic
isotope effect (1.05) for the oxidative addition of Ph3-
SiH to CpMn(CO)2 to give CpMn(CO)2(H)(SiPh3).45
A limited amount of mechanistic information is avail-
able concerning the migration reactions which have thus
far been reported to yield base-free silylene com-
plexes,3,4,7,15,16,18,37 compared to that for carbene com-
plexes. Examples of R-hydride migration have been
reported in which alkylidene complexes are generated
for both early and late transition metals, and in a
number of cases the mechanism of the reaction has been
probed with isotope effects. An elegant study of this
process was reported recently by Schrock et al., in which
the primary kinetic isotope effect for molybdenum-
alkylidene production was found to be kH/kD(64 °C) )
3.1 ( 0.5.46 Similarly, Fryzuk et al. reported a primary
kinetic isotope, kH/kD(70 °C) ) 3.0(5), in the synthesis
of a zirconium alkylidene.47 Green and co-workers
studied the reverse reaction, in which a tungsten
methylidene hydride is converted to a tungsten methyl
complex. They found that deuteration of the “active”
methyl group led to an enhanced rate, with an inverse
isotope effect of kH/kD(70 °C) ) 0.80 ( 0.02.48 Luecke
Con clu sion
After exploring the reaction scope of Cp*(PMe3)Ir(Me)-
OTf with silanes, it is apparent that a rich variety of
migration types are possible within this system. These
include 1,3-migration in the case of HSi(SiMe3)3 and
silane redistribution in the case of HSi(OEt)3. Addition-
ally, two reaction pathways that appear to be compa-
rable in energy for 16-electron silyliridium(III) com-
plexes are metalation to give Ir(V) products and 1,2-
migration to afford silylene complexes. Base-free silylene
complexes have been generated and characterized, and
our data support a 1,2-migration mechanism that
proceeds via these species as reactive intermediates. The
similar rates of both the rearrangement reactions to
Cp*(PMe3)Ir(SiR2OTf)(R) and the production of the
silylene complex [Cp*(PMe3)Ir(SiPh2)(H)][B(C6F5)4] from
H2SiPh2 and [Cp*(PMe3)Ir(CH3)(CH2Cl2)] [B(C6F5)4] (17)
represents our most persuasive evidence for this conclu-
sion.
Exp er im en ta l Section
Gen er a l P r oced u r es. Unless otherwise noted, reactions
and manipulations were performed at 25 °C in an inert-
atmosphere (N2) glovebox or using standard Schlenk and high-
vacuum-line techniques. Except where noted, all NMR spectra
were acquired at room temperature. In cases where assign-
ment of the 13C{1H} NMR spectrum was ambiguous, reso-
nances were assigned using standard DEPT 45, 90, and/or 135
pulse sequences. Infrared (IR) spectra were recorded using
samples prepared as KBR pellets. Mass spectrometric (MS)
analyses were obtained at the University of California, Ber-
keley Mass Spectrometry Facilty on VT ProSpec, ZAB2-EQ,
and 70-FE mass spectrometers. Elemental analyses were
performed at the University of California, Berkeley Microana-
lytical facility, on a Perkin-Elmer 2400 Series II CHNO/S
Analyzer. Melting points were determined with a Thomas-
Hoover Unimelt capillary melting point apparatus using sealed
capillary tubes under nitrogen, are uncorrected, and are
reported in °C.
Sealed NMR tubes were prepared by attaching the NMR
tube directly to a Kontes high-vacuum stopcock using a Cajon
Ultra-Torr reducing union and then flame-sealing on a vacuum
line. Reactions with gases and low-boiling liquids involved
condensation of a calculated pressure of gas from a bulb of
known volume into the reaction vessel at -196 °C. Known-
volume bulb vacuum transfers were accomplished with a
digital MKS Baratron gauge attached to a high-vacuum line.
Ma ter ia ls. Unless otherwise noted, reagents were pur-
chased from commercial suppliers and used without further
purification. Potassium bromide (Aldrich), Celite (Aldrich),
silica gel (Merck 60, 230-400 mesh), and alumina (Brockman
I, Aldrich) were dried in vacuo at 250 °C for 48 h. Toluene,
pentane, hexanes, methylene chloride, benzene, and toluene
(Fisher) were passed through a column of activated alumina
(type A2, size 12 × 32, Purifry Co.) under nitrogen pressure
and sparged with N2 prior to use.49 Diethyl ether and tetra-
(44) Hostetler, M. J .; Butts, M. D.; Bergman, R. G. Organometallics
1993, 12, 65.
(45) Hart-Davis, A. J .; Graham, W. A. G. J . Am. Chem. Soc. 1971,
94, 4388.
(46) Schrock, R. R.; Seidel, S. W.; Mosch Zanetti, N. C.; Shih, K. Y.;
O’Donoghue, M. B.; Davis, W. M.; Reiff, W. M. J . Am. Chem. Soc. 1997,
119, 11876.
(47) Fryzuk, M. D.; Duval, P. B.; Mao, S. S. S. H.; Zaworotko, M. J .;
MacGillivray, L. R. J . Am. Chem. Soc. 1999, 121, 2478.
(48) Green, J . C.; Green, M. L. H.; Morley, C. P. Organometallics
1985, 4, 1302.
(49) Alaimo, P. J .; Peters, D. W.; Arnold, J .; Bergman, R. G. J . Chem.
Educ. 2001, 78, 64.

Reactions of Cp*(PMe3)Ir(Me)OTf with Silanes
Organometallics, Vol. 21, No. 16, 2002 3385
hydrofuran (Fisher) were distilled from purple sodium/ben-
zophenone ketyl under N2 prior to use. Deuterated solvents
(Cambridge Isotope Laboratories) were purified by standard
procedures.50 Our supplier of lithium tetrakis(pentafluorophen-
yl)borate etherate is Boulder Scientific Co. H2SiMes2 was
prepared according to the literature procedure,18 as were
compounds 1-3.9
1.70 (d, J P-H ) 10.2 Hz, 9H, PMe3), 1.68 (s, 9H, StBu), 1.58 (s,
9H, StBu), 1.45 (s, 9H, StBu). 13C{1H} NMR (126 MHz: the
CF3 group was not detectable within a reasonable number of
scans; δ 98.8 (s, C5Me5), 53.3 (s, SiSC(CH3)3), 52.6 (br s,
IrSC(Me)3), 52.5 (s, SiSC(Me)3), 35.1 (s, SiSC(Me)3), 35.0 (s,
Si-SC(CH3)3), 32.5(s, IrSC(Me)3), 17.8 (br s, PMe3), 11.5 (s,
C5Me5). 31P{1H} NMR (162 MHz): δ -45.4 (s). 19F{1H} NMR
(376 MHz): δ -78.9 (s). 29Si{1H} NMR (99 MHz): δ -12.4 (d,
J Si-P ) 14 Hz). IR: 2965, 2922, 1460, 1277, 1255, 1160, 1031,
956, 638 cm-1. Anal. Calcd for C26H51F3IrO3PS4Si: C, 36.82;
H, 6.06. Found: C, 36.85; H, 6.28.
Cp *(P Me3)Ir [Si(SiMe3)2Me](SiMe2OTf) (4). A 20 mL
scintillation vial was charged with 5 mL of a CH2Cl2 solution
of Cp*(PMe3)Ir(Me)OTf (95.8 mg, 0.169 mmol) and a magnetic
stir bar. To this stirred orange solution was added a solution
of HSi(SiMe3)3 (52.1 µL, 0.169 mmol) in CH2Cl2 (2 mL)
dropwise over a period of 10 s. The reaction mixture was
stirred for 5 h, by which time the solution had turned yellow.
Removal of the solvent in vacuo afforded 111 mg (82%) of 6 as
Cp *(P Me3)Ir [Si(StBu )2F ](StBu ) (8). A 20 mL scintillation
vial was charged with 5 mL of a CH2Cl2 solution of [Cp*(PMe3)-
Ir(κ2-Si(StBu)2StBu)][OTf] (7; 35.1 mg, 0.041 mmol), CH2Cl2 (5
mL) and a magnetic stir bar. To this stirred solution was added
dropwise over 10 s a solution of tris(dimethylamino)sulfur
(trimethylsilyl)difluoride (11.4 mg, 0.041 mmol) in CH2Cl2 (2
mL). The reaction mixture was stirred for 20 min at room
temperature. The solvent was removed in vacuo to give a
yellow powder that could be recrystallized from pentane/Et2O
at -35 °C to afford 24.2 mg (82%) of yellow 8. Mp: 185-187
°C dec. 1H NMR (500 MHz): δ 1.80 (d, J P-H ) 1.8 Hz, 15H,
C5Me5), 1.70 (d, J P-H ) 10.4 Hz, 9H, PMe3), 1.53 (s, 9H, StBu),
1.52 (s, 9H, StBu), 1.34 (s, 9H, StBu). 13C{1H} NMR (126
MHz): δ 98.91 (d, J P-C ) 2.9 Hz, C5Me5), 50.31 (s, Si-
SC(Me)3), 50.23 (s, SiSC(Me)3), 40.12 (d, J P-C ) 4.6 Hz, Ir-
SC(CH3)3), 36.26 (s, SiSC(Me)3), 35.64 (d, J P-C ) 1.5 Hz,
IrSC(Me)3), 35.12(s, SiSC(Me)3), 17.20 (d, J P-C ) 42.1 Hz,
PMe3), 10.67 (s, C5Me5) ppm. 31P{1H} NMR (162 MHz): δ -45.5
(s). 19F{1H} NMR (376 MHz): δ -104 (s). 29Si{1H} NMR (99
MHz): δ 9.1 (dd, J Si-F ) 400 Hz, J P-Si ) 25 Hz). IR: 2560,
2909, 2856, 2365 (w), 1734 (w), 1454, 1361, 1277, 1156, 1026,
958, 938, 859, 792, 720, 677, 571, 511, 468 cm-1. Anal. Calcd
for C25H51FIrPS3Si: C, 41.81; H, 7.16. Found: C, 42.16; H,
7.38.
1
a sticky, peach-colored foam. Mp: 138-140 °C dec. H NMR
(400 MHz): δ 1.89 (s, 15H, C5Me5), 1.61 (d, J P-H ) 9.8 Hz,
PMe3), 0.96 (s, 3H, Si-Me), 0.78 (s, 3H, Si-Me), 0.44 (s, 3H,
Si-Me), 0.17 (s, 9H, SiMe3), 0.15 (s, 9H, SiMe3). 13C{1H} NMR
(126 MHz): the CF3 group was not detectable within a
reasonable number of scans; δ 99.4 (s, C5Me5), 21.1 (d, J C-P
)
40 Hz, PMe3), 12.8 (s, CH3), 10.3 (s, CH3), 9.9 (s,CH3), 4.0 (s,
SiMe), 3.6 (s, SiMe), -1.1 (s, SiMe). 31P{1H} NMR (162 MHz):
δ -54.0 (s). 19F{1H} NMR (376 MHz): δ -78.9 (s). 29Si{1H}
NMR (99 MHz): δ 62.2 (d, J Si-P ) 21 Hz, Ir-Si(Me2OTf), -15.5
(s, SiMe3), -17.2 (s, SiMe3), -79.0 (d, J Si-P ) 12.9 Hz, Ir-
Si(SiMe3)2Me). IR: 1273, 1257, 1163, 1045, 952, 843, 773, 652
cm-1. Anal. Calcd for C23H51F3O3IrPSSi4: C, 34.52; H, 6.42.
Found: C, 34.63; H, 6.55.
[Cp *(P Me3)Ir (SiMes2)(H)][OTf] (6). A 20 mL scintillation
vial was charged with 10 mL of a CH2Cl2 solution of Cp*-
(PMe3)Ir(Me)OTf (1; 250 mg, 0.441 mmol) and a magnetic stir
bar. To this stirred orange solution was added a solution of
H2SiMes2 (118 mg, 0.441 mmol) in CH2Cl2 (2 mL) dropwise
over a period of 10 s. Removal of the solvent in vacuo and
washing the resulting bright yellow foam with 10 mL of 1:1
ether/pentane afforded 259 mg (0.316 mmol, 72%) of analyti-
Cp *(P Me3)Ir [Si(OEt)2OTf](H) (9). A 20 mL scintillation
vial was charged with 5 mL of a CH2Cl2 solution of Cp*(PMe3)-
Ir(Me)OTf (52.2 mg, 0.0920 mmol) and a magnetic stir bar.
To this stirred solution was added dropwise over 10 s a solution
of HSi(OEt)3 (60 µL, 0.32 mmol) in CH2Cl2 (2 mL). The reaction
mixture was stirred for 5 min at room temperature, and then
the solvent was removed in vacuo to afford 52.5 mg (85%) of 9
as a sticky light yellow oil that was >95% pure by 1H NMR
spectroscopy. Repeated recrystallization attempts failed to
produce a solid. 1H NMR (400 MHz): δ 3.83 (m, 4H, Si-OEt),
2.03 (d, J P-H ) 1.5 Hz, 15H, C5Me5), 1.60 (d, J P-H ) 10.5 Hz,
9H, PMe3), 1.21 (m, 6H, Si-OEt), -18.13 (d, J P-H ) 27 Hz,
1H, Ir-H). 13C{1H} NMR (100 MHz): the CF3 group was not
detectable within a reasonable number of scans; δ 95.91 (d,
J P-C ) 2.5 Hz, C5Me5), 59.30 (s, OCH2CH3), 59.27 (s, OCH2-
CH3), 22.19 (d, J P-C ) 40 Hz, PMe3), 18.28 (s, OCH2CH3), 18.25
(d, OCH2CH3), 10.74 (s, C5Me5). 31P{1H} NMR (162 MHz): δ
-46.1 (s). 19F{1H} NMR (376 MHz): δ -78.9 (s). 29Si{1H} NMR
(99 MHz): δ -29.2 (d, J P-Si ) 27 Hz). IR: 1280, 1245, 960,
800, 742, 652, 579, 519 cm-1. MS (EI): m/ z 672 (M+). HRMS
(EI): m/z (M+) for C18H35F3IrO5PSSi calcd 672.1294, obsd
672.1288.
1
cally pure 6 as a yellow foam. H NMR (500 MHz): δ 6.98 (s,
1H, Ar), 6.94 (s, 1H, Ar H), 6.82 (s, 1H, Ar H), 6.75(s, 1H, Ar
H), 2.68 (s, 6H, coincident Ar Me), 2.32 (s, 3H, Ar Me), 2.27 (s,
3H, Ar Me), 2.17 (s, 3H, Ar Me), 2.15 (s, 3H, Ar Me), 1.90 (d,
J P-H ) 1.5 Hz, C5Me5), 1.58 (d, J P-H ) 10.8 Hz, 9H, PMe3),
-15.90 (d, J P-H ) 28 Hz, 1H, Ir-H). 13C{1H} NMR (126
MHz): the CF3 group was not detectable within a reasonable
number of scans; δ 143.8 (s, Ar C), 142.9 (s, Ar C), 142.9 (s, Ar
C), 142.3 (s, Ar C), 141.9 (s, Ar C), 139.5 (s, Ar C), 139.4 (s, Ar
C), 139.1 (s, Ar C), 130.6, (s, Ar CH), 129.7 (s, Ar CH), 129.3
(s, Ar CH), 129.1 (s, Ar CH), 100.2 (s, C5Me5), 24.8 (s, Ar Me),
23.9 (s, Ar Me), 23.3 (s, Ar Me), 23.1 (s, Ar Me), 22.1 (d, J C-P
) 43 Hz, PMe3) 21.6 (s, Ar Me), 21.5 (s, Ar Me), 10.1 (s, C5Me5).
31P{1H} NMR (162 MHz): δ -45.1 (s). 19F{1H} NMR (376
MHz): δ -78.9 (s). 29Si{1H} NMR (99 MHz) δ 304.9 (dd, J Si-H
) 10 Hz, J Si-P ) 11 Hz). IR: 2145, 1605, 1548, 1475, 1454,
1418, 1383, 1285, 1250, 1225, 1161, 1077, 1031, 959, 827, 638
cm-1. Anal. Calcd for C32H47F3IrO3PSSi: C, 46.87; H, 5.78.
Found: C, 46.68; H, 6.07.
[Cp *(P Me3)Ir (K2-Si(StBu )2StBu )][OTf] (7). A 20 mL scin-
tillation vial was charged with 5 mL of a CH2Cl2 solution of
Cp*(PMe3)Ir(Me)OTf (1; 70.0 mg, 0.0123 mmol) and a magnetic
stir bar. To this stirred solution was added dropwise over 10
s a solution of HSi(StBu)3 (36.6 mg, 0.0123 mmol) in CH2Cl2
(2 mL). Gas evolution was observed upon mixing, and the
solution was stirred for 10 min at room temperature. The
solvent was removed in vacuo to give a yellow powder that
could be recrystallized from CH2Cl2/pentane at -35 °C to afford
92.0 mg (88%) of pure, bright yellow 7. Mp: 116-120 °C dec.
1H NMR (400 MHz): δ 2.05 (d, J P-H ) 2.2 Hz, 15H, C5Me5),
Cp *(P Me3)Ir [Si(OEt)2OTf](Cl) (10). A 20 mL scintillation
vial was charged with 5 mL of a CH2Cl2 solution of Cp*-
(PMe3)Ir(H)(Si(OEt)2OTf (9; 52.5 mg, 0.0781 mmol) and a
magnetic stir bar. To this stirred solution was added neat CCl4
(30.1 µL, 0.31 mmol). The reaction mixture was stirred for 2
h at room temperature, and then the solvent was removed in
vacuo. Subsequent extraction into ether/pentane (1:1) and
removal of volatile materials in vacuo afforded 44.2 mg (0.0625
mmol, 80%) of 10 as a yellow oil that was >95% pure by 1H
NMR spectroscopy. Repeated recrystallization attempts failed
1
to yield a solid. H NMR (400 MHz): δ 3.97 (m, 4H, SiOEt),
1.76 (d, J P-H ) 1.8 Hz, 15H, C5Me5), 1.64 (d, J P-H ) 10.8 Hz,
(50) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: New York, 1988.
9H, PMe3), 1.22 (m, 6H, SiOEt). 13C{1H} NMR (126 MHz): the

3386 Organometallics, Vol. 21, No. 16, 2002
Klei et al.
CF3 group was not detectable within a reasonable number of
scans; δ 97.5 (d, J P-C ) 2.5 Hz, C5Me5), 60.18 (s, OCH2CH3),
60.13 (OCH2CH3), 18.33 (s, OCH2CH3), 18.27 (s, OCH2CH3),
17.2 (d, J P-C ) 40 Hz, PMe3), 9.64 (s, C5Me5). 31P{1H} NMR
(162 MHz): δ -37.6 (s). 19F{1H} NMR (376 MHz): δ -78.9
(s). 29Si{1H} NMR (99 MHz): δ -40.0 (d, J P-Si ) 35 Hz). IR:
residue was redissolved in 3 mL of CH2Cl2, filtered through
fiberglass, and layered with 12 mL of pentane. The vial was
stored at -35 °C for 2 days, and pale yellow crystals grew
during this time (54.0 mg, 0.004 67 mmol, 43%). The crystals
were isolated by decanting the mother liquors, washing with
2 × 1 mL of pentane, and drying in vacuo. 1H NMR (400
2921, 2857, 1642, 1599, 1449, 1260, 1105, 1019, 803, 695 cm-1
.
MHz): δ 1.97 (d, J P-H ) 2.0 Hz, 15H, C5Me5), 1.50 (d, J P-H )
MS (EI): m/ z 706 (M+). HRMS (EI): m/z for C18H34F3IrO5-
PSSiCl calcd 706.0904, obsd 706.0907.
10.8 Hz, 9H, PMe3), 0.77 (s, 3H, Si-Me), 0.72 (s, 3H, Si-Me),
0.46 (d, J H-H ) 14 Hz, 1H, Ir-CH2), 0.06 (dd, J H-H ) 14 Hz,
J P-H ) 19 Hz, 1H, Ir-CH2), -14.8 (d, J P-H ) 20 Hz, 1H, Ir-
H). 13C{1H} NMR (126 MHz): δ 149.9 (m, B(C6F5)), 138.0 (m,
B(C6F5)), 136.0 (m, B(C6F5)), 124.0 (m, B(C6F5)), 99.9 (s, C5-
Me5), 18.4 (d, J P-C ) 41 Hz, PMe3), 10.2 (C5Me5), -2.7 (s, Si-
Me), -3.0 (s, Si-Me), -16.8 (bs, Ir-CH2). 31P NMR (162 MHz);
Cp *(P Me3)Ir (SiP h 2Cl)Cl (11). To a 20 mL scintillation vial
containing HClSiPh2 (40.3 µL, 0.206 mmol) and Cp*(PMe3)-
Ir(Me)(OTf) (117 mg, 0.206 mmol) was added 5 mL of CH2Cl2.
The resulting yellow solution was mixed thoroughly for 30 s
with a pipet, and gas evolution was observed. This solution
was added to solid bis(triphenylphosphoranylidene)ammonium
chloride (118.2 mg, 0.2059 mmol) in another vial, and the
resulting solution was similarly mixed and then allowed to
stand for 15 min. The solvent was removed in vacuo and the
residue extracted with 2 × 3 mL of benzene. The benzene was
removed in vacuo to give a bright yellow-orange powder, which
was recrystallized from CH2Cl2/CH3CN at -35 °C. The yield
δ -39.5 (s). 19F NMR (376 MHz): δ -133 (s), -164 (t, J B-F
)
19 Hz), -167 (s). 29Si NMR (99 MHz): δ 2.1 (d, J P-Si ) 13 Hz).
IR: 2991, 2140, 2034, 1642, 1513, 1464, 1384, 1276, 1088, 980,
774, 756 cm-1. Anal. Calcd for C40H33F20IrBPSi: C, 41.57; H,
2.88. Found: C, 41.87; H, 2.87.
{Cp *(P Me3)Ir [SiMe2(Et2O)](Me)}[B(C6F 5)4] (14). This
complex is observed to be in equilibrium with 13 and was not
isolated. 1H NMR (190 K, 500 MHz): δ 4.33 (m, 2H, diaste-
reotopic CH3CH2OEt), 4.22 (m, 2H, diastereotopic CH3CH2-
OEt), 1.64 (s, 15H, Cp*), 1.38 (d, J P-H ) 11 Hz, 9H, PMe3),
1.30 (vt, J H-H ) 5 Hz, 6H, CH3CH2OCH2CH3), 0.49 (s, 3H, Si-
Me), 0.43 (s, 3H, Si-Me), -0.06 (d, J P-H ) 5 Hz, 3H, Ir-Me).
13C{1H} NMR (190 K, 126 MHz): δ 149.9 (m, B(C6F5)), 138.0
(m, B(C6F5)), 136.0 (m, B(C6F5)), 124.0 (m, B(C6F5)), 95.6 (s,
C5Me5), 68.0 (s, Si-bound CH3CH2OEt), 14.7 (br s, PMe3
overlapping with CH3CH2OEt of free Et2O), 12.5 (s, Si-bound
CH3CH2OEt), 8.7 (C5Me5), 7.2 (s, Si-Me), 6.6 (s, Si-Me), -32.0
(d, J P-C ) 8 Hz, Ir-Me). 31P NMR (190 K, 202 MHz): δ -43.7
(br s). 19F NMR (376 MHz): δ -133 (s), -164 (t, J B-F ) 19
Hz), -167 (s). 29Si NMR INEPT (190 K): δ 10.9.
[Cp *(P Me3)Ir (SiP h 2)(H)][B(C6F 5)4] (16). To a 20 mL
scintillation vial containing 5 mL of a CH2Cl2 solution of Cp*-
(PMe3)Ir(Me)(OTf) (22.3 mg, 0.0393 mmol) was added H2SiPh2
(7.3 µL, 0.0393 mmol) by syringe. Upon mixing with a pipet,
the solution became pale yellow and effervescence was ob-
served. After 30 s, this solution was pipetted onto solid (Et2O)2-
LiB(C6F5)4 (32.8 mg, 0.0393 mmol), which produced a slightly
darker yellow slurry. This slurry was mixed for 30 s with a
pipet. The slurry was then filtered through a Celite/fiberglass
filter and the filter plug washed with 1 mL of CH2Cl2. The
solvent was then removed in vacuo to give an off-white foam
(46.8 mg, 94%). Because precipitation of (Et2O)xLiOTf in the
salt metathesis reaction was not an effective means of puri-
fication, samples of 16 prepared in this manner were typically
contaminated with 0.2-0.5 equiv of lithium etherate salts.
Prolonged metathesis reaction times (2 h) had no effect on the
product composition, and the presence of these salts had no
apparent effect on the reactivity of 16. 1H NMR (400 MHz): δ
7.62 (d, J H-H ) 7 Hz, 4H, Si-Ar), 7.46 (m, 6 H, Si-Ar), 1.84
(d, J P-H ) 2 Hz, 15 H, C5Me5), 1.29 (d, J P-H ) 14 Hz, 9H, PMe3),
-17.40 (d, J P-H ) 36 Hz, 1 H, Ir-H). 13C{1H} NMR (126
MHz): δ 149.9 (m, B(C6F5)), 138.6 (s, Ar C), 138.0 (m, B(C6F5)),
136.0 (m, B(C6F5)), 134.3 (s, Ar CH), 130.0 (s, Ar CH), 128.1
1
of recrystallized material was 66.0 mg (0.100 mmol, 49%). H
NMR (500 MHz): δ 7.85 (m, 4 H, Si-Ph), 7.21 (m, 6 H, Si-
Ph), 1.54 (d, J P-H ) 2 Hz, 15 H, C5Me5), 1.26 (d, J P-C ) 14 Hz,
9 H, PMe3). 13C{1H} NMR (126 MHz): δ 146.2 (s, Ar C), 145.1
(s, Ar C), 135.4 (s, Ar CH), 134.7 (Ar CH), 128.3 (s, Ar CH),
128.1 (s, Ar CH), 127.6 (s, Ar CH), 127.2 (s, Ar CH), 97.8 (d,
J P-C ) 3 Hz, C5Me5), 16.9 (d, J P-C ) 39 Hz, PMe3), 9.5 (s,
C5Me5). 31P{1H} NMR (162 MHz): δ -38.7. 29Si NMR (INEPT,
99 MHz): δ 6.7. IR: 3046, 2960, 2915, 1426, 1261, 1092, 1029,
955, 803, 705, 515, 485 cm-1. Anal. Calcd for C25H34PIrSiCl2:
C, 45.72; H, 5.22. Found: C, 45.64; H, 5.16.
[Cp *(P Me3Ir (η2-SiP h 2(C6H4))(H)][B(C6F 5)4] (12). A 20
mL scintillation vial was charged with 2 mL of a CH2Cl2
solution of Cp*(PMe3)Ir(Me)OTf (1; 101 mg, 0.179 mmol). To
this was added a CH2Cl2 solution (2 mL) of HSiPh3 (46.5 mg,
0.179 mmol) at room temperature. Gas evolution was observed
immediately after addition. The solution was stirred for 5 min
and then cooled in a -35 °C freezer for 5 min. The solution
was then added to a 2 mL CH2Cl2 solution of (Et2O)2LiB(C6F5)4
(136 mg, 0.179 mmol) which had also been cooled in a -35 °C
freezer for 5 min. The resulting mixture immediately became
cloudy. The reaction mixture was returned to the -35 °C
freezer for 10 min and was then filtered through a glass fiber
filter. The solvent was removed in vacuo, and the resulting
light cream colored foam was recrystallized from Et2O/pentane
at -35 °C to afford 166 mg (81%) of 12 as a pale yellow
crystalline solid. 1H NMR (500 MHz): δ 7.81 (br s, 2H, Ar H),
7.38 (m, 12H, Ar H), 7.18 (s, 2H, Ar H), 1.71 (d, J P-H ) 2.0
Hz, 15H, C5Me5), 1.18 (d, J P-H ) 11 Hz, 9H, PMe3), -12.7 (d,
J P-H ) 20 Hz, 1H, Ir-H). 13C{1H} NMR (126 MHz): δ 152.4,
(s, Ar C), 149.9 (m, B(C6F5), 138.0 (m, B(C6F5)), 136.0 (m,
B(C6F5)), 136.4 (s, Ar CH), 134.7 (s, Ar CH), 134.5 (s, Ar C),
134.1 (s, Ar CH), 133.1 (s, Ar CH), 133.1(s, Ar CH), 132.4 (d,
J P-C ) 4 Hz, Ar CH), 131.8 (s, Ar CH), 131.2 (s, Ar CH), 131.2
(s, Ar C), 129.6 (s, Ar CH), 128.9 (s, Ar C), 129.0 (s, Ar CH),
128.4 (s, Ar C), 126.1 (s, Ar CH), 124.0 (m, B(C6F5)), 102.9 (d,
J C-P ) 2 Hz, C5Me5), 16.4 (d, J C-P ) 43 Hz, PMe3), 9.6 (s,
(s, Ar CH), 124.0 (m, B(C6F5)), 96.9 (s, C5Me5), 21.2 (d, J P-C
)
C5Me5). 31P{1H} NMR (162 MHz): δ -35.9 (s). 19F{1H} NMR
40 Hz, PMe3), 9.7 (s, C5Me5). 31P{1H} NMR (162 MHz):
δ
29
(376 MHz): δ -133 (s), -164 (t, J B-F ) 19 Hz), -167 (s).
-
-49.3. 29Si NMR (INEPT, 99 MHz): δ 351.1. 19F{1H} NMR
(376 MHz): δ -133 (s), -164 (t, J B-F ) 19 Hz), -167 (s). IR:
2984, 2921, 2142 (Ir-H), 1643, 1514, 1467, 1383, 1275, 1089,
980, 756, 703, 661, 502 cm-1. Satisfactory elemental analysis
could not be obtained.
Si{1H} NMR (99 MHz): δ -62.5 (br s). IR: 3050, 3000, 2919,
2084, 1643, 1514, 1465, 1382, 1274, 1085, 979, 856, 703, 511
cm-1. Anal. Calcd for C55H39F20IrPBSi: C, 49.23; H, 2.93.
Found: C, 49.0; H, 3.32.
[Cp *(P Me3)Ir (η2-CH2SiMe2)(H)][B(C6F 5)4] (13). A 20 mL
scintillation vial was charged with 5 mL of a CH2Cl2 solution
of Cp*(PMe3)Ir(SiMe2OTf)(Me) (3; 68.2 mg, 0.109 mmol). The
solution was pipetted onto solid (Et2O)2LiB(C6F5)4 (95.0 mg,
0.109 mmol), and the resulting slurry was mixed with the pipet
for 30 s. The slurry was then filtered through a Celite/
fiberglass plug, and the filtrate was removed in vacuo. The
Deter m in a tion of Ra te Con sta n ts a n d Isotop e Effects.
The solutions used for kinetic runs were prepared by pipetting
a 0.5 mL CD2Cl2 solution of Cp*(PMe3)Ir(Me)(OTf) onto solid
H2SiMes2 and transferring this solution to a Wilmad PS-504
NMR tube containing a known amount of 1,3,5-trimethoxy-
benzene internal standard. The tube was then attached
directly to a Kontes high-vacuum stopcock using a Cajon Ultra-

Reactions of Cp*(PMe3)Ir(Me)OTf with Silanes
Organometallics, Vol. 21, No. 16, 2002 3387
Torr reducing union, flame-sealed under active vacuum, and
kept frozen until directly before the kinetic run. The competi-
tion kinetic isotope effect using HSiPh3 and DSiPh3 was
determined by first charging a Wilmad PS-504 NMR tube with
1.0 and 50 equiv each of HSiPh3 and DSiPh3. The tube was
then attached to a Kontes high-vacuum stopcock using a Cajon
Ultra-Torr reducing union, and 0.5 mL of CD2Cl2 was vacuum-
transferred into the tube at -196 °C. The tube was warmed
first to 0 °C over 2 min and then to room temperature. The
relative amounts of CH3D and CH4 were determined by
integration of the 1H NMR spectrum and then statistically
correcting the data.
structures of 2, 4, and 7 and Drs. J . S. Yeston, D. M.
Tellers, and P. J . Alaimo for helpful discussions. S.R.K.
thanks the National Science Foundation for a graduate
fellowship. We are grateful for support of this work by
the Director, Office of Energy Research, Office of Basic
Energy Sciences, Chemical Sciences Division, U.S.
Department of Energy, under Contract No. DE-AC03-
76SF00098, and by the National Science Foundation
(T.D.T.).
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
structural data for complexes 2, 4, and 7. This material is
available free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. We thank Dr. Dana Caulder and
Dr. Fred Hollander of the UC Berkeley X-ray Diffraction
Facility (CHEXRAY), for determination of the crystal
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