Synthesis and characterization of dmap-stabilized aryl(silylene) complexes and (arylsilyl)(dmap) complexes of tungsten mechanistic study on the interconversion between these complexes via 1,2-aryl migration

Article abstract of DOI:10.1021/om801140d

Photoreaction of a mixture of Cp*(CO)₃WMe (Cp* = η⁵-C₅Me₅) and HSiR₂Ar [R ₂Ar = Me₂Ph, Me₂(p-Tol), Me(p-Tol)₂, and (p-Tol)₂] in the presence of 4

Full text of DOI:10.1021/om801140d

Organometallics 2009, 28, 1791–1799
1791
Synthesis and Characterization of DMAP-Stabilized Aryl(silylene)
Complexes and (Arylsilyl)(DMAP) Complexes of Tungsten:
Mechanistic Study on the Interconversion between These
Complexes via 1,2-Aryl Migration
Eiji Suzuki,† Takashi Komuro,† Masaaki Okazaki,‡ and Hiromi Tobita*,†
Department of Chemistry, Graduate School of Science, Tohoku UniVersity, Aoba-ku,
Sendai 980-8578, Japan, and International Research Center for Elements Science, Institute for Chemical
Research, Kyoto UniVersity, Uji, Kyoto 611-0011, Japan
ReceiVed NoVember 30, 2008
Photoreaction of a mixture of Cp*(CO)3WMe (Cp* ) η5-C5Me5) and HSiR2Ar [R2Ar ) Me2Ph, Me2(p-
Tol), Me(p-Tol)2, and (p-Tol)3] in the presence of 4-(dimethylamino)pyridine (DMAP) gave DMAP-
stabilized aryl(silylene) complexes Cp*(CO)2W(Ar)(dSiR2 · DMAP) [1a, R ) Me, Ar ) Ph; 1b, R )
Me, Ar ) p-Tol; 1c, R2 ) Me(p-Tol), Ar ) p-Tol; 1d, R ) Ar ) p-Tol] via 1,2-migration of the aryl
group from a silyl ligand to a tungsten center. Thermal reactions of Cp*(CO)2W(DMAP)Me (2) with
HSiR2Ar at room temperature also gave 1a-d, and in all cases the yields were higher than those in
the photoreaction. Silylene complexes 1a-d easily isomerized to arylsilyl complexes Cp*(CO)2-
W(DMAP)(SiR2Ar) [3a, R ) Me, Ar ) Ph; 3b, R ) Me, Ar ) p-Tol; 3c, R2 ) Me(p-Tol), Ar ) p-Tol;
3d, R ) Ar ) p-Tol] at 40-55 °C. On the other hand, irradiation of arylsilyl complexes 3a-d reproduced
silylene complexes 1a-d, implying that the 1,2-aryl-migration between tungsten and silicon is reversible.
The molecular structures of 1c, 2, 3a, and 3d were determined by X-ray crystallography. A kinetic study
on the 1,2-aryl-migration in the thermal isomerization from 1a-d to 3a-d suggests that the
rate-determining step involves dissociation of DMAP from 1a-d.
with Si-C bond cleavage/formation reactions mediated by
metal-silicon complexes.8 However, the experimental inves-
tigations on the 1,2-migration have been limited to several late
transition-metal complexes: Bergman et al. reported alkyl- and
aryl-migration reactions between cationic iridium-silyl and
-silylene complexes.4 1,2-Migration reactions of an alkyl or an
aryl group on a metal center to a silylene ligand have also been
proposed in several reactions of iridium1a,9 and platinum10
complexes. On the other hand, we have recently reported on
the irreversible 1,2-migration of an aryl group in an early
transition-metal silyl complex where the Si,N-chelated tungsten
complex Cp*(CO)2W{κ2(Si,N)-Me2N(o-C6H4SiMe2)} is ther-
mally unstable and is converted to the base-stabilized aryl-
(silylene) complex Cp*(CO)2W{κ2(Si,C)-SiMe2NMe2(o-C6H4)}
at room temperature.6 Because of the lability of the amine
ligand, the Si,N-chelate complex can easily generate a 16-
electron silyl complex that is a crucial intermediate for the 1,2-
aryl-migration. As a closely related example, Sakaba et al.
recently observed the 1,2-migration of an alkynyl group in the
Introduction
Transition-metal silylene complexes are proposed as key
intermediates for metal-mediated scrambling of the substituents
of silanes, dehydrogenative coupling of silanes, etc.1 In these
transformation reactions, silylene complexes are generally
formed through silyl complexes generated from metal complexes
and hydrosilanes, and these processes are mostly reversible. The
interconversion between the silylene complexes and silyl
complexes is supposed to proceed via 1,2-migration of a
substituent R′ as shown in Scheme 1. Although there are many
reports on the 1,2-migration of a hydrogen2 or a silyl group3
on a silyl ligand giving silylene complexes, those on 1,2-
migration of a hydrocarbyl4-7 group have been rare.
The 1,2-migration of hydrocarbyl groups between transition
metal and silicon atoms is interesting because of its relationship
* To whom correspondence should be addressed. Tel: +81-22-795-6539.
Fax: +81-22-795-6543. E-mail: tobita@m.tains.tohoku.ac.jp.
† Tohoku University.
‡ Kyoto University.
(1) (a) Okazaki, M.; Tobita, H.; Ogino, H. Dalton Trans. 2003, 493,
and references therein. (b) Ogino, H. Chem. Rec. 2002, 2, 291.
(2) (a) Sakaba, H.; Tsukamoto, M.; Hirata, T.; Kabuto, C.; Horino, H.
J. Am. Chem. Soc. 2000, 122, 11511. (b) Watanabe, T.; Hashimoto, H.;
Tobita, H. Angew. Chem., Int. Ed. 2004, 43, 218. (c) Ochiai, M.; Hashimoto,
H.; Tobita, H. Angew. Chem., Int. Ed. 2007, 46, 8192. (d) Waterman, R.;
Hayes, P. G.; Tilley, T. D. Acc. Chem. Res. 2007, 40, 712.
(3) (a) Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351. (b)
Ueno, K.; Asami, S.; Watanabe, N.; Ogino, H. Organometallics 2002,
21, 1326. (c) Tobita, H.; Matsuda, A.; Hashimoto, H.; Ueno, K.; Ogino,
H. Angew. Chem., Int. Ed. 2004, 43, 221. (d) Hirotsu, M.; Nunokawa, T.;
Ueno, K. Organometallics 2006, 25, 1554. (e) Ueno, K.; Masuko, A.; Ogino,
H. Organometallics 1997, 16, 5023. (f) Ueno, K.; Sakai, M.; Ogino, H.
Organometallics 1998, 17, 2138. (g) Tobita, H.; Kurita, H.; Ogino, H.
Organometallics 1998, 17, 2844.
(4) (a) Burger, P.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 10462.
(b) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc. 2000, 122,
1816. (c) Klei, S. R.; Tilley, T. D.; Bergman, R. G. Organometallics 2001,
20, 3220. (d) Klei, S. R.; Tilley, T. D.; Bergman, R. G. Organometallics
2002, 21, 4648.
(5) (a) Sakaba, H.; Yoshida, M.; Kabuto, C.; Kabuto, K. J. Am. Chem.
Soc. 2005, 127, 7276. (b) Mausumi, R.; Yoshihide, N.; Sato, H.; Sakaba,
H.; Sakaki, S. J. Am. Chem. Soc. 2006, 128, 11927.
(6) Okazaki, M.; Suzuki, E.; Miyajima, N.; Tobita, H.; Ogino, H.
Organometallics 2003, 22, 4633.
(7) Begum, R.; Komuro, T.; Tobita, H. Chem. Lett. 2007, 650.
(8) Schubert, U. Angew. Chem., Int. Ed. Engl. 1994, 33, 419.
(9) Okazaki, M.; Tobita, H.; Ogino, H. J. Chem. Soc., Dalton Trans.
1997, 3531.
(10) Ozawa, F.; Kitaguchi, M.; Katayama, H. Chem. Lett. 1999, 1289.
10.1021/om801140d CCC: $40.75
2009 American Chemical Society
Publication on Web 02/27/2009

1792 Organometallics, Vol. 28, No. 6, 2009
Suzuki et al.
Scheme 1. 1,2-Migration of the Substituent R′ in the
Conversion between Silyl Complexes and Silylene Complexes
intermediary alkynylsilyl tungsten complexes giving alkynyl-
bridged W–Si complexes.5
Here we report the synthesis of aryl(silylene) tungsten
complexes via 1,2-aryl-migration from 16-electron silyl com-
plexes in the presence of an external base, 4-(dimethylami-
no)pyridine (DMAP). DMAP is commonly used as a base to
stabilize silylene complexes by its coordination to the Lewis
acidic silylene silicon atom,11 which can facilitate the formation
of the silylene complexes. To generate the 16-electron silyl
complexes, we employed two routes: (1) photoreaction of
Cp*(CO)3WMe with tertiary arylsilanes and (2) thermal reaction
of Cp*(CO)2W(DMAP)Me (2) with tertiary arylsilanes. In
route 1, the photoinduced dissociation of a CO ligand in
Cp*(CO)3WMe generates 16e methyl complex Cp*(CO)2WMe
that can react with hydrosilanes HSiR3 to give 16e silyl tungsten
complexes Cp*(CO)2W(SiR3) via Si–H oxidative addition of
silanes and methane elimination. In relation to route 2, Sakaba
et al. previously reported that the thermally labile pyridine
complex Cp*(CO)2W(py)Me (A, py ) pyridine) is versatile for
the synthesis of pyridine-stabilized hydrido(silylene) complexes
Cp*(CO)2W(H)(dSiR2 · py) (R2 ) Ph2, MePh, Et2) by the
reaction with secondary silanes. This reaction proceeds via 1,2-H
migration on the 16e silyl complexes Cp*(CO)2W(SiHR2) (R2
) Ph2, MePh, Et2) generated as intermediates.2a In route 2 of
our reaction, complex 2, the DMAP analogue of complex A,
acts as a good precursor of DMAP-stabilized silylene complexes,
and the stronger Lewis basicity of DMAP compared to that of
pyridine resulted in the cleavage of more robust silicon-carbon
bonds. A part of this work has been published as a preliminary
report.12
Figure 1. ORTEP drawing of 2. Thermal ellipsoids are drawn at
the 50% probability level, and all hydrogen atoms are omitted for
clarity. The sites of the methyl ligand and the carbonyl ligand are
mutually disordered with the occupancy factors 61:39. Each one
of the disordered atoms with the higher occupancy factors (O2A,
C1A, and C3A) is depicted.
Table 1. Selected Bond Distances (Å) and Angles (deg) in
Cp*(CO)2W(DMAP)Me (2)
W-N1
2.269(6)
2.34(3)
1.938(14)
83.3(5)
129.3(3)
83.4(7)
79.1(7)
122.5(9)
71.4(7)
W-C1A
2.276(18)
1.930(7)
2.01(2)
78.6(7)
84.6(4)
77.2(5)
127.6(6)
72.0(5)
W-C1B
W-C2
W-C3A
W-C3B
N1-W-C1A
N1-W-C2
N1-W-C3B
C1B-W-C2
C1B-W-C3B
C2-W-C3B
N1-W-C1B
N1-W-C3A
C1A-W-C2
C1A-W-C3A
C2-W-C3A
structure analysis (Figure 1, Table 1). The DMAP ligand and
the methyl ligand were located at mutually cis positions on the
tungsten center. This geometry is consistent with the observation
of two inequivalent signals (250.8, 266.2 ppm) assignable to
the CO ligands in the 13C{1H} NMR spectrum of 2.
Results and Discussion
Synthesis of Cp*(CO)2W(DMAP)Me (2). A methyl tungsten
complex having a DMAP ligand Cp*(CO)2W(DMAP)Me (2),
an important precursor of silylene complexes in this research,
was synthesized according to a method analogous to that for
the synthesis of pyridine complex Cp*(CO)2W(py)Me (A).2a
Thus, irradiation of Cp*(CO)3WMe in MeCN with a 450 W
medium-pressure Hg lamp (λ > 300 nm) led to the dissociation
of a CO ligand followed by coordination of MeCN to give
Cp*(CO)2W(NCMe)Me (B).2a,5,6,13 Then the substitution of the
labile MeCN ligand in B with a DMAP molecule at room
temperature in toluene gave the DMAP complex 2 in 86% yield
(eq 1). Complex 2 was characterized by spectroscopy and
elemental analysis. The molecular structure of 2 having a four-
legged piano-stool geometry was confirmed by X-ray crystal
Synthesis of Silylene Complexes Cp*(CO)2W(Ar)(dSiR2 ·
DMAP) (1a-d) (Ar ) Ph, p-Tol; R ) Me, p-Tol). Aryl(silylene)
complexes 1a-d have been synthesized by two methods:
photochemical and nonphotochemical routes (Scheme 2, Table
2). Thus, irradiation (λ > 300 nm) of a solution of
Cp*(CO)3WMe, arylsilane HSiR2Ar [R2Ar ) Me2Ph, Me2(p-
Tol), Me(p-Tol)2, and (p-Tol)3], and DMAP in toluene or C6D6
at ca. 5 °C gave silylene complexes Cp*(CO)2W(Ar)(dSiR2 ·
DMAP) [1a, Ar ) Ph, R2 ) Me2; 1b, Ar ) p-Tol, R2 ) Me2;
1c, Ar ) p-Tol, R2 ) Me(p-Tol); 1d, Ar ) R ) p-Tol]. The
thermal reaction of Cp*(CO)2W(DMAP)Me (2) with HSiR2Ar
also gave 1a-d at room temperature. The thermal reaction
(11) (a) Grumbine, S. D.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L.
J. Am. Chem. Soc. 1993, 115, 7884. (b) Grumbine, S. K.; Straus, D. A.;
Tilley, T. D.; Rheingold, A. L. Polyhedron 1995, 14, 127. (c) Mitchell,
G. P.; Tilley, T. D. Angew. Chem., Int. Ed. 1998, 37, 2524. (d) Glaser,
P. B.; Tilley, T. D. Organometallics 2004, 23, 5799. (e) Watanabe, T.;
Hashimoto, H.; Tobita, H. J. Am. Chem. Soc. 2006, 128, 2176.
(12) Suzuki, E.; Okazaki, M.; Tobita, H. Chem. Lett. 2005, 1026.
(13) (a) Sakaba, H.; Ishida, K.; Horino, H. Chem. Lett. 1995, 1145. (b)
Sakaba, H.; Ishida, K.; Horino, H. Chem. Lett. 1998, 149. (c) Sakaba, H.;
Watanabe, S.; Kabuto, C.; Kabuto, K. J. Am. Chem. Soc. 2003, 125, 2842.
(d) Suzuki, E.; Komuro, T.; Okazaki, M.; Tobita, H. Organometallics 2007,
26, 4379.

DMAP-Stabilized Aryl(silylene) and (Arylsilyl)(DMAP) Complexes
Organometallics, Vol. 28, No. 6, 2009 1793
Scheme 2. Synthesis of Aryl(silylene) Complexes 1a-d
Table 2. Summary of Isolated Yields of Silylene Complexes 1a-d
thermal reaction
photoreaction
(room temperature)
irradiation
time, min
isolated
yield, %
time,
h
isolated
yield, %
compound
Figure 2. ORTEP drawing of 1c. Thermal ellipsoids are drawn at
the 50% probability level, and all hydrogen atoms are omitted for
clarity.
1a
1b
1c
1d
120
180
150
70
42
61
60
1
1
1
2
68
69
71
66
34 (NMR yield)a
Table 3. Selected Bond Distances (Å) and Angles (deg) in
Cp*(CO)2W(p-Tol){dSiMe(p-Tol) · DMAP} (1c)
a 1d could not be isolated in the photoreaction because of the
difficulty of the separation from unidentified byproduct.
W-Si
2.505(4)
1.945(18)
1.898(11)
W-C1
W-C9
2.290(13)
1.968(14)
W-C8
Si-N1
Si-W-C1
Si-W-C9
C1-W-C9
W-Si-N1
W-Si-C18
132.8(4)
72.8(4)
76.7(5)
113.4(4)
120.4(4)
Si-W-C8
74.2(4)
80.8(6)
106.0(5)
118.8(6)
104.3(7)
resulted in higher yield in all cases (Table 2). Isolation of
complex 1d from the reaction mixture of the photoreaction was
not successful because of the difficulty of the separation of
unidentified byproducts from 1d but was successful in the
thermal reaction. These results indicate that the thermal reaction
is superior to the photochemical one for the synthesis of 1a-d.
The aryl(silylene) complexes 1a-d were characterized on
the basis of spectroscopy and elemental analysis. In the 29Si
NMR spectra of 1a-d, the signals assignable to the silylene
silicon atoms were observed at 86.7 (1a), 86.5 (1b), 83.7 (1c),
and 85.8 (1d) ppm,which are in the typical range for base-
stabilized silylenetungsten complexes (62-145 ppm).3b The IR
spectra of 1a-d show two bands for a symmetric and an
asymmetric CO vibration, where the intensity of the latter band
is stronger than that of the former one. This observation implies
that the two carbonyl ligands in 1a-d are mutually in trans
arrangement.
C1-W-C8
C8-W-C9
W-Si-C17
C17-Si-C18
Scheme 3. A Possible Mechanism for the Formation of
Silylene Complexes 1a-d
The crystal structures of complexes 1a and 1c have been
determined by X-ray crystallography (Figure 2, Table 3). The
structure of 1a has already been reported in the preliminary
communications.12 Complex 1c adopts a four-legged piano-stool
geometry: the tungsten center possesses a pentamethylcyclo-
pentadienyl, a p-tolyl, a silylene, and two carbonyl ligands, in
which the p-tolyl and the silylene ligands are located at mutually
trans positions. The W-Si bond length [2.505(4) Å] is within
the range of those of the base-stabilized silylenetungsten
complexes (2.45-2.51 Å).6 The Si-N1 bond [1.898(11) Å] is
comparable to those of nitrogen-donor-coordinated silylene
complexes [1.908(2)-2.007(9) Å]3d and significantly longer than
those of normal Si-N covalent bonds (1.70-1.76 Å).14 The
sum of the bond angles between the three bonds except the
Si-N1 bond around the silicon atom is 344(2)°, which is in
the middle of the tetrahedral (327°) and trigonal (360°) valence
angles. The W-C1 bond length [2.290(13) Å] is within the
normal range of W-C(aryl) bond lengths (2.16-2.33 Å).6
A possible formation mechanism of 1a-d is illustrated in
Scheme 3. Photochemical dissociation of a CO ligand in
Cp*(CO)3WMe or thermal dissociation of the DMAP ligand
in 2 generates the 16e methyl complex Cp*(CO)2WMe. Then,
oxidative addition of the Si-H bond of arylsilane HSiR2Ar,
reductive elimination of methane, 1,2-aryl-migration, and final
coordination of a DMAP molecule to the silylene ligand give
1a-d. In the reactions forming complexes 1a-c, the alternative
process is 1,2-methyl-migration from silicon to tungsten to form
methyl(silylene)tungsten complexes, but no signals assignable
to the methyl(silylene) complex were observed in the 1H NMR
spectrum of the reaction mixture. This implies that 1,2-migration
of an aryl group is easier than that of a methyl group. A similar
(14) Sheldrick, W. S. In The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 3, p 227.

1794 Organometallics, Vol. 28, No. 6, 2009
Suzuki et al.
result has been reported on the reaction of iridium complex
Cp*(PMe3)Ir(CH3)(OTf) with phenyldimethylsilane that leads
exclusively to 1,2-migration of a phenyl group to yield
Cp*(PMe3)Ir(Ph)(SiMe2OTf).4a Silylene complexes 1a-d were
exclusively obtained as the trans form where the silylene and
the aryl ligands were mutually in trans arrangement. We did
not observe the corresponding cis isomers of 1a-d in the
reaction mixture by NMR spectroscopy. This result is possibly
attributable to the steric repulsion between the silylene and the
aryl ligands, which is larger in the cis isomers than in the trans
forms 1a-d.
Synthesis of Silyl Complexes 3a-d via Thermal Isomer-
ization of Silylene Complexes 1a-d. Heating (40-55 °C,
16-72 h) of silylene complexes 1a-d in toluene led to the
formation of the corresponding silyl complexes Cp*(CO)2-
W(DMAP)(SiR2Ar) (3a-d) in 76-96% yields (eq 2). The 1,2-
aryl-migration from tungsten to silicon occurred in these
reactions. These results imply that silyl complexes 3a-d are
thermodynamically more stable than silylene complexes 1a-d.
Figure 3. ORTEP drawing of 3a. Thermal ellipsoids are drawn at
the 50% probability level, and all hydrogen atoms are omitted for
clarity.
Silyl complexes 3a-d were characterized by spectroscopy
and elemental analyses. In each of the 29Si NMR spectra of
3a-d, one signal appears at 15.8-24.3 ppm that is significantly
high-field-shifted compared with those of silylene complexes
1a-d (83.7-86.7 ppm) and is in a typical chemical shift range
for silyltungsten complexes (0-70 ppm).6 The coupling con-
stants between the 29Si and 183W nuclei of 3a and 3b [1JW-Si
)
31 (3a), 31 (3b) Hz] are considerably smaller than those of the
silylene complexes 1a and 1b [1JW-Si ) 71 (1a), 70 (1b) Hz],
because the s-character contribution of the orbital of silicon used
for formation of the W-Si bond is smaller for silyl complexes
3a,b than for silylene complexes 1a,b.
Figure 4. ORTEP drawing of 3d. Thermal ellipsoids are drawn at
the 50% probability level, and all hydrogen atoms are omitted for
clarity.
Table 4. Selected Bond Distances (Å) and Angles (deg) in
Cp*(CO)2W(DMAP)(SiMe2Ph) (3a)
The crystal structures of 3a and 3d were determined by X-ray
crystallography (Figures 3 and 4, Tables 4 and 5). The structure
of 3b has also been determined and reported in the preliminary
communications.12 Complexes 3a and 3d adopt a four-legged
piano-stool geometry: the tungsten center possesses one Cp*,
one DMAP, one silyl, and two carbonyl ligands, in which one
phenyl and two methyl groups (in 3a) or three p-tolyl groups
(in 3d) are bonded to the silicon atom. The silyl and the DMAP
ligands are located at mutually trans positions, which is
consistent with the observation of only one CO resonance in
the 13C NMR spectra of 3a and 3d and also the stronger intensity
of the νCO band for the asymmetric stretching [1790 (3a), 1786
(3d) cm-1] compared to that for the symmetric band [1876 (3a),
1874 (3d) cm-1] in the IR spectra. The W-Si bond distances
in 3a and 3d [2.615(2) (3a), 2.6110(13) (3d) Å] are ca. 0.1 Å
longer than those of silylene complexes 1a and 1c [2.511(5),
2.534(5) (1a);14 2.505(4) (1c) Å] and are within the range
(2.53-2.63 Å) of typical tungsten-silicon single bonds.6 The
Si-W-C(carbonyl) bond angles in 3a are almost identical [av
69.8(3)°], whereas those in 3d are substantially different from
each other where the Si-W-C1 angle [75.00(16)°] is wider
than the Si-W-C2 angle [68.28(14)°]. This geometric differ-
W-Si
2.615(2)
1.956(9)
132.7(2)
69.9(3)
84.1(3)
115.6(3)
114.5(3)
101.9(4)
W-N1
2.231(8)
1.957(9)
69.7(3)
W-C1
W-C2
Si-W-N1
Si-W-C2
N1-W-C2
W-Si-C3
W-Si-C5
C3-Si-C5
Si-W-C1
N1-W-C1
C1-W-C2
W-Si-C4
C3-Si-C4
C4-Si-C5
83.7(3)
109.3(4)
115.9(3)
104.0(5)
103.1(4)
Table 5. Selected Bond Distances (Å) and Angles (deg) in
Cp*(CO)2W(DMAP){Si(p-Tol)3} (3d)
W-Si
W-C1
2.6110(13)
1.951(6)
W-N1
W-C2
2.226(4)
1.970(5)
75.00(16)
83.0(2)
107.0(2)
116.83(16)
103.6(2)
101.5(2)
Si-W-N1
Si-W-C2
N1-W-C2
W-Si-C3
W-Si-C17
C3-Si-C17
133.99(12)
68.28(14)
80.74(19)
116.52(17)
112.64(15)
103.9(2)
Si-W-C1
N1-W-C1
C1-W-C2
W-Si-C10
C3-Si-C10
C10-Si-C17
ence reflects the large steric hindrance between the Si(p-Tol)3
moiety and one CO ligand, i.e., C1 and O1, in 3d.
The NMR spectra of the solution of 3c and 3d suggest the
presence of the hindered rotation around the W–Si bond. The
1H NMR spectrum of 3d in C6D6 at room temperature exhibits

DMAP-Stabilized Aryl(silylene) and (Arylsilyl)(DMAP) Complexes
Organometallics, Vol. 28, No. 6, 2009 1795
Table 6. Temperature Dependence of Rate Constants (10-5 s-1) for
the Isomerization of Aryl(silylene) Complexes 1a-d to Arylsilyl
Complexes 3a-d in C6D6 at Several Temperatures
temperature
compound 298 K 303 K 308 K 313 K 318 K 323 K 328 K
1a
1b
1c
1d
0.118(2)
0.98(4) 1.96(6) 4.82(6) 14.6(5)
0.287(7) 1.30(2) 4.74(4) 17.4(6) 38.0(8)
0.266(5) 0.53(1) 2.06(4) 5.50(8) 10.7(1)
0.36(1) 0.885(4) 1.77(4) 5.4(3) 10.4(3)
two sets of the signals assignable to the p-tolyl groups with 2:1
intensity ratio, indicating that the rotation around the W-Si(p-
Tol)3 bond is slow on the NMR time scale. This rotation became
faster at higher temperature: on raising the temperature to 75
1
°C, the two sets of the H NMR signals of the p-tolyl groups
1
were merged into one set. On the other hand, the H NMR
spectrum of 3c in C6D6 at room temperature shows one set of
the signals of the p-tolyl groups, indicating that the rotation
around the W–SiMe(p-Tol)2 bond is fast on the NMR time scale.
Figure 5. Eyring plots [ln (k/T) vs 1000/T] for the isomerization
of silylene complexes 1a-d to silyl complexes 3a-d: (0) isomer-
ization of 1a, (O) isomerization of 1b, (9) isomerization of 1c,
and (b) isomerization of 1d.
1
The variable-temperature H NMR spectra of 3c in CD2Cl2
exhibit temperature-dependent dynamic behavior. One set of
the signals of the p-tolyl groups (one singlet at 2.24 ppm for
the methyl protons and two broad signals at 6.96 and 7.47 ppm
for the aromatic protons) are observed in the 1H NMR spectrum
for the CD2Cl2 solution of 3c at 298 K. On cooling the solution
to 243 K, the two sets of signals for two rotamers were observed
with ca. 6:1 intensity ratio. A similar hindered rotation around
the tungsten-silicon bond was reported for the sterically
congested tungsten bis(silyl) complex Cp2W(SiMe3){Si(t-
Bu)2H}.15 Thus, the hindered rotation in 3c and 3d is also
attributable to the steric effect of other ligands on the silyl ligand.
The steric hindrance is explicit in the crystal structure of 3d
(Figure 4). The distances between the aryl carbon (C3, C4) on
a p-Tol group and the methyl carbon (C37) on Cp* [C3 · · · C37,
3.532(8); C4 · · · C37, 3.303(9) Å] and between the aryl carbon
(C10, C11) on another p-Tol group and the methyl carbon (C36)
on Cp* [C10 · · · C36, 3.660(8); C11 · · · C36, 3.451(8) Å] are
shorter than the sum (3.7 Å) of the van der Waals radii of a
methyl group (2.0 Å) and the half-thickness of the plane of an
aromatic ring (1.7 Å).16 The distance [3.122(8) Å] between the
aryl carbon (C22) on a p-Tol group and the oxygen (O1) of a
CO ligand is comparable to the sum (3.1 Å) of the van der
Waals radii of an oxygen atom (1.4 Å) and the half-thickness
of the plane of an aromatic ring (1.7 Å).16 These observations
imply the existence of considerable steric repulsion between
the Si(p-Tol)3 group and the Cp*(CO)2W(DMAP) moiety in
3d, leading to the hindered rotation around the W-Si(p-Tol)3
bond in the solution.
Table 7. Activation Parameters for the Conversion Reactions of
Aryl(silylene) Complexes 1a-d into Arylsilyl Complexes 3a-d in
C6D6
compound
∆Hq, kJ mol-1
∆Sq, J mol-1 K-1
∆Gq298, kJ mol-1
1a
1b
1c
1d
155(3)
199(5)
161(5)
132(3)
152(9)
307(17)
169(17)
93(10)
110(6)
108(10)
111(10)
104(6)
Scheme 4. A Possible Mechanism for the Isomerization from
Silylene Complexes 1a-d to Silyl Complexes 3a-d
imply that the isomerization reactions proceed through a
dissociative mechanism (Scheme 4). Thus, the thermal isomer-
ization of 1a-d to 3a-d is considered to start with dissociation
of DMAP from the silylene silicon atom in 1a-d as the rate-
determining step. The resulting base-free silylene complexes
C undergo 1,2-migration of the aryl group to generate 16-
electron silyl complexes D, and finally coordination of DMAP
to the tungsten center in D affords silyl complexes 3a-d. The
unusually large ∆Sq values suggest the generation of a consider-
ably loose transition state compared to 1a-d, which is attribut-
able to a nearly complete dissociation of DMAP in the rate-
determiningstep.Theactivationenthalpy∆Hq fortheisomerization
of 1d is the smallest among those of 1a-d [155(3) (1a), 199(5)
(1b), 161(5) (1c), and 132(3) (1d) kJ mol-1]. This result is
attributable to the largest steric hindrance of the silylene ligand
of 1d having two p-tolyl substituents, which would make the
coordination of DMAP the weakest among the silylene com-
plexes 1a-d.
A Possible Mechanism for the Isomerization of Silylene
Complexes 1a-d to Silyl Complexes 3a-d. To clarify the
mechanism of the isomerization of 1a-d to 3a-d, a kinetic
study was carried out. The rate constants of the isomerization
reactions, which obey first-order kinetics, were determined by
monitoring the decrease of the intensity of the Cp* signal (for
1a,b,d) or a signal of the aromatic protons of DMAP (for 1c)
1
in the H NMR spectra in C6D6 at several temperatures from
298 to 328 K (Table 6). The Eyring plots based on the rate
constants are shown in Figure 5, and the determined activation
parameters are summarized in Table 7.
The large positive values of the activation entropy ∆Sq [152(9)
(1a), 307(17) (1b), 169(17) (1c), and 93(10) (1d) J mol-1 K-1
]
(15) Koloski, T. S.; Pestana, D. C.; Carroll, P. J.; Berry, D. H.
Organometallics 1994, 13, 489.
(16) Pauling, L. The Nature of the Chemical Bonds, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; pp 257-264.

1796 Organometallics, Vol. 28, No. 6, 2009
Suzuki et al.
Table 8. 1H NMR Yields of Silylene Complexes 1a-d Derived by
the Photoreaction of Silyl Complexes 3a-d in C6D6
used as received. Cp*(CO)3WMe was prepared according to the
literature method.17
Physical Measurements. 1H, 13C{1H}, and 29Si{1H} NMR
spectra were recorded on a Bruker ARX-300 or AVANCE-300
spectrometer. 29Si{1H} NMR experiments were performed using
the DEPT pulse sequence. The residual proton and the carbon
resonances of deuterated solvents were used as internal references
compound
irradiation time, min
NMR yield,a
%
1a-d:3a-d
3a
1.75
3
0.25
1.25
63
64
41
69
1:0.031
1:0.048
1:0c
3b
3cb
3d
1:0c
1
for H and 13C resonances, respectively. 29Si{1H} NMR chemical
a The NMR yields were determined by comparing the intensity of the
Cp* signal of 3a-d in the 1H NMR spectra to that of the internal
standard [cyclohexane (for 3a, 3b, and 3d) or Si(SiMe3)4 (for 3c)]. b The
concentration of 3c was about half of the others because of the low
solubility of 3c in C6D6. c No signals of the silyl complex were
observed.
shifts were referenced to SiMe4 as an external standard. The NMR
data were collected at room temperature unless indicated otherwise.
Infrared spectra were obtained using a HORIBA FT-730 spectro-
photometer. Mass and high-resolution mass spectra were recorded
on a Hitachi M-2500S spectrometer operating in the electron impact
(EI) mode or a Bruker Daltonics APEX-(III) spectrometer operating
in the electrospray ionization (ESI) mode. Mass spectrometric
analysis and elemental analysis were performed at the Research
and Analytical Center for Giant Molecules, Tohoku University.
Synthesis of Cp*(CO)2W(DMAP)Me (2). Compound 2 was
prepared by modifying a literature method for the synthesis of
Cp*(CO)2W(py)Me (A).2a An acetonitrile (5 mL) solution of
Cp*(CO)3WMe (100 mg, 0.239 mmol) in a Pyrex sample tube with
a Teflon vacuum valve was irradiated for 2 h with a 450 W medium-
pressure Hg lamp immersed in a water bath (ca. 5 °C). During the
photoreaction, the mixture was degassed after 20, 60, and 120 min
of irradiation by a conventional freeze-pump-thaw cycle on a
vacuum line. The reaction mixture containing Cp*(CO)2W(NCMe)-
Me (B) was transferred into a round-bottomed flask and evaporated
to dryness under reduced pressure. After addition of DMAP (34
mg, 0.28 mmol) and toluene (5 mL), the mixture was allowed to
stand at room temperature for 4.5 h. The reaction mixture was
evaporated to dryness, and then the residue was washed with hexane
to give a red powder of 2 (105 mg, 0.205 mmol) in 86% yield. 1H
NMR (300 MHz, C6D6): δ 0.52 (s, 3H, WMe), 1.77 (s, 15H, Cp*),
2.08 (s, 6H, NMe2), 5.53 (m, 2H, py-H), 8.00 (m, 2H, py-H).
13C{1H} NMR (75.5 MHz, C6D6): δ -2.3 (WMe), 10.7 (C5Me5),
38.3 (NMe2), 101.9 (C5Me5), 107.6, 150.5, 155.5 (py), 250.8, 266.2
(CO). IR (C6D6, cm-1): 1898 (s, νCOsym), 1792 (m, νCOasym). Anal.
Calcd for C20H28N2O2W: C, 46.89; H, 5.51; N, 5.47. Found: C,
46.74; H, 5.54; N, 5.37.
Photoreaction of Silyl Complexes 3a-d. The 1,2-migration
of the aryl group is reversible between the silyl complexes 1a-d
and silylene complexes 3a-d: irradiation (λ > 300 nm) of silyl
complexes 3a-d in C6D6 reproduced the corresponding silylene
1
complexes 1a-d in 41-69% NMR yields based on H NMR
peak intensities (eq 3, Table 8). These photoisomerization
reactions were completed within a few minutes. This result
implies that silylene complexes 1a-d dominate over silyl
complexes 3a-d in the photostationary states. A plausible
mechanism for this photochemical isomerization involves pho-
toinduced dissociation of the DMAP ligand in 3a-d. The
dissociation can lead to the 1,2-aryl-migration from the silicon
atom to the metal center to generate silylene complexes C in
Scheme 4, and then the coordination of DMAP to the silylene
silicon atom forms 1a-d. However, an alternative mechanism
starting from photoinduced dissociation of a CO ligand in 3a-d
cannot be ruled out.
Synthesis of Cp*(CO)2W(Ph)(dSiMe2 · DMAP) (1a). Method
1: Photoreaction of a Mixture of Cp*(CO)3WMe, HSiMe2Ph,
and DMAP. A toluene (8 mL) solution of Cp*(CO)3WMe (150
mg, 0.359 mmol), DMAP (50 mg, 0.41 mmol), and HSiMe2Ph (75
mg, 0.55 mmol) in a Pyrex tube with a Teflon vacuum valve was
irradiated for 2 h with a 450 W medium-pressure Hg lamp immersed
in a water bath (ca. 5 °C). The reaction mixture was transferred
into a round-bottomed flask and cooled at -35 °C. Silylene complex
1a was obtained as a yellow solid in 42% yield (98 mg, 0.15 mmol).
Method 2: Reaction of 2 with HSiMe2Ph. A toluene (4 mL)
solution of complex 2 (118 mg, 0.230 mmol) and HSiMe2Ph (66
mg, 0.48 mmol) was stirred at room temperature for 1 h. The
reaction mixture was evaporated to dryness, and the residue was
washed with hexane. Recrystallization from toluene/hexane at -35
°C gave 1a (99 mg, 0.16 mmol) as a yellow powder in 68% yield.
1H NMR (300 MHz, C6D6): δ 1.07 (s, 6H, SiMe2), 1.69 (s, 6H,
NMe2), 1.92 (s, 15H, Cp*), 5.18 (m, 2H, py-H), 7.17 (m, 1H,
p-ArH), 7.33 (t, J ) 7.3 Hz, 2H, m-ArH), 8.08 (m, 2H, o-ArH),
8.58 (m, 2H, py-H). 13C{1H} NMR (75.5 MHz, C6D6): δ 7.6
(SiMe2), 11.5 (C5Me5), 38.1 (NMe2), 100.7 (C5Me5), 106.1, 122.5,
127.9, 146.3, 148.4, 149.5, 154.8 (aromatic carbons), 242.7 (CO).
29Si{1H} NMR (59.6 MHz, C6D6): δ 86.7 (JW-Si ) 71 Hz). IR
(C6D6, cm-1): 1869 (m, νCOsym), 1784 (s, νCOasym). MS (EI): m/z
632 (M+, 4), 604 (M+ - CO, 4), 510 (M+ - DMAP, 17). Anal.
Calcd for C27H36N2O2SiW: C, 51.27; H, 5.75; N, 4.43. Found: C,
51.45; H, 5.86; N, 4.32.
Conclusion
In this work, we investigated the synthesis of DMAP-
stabilized aryl(silylene) tungsten complexes 1a-d and (aryl-
silyl)(DMAP) tungsten complexes 3a-d. Complexes 1a-d
were synthesized via 1,2-aryl-migration from 16-electron silyl
complexes in the presence of the external base DMAP to
stabilize silylene complexes. Silylene complexes 1a-d isomer-
ized to silyl complexes 3a-d at 40-55 °C, and UV irradiation
of 3a-d resulted in the reverse isomerization giving 1a-d.
These results indicate that 1a-d and 3a-d are interconvertible
through 1,2-aryl-migration. The kinetic study on the thermal
isomerization of 1a-d to 3a-d implies that the dissociation of
DMAP is the rate-determining step. Thus, we suggest that
possible intermediates in this isomerization reaction are base-
free silylene complexes C and 16-electron silyl complexes D
(Scheme 4).
Experimental Section
General Procedures. All manipulations were carried out under
dry nitrogen using either a glovebox or both high-vacuum line and
standard Schlenk techniques. Benzene-d6, dichloromethane-d2,
toluene, hexane, and acetonitrile were dried over calcium hydride
and distilled before use. All commercially available reagents were
(17) Mahmoud, K. A.; Rest, A. J.; Alt, H. G.; Eichner, M. E.; Jansen,
B. M. J. Chem. Soc., Dalton Trans. 1984, 175.

DMAP-Stabilized Aryl(silylene) and (Arylsilyl)(DMAP) Complexes
Organometallics, Vol. 28, No. 6, 2009 1797
Synthesis of Cp*(CO)2W(p-Tol)(dSiMe2 · DMAP) (1b). Method
1: Photoreaction of a Mixture of Cp*(CO)3WMe, HSiMe2(p-
Tol), and DMAP. A toluene (9.5 mL) solution of Cp*(CO)3WMe
(201 mg, 0.481 mmol), DMAP (68 mg, 0.56 mmol), and HSiMe2(p-
Tol) (107 mg, 0.712 mmol) was irradiated for 3 h in a manner
similar to that for 1a. The reaction mixture was transferred into a
round-bottomed flask and concentrated to ca. 6 mL under reduced
pressure. Cooling at -35 °C afforded a yellow solid of 1b in 61%
yield (190 mg, 0.294 mmol).
isolated, and the NMR yield was determined by comparing the
intensity of the Cp* signal of 1d in the H NMR spectrum to that
of cyclohexane as an internal standard.
1
Method 2: Reaction of 2 with HSi(p-Tol)3. A toluene (4 mL)
solution of complex 2 (100 mg, 0.195 mmol) and HSi(p-Tol)3 (234
mg, 0.774 mmol) was stirred at room temperature for 2 h. The
reaction mixture was concentrated to 3 mL under reduced pressure.
Hexane (6 mL) was added to the solution, and the mixture was
cooled to -35 °C. A yellow powder of 1d · 0.5toluene was obtained
1
Method 2: Reaction of 2 with HSiMe2(p-Tol). A toluene (4 mL)
solution of 2 (114 mg, 0.222 mmol) and HSiMe2(p-Tol) (62 mg,
0.41 mmol) was stirred at room temperature for 1 h. The reaction
mixture was evaporated to dryness, and the residue was washed
with hexane. Recrystallization from toluene/hexane at -35 °C gave
a yellow powder of 1b · 0.5toluene (107 mg, 0.165 mmol) in 69%
in 66% yield (109 mg, 0.129 mmol). H NMR (300 MHz, C6D6):
δ 1.61 (s, 6H, NMe2), 1.82 (s, 15H, Cp*), 2.21 (s, 6H, C6H4Me),
2.35 (s, 3H, C6H4Me), 5.03 (d, J ) 7.8 Hz, 2H, py-H), 7.20-7.27
(m, 6H, ArH), 8.00 (d, J ) 7.8 Hz, 4H, ArH), 8.32 (d, J ) 7.8 Hz,
2H, ArH), 8.59 (d, J ) 7.8 Hz, 2H, py-H). 13C{1H} NMR (75.5
MHz, C6D6): δ 11.4 (C5Me5), 21.3, 21.4 (C6H4Me), 38.0 (NMe2),
100.8 (C5Me5), 105.9, 127.9, 128.5, 128.8, 131.2, 137.4, 138.3,
140.4, 147.7, 147.9, 154.9 (aromatic carbons), 241.9 (CO). 29Si{1H}
NMR (59.6 MHz, C6D6): δ 85.8. IR (KBr pellet, cm-1): 1861 (m,
1
yield. H NMR (300 MHz, C6D6): δ 1.08 (s, 6H, SiMe2), 1.70 (s,
6H, NMe2), 1.95 (s, 15H, Cp*), 2.34 (s, 3H, C6H4Me), 5.19 (m,
2H, py-H), 7.20 (d, J ) 7.4 Hz, 2H, ArH), 8.09 (m, 2H, py-H),
8.49 (d, J ) 7.4 Hz, 2H, ArH). 13C{1H} NMR (75.5 MHz, C6D6):
δ 7.7 (SiMe2), 11.6 (C5Me5), 21.3 (C6H4-Me), 38.1 (NMe2), 100.7
(C5Me5), 106.1, 128.6, 130.8, 144.0, 146.3, 148.2, 154.8 (aromatic
carbons), 242.7 (CO). 29Si{1H} NMR (59.6 MHz, C6D6): δ 86.5
(JW-Si ) 70 Hz). IR (C6D6, cm-1) 1869 (w, νCOsym), 1784 (s,
ν
COsym), 1763 (s, νCOasym). Anal. Calcd for C43.5H50N2O2SiW
(1d · 0.5toluene): C, 61.84; H, 5.97; N, 3.32. Found: C, 62.02; H,
6.08; N, 3.24.
Synthesis of Cp*(CO)2W(DMAP)(SiMe2Ph) (3a). A toluene (4
mL) solution of 1a (82 mg, 0.13 mmol) in a Pyrex tube (12 mm
o.d.) with a Teflon vacuum valve was attached to a vacuum line.
The tube was flame-sealed under high vacuum and heated at 55
°C for 16 h. The reaction mixture was transferred into a round-
bottomed flask and evaporated to dryness. The residue was washed
with hexane to give 3a (73 mg, 0.12 mmol) as a yellow powder in
89% yield. 1H NMR (300 MHz, C6D6): δ 1.32 (s, 6H, SiMe2), 1.66
(s, 15H, Cp*), 1.95 (s, 6H, NMe2), 5.33 (m, 2H, py-H), 7.23 (m,
1H, p-ArH), 7.39 (t, J ) 7.4 Hz, 2H, m-ArH), 8.24 (m, 2H, o-ArH),
8.34 (m, 2H, py-H). 13C{1H} NMR (75.5 MHz, C6D6): δ 6.1
(SiMe2), 10.9 (C5Me5), 38.0 (NMe2), 101.1 (C5Me5), 108.1, 127.3,
127.9, 135.7, 150.2, 153.2, 159.4 (aromatic carbons), 243.1 (CO).
29Si{1H} NMR (59.6 MHz, C6D6): δ 15.8 (JW-Si ) 31 Hz). IR
(C6D6, cm-1) 1876 (m, νCOsym), 1790 (s, νCOasym). MS (ESI): m/z
ν
COasym). MS (ESI): m/z 669 (M + Na+, 40), 547 (M + Na+
-
DMAP, 89). Anal. Calcd for C31.5H42N2O2SiW (1b · 0.5toluene):
C, 54.62; H, 6.11; N, 4.04. Found: C, 54.01; H, 5.98; N, 4.11.
Synthesis of Cp*(CO)2W(p-Tol){dSiMe(p-Tol) · DMAP} (1c).
Method 1: Photoreaction of a Mixture of Cp*(CO)3WMe, HSiMe(p-
Tol)2, and DMAP. A toluene (8 mL) solution of Cp*(CO)3WMe
(214 mg, 0.512 mmol), DMAP (70 mg, 0.57 mmol), and HSiMe(p-
Tol)2 (205 mg, 0.906 mmol) was irradiated for 2.5 h in a manner
similar to that for 1a. The reaction mixture was transferred into a
round-bottomed flask and concentrated to ca. 3 mL. Hexane (6 mL)
was added to the solution, and then the mixture was allowed to
stand at room temperature.
A yellow solid of a solvate
1c · 0.5toluene was obtained in 60% yield (237 mg, 0.308 mmol).
Method 2: Reaction of 2 with HSiMe(p-Tol)2. A toluene solution
(4 mL) of complex 2 (135 mg, 0.264 mmol) and HSiMe(p-Tol)2
(106 mg, 0.468 mmol) was stirred at room temperature for 1 h.
The reaction mixture was evaporated to dryness, and then the
residue was washed with hexane. Recrystallization from toluene/
hexane at -35 °C gave 1c (136 mg, 0.188 mmol) as a yellow
1287 (M2 + Na+, 12), 655 (M + Na+, 42), 533 (M + Na+
-
DMAP, 74). Anal. Calcd for C27H36N2O2SiW: C, 51.27; H, 5.75;
N, 4.43. Found: C, 51.64; H, 5.74; N, 4.26.
Synthesis of Cp*(CO)2W(DMAP){SiMe2(p-Tol)} (3b). A sealed
tube (12 mm o.d.) of a toluene (4 mL) solution of 1b (80 mg, 0.12
mmol), prepared in a manner similar to that for the synthesis of
3a, was heated at 40 °C for 72 h. The reaction mixture was
transferred into a round-bottomed flask and evaporated to dryness.
The residue was washed with hexane to give 3b (61 mg, 0.095
1
powder in 71% yield. H NMR (300 MHz, C6D6): δ 1.34 (s, 3H,
SiMe), 1.67 (s, 6H, NMe2), 1.81 (s, 15H, Cp*), 2.22 (s, 3H,
C6H4Me), 2.35 (s, 3H, C6H4Me), 5.01 (d, J ) 7.8 Hz, 2H, py-H),
7.18-7.26 (m, 4H, ArH), 8.04 (d, J ) 7.8 Hz, 2H, ArH), 8.11 (d,
J ) 7.8 Hz, 2H, ArH), 8.56 (d, J ) 7.8 Hz, 2H, py-H). 13C{1H}
NMR (75.5 MHz, C6D6): δ 5.9 (SiMe2), 11.3 (C5Me5), 21.3, 21.4
(C6H4Me), 38.1 (NMe2), 100.6 (C5Me5), 106.0, 128.80, 128.82,
131.2, 135.5, 138.3, 143.2, 143.9, 147.6, 147.9, 154.9 (aromatic
carbons), 242.0, 243.1 (CO). 29Si{1H} NMR (59.6 MHz, C6D6): δ
83.7. IR (KBr pellet, cm-1) 1857 (m, νCOsym), 1759 (s, νCOasym).
MS (ESI): m/z 845 (M + DMAP + H+, 70), 745 (M + Na+, 33),
631 (M+ - p-Tol, 100). Anal. Calcd for C37.5H46N2O2SiW
(1c · 0.5toluene): C, 58.59; H, 6.03; N, 3.64. Found: C, 58.79; H,
6.04; N, 3.77.
1
mmol) as a yellow powder in 76% yield. H NMR (300 MHz,
C6D6): δ 1.33 (s, 6H, SiMe2), 1.68 (s, 15H, Cp*), 1.97 (s, 6H,
NMe2), 2.26 (s, 3H, C6H4Me), 5.35 (m, 2H, py-H), 7.23 (d, J )
7.2 Hz, 2H, ArH), 8.21-8.28 (m, 4H, ArH and py-H). 13C{1H}
NMR (75.5 MHz, C6D6): δ 6.3 (SiMe2), 10.9 (C5Me5), 21.4
(C6H4Me), 38.0 (NMe2), 101.1 (C5Me5), 108.1, 128.1, 135.8, 136.2,
146.4, 153.2, 159.4 (aromatic carbons), 243.1 (CO). 29Si{1H} NMR
(59.6 MHz, C6D6): δ 15.8 (JW-Si ) 31 Hz). IR (C6D6, cm-1): 1876
(w, νCOsym), 1790 (s, νCOasym). MS (ESI): m/z 1315 (M2 + Na+,
23), 669 (M + Na+, 51), 547 (M+ + Na+ - DMAP, 100). Anal.
Calcd for C28H38N2O2SiW: C, 52.01; H, 5.92; N, 4.35. Found: C,
51.77; H, 5.84; N, 4.30.
Synthesis of Cp*(CO)2W(DMAP){SiMe(p-Tol)2} (3c). A sealed
tube (12 mm o.d.) of a toluene (4 mL) solution of 1c · 0.5toluene
(65 mg, 0.085 mmol), prepared in a manner similar to that for the
synthesis of 3a, was heated at 50 °C for 64 h. The reaction mixture
was transferred into a round-bottomed flask and evaporated to
dryness. The residue was washed with hexane to afford 3c (56 mg,
0.077 mmol) as a yellow powder in 91% yield. 1H NMR (300 MHz,
C6D6, room temparature): δ 1.51 (br, 3H, SiMe), 1.66 (s, 15H, Cp*),
1.96 (s, 6H, NMe2), 2.17 (br, 6H, C6H4Me), 5.34 (m, 2H, py-H),
Synthesis of Cp*(CO)2W(p-Tol){dSi(p-Tol)2 · DMAP} (1d).
Method 1: Photoreaction of a Mixture of Cp*(CO)3WMe, HSi(p-
Tol)3, and DMAP. A Pyrex NMR tube with a Teflon vacuum valve
charged with a C6D6 (0.5 mL) solution of Cp*(CO)3WMe (10 mg,
0.024 mmol), DMAP (5 mg, 0.04 mmol), HSi(p-Tol)3 (10 mg, 0.033
mmol), and cyclohexane (less than 1 mg, internal standard) was
attached to a vacuum line. The NMR tube was flame-sealed under
high vacuum. The photoreaction was monitored by 1H NMR
spectroscopy. After irradiation for 70 min with a 450 W medium-
pressure Hg lamp immersed in a water bath (ca. 5 °C), silylene
complex 1d was formed in 34% NMR yield. Complex 1d was not

1798 Organometallics, Vol. 28, No. 6, 2009
Suzuki et al.
Table 9. Crystallographic Data for 1c, 2, 3a, and 3d
1c · 0.5C7H8
2 · 0.5C7H8
3a
3d · 2C6D6
formula
C37.5H46N2O2SiW
768.70
C23.5H32N2O2W
558.36
C27H36N2O2SiW
632.52
C52H58N2O2SiW
954.94
formula wt
cryst size, mm
cryst color
0.29 × 0.21 × 0.10
0.20 × 0.20 × 0.03
0.19 × 0.11 × 0.11
0.35 × 0.34 × 0.20
yellow
red
yellow
yellow
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
C2/c (No. 15)
32.348(7)
9.7497(16)
24.761(4)
monoclinic
P21/n (No. 14)
8.7537(3)
21.3505(6)
12.2441(3)
monoclinic
P2/a (No. 13)
17.6549(13)
8.6900(6)
17.7595(15)
89.2410(13)
104.716(4)
65.4601(13)
2635.3(3)
4
triclinic
P-1 (No. 2)
11.2137(2)
12.3983(2)
18.9190(9)
R, deg
ꢀ, deg
117.067(6)
97.3584(17)
75.7590(7)
γ, deg
V, Å3
6954(2)
8
1.468
2269.53(11)
4
1.634
2307.38(12)
2
1.374
Z
Dcalcd, g cm-3
F(000)
1.594
1264
3112
1108
976
µ(Mo KR), mm-1
reflections collected
unique reflections (Rint)
refined parameters
R1, wR2 (all data)
R1, wR2 [I > 2 σ(I)]
GOF
3.39
17256
5.11
21951
4.45
21289
2.57
21990
7167 (0.112)
391
0.117, 0.243
0.079, 0.199
1.16
5204 (0.064)
251
0.055, 0.118
0.042, 0.106
1.28
5888 (0.132)
307
0.093, 0.128
0.073, 0.121
1.19
10481 (0.068)
473
0.057, 0.142
0.051, 0.133
1.15
largest residual peak, hole, e Å-3
1.27, -2.52
1.34, -1.78
2.52, -2.31
3.48, -3.71
8.18 (d, J ) 7.7 Hz, 4H, ArH), 8.28 (m, 2H, py-H).18 1H NMR
(300 MHz, CD2Cl2, 298 K): δ 0.78 (s, 3H, SiMe), 1.60 (s, 15H,
Cp*), 2.24 (s, 6H, C6H4Me), 3.00 (s, 6H, NMe2), 6.35 (m, 2H, py-
H), 6.96 (br, 4H, ArH), 7.47 (br, 4H, ArH), 8.26 (m, 2H, py-H).18
1H NMR (300 MHz, CD2Cl2, 243 K, major rotamer): δ 0.68 (s,
3H, SiMe), 1.53 (s, 15H, Cp*), 2.11 (s, 3H, C6H4Me), 2.25 (s, 3H,
C6H4Me), 2.97 (s, 6H, NMe2), 6.31 (d, J ) 7.4 Hz, 2H, py-H),
6.83 (d, J ) 7.7 Hz, 2H, ArH), 7.02 (d, J ) 7.7 Hz, 2H, ArH),
7.21 (d, J ) 7.7 Hz, 2H, ArH), 7.57 (d, J ) 7.7 Hz, 2H, ArH),
8.18 (d, J ) 7.4 Hz, 2H, py-H).18 13C{1H} NMR (75.5 MHz,
CD2Cl2, 243 K, major rotamer): δ 2.6 (SiMe), 10.3 (C5Me5), 20.8,
20.9 (C6H4-Me), 39.1 (NMe2), 101.3 (C5Me5), 108.3, 127.1, 127.3,
135.4, 135.7, 136.1, 136.4, 143.4, 144.5, 153.1, 158.6 (aromatic
carbons), 221.1, 243.0 (CO).18 29Si{1H} NMR (59.6 MHz, CD2Cl2,
243 K, major rotamer): δ 17.8.18 IR (KBr pellet, cm-1) 1880 (m,
1a (2 mg, 3 µmol) and cyclohexane (less than 1 mg, internal
standard) in benzene-d6 (0.5 mL). This NMR tube was attached to
a vacuum line and flame-sealed under high vacuum. Five sealed
NMR sample tubes were prepared in this method. Each sealed tube
was heated at 30, 40, 45, 50, or 55 °C, and the reaction was
1
monitored by H NMR spectroscopy. The ratio of the intensity of
the Cp* signal of 1a against the initial intensity, which is equivalent
to the ratio of their concentrations [1a]/[1a]0, was fitted to first-
order plots of ln [1a]/[1a]0 versus time according to the following
equation: ln [1a]/[1a]0 ) -kt. The rate constants k at the
corresponding temperatures were determined from the slopes.
The rate constants for the thermal reactions of silylene complexes
1b-d were determined in a manner similar to that for 1a.19 For
1c, the intensity of a signal of the aromatic protons of DMAP in
1
the H NMR spectrum was used for the determination of the rate
νCOsym), 1786 (s, νCOasym). Anal. Calcd for C34H42N2O2SiW: C, 56.51;
constants. The results are summarized in Table 6.
H, 5.86; N, 3.88. Found: C, 56.50; H, 5.84; N, 3.73.
Monitoring the Photoreaction of Silyl Complexes 3a-d to
Give Silylene Complexes 1a-d. A Pyrex NMR tube equipped with
a ground joint was charged with a solution of silyl complex 3a (2
mg, 3 µmol) and cyclohexane (less than 1 mg, internal standard)
in benzene-d6 (0.5 mL). This NMR tube was attached to a vacuum
line and flame-sealed under high vacuum. The sealed tube was
irradiated with a 450 W medium-pressure Hg lamp immersed in a
water bath (ca. 5 °C), and the reaction was monitored by 1H NMR
spectroscopy. After irradiation for 1.75 min, the intensity of the
signal assignable to silylene complex 1a reached to a maximum
(63% NMR yield, 1a:3a ) 32:1).
Synthesis of Cp*(CO)2W(DMAP){Si(p-Tol)3} (3d). A sealed tube
(12 mm o.d.) of a toluene (3 mL) solution of 1d (79 mg, 0.099
mmol), prepared in a manner similar to that for the synthesis of
3a, was heated at 40 °C for 44 h. The reaction mixture was
transferred into a round-bottomed flask and evaporated to dryness.
The residue was washed with hexane to give 3d (76 mg, 0.095
1
mmol) as a yellow powder in 96% yield. H NMR (300 MHz,
C6D6): δ 1.68 (s, 15H, Cp*), 1.95 (s, 6H, NMe2), 2.03 (s, 3H, C6H4-
Me), 2.24 (s, 6H, C6H4Me), 5.34 (m, 2H, py-H), 7.05 (d, J ) 7.7
Hz, 2H, ArH), 7.22 (d, J ) 7.7 Hz, 4H, ArH), 8.17 (d, J ) 7.7 Hz,
4H, ArH), 8.26 (d, J ) 7.7 Hz, 2H, ArH), 8.29 (m, 2H, py-H).
13C{1H} NMR (75.5 MHz, C6D6): δ 10.9 (C5Me5), 21.2, 21.5
(C6H4Me), 38.0 (NMe2), 101.5 (C5Me5), 108.3, 127.9, 128.9, 136.0,
136.7, 137.5, 138.8, 141.6, 144.8, 153.3, 159.1 (aromatic carbons),
244.2 (CO). 29Si{1H} NMR (59.6 MHz, C6D6): δ 24.3. IR (KBr
pellet, cm-1) 1874 (m, νCOsym), 1786 (s, νCOasym). Anal. Calcd (%)
for C40H46N2O2SiW: C, 60.15; H, 5.80; N, 3.51. Found: C, 60.52;
H, 5.82; N, 3.38.
Photoreactions of silyl complex 3b-d were monitored by a
method analogous to that for 3a. For 3c, Si(SiMe3)4 (less than 1
mg) instead of cyclohexane was used as the internal standard. The
concentration of 3c was about a half of other silyl complexes 3a,
3b, and 3d because of its low solubility in C6D6. The NMR yields
were determined by comparing the intensity of the Cp* signal of
1
3a-d in the H NMR spectra to that of the internal standard. The
results are summarized in Table 8.
Kinetic Study on the Thermal Reaction of Silylene Complexes
1a-d to Form Silyl Complexes 3a-d. A Pyrex NMR tube equipped
with a ground joint was charged with a solution of silylene complex
X-Ray Crystal Structure Determination. Selected crystallo-
graphic data for 1c, 2, 3a, and 3d are summarized in Table 9. X-ray
quality single crystals were obtained from toluene (for 1c · 0.5C7H8
and 2 · 0.5C7H8 as yellow plates and red plates, respectively),
toluene/hexane (for 3a as yellow plates), and benzene-d6 (for
3d · 2C6D6 as yellow plates). Intensity data for the analysis were
collected on a Rigaku RAXIS-RAPID imaging plate diffractometer
with graphite monochromated Mo KR radiation (λ ) 0.71069 Å)
under a cold nitrogen stream (T ) 150 K). Numerical absorption
(18) Signals of four aromatic protons were overlapped with that of
C6D5H because complex 3c is only slightly soluble in C6D6. The low
solubility of 3c in C6D6 prevents us from measuring the 13C and 29Si NMR
spectra in C6D6. Thus, a CD2Cl2 solution was used to measure the 13C and
29Si NMR spectra of the major rotamer at 243 K. 3c is fluxtional in C6D6
and CD2Cl2 solutions (see text).

DMAP-Stabilized Aryl(silylene) and (Arylsilyl)(DMAP) Complexes
Organometallics, Vol. 28, No. 6, 2009 1799
corrections were applied to the data. The structures were solved
by the Patterson method using the DIRDIF-99 program20 and
refined by full matrix least-squares techniques on all F2 data with
SHELXL-97.21 For 2, the sites of the methyl ligand and a carbonyl
ligand were mutually disordered with the occupancy factors
61:39. In the case of 1c and 2, a toluene molecule, solvent of
crystallization, was disordered over two sites related by a 2-fold
rotation axis (for 1c) or an inversion center (for 2). Except for the
solvent molecules and the disordered atoms, anisotropic refinement
was applied to all non-hydrogen atoms, and all hydrogen atoms
were put at calculated positions. The disordered atoms and the atoms
of the crystal solvents were isotropically refined, and no hydrogen
atoms on these atoms were included. In the final difference Fourier
synthesis of silyl complex 3d, the residual peak of 3.48 e Å-3 was
observed within 0.87 Å of the tungsten atom. CCDC reference
numbers: 714828 (1c), 714829 (2), 714830 (3a), and 714831 (3d).
Crystallographic data are available as a CIF.
Acknowledgment. This work was supported by Grants-
in-Aid for Scientific Research (nos. 18350027, 18064003,
and 20750040) from the Ministry of Education, Culture,
Sports, Science and Technology of Japan.
Supporting Information Available: X-ray crystallographic data
as a CIF file. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM801140D
(20) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Garcia-Granda,
S.; Gould, R. O.; Israel, R.; Smits, J. M. M. The DIRDIF-99 Program
System; Crystallography Laboratory, University of Nijmegen: Nijmegen,
The Netherlands, 1999.
(21) Sheldrick, G. M. SHELXL-97, Programs for Refining X-ray Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(19) When we monitored the thermal reaction of 1d by 1H NMR
spectroscopy, we observed the signals of unidentified reaction intermediates,
which finally completely changed to silyl complex 3d.