Synthesis, structure, and dynamic behavior of tungsten dihydride silyl complexes Cp*(CO)2W(H)2(SiHPhR) (R = Ph, H, Cl)

Article abstract of DOI:10.1021/om060101r

Dihydride silyl complexes Cp*(CO)₂W(H)₂(SiHPhR) (R = Ph, 7; H, 8) were synthesized by treating the donor-stabilized silylene complexes cis-Cp*(CO)₂(H)W=SiRPh·Do (R = Ph, H; Do = Py, THF) with LiAlH₄, to give Li[Cp*(CO)₂W(H)(SiHPhR)] (R = Ph, 5; H, 6) followed by protonation using CF₃-COOH. X-ray analyses of the crystals of 7 and 8 revealed that the former adopts a distorted pseudooctahedral structure (7a), while the latter possesses a pseudo-trigonal-prismatic structure (8b). In solution, both complexes exist as equilibrium mixtures of these two structural isomers: the distorted pseudooctahedral isomer (7a/8a) and the pseudo-trigonal-prismatic isomer (7b/8b). In addition to this interconversion process, two dynamic processes involving site exchanges of hydride and silyl ligands in the pseudo-trigonal-prismatic isomer were shown for 8b by detailed NMR studies. The addition of HCl to cis-Cp*(CO)₂(H)W=SiHPh·THF afforded Cp*(CO)₂W(H)₂(SiHPhCl) (9), which also gave an equilibrium mixture of the distorted pseudo-octahedral isomer (9a) and the pseudo-trigonal-prismatic isomer (9b). The presence of an additional dynamic process, hydride site exchange in the distorted pseudooctahedral isomer, was revealed for 9a due to its chiral silicon center.

Full text of DOI:10.1021/om060101r

Organometallics 2006, 25, 5145-5150
5145
Synthesis, Structure, and Dynamic Behavior of Tungsten Dihydride
Silyl Complexes Cp*(CO)2W(H)2(SiHPhR) (R ) Ph, H, Cl)
Hiroyuki Sakaba,* Takeshi Hirata, Chizuko Kabuto, and Kuninobu Kabuto
Department of Chemistry, Graduate School of Science, Tohoku UniVersity, Aoba-ku,
Sendai 980-8578, Japan
ReceiVed February 2, 2006
Dihydride silyl complexes Cp*(CO)2W(H)2(SiHPhR) (R ) Ph, 7; H, 8) were synthesized by treating
the donor-stabilized silylene complexes cis-Cp*(CO)2(H)WdSiRPh‚Do (R ) Ph, H; Do ) Py, THF)
with LiAlH4 to give Li[Cp*(CO)2W(H)(SiHPhR)] (R ) Ph, 5; H, 6) followed by protonation using CF3-
COOH. X-ray analyses of the crystals of 7 and 8 revealed that the former adopts a distorted pseudo-
octahedral structure (7a), while the latter possesses a pseudo-trigonal-prismatic structure (8b). In solution,
both complexes exist as equilibrium mixtures of these two structural isomers: the distorted pseudo-
octahedral isomer (7a/8a) and the pseudo-trigonal-prismatic isomer (7b/8b). In addition to this
interconversion process, two dynamic processes involving site exchanges of hydride and silyl ligands in
the pseudo-trigonal-prismatic isomer were shown for 8b by detailed NMR studies. The addition of HCl
to cis-Cp*(CO)2(H)WdSiHPh‚THF afforded Cp*(CO)2W(H)2(SiHPhCl) (9), which also gave an
equilibrium mixture of the distorted pseudo-octahedral isomer (9a) and the pseudo-trigonal-prismatic
isomer (9b). The presence of an additional dynamic process, hydride site exchange in the distorted pseudo-
octahedral isomer, was revealed for 9a due to its chiral silicon center.
Introduction
Recently, much attention has been given to transition metal
silyl polyhydride complexes, which display intriguing structural
features, such as classical or nonclassical formulation and high
fluxionality.1 For LnMH2SiR3-type complexes, a number of
complexes have been characterized for late transition metals
such as Ru,2 Os,3 Rh,4 and Ir.5 Especially, recent extensive
studies of ruthenium complexes have shown an interesting
variation in the formulation: the nonclassical η2-silane formula-
tion for Tp(Ph3P)Ru(H)(η2-HSiR3),2d the η2-Si-H and SISHA
(secondary interactions between silicon and hydrogen atoms)
formulation for RuH(η2-HSiR3){(η3-C6H8)PCy2}(PCy3),2f the
classical dihydride silyl formulation for Cp*(Ph3P)Ru(H)2-
(SiClMe2),2e,g and the IHI (interligand hypervalent interaction)
for Cp*(iPr2MeP)Ru(H)2(SiClMe2).2g
In contrast to the rich chemistry of these late transition metal
complexes, LnMH2SiR3-type complexes are quite rare for group
6 metals. One such example is the dihydride silyl complex Cp*-
(CO)2W(H)2(SiPh2Cl) (2), which was obtained in our recent
study of the reactivity of the donor-stabilized silylene complex
cis-Cp*(CO)2(H)WdSiPh2‚Py (1) toward HCl.6 The HCl adduct
2 adopts a distorted pseudo-octahedral structure with the Cp*
ligand occupying one coordination site at the tungsten in the
solid state. The 1H NMR spectrum of 2 showed a broad hydride
signal at room temperature. On decreasing the temperature, the
signal became sharp and additional very weak signals appeared
in the hydride region. Although this dynamic behavior suggested
the existence of the interconversion process of 2 with a trace
component, structural information on the latter was unavailable.
* To whom correspondence should be addressed. E-mail: sakaba@
funorg.chem.tohoku.ac.jp.
(1) For reviews, see: (a) Schubert, U. AdV. Organomet. Chem. 1990,
30, 151. (b) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175.
(c) Kubas, G. J. Metal Dihydrogen and σ-Bond Complexes: Structure,
Theory, and ReactiVity; Kluwer Academic/Plenum Publishers: New York,
2001; Chapter 11. (d) Lin, Z. Chem. Soc. ReV. 2002, 31, 239.
(2) For example, see: (a) Campion, B. K.; Heyn, R. H.; Tilley, T. D.
Chem. Commun. 1992, 1201. (b) Johnson, T. J.; Coan, P. S.; Caulton, K.
G. Inorg. Chem. 1993, 32, 4594. (c) Rodriguez, V.; Donnadieu, B.; Sabo-
Etienne, S.; Chaudret, B. Organometallics 1998, 17, 3809. (d) Ng, S. M.;
Lau, C. P.; Fan, M.-F.; Lin, Z. Organometallics 1999, 18, 2484. (e) Duckett,
S. B.; Kuzmina, L. G.; Nikonov, G. I. Inorg. Chem. Commun. 2000, 3,
126. (f) Lachaize, S.; Sabo-Etienne, S.; Donnadieu, B.; Chaudret, B. Chem.
Commun. 2003, 214. (g) Osipov, A. L.; Gerdov. S. M.; Kuzmina, L. G.;
Howard, J. A. K.; Nikonov, G. I. Organometallics 2005, 24, 587.
(3) For example, see: (a) Glaser, P. B.; Tilley, T. D. Organometallics
2004, 23, 5799. (b) Baya, M.; Crochet, P.; Esteruelas, M. A.; Onate, E.
Organometallics 2001, 20, 240. (c) Maseras, F.; Lledos, A. Organometallics
1996, 154, 1218. (d) Esteruelas, M. A.; Oro, L. A.; Valero, C. Organome-
tallics 1991, 10, 462.
(4) For example, see: (a) Osakada, K.; Sarai, S.; Koizumi, T.; Yamamoto,
T. Organometallics 1997, 16, 3973. (b) Osakada, K.; Koizumi, T.; Sarai,
S.; Yamamoto, T. Organometallics 1998, 17, 1868. (c) Noveski, D.; Braun,
T.; Schulte, M.; Neumann, B.; Stammler, H.-G. Dalton Trans. 2003, 4075.
(d) Turculet, L.; Feldman, J. D.; Tilley, T. D. Organometallics 2004, 23,
2488. (e) Taw, F. L.; Bergman, R. G.; Brookhart, M. Organometallics 2004,
23, 886. (f) Cook, K. S.; Incarvito, C. D.; Webster, C. E.; Fan, Y.; Hall, M.
B.; Hartwig, J. F. Angew. Chem., Int. Ed. 2004, 43, 5474.
(5) For example, see: (a) Fernandez, M. J.; Esteruelas, M. A.; Oro, L.
A.; Apreda, M. C.; Foces-Foces, C.; Cano, F. H. Organometallics 1987, 6,
1751. (b) Rappoli, B. J.; Janik, T. S.; Churchill, M. R.; Thompson, J. S.;
Atwood, J. D. Organometallics 1988, 7, 1939. (c) Hays, M. K.; Eisenberg,
R. Inorg. Chem. 1991, 30, 2623. (d) Esteruelas, M. A.; Nuernberg, O.;
Olivan, M.; Oro, L. A.; Werner, H. Organometallics 1993, 12, 3264. (e)
Cleary, B. P.; Mehta, R.; Eisenberg, R. Organometallics 1995, 14, 2297.
(f) Zarate, E. A.; Kennedy, V. O.; McCune, J. A.; Simons, R. S.; Tessier,
C. A. Organometallics 1995, 14, 1802. (g) Chen, W.; Edwards, A. J.;
Esteruelas, M. A.; Lahoz, F. J.; Olivan, M.; Oro, L. A. Organometallics
1996, 15, 2185. (h) Simons, R. S.; Gallucci, J. C.; Tessier, C. A.; Youngs,
W. J. J. Organomet. Chem. 2002, 654, 224. (i) Simons, R. S.; Panzner, M.
J.; Tessier, C. A.; Youngs, W. J. J. Organomet. Chem. 2003, 681, 1.
(6) Sakaba, H.; Hirata, T.; Kabuto, C.; Horino, H. Chem. Lett. 2001,
1078.
10.1021/om060101r CCC: $33.50 © 2006 American Chemical Society
Publication on Web 09/15/2006

5146 Organometallics, Vol. 25, No. 21, 2006
Sakaba et al.
Table 1. Crystal Data for 7a and 8b
7a
8b
formula
fw
C24H28O2SiW
560.42
C18H24O2SiW
484.32
cryst syst
space group
color
triclinic
P1h (No. 2)
yellow
monoclinic
P21/n (No. 14)
yellow
Z
2
4
a, Å
b, Å
c, Å
10.086(3)
10.642(3)
11.511(3)
74.631(9)
87.934(11)
76.153(9)
1156.2(5)
1.610
8.5362(18)
15.006(3)
14.409(3)
R, deg
â, deg
γ, deg
V, Å3
91.597(4)°
1845.0(7)
1.743
D
calcd, g/cm3
T, K
173
0.0207
0.0580
1.027
173
Figure 1. ORTEP drawing of 7a. Methyl and phenyl hydrogen
atoms are omitted for clarity. Selected bond distances (Å) and angles
(deg): W(1)-Si(1) 2.5798(7), W(1)-C(1) 2.012(2), W(1)-C(2)
1.989(2), W(1)-H(1) 1.77(4), W(1)-H(2) 1.66(4), Si(1)-C(13)
1.900(2), Si(1)-C(19) 1.885(2), Si(1)-H(3) 1.45(3), C(1)-O(1)
1.134(3), C(2)-O(2) 1.143(3); Si(1)-W(1)-C(1) 81.88(8), Si(1)-
W(1)-C(2) 78.16(8), Si(1)-W(1)-H(1) 50.6(15), Si(1)-W(1)-
H(2) 47.8(11), C(1)-W(1)-C(2) 84.92(10), C(1)-W(1)-H(1)
75.9(15), C(2)-W(1)-H(2) 76.3(13), H(1)-W(1)-H(2) 78.3(19).
R1 (I > 2σ(I))
wR2 (all data)
GOF
0.0244
0.0670
1.111
Scheme 1
Figure 2. Variable-temperature 1H NMR spectra of 7 in toluene-
d8 showing SiH signals (left) and WH signals (right).
W1-H2 (1.66(4) Å) lengths are comparable to the W-H bond
lengths in the X-ray structures of CpWHL3-type complexes.7
Although it is difficult to determine accurately the positions of
hydrogens bound to heavy atoms by X-ray analysis, the H1‚‚
‚H2 separation of 2.17(5) Å would exclude the possibility of
an η2-H2 coordination. This is supported by a T1(min) value of
540 ms at -50 °C (400 MHz) for the hydride signal (vide infra
for spectral characterization). The Si1‚‚‚H1 and Si1‚‚‚H2
distances of 2.00(4) and 1.91(3) Å, respectively, are longer than
typical η2-Si-H bond distances (1.6-1.8 Å)1c and are at the
boundary between silyl(hydrido) and η2-Si-H coordination.
Considering that substantial silyl-hydrido interaction has been
suggested for Si‚‚‚H distances up to 2.1 Å,1d there may be some
interactions in the WSiH2 moiety, although it is difficult to
evaluate interactions by X-ray data.
In further studies of structurally related complexes Cp*-
(CO)2W(H)2(SiHPhR) (R ) Ph, 7; H, 8; Cl, 9), we found a
rare example of equilibrium between distorted pseudo-octahedral
and pseudo-trigonal-prismatic isomers of CpL2M(H)2(SiR3)-type
complexes, shedding light on the unresolved dynamic behavior
of 2. In addition, three dynamic processes involving site
exchanges of hydride and silyl ligands in these isomers were
revealed by detailed variable-temperature 1H NMR studies.
Here, we describe the structure, isomerism, and dynamic
behavior of Cp*(CO)2W(H)2(SiHPhR) complexes.
Results and Discussion
The 1H NMR spectrum of a toluene-d8 solution of the
crystalline 7 showed broad SiH (δ 6.40) and WH (δ -6.79)
signals at room temperature (Figure 2). A decrease in temper-
ature led to their decoalescence to give two sets of SiH and
WH signals: δ 6.64 (s, 1H, JSiH ) 198 Hz) and -6.83 (s, 2H,
JWH ) 58 Hz, JSiH ) 16 Hz) for the major isomer and δ 5.80
Protonation using CF3COOH of the lithium tungstate Li[Cp*-
(CO)2W(H)(SiHPh2)] (5), which was prepared by the reaction
of cis-Cp*(CO)2(H)WdSiPh2‚Do (Do ) pyridine, 1; THF, 3)
with LiAlH4,6 afforded Cp*(CO)2W(H)2(SiHPh2) (7) as air-
sensitive yellow crystals in 54% yield after recrystallization from
hexane at -60 °C (Scheme 1).
X-ray analysis of the yellow crystals showed the distorted
pseudo-octahedral structure 7a (Figure 1, Table 1). Two hydrides
are located nearly symmetrically with respect to the plane
defined by the W1 and Si1 atoms and the centroid (CNT) of
the Cp* ligand. The W1-Si1 bond is bent by 26.5(1)° away
from the CNT-W1 vector toward the hydrides. A similar
structure has been found for 2.6 The W1-H1 (1.77(4) Å) and
(t, 1H, JHH ) 2.7 Hz, JSiH ) 193 Hz) and -4.78 (d, 2H, JHH
)
2.7 Hz, JWH ) 52 Hz) for the minor isomer in a ratio of 89:11
at -52 °C. Interestingly, on further cooling to -94 °C, the
(7) For example, see: (a) Baker, R. T.; Calabrese, J. C.; Harlow, R. L.;
Williams, I. D. Organometallics 1993, 12, 830. (b) Malisch, W.; Hirth,
U.-A.; Grun, K.; Schmeusser, M.; Fey, O.; Weis, U. Angew. Chem., Int.
Ed. Engl. 1995, 34, 2500.

Tungsten Dihydride Silyl Complexes
Organometallics, Vol. 25, No. 21, 2006 5147
Figure 3. ORTEP drawing of 8b with a schematic representation
of pseudo-trigonal-prismatic structure. Methyl and phenyl hydrogen
atoms are omitted for clarity. Selected bond distances (Å) and angles
(deg): W(1)-Si(1) 2.5691(10), W(1)-C(1) 1.973(3), W(1)-C(2)
1.986(3), W(1)-H(1) 1.66(5), W(1)-H(2) 1.71(4), Si(1)-C(13)
1.874(3), Si(1)-H(3) 1.42(4), Si(1)-H(4) 1.41(5), C(1)-O(1)
1.145(4), C(2)-O(2) 1.149(4); Si(1)-W(1)-C(1) 67.68(11), Si-
(1)-W(1)-H(2) 51.7(15), C(1)-W(1)-H(1) 67.0(17), C(2)-
W(1)-H(1) 73.2(17), C(2)-W(1)-H(2) 63.0(13).
Figure 5. Variable-temperature 1H NMR spectra of 8b in THF-d8
showing SiH signals.
Scheme 2
to the CNT-W1-H1 plane, the two CO ligands are located
fairly symmetrically, as shown by the bond angles of C1-W1-
H1 ) 67(2)° and C2-W1-H1 ) 73(2)°, and the silyl and
hydride (H2) ligands are also coordinated symmetrically: H2-
W1-CNT ) 113.5(1)° and Si1-W1-CNT ) 112.5(1)°. The
W1-H1 and W1-H2 bond lengths are 1.66(5) and 1.71(4) Å,
respectively. The Si1‚‚‚H2 distance of 2.02(4) Å is also at the
boundary between silyl(hydrido) and η2-silane coordination,
similar to the case of 7a.
Variable 1H NMR spectra of 8 in toluene-d8 also showed the
existence of two isomers, as shown in Figure 4. At room
temperature, two very broad SiH signals were observed near δ
5.35 and 4.98, along with two broad WH signals at δ -4.87
and -6.73, and these signals became sharp upon cooling to
-21 °C: δ 4.90 (s, 2H, JSiH ) 190 Hz) and -4.84 (br s, 2H,
Figure 4. Variable-temperature 1H NMR spectra of 8 in toluene-
d8 showing SiH signals (left) and WH signals (right).
JWH ) 49 Hz) for the major isomer and δ 5.66 (s, 2H, JSiH
)
hydride signal of the minor isomer was split into an AB-type
signal at δ -4.82 (dd, J ) 8.6, 5.4 Hz) and -4.69 (d, J ) 8.6
Hz) for the ABX system involving a SiH doublet signal (δ 5.89,
J ) 5.4 Hz) as the X part, while no such signal splitting was
seen for the hydride of the major isomer. The major isomer is
assigned to 7a, and the minor isomer is characterized as the
pseudo-trigonal-prismatic complex 7b from the spectral char-
acteristics and with the help of the structure determination of
the corresponding monophenyl derivative 8b (vide infra). These
spectral changes indicate that 7a is in equilibrium with 7b and
that a rapid dynamic process averages the inequivalent hydride
signals of 7b.
Protonation of Li[Cp*(CO)2W(H)(SiH2Ph)] (6) obtained by
treating cis-Cp*(CO)2(H)WdSiHPh‚THF (4) with LiAlH4 gave
Cp*(CO)2W(H)2(SiH2Ph) (8) as pale yellow crystals in 50%
yield after recrystallization from pentane at -60 °C (Scheme
1). The X-ray crystal analysis revealed a rare example of a
pseudo-trigonal-prismatic half-sandwich CpML5 structure, 8b
(Figure 3, Table 1). To our knowledge, the only previous
example of this type of structure determined by X-ray analysis
is Cp*MoH3(dppe), reported by Poli.8a,b In 8b, one triangular
face is defined by one of the hydrides (H1) and two carbonyl
carbons (C1 and C2), and the other triangular face is defined
by the Cp*(CNT), Si1, and second hydride (H2). With respect
194 Hz) and -6.87 (s, 2H, JWH ) 56 Hz) for the minor isomer.
The WH signal at δ -4.84 (major) was further split into two
doublets at δ -4.32 (1H, JHH ) 9.1 Hz, JWH ) 43 Hz) and
-5.28 (1H, JHH ) 9.1 Hz, JWH ) 57 Hz) at -94 °C, while the
signal at δ -6.87 (minor) remained a singlet, showing spectral
changes similar to those observed for 7a,b. The major isomer
affording the two WH signals is assigned to 8b, where two
inequivalent signals are expected for the diastereotopic SiH
protons (Hc and Hd in Scheme 2) in a slow-exchange limiting
spectrum. At -94 °C in THF-d8, the SiH signal of 8b was still
observed as a slightly broad singlet, but further lowering to
-114 °C led to the expected decoalescence, giving two broad
SiH signals at δ 4.35 and 4.49 (Figure 5). This behavior indicates
the existence of an extremely rapid process equalizing the
diastereotopic SiH signals. The minor isomer giving a single
WH signal is characterized as 8a on the basis of the similarity
of its spectral characteristics to 7a, including the T1(min) values
(400 MHz) of their hydrides: 540 ms at -50 °C for 7a and
550 ms at -60 °C for 8a. The hydride signal of 8a was observed
(8) (a) Fettinger, J. C.; Pleune, B. A.; Poli, R. J. Am. Chem. Soc. 1996,
118, 4906. (b) Pleune, B.; Poli, R.; Fettinger, J. C. Organometallics 1997,
16, 1581. (c) Abugideiri, F.; Fettinger, J. C.; Pleune, B.; Poli, R.; Bayse,
C. A.; Hall, M. B. Organometallics 1997, 16, 1179.

5148 Organometallics, Vol. 25, No. 21, 2006
Sakaba et al.
Scheme 3
as a singlet down to -114 °C in THF-d8, showing no sign of
decoalescence. Thus, we observed three dynamic processes for
8: the equilibrium between 8a and 8b (Scheme 1), the averaging
process of the hydride signals in 8b (process A in Scheme 2),
and that of the diastereotopic SiH signals (enantiomer inter-
conversion, process B). For these processes, the following
activation parameters were obtained from variable-temperature
1H NMR spectra and their simulations: ∆Hq ) 13.5 ( 0.7 kcal
mol-1 and ∆Sq ) -1.1 ( 1.7 eu for 8a to 8b in toluene-d8,
∆Hq ) 9.8 ( 0.6 kcal mol-1 and ∆Sq ) 0.3 ( 2.1 eu for the
process A in toluene-d8, and ∆Hq ) 8.0 ( 0.9 kcal mol-1 and
∆Sq ) 3.1 ( 3.8 eu for the process B in THF-d8.9 These
activation entropies are close to zero, in accordance with
intramolecular processes.
1
Figure 6. Variable-temperature H NMR spectra of 9 in THF-d8
showing SiH signals (left) and WH signals (right).
unresolved observation for 2.6 A further increase in the bulkiness
of the SiPh2Cl group in 2 compared to 9 is expected to favor
the distorted pseudo-octahedral isomer to reduce the pseudo-
trigonal-prismatic isomer to a trace level, suggesting that the
trace component may be assignable to the pseudo-trigonal-
prismatic isomer of 2.
To investigate the possibility of hydride site exchange in the
distorted pseudo-octahedral isomer, Cp*(CO)2W(H)2(SiHPhCl)
(9), having a chiral silicon center, was synthesized by the
reaction of 4 with HCl (Scheme 3). Even though this exchange
process exists in 7a and 8a, it cannot be observed, as these
In summary, the dihydride silyl complexes Cp*(CO)2W(H)2-
(SiHPhR) (R ) Ph, 7; H, 8; Cl, 9) were synthesized from the
donor-stabilized silylene complexes cis-Cp*(CO)2(H)WdSiRPh‚
Do and revealed the solid-state and solution structures of their
two structural isomers: distorted pseudo-octahedral isomers 7a-
9a and pseudo-trigonal-prismatic isomers 7b-9b. Variable-
temperature NMR studies also revealed the details of four
dynamic processes in the isomers, i.e., (1) the equilibrium
between distorted pseudo-octahedral isomer 8a and pseudo-
trigonal-prismatic isomer 8b (Scheme 1), (2) the averaging
process of the hydride signals in 8b (process A in Scheme 2),
(3) the averaging process of the diastereotopic SiH signals in
8b (process B in Scheme 2), and (4) the hydride site exchange
in distorted pseudo-octahedral isomer 9a. The activation barriers
for the four processes decrease in the order (1) > (2) > (3) ≈
(4). Further theoretical studies are needed to elucidate fully the
mechanisms of these dynamic processes and the degree of Si‚
‚‚H interactions in these complexes. A pseudo-Bailar twist
mechanism has been proposed for the fluxional processes of
Cp*Mo(H)3(dppe) and related complexes.8
1
complexes lack the chiral center. The H NMR spectrum of 9
in THF-d8 at 20 °C showed broad SiH and WH signals at δ
6.78 and -6.67, respectively (Figure 6). When the temperature
was decreased, these signals were split into two sets of signals
assigned to 9a (major) and 9b (minor). At -21 °C, 9a showed
sharp SiH and WH signals at δ 6.86 (1H) and -6.87 (2H),
respectively, while 9b gave very broad SiH and WH signals at
δ 6.16 (1H) and -5.01 (2H), respectively. At -84 °C, the WH
signal of 9b decoalesced into two signals at δ -4.05 (d, J )
ca. 8.0 Hz) and -6.14, and the SiH signal was observed as a
triplet at δ 6.12 (J ) ca. 3.5 Hz). These spectral changes for
9b are explained by a slowing of hydride site exchange, as seen
for 8b. Importantly, a hydride signal due to 9a at δ -7.06
broadened at -84 °C and split into two signals at δ -6.54 and
-7.73 at -114 °C, which demonstrates the existence of the
hydride site exchange in the distorted pseudo-octahedral isomer.
For this process, ∆Hq ) 8.1 ( 0.6 kcal mol-1 and ∆Sq ) 3.2
( 2.4 eu were estimated by spectral simulation.9
Interconversion between the pseudo-trigonal-prismatic isomer
and the pseudo-octahedral isomer has been proposed for the
fluxional behaviors of [Cp*Mo(H)3-n(MeCN)n(dppe)]n+ (n )
0, 1, 2) and Cp*Mo(H)3(PMe2Ph)2, where the former structure
has been determined for Cp*Mo(H)3(dppe) and the latter
structure for [Cp*MoH(MeCN)2(dppe)]2+ and Cp*Mo(H)3-
(PMe2Ph)2 by X-ray analyses.8 Interestingly, in our Cp*(CO)2W-
(H)2(SiR3) system, simple variation of the substituents on the
silyl ligand allowed us to determine both types of structures
and to reveal clearly the details of the dynamic processes as
shown above.
The equilibrium between the distorted pseudo-octahedral
isomers 7a-9a and the pseudo-trigonal-prismatic isomers 7b-
9b is shifted toward the former by substitution of a hydrogen
atom at the silyl group of 8 with bulky and electronegative
substituents, as shown by isomeric ratios of 9a:9b (SiHPhCl)
) 94:6, 7a:7b (SiHPh2) ) 89:11, and 8a:8b (SiH2Ph) ) 37:63
at -51 °C, shedding light on understanding the previous
Experimental Section
General Methods. All reactions and procedures were carried
out under an atmosphere of nitrogen using standard glovebox,
Schlenk, and high-vacuum-line techniques. Photolyses were carried
out using an Ushio UM-103 100 W medium-pressure Hg lamp
placed in a water-cooled Pyrex jacket. NMR spectra were recorded
on a JEOL JNM-GSX400 (1H, 399.7 MHz; 13C, 100.4 MHz; 29Si,
79.3 MHz) spectrometer. IR spectra were obtained on a Shimadzu
FTIR-8100M spectrometer. Mass spectra were recorded on a JEOL
HX-110 mass spectrometer, and X-ray crystal analyses were
performed using a Rigaku/MSC Mercury CCD diffractometer at
the Instrumental Analysis Center for Chemistry, Tohoku University.
Diethyl ether, hexane, tetrahydrofuran, toluene, tetrahydrofuran-
d8, and toluene-d8 were distilled from sodium benzophenone ketyl.
Cp*(CO)3WMe was prepared according to the literature methods.10
LiAlH4 (1.0 M solution in Et2O, Aldrich) was used as received.
Ph2SiH2 (Tokyo Kasei) and PhSiH3 (Tokyo Kasei) were stored over
(10) Mahmoud, K. A.; Rest, A. J.; Alt, H. G.; Eichner, M. E.; Jansen,
B. M. J. Chem. Soc., Dalton Trans. 1984, 175.
(9) For details, see Supporting Information.

Tungsten Dihydride Silyl Complexes
Organometallics, Vol. 25, No. 21, 2006 5149
1
4 Å molecular sieves under a nitrogen atmosphere. CF3COOH
(Aldrich) was degassed and vacuum transferred immediately prior
to use.
6 (373 mg, 0.761 mmol, 90%). H NMR (400 MHz, THF-d8): δ
-7.57 (s, JWH ) 73.6 Hz, 1H, WH), 2.02 (s, 15H, Cp*), 4.64 (s,
JSiH ) 159.0 Hz, 2H, SiH), 6.96 (t, J ) 7.5 Hz, 1H, Ph), 7.03 (t,
J ) 7.5 Hz, 2H, Ph), 7.66 (d, J ) 7.5 Hz, 2H, Ph). 13C{1H} NMR
(100 MHz, THF-d8): δ 11.8 (C5Me5), 99.2 (C5Me5), 126.3 (Ph),
126.7 (Ph), 137.4 (Ph), 148.2 (Ph (ipso)), 241.1 (CO, JWC ) 168.8
Hz). 29Si{1H} NMR (79 MHz, THF-d8): δ -6.9 (JWSi ) 71.0 Hz).
cis-Cp*(CO)2(H)WdSiPh2‚THF (3). A solution of Cp*-
(CO)3WMe (806 mg, 1.93 mmol) and Ph2SiH2 (0.7 mL, 4 mmol)
in THF (30 mL) was irradiated for 50 min with a 100 W medium-
pressure Hg lamp. After removal of the solvent, the residue was
washed with hexane (8 mL) to give a pale yellow powder of 3
(836 mg, 1.33 mmol, 69%). The sample for elemental analysis was
recrystallized from THF. Upon dissolving 3 in THF-d8, the
coordinated THF is replaced by THF-d8 to give 3-d8 and free THF.
1H NMR (400 MHz, THF-d8): δ -9.20 (s, JWH ) 68.8 Hz, 1H,
WH), 1.77 (m, 4H, free THF), 1.94 (s, 15H, Cp*), 3.62 (m, 4H,
free THF), 7.23-7.31 (m, 6H, Ph), 7.49 (dd, J ) 8.1, 1.6 Hz, 4H,
Ph). 13C{1H} NMR (100 MHz, THF-d8): δ 11.7 (C5Me5), 26.3 (free
THF), 68.2 (free THF), 100.7 (C5Me5), 128.1 (Ph), 128.9 (Ph), 135.6
(Ph), 146.4 (Ph (ipso)), 234.8 (CO, JWC ) 161.2 Hz). 29Si{1H}
NMR (79 MHz, THF-d8): δ 119.3 (JWSi ) 103.3 Hz). IR (THF):
1896 (s, νCO), 1809 (m, νCO) cm-1. Anal. Calcd for C28H34O3SiW:
C, 53.34; H, 5.44. Found: C, 53.49; H, 5.90.
IR (THF): 1867 (s, νCO), 1717 (s, νCO) cm-1
.
Cp*(CO)2W(H)2(SiHPh2) (7). A flask was charged with Li-
[Cp*(CO)2W(H)(SiHPh2)] (5) (236 mg, 0.417 mmol) in the
glovebox. On the vacuum line, toluene (6 mL) and CF3COOH (0.46
mmol) were added via vacuum transfer at -196 °C. The mixture
was stirred at -60 °C for 8 min. The solvent was removed, and
the residue was extracted with hexane (4 × 6 mL). The extracts
were filtered through glass fiber filter paper. After removal of the
solvent, the residue was recrystallized from hexane at -60 °C to
1
give yellow crystals of 7 (126 mg, 0.225 mmol, 54%). H NMR
(400 MHz, toluene-d8, 27 °C): δ -6.79 (br, 2H, WH, 7a + 7b),
1.79 (s, 15H, Cp*, 7a + 7b), 6.40 (br, 1H, SiH, 7a + 7b), 7.12 (t,
J ) 7.5 Hz, 2H, Ph, 7a + 7b), 7.22 (t, J ) 7.5 Hz, 4H, Ph, 7a +
1
7b), 7.79 (d, J ) 7.5 Hz, 4H, Ph, 7a + 7b). H NMR (400 MHz,
cis-Cp*(CO)2(H)WdSiHPh‚THF (4). A solution of Cp*-
(CO)3WMe (805 mg, 1.93 mmol) and PhSiH3 (0.9 mL, 7 mmol)
in THF (15 mL) was irradiated for 55 min with a 100 W medium-
pressure Hg lamp. After removal of the solvent, the residue was
washed with hexane (10 mL) to give a pale yellow powder of 4
(747 mg, 1.35 mmol, 70%). The sample for elemental analysis was
recrystallized from THF. Upon dissolving 4 in THF-d8, the
coordinated THF is replaced by THF-d8 to give 4-d8 and free THF.
toluene-d8, -94 °C): δ -6.80 (s, JWH ) 57.2 Hz, 2H, WH, 7a),
-4.82 (dd, J ) 8.6, 5.4 Hz, 1H, WH, 7b), -4.69 (d, J ) 8.6 Hz,
WH, 7b), 1.53 (s, 15H, Cp*, 7b), 1.63 (s, 15H, Cp*, 7a), 5.89 (s,
J ) 5.4 Hz, 1H, SiH, 7b), 5.90 (s, JSiH ) 196.6 Hz, 1H, SiH, 7a),
7.07-7.23 (m, 6H, Ph, 7b), 7.18 (t, J ) 7.0 Hz, 2H, Ph, 7a), 7.31
(t, J ) 7.0 Hz, 4H, Ph, 7a), 7.94 (d, J ) 7.0 Hz, 2H, Ph, 7a), 8.00
(d, J ) 7.0 Hz, 2H, Ph, 7b). 13C{1H} NMR (100 MHz, toluene-d8,
-60 °C): δ 10.8 (C5Me5, 7b), 11.2 (C5Me5, 7a), 100.3 (C5Me5,
7a), 102.2 (C5Me5, 7b), 135.3 (Ph, 7a), 135.8 (Ph, 7b), 140.9 (Ph
(ipso), 7b), 145.0 (Ph (ipso), 7a), 212.3 (CO, JWC ) 134.2 Hz,
7b), 224.7 (CO, JWC ) 147.2 Hz, 7a). 29Si{1H} NMR (79 MHz,
1H NMR (400 MHz, THF-d8): δ -9.91 (d, 3JHH ) 4.3 Hz, JWH
)
67.7 Hz, 1H, WH), 1.78 (m, 4H, free THF), 2.12 (s, 15H, Cp*),
3.62 (m, 4H, free THF), 7.23 (d, 3JHH ) 4.3 Hz, JSiH ) 178.4 Hz,
1H, SiH), 7.2-7.3 (m, 3H, Ph), 7.66 (dd, J ) 8.1, 2.1 Hz, 2H,
Ph). 13C{1H} NMR (100 MHz, THF-d8): δ 11.9 (C5Me5), 26.3 (free
THF), 68.2 (free THF), 100.7 (C5Me5), 128.2 (Ph), 129.5 (Ph), 136.4
(Ph), 145.9 (Ph (ipso)), 234.4 (CO, JWC ) 160.2 Hz). 29Si{1H}
NMR (79 MHz, THF-d8): δ 117.1 (JWSi ) 109.9 Hz). IR (THF):
1900 (s, νCO), 1813 (s, νCO) cm-1. Anal. Calcd for C22H30O3SiW:
C, 47.66; H, 5.45. Found: C, 47.54; H, 5.43.
toluene-d8, -60 °C): δ -6.5 (JWSi ) 5.8 Hz, 7a), 14.3 (JWSi
22.8 Hz, 7b). IR (toluene): 2062 (w, νSiH), 1991 (s, νCO), 1976
(sh, νCO), 1927 (s, νCO), 1898 (w, νCO), ca. 1860 (br, w, νWH) cm-1
)
.
Anal. Calcd for C24H28O2SiW: C, 51.44; H, 5.04. Found: C, 51.28;
H, 5.07.
Cp*(CO)2W(H)2(SiH2Ph) (8). A flask was charged with Li-
[Cp*(CO)2W(H)(SiH2Ph)] (6) (228 mg, 0.465 mmol) in the
glovebox. On the vacuum line, toluene (6 mL) and CF3COOH (0.51
mmol) were added via vacuum transfer at -196 °C. The mixture
was stirred at -60 °C for 8 min. The solvent was removed in vacuo,
and the residue was extracted with hexane (5 × 5 mL). The extracts
were filtered through glass fiber filter paper. After removal of the
solvent, the residual solid was recrystallized from pentane at -60
Li[Cp*(CO)2W(H)(SiHPh2)] (5). A flask was charged with cis-
Cp*(CO)2(H)WdSiPh2‚THF (3) (836 mg, 1.33 mmol) in the
glovebox. On the vacuum line, Et2O (5 mL) was added via vacuum
transfer at -196 °C. At this temperature, LiAlH4 (1.0 M solution
in Et2O, 1.4 mL, 1.4 mmol) was added via syringe under a nitrogen
atmosphere. The solution was stirred at -60 °C for 3 min and then
at room temperature for 7 min. The resulting pale yellow solid was
filtered through a glass frit, washed with small amounts of Et2O,
and dried in vacuo to give 5 (756 mg, 1.33 mmol, 100%). 1H NMR
(400 MHz, THF-d8): δ -7.18 (s, JWH ) 74.1 Hz, 1H, WH), 1.92
(s, 15H, Cp*), 5.35 (d, JSiH ) 159.6 Hz, 1H, SiH), 6.93 (t, J ) 7.5
Hz, 2H, Ph), 7.01 (t, J ) 7.5 Hz, 4H, Ph), 7.65 (d, J ) 7.5 Hz, 4H,
Ph). 13C{1H} NMR (100 MHz, THF-d8): δ 11.9 (C5Me5), 99.7 (C5-
Me5), 126.3 (Ph), 126.8 (Ph), 137.1 (Ph), 150.9 (Ph (ipso)), 241.2
(CO, JWC ) 169.9 Hz). 29Si{1H} NMR (79 MHz, THF-d8): δ 29.4
1
°C to give yellow crystals of 8 (113 mg, 0.233 mmol, 50%). H
NMR (400 MHz, toluene-d8, 27 °C): δ -6.73 (br, 2H, WH, 8a),
-4.87 (br, 2H, WH, 8b), 1.78 (s, 15H, Cp*, 8a + 8b), 5.16 (br,
2H, SiH, 8a + 8b), 7.13 (t, J ) 7.5 Hz, 1H, Ph, 8a + 8b), 7.22 (t,
J ) 7.5 Hz, 2H, Ph, 8a + 8b), 7.83 (dd, J ) 8.1, 1.1 Hz, 2H, Ph,
8a + 8b). H NMR (400 MHz, toluene-d8, -94 °C): δ -6.96 (s,
JWH ) 56.1 Hz, 2H, WH, 8a), -5.28 (d, JHH ) 9.1 Hz, JWH
57.1 Hz, 1H, WH, 8b), -4.32 (d, JHH ) 9.1 Hz, JWH ) 43.1 Hz,
1H, WH, 8b), 1.59 (s, 15H, Cp*, 8a), 1.62 (s, 15H, Cp*, 8b), 5.04
(s, JSiH ) 189.7 Hz, 2H, SiH, 8b), 5.96 (s, JSiH ) 191.5 Hz, 2H,
SiH, 8a), 7.09 (t, J ) 7.5 Hz, 1H, Ph, 8b), 7.24 (t, J ) 7.5 Hz, 2H,
Ph, 8b), 7.27 (t, J ) 7.5 Hz, 1H, Ph, 8a), 7.38 (t, J ) 7.5 Hz, 2H,
Ph, 8a), 8.01 (d, J ) 7.5 Hz, 2H, Ph, 8a), 8.09 (d, J ) 7.5 Hz, 2H,
Ph, 8b). 1H NMR (400 MHz, THF-d8, -114 °C): δ -7.31 (s, JWH
1
)
(JWSi ) 71.7 Hz). IR (THF): 1867 (s, νCO), 1717 (s, νCO) cm-1
.
Li[Cp*(CO)2W(H)(SiH2Ph)] (6). A flask was charged with cis-
Cp*(CO)2(H)WdSiHPh‚THF (4) (466 mg, 0.841 mmol) in the
glovebox. On the vacuum line, Et2O (10 mL) was added via vacuum
transfer at -196 °C. At this temperature, LiAlH4 (1.0 M solution
in Et2O, 0.86 mL, 0.86 mmol) was added via syringe under a
nitrogen atmosphere. The solution was stirred at -60 °C for 4 min
and then at room temperature for 15 min. Methanol (2.6 mmol)
was added via vacuum transfer at -196 °C to quench any unreacted
LiAlH4. After the mixture was stirred at room temperature for 4
min, the solvent was removed in vacuo. The residue was extracted
with Et2O (4 × 6 mL), and the extracts were filtered through glass
fiber filter paper. After removal of the solvent, the residual yellow
solid was washed with pentane (2 mL) and dried in vacuo to give
2
) 55.5 Hz, 2H, WH, 8a), -5.67 (d, JHH ) 9.2 Hz, JWH ) 57.1
Hz, 1H, WH, 8b), -4.66 (d, JHH ) 9.2 Hz, JWH ) 43.1 Hz, 1H,
2
WH, 8b), 2.22 (s, 15H, Cp*, 8b), 2.31 (s, 15H, Cp*, 8a), 4.35 (br,
1H, SiH, 8b), 4.49 (br, 1H, SiH, 8b), 4.90 (s, JSiH ) 188.7 Hz, 2H,
SiH, 8a), 7.32-7.38 (m, 3H, Ph, 8a + 8b), 7.52 (m, 1H, Ph, 8a +
8b), 7.62 (m, 1H, Ph, 8a + 8b). 13C{1H} NMR (100 MHz, toluene-
d8, -80 °C): δ 10.4 (C5Me5, 8b), 11.0 (C5Me5, 8a), 100.1 (C5-
Me5, 8a), 101.8 (C5Me5, 8b), 135.8 (Ph, 8a), 136.0 (Ph, 8b), 211.1

5150 Organometallics, Vol. 25, No. 21, 2006
Sakaba et al.
(CO, JWC ) 132.0 Hz, 8b), 224.1 (CO, JWC ) 145.0 Hz, 8a). 13C-
{1H} NMR (100 MHz, THF-d8, -114 °C): δ 10.8 (C5Me5, 8b),
11.6 (C5Me5, 8a), 101.9 (C5Me5, 8a), 103.2 (C5Me5, 8b), 128.3
(Ph, 8a), 128.5 (Ph, 8b), 129.2 (Ph, 8a), 129.7 (Ph, 8b), 136.0 (Ph,
8a), 136.1 (Ph, 8b), 138.5 (Ph, 8b), 141.8 (Ph, 8a), 211.6 (br, JWC
) 129.9 Hz, CO, 8b), 224.8 (JWC ) 146.1 Hz, CO, 8a). 29Si{1H}
NMR (79 MHz, toluene-d8, -80 °C): δ -31.9 (8a), -17.2 (JWSi
) 23.7 Hz, 8b). IR (toluene): 2074 (w, νSiH), 1990 (sh, νCO), 1979
(C5Me5, 9b), 127.9 (Ph, 9a), 129.4 (Ph, 9a), 134.4 (Ph, 9a), 146.6
(Ph, 9a), 221.2 (CO, JWC ) 142.8 Hz, 9a), 221.9 (CO, JWC ) 147.2
Hz, 9a). 29Si{1H} NMR (toluene-d8, -80 °C): δ 11.3 (JWSi ) 5.1
Hz, 9a), 37.6 (JWSi ) 33.6 Hz, 9b). Anal. Calcd for C18H23ClO2-
SiW: C, 41.68; H, 4.47. Found: C, 41.92; H, 4.52.
Variable-Temperature NMR Studies and Dynamic NMR
Simulations. The temperature of the NMR probe was calibrated
with methanol. Line shape analyses were carried out using the
gNMR program version 4.1 (Cherwell Scientific). The rates as a
function of temperature were determined by visual comparison of
the experimental and simulated spectra. The activation parameters
were calculated from the Eyring equations by using a linear least-
squares procedure, and the errors were computed from error
propagation formulas.11
X-ray Crystal Structure Determination. Single crystals of 7a
and 8b were obtained by recrystallization at -60 °C from hexane
and pentane, respectively. All measurements were made on a Rigaku
Mercury CCD area detector with graphite-monochromated Mo KR
radiation (λ ) 0.71070 Å). The data were corrected for Lorenz
and polarization effects. The structures were solved by the direct
method (SIR92)12 and expanded using difference Fourier techniques
(DIRDIF99).13 The refinement was carried out using full-matrix
least-squares method on F2. All non-hydrogen atoms were refined
anisotropically, and the hydrogen atoms of the Cp* and Ph groups
were calculated and refined with a riding model. Tungsten and
silicon hydrides were located in the difference map and refined
isotropically. Atomic scattering factors were taken from Interna-
tional Tables for X-ray Crystallography.14 All calculations were
performed using the CrystalStructure crystallographic software
package.15
(s, νCO), 1929 (m, νCO), 1902 (s, νCO), ca. 1855 (br, w, νWH) cm-1
.
Anal. Calcd for C18H24O2SiW: C, 44.64; H, 4.99. Found: C, 44.55;
H, 5.09.
Cp*(CO)2W(H)2(SiHPhCl) (9). A flask was charged with cis-
Cp*(CO)2(H)WdSiHPh‚THF (4) (454 mg, 0.819 mmol) in the
glovebox. On the vacuum line, THF (7 mL) and HCl (0.90 mmol)
were added via vacuum transfer at -196 °C. The mixture was
allowed to warm to room temperature and stirred for 15 min. After
removal of the solvent and washing with hexane (5 mL), the residue
was recrystallized from toluene/hexane (3 mL/3.5 mL) at -20 °C
to give yellow crystals of 9 (325 mg, 0.626 mmol, 77%). 1H NMR
(400 MHz, THF-d8, 20 °C): δ -6.67 (br, 2H, WH, 9a + 9b), 2.25
(s, 15H, Cp*, 9a + 9b), 6.78 (br, 1H, SiH, 9a + 9b), 7.23-7.35
(m, Ph, 9a + 9b), 7.64-7.70 (m, Ph, 9a + 9b). 1H NMR (THF-d8,
-84 °C): δ -7.06 (br, 2H, WH, 9a), -6.14 (br, 1H, WH, 9b),
-4.05 (d, JHH ) ca. 8.0 Hz, 1H, WH, 9b), 2.27 (s, 15H, Cp*, 9b),
2.30 (s, 15H, Cp*, 9a), 6.12 (t, JHH ) ca. 3.5 Hz, 1H, SiH, 9b),
6.88 (s, JSiH ) 224 Hz, 1H, SiH, 9a), 7.10-7.25 (m, 3H, Ph, 9b),
7.32-7.43 (m, 3H, Ph, 9a), 7.60 (d, JHH ) 7 Hz, 2H, Ph, 9b), 7.68
(d, JHH ) 7 Hz, 2H, Ph, 9a). 13C{1H} NMR (toluene-d8, -60 °C):
δ 10.7 (C5Me5, 9b), 10.8 (C5Me5, 9a), 100.9 (C5Me5, 9a), 103.7
(11) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
(12) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(13) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-99 program system;
Technical Report of the Crystallography Laboratory; University of
Nijmegen: The Netherlands, 1999.
(14) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, UK, 1974; Vol IV.
(15) CrystalStructure 3.7, Crystal Structure Analysis Package; Rigaku
and Rigaku/MSC, 2000-2005.
Supporting Information Available: Experimental and simu-
lated variable-temperature NMR spectra for complexes 7-9 (PDF).
X-ray crystallographic data for 7a and 8b (PDF, CIF). This material
is available free of charge via the Internet at http://pubs.acs.org.
OM060101R