Three- and five-membered W/C/N metallacycles formed by incorporation of acetonitrile molecules into silyltungsten intermediates

Article abstract of DOI:10.1021/om700514d

Treatment of Cp*(CO)₂W(NCMe)Me (Cp* = η⁵-C₅Me₅) with HSiR₃ (R = Et, p-Tol) afforded N-silylated η²-iminoacyl tungsten complexes Cp*(CO)₂W{κ²(C,N)-C(Me)= N(SiR₃)} (1a, R = Et; 1b, R = p-Tol). Analogous reactions in the presence of excess acetonitrile for a prolonged reaction time led to the formation of five-membered metallacycles Cp*(CO)₂W{κ²(C,N)-C(Me)=N-C(Me) =N(H)} (2) and Cp*(CO)₂W{κ²(C,N)-C(CH ₂SiR₃)=N-C(Me)=N(H)} (3, R = p-Tol) through a C-N coupling of nitrile molecules and migration of a silyl group.

Full text of DOI:10.1021/om700514d

Organometallics 2007, 26, 4379-4382
4379
Three- and Five-Membered W/C/N Metallacycles Formed by
Incorporation of Acetonitrile Molecules into Silyltungsten
†
Intermediates
‡
‡
§
,‡
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 May 24, 2007
Summary: Treatment of Cp*(CO)2W(NCMe)Me (Cp*
η -C5Me5) with HSiR3 (R ) Et, p-Tol) afforded N-silylated
)
Scheme 1
5
2
2
η -iminoacyl tungsten complexes Cp*(CO)2W{κ (C,N)-C(Me)d
N(SiR3)} (1a, R ) Et; 1b, R ) p-Tol). Analogous reactions
in the presence of excess acetonitrile for a prolonged reac-
tion time led to the formation of fiVe-membered metallacy-
2
cles Cp*(CO)2W{κ (C,N)-C(Me)dN-C(Me)dN(H)} (2) and
2
Cp*(CO)2W{κ (C,N)-C(CH2SiR3)dN-C(Me)dN(H)} (3, R )
p-Tol) through a C-N coupling of nitrile molecules and
migration of a silyl group.
Transition-metal-mediated transformation of nitriles, e.g.,
insertion, coupling, C-N or C-C bond formation, and cyclo-
addition, is of considerable interest because of its potential
application for the synthesis of nitrogen-containing organic
1
2
compounds. Recently, a new type of reaction between transi-
describe the synthesis of N-silylated η -iminoacyl tungsten
complexes, having a three-membered metallacycle structure, by
treatment of Cp*(CO)2W(NCMe)Me with tertiary silanes, and
also their unexpected ring expansion to W-C-N-C-N five-
membered metallacycles by treatment with an excess amount
of acetonitrile.
tion-metal silyl complexes and nitriles has been discovered, and
2
,3
its application to a catalytic reaction has been investigated.
In this reaction, importantly the C-C bond cleavage of nitriles
resulted in the formation of silylisocyanide complexes having
an alkyl or aryl ligand. A key intermediate of this reaction is a
2
N-silylated η -iminoacyl complex derived from a silyl-nitrile
Reaction of Cp*(CO)2W(NCMe)Me, prepared by irradiation
of Cp*(CO)3WMe in acetonitrile, with HSiEt3 in acetonitrile
or HSi(p-Tol)3 in toluene at room temperature gave N-silylated
η -iminoacyl complexes Cp*(CO)2W{κ (C,N)-C(Me)dN(SiR3)}
[1a, R ) Et (74%); 1b, R ) p-Tol (59%)] (Scheme 1). The
products were characterized by analytical and spectroscopic
complex through insertion of the nitrile into a metal-silicon
2
bond. We recently reported the formation of a N-silylated η -
2
2
iminoacyl complex by the reaction of a tungsten complex
3
containing the hemilabile κ (Si,Si,O)-bis(silyl) ligand xantsil with
4
t-BuCN. As an extension of our study on nitrile activation
8,9
chemistry mediated by metal silyl complexes, we focused on
the tungsten methyl acetonitrile complex Cp*(CO)2W(NCMe)-
methods. This transformation can be explained by the mech-
5
(6) (a) Sakaba, H.; Ishida, K.; Horino, H. Chem. Lett. 1998, 149. (b)
Sakaba, H.; Sanae, W.; Kabuto, C.; Kabuto, K. J. Am. Chem. Soc. 2003,
25, 2842. (c) Sakaba, H.; Yoshida, M.; Kabuto, C.; Kabuto, K. J. Am.
Chem. Soc. 2005, 127, 7276.
7) Okazaki, M.; Suzuki, E.; Miyajima, N.; Tobita, H. Organometallics
Me as a useful precursor of tungsten silyl acetonitrile com-
plexes, because the lability of the MeCN ligand facilitates
1
oxidative addition of silanes.6 In this communication, we
,7
(
†
This paper is dedicated to the late Professor Yoshihiko Ito for his
2003, 22, 4633.
outstanding contribution to synthetic chemistry and organometallic chem-
istry.
(8) Data for 1a: 1H NMR (300 MHz, C6D6, room temperature): δ 0.47-
0.68 (m, 6 H, SiCH2CH3), 0.84 (t, J ) 7.8 Hz, 9 H, SiCH2CH3), 1.83 (s,
15 H, Cp*), 2.42 (s, 3 H, NdCMe). 13C{ H} NMR (75.5 MHz, C6D6, room
temperature): δ 4.8, 6.9 (SiEt), 11.3 (C5Me5), 22.4 (NdCMe), 104.1
1
*
Author to whom correspondence should be addressed. Tel: +81-22-
7
95-6539. Fax: +81-22-795-6543. E-mail: tobita@mail.tains.tohoku.ac.jp.
‡
29
1
Tohoku University.
Kyoto University.
(C5Me5), 228.7 (JW-C ) 53 Hz, NdCMe), 242.1, 246.0 (CO). Si{ H}
NMR (59.6 MHz, C6D6, room temperature): δ 15.2. IR (C6D6): 1901 (s,
§
-
1
+
(
1) (a) Michelin, R. A.; Mozzon, M.; Bertani, R. Coord. Chem. ReV.
νCO), 1801 (s, νCO), 1637 (w, νCN) cm . EI-MS (70 eV): m/z 531 (M ,
+
1
2
996, 147, 299. (b) Kukushkin, V. Yu.; Pombeiro, A. J. L. Chem. ReV.
002, 102, 1771.
17), 503 (M - CO, 15), 473 (100). Exact mass (EI) for C20H33NO2SiW:
calcd m/z 531.1784, found m/z 531.1779. Contamination with trace of
impurities has prevented correct elemental analysis.
(2) (a) Taw, F. L.; White, P. S.; Bergman, R. G.; Brookhart, M. J. Am.
Chem. Soc. 2002, 124, 4192. (b) Taw, F. L.; Mueller, A. H.; Bergman, R.
G.; Brookhart, M. J. Am. Chem. Soc. 2003, 125, 9808. (c) Klei, S. R.; Tilley,
T. D.; Bergman, R. G. Organometallics 2002, 21, 4648. (d) Nakazawa, H.;
Kawasaki, T.; Miyoshi, K.; Suresh, C. H.; Koga, N. Organometallics 2004,
(9) Data for 1b: 1H NMR (300 MHz, C6D6, room temperature): δ 1.79
(s, 15 H, Cp*), 2.06 (s, 9 H, C6H4Me), 2.49 (s, 3 H, NdCMe), 7.04 (d, J
1
3
1
) 7.7 Hz, 6 H, Ar-H), 7.63 (d, J ) 7.7 Hz, 6 H, Ar-H). C{ H} NMR
(75.5 MHz, C6D6, room temperature): δ 11.2 (C5Me5), 21.5 (C6H4Me),
23.9 (NdCMe), 104.3 (C5Me5), 129.3, 129.8, 136.3, 140.5 (aromatic
carbons), 235.2 (JW-C ) 53 Hz, NdCMe), 242.4, 244.8 (br, CO).
2
2
3, 117. (e) Hashimoto, H.; Matsuda, A.; Tobita, H. Organometallics 2006,
5, 472.
29
1
(
3) (a) Nakazawa, H.; Kamata, K.; Itazaki, M. Chem. Commun. 2005,
Si{ H} NMR (59.6 MHz, C6D6, room temperature): δ -17.9. IR (KBr-
-1
4
004. (b) Itazaki, M.; Nakazawa, H. Chem. Lett. 2005, 34, 1054. (c) Tobisu,
pellet): 1894 (s, νCO), 1792 (s, νCO), 1620 (m, νCN) cm . EI-MS (70 eV):
+
+
+
M.; Kita, Y.; Chatani, N. J. Am. Chem. Soc. 2006, 128, 8152.
m/z 717 (M , 15), 659 (13), 645 (M - 2 CO - MeH, 19), 620 (M - 2
CO - MeCN, 100). Anal. Calcd for C35H39NO2SiW: C, 58.58; H, 5.48;
N, 1.95. Found: C, 59.16; H, 5.74; N, 1.77.
(
(
4) Begum, R.; Komuro, T.; Tobita, H. Chem. Commun. 2006, 432.
5) Sakaba, H.; Ishida, K.; Horino, H. Chem. Lett. 1995, 1145.
1
0.1021/om700514d CCC: $37.00 © 2007 American Chemical Society
Publication on Web 07/24/2007

4
380 Organometallics, Vol. 26, No. 18, 2007
Communications
Chart 1
Scheme 2
Figure 1. Molecular structure of 1b (50% probability ellipsoids).
Hydrogen atoms are omitted for clarity. Selected bond distances
(
)
Å) and angles (deg): W-N ) 2.215(7), W-C3 ) 2.086(9), Si-N
1.750(8), N-C3 ) 1.266(12); W-N-Si ) 149.4(4), W-N-
C3 ) 67.4(5), N-W-C3 ) 34.1(3), Si-N-C3 ) 140.4(7),
W-C3-N ) 78.5(6), W-C3-C4 ) 152.6(7), N-C3-C4 )
resonance hybrid of 1 (Chart 1) is fairly high. The W-N bond
of 1b [2.215(7) Å] is slightly longer than that of the N-alky-
1
28.8(9).
2
5
2
lated η -iminoacyl complex (η -C9H7)(CO)2W{κ (C,N)-C(Me)d
anism involving oxidative addition of HSiR3, reductive elimina-
tion of MeH, coordination of acetonitrile, and final silyl migra-
tion to nitrogen (Scheme 1). Since the reaction of Cp*(CO)2W-
1
2
N(t-Bu)} [2.144(5) Å]. This elongation of the W-N bond is
probably due to the larger steric repulsion between the bulky
silyl group on the N atom and the Cp*(CO)2W{C(Me)dN}
moiety in 1b: the distances between the aryl carbon C5 on a
p-Tol group and the methyl carbon C33 on Cp* [3.877(14) Å]
and between the methyl carbon C4 bonded to the iminoacyl
carbon and the aryl carbon C19 on a p-Tol group [3.632(14)
Å] are comparable to the sum (3.7 Å) of the van der Waals
radii of the methyl group (2.0 Å) and the half-thickness of the
(
NCMe)Me with HSi(p-Tol)3 in acetonitrile at room temperature
afforded not only 1b but also the five-membered-ring complex
that was derived by the reaction of 1b with acetonitrile (Vide
2
infra), toluene was used as a solvent for the synthesis of 1b.
This higher reactivity of 1b compared to that of 1a toward
acetonitrile can be rationalized by the decrease in the electron-
releasing character of the group (p-Tol)3Si compared to Et3Si
that facilitates the substitution of the coordinated iminoacyl
nitrogen with an acetonitrile molecule. In contrast to N-silylated
1
3
plane of the aromatic rings (1.7 Å).
2
The lability of η -iminoacyl complex 1b in acetonitrile
prompted us to investigate the thermal reactions of both 1a and
1b with excess acetonitrile. Heating of a mixture of isolated
2
η -iminoacyl complexes of groups 8 and 9 metals, where C-C
2
bond scission occurs rapidly at room temperature, complexes
2
η -iminoacyl complex 1a and a large excess of acetonitrile in
1
did not show any sign of decomposition in C6D6 at room
1
C D at 40-70 °C afforded five-membered-ring complex
temperature over 2 days, according to their H NMR spectra.
6
6
2
2
Cp*(CO) W{κ (C,N)-C(Me)dN-C(Me)dN(H)} (2) as a major
The structure of η -iminoacyl complex 1b was confirmed by
2
product. A preparative-scale one-pot synthesis of 2 in 69%
X-ray crystal structure analysis (Figure 1), where 1b adopts a
isolated yield was achieved by the thermal reaction of a mixture
of Cp*(CO) W(NCMe)Me and HSiEt in acetonitrile (ca. 300
equiv) at 70 °C for 2 days, where the η -iminoacyl complex 1a
should be generated transiently (Scheme 2). This reaction
involves incorporation and coupling of two acetonitrile mol-
ecules. We observed silyl nitrile Et SiCH CN as a silicon-
3 2
containing byproduct in the NMR and IR spectra of the reaction
mixture.
On the other hand, the thermal reaction of isolated η2-
iminoacyl complex 1b with a large excess of acetonitrile in C6D6
at 40 °C for 3 days, which was monitored by 1H NMR
spectroscopy, mainly afforded a 1:1 mixture of complex 2 and
four-legged piano-stool geometry: the tungsten center possesses
2
one Cp*, two carbonyls, and one η -iminoacyl ligand having a
2
3
2
silyl group on the nitrogen atom. The bond distances and angles
in the W-C-N three-membered ring are comparable with those
2
in the previously reported tungsten N-silylated η -iminoacyl
3
4
complex Cp*(CO)(H)W{κ (C,N,Si)-C(t-Bu)dN(xantsil)}. It is
noteworthy that the crystal structure analysis of N-silylated
1
4
2
η -iminoacyl complexes has been limited to only two ex-
4
2b
amples: tungsten and cationic rhodium complexes. The short
W-C(iminoacyl) bond distance [2.086(9) Å] is similar to that
of the carbene complex Cp*(CO)2(Cl)W{dC(H)NEt2} [2.141-
3) Å].10 Moreover, the C{ H} NMR spectra of 1a and 1b
13
1
(
show the resonances of the iminoacyl carbons at 228.7 ppm
for 1a and 235.2 ppm for 1b with 183W satellites [JW-C ) 53
(11) James Daff, P.; Monge, A.; Palma, P.; Poveda, M. L.; Ruiz, C.;
Valerga, P.; Carmona, E. Organometallics 1997, 16, 2263.
(
1a), 53 (1b) Hz]. These resonances are even more downfield-
(12) Amador, U.; James Daff, P.; Poveda, M. L.; Ruiz, C.; Carmona, E.
2
shifted than those of N-alkylated η -iminoacyl tungsten com-
plexes Cp*(CO)2W{κ (C,N)-C(Me)dN(R)} [195.5 (R ) t-Bu),
1
J. Chem. Soc., Dalton Trans. 1997, 3145.
(13) Pauling L. The Nature of the Chemical Bonds, 3rd ed.; Cornell
2
1
1
University Press: Ithaca, New York, 1960; pp 257-264.
95.9 (R ) i-Pr) ppm]. These observations imply that the
1
(
14) Et3SiCH2CN was identified on the basis of comparisons of its H,
contribution of the amido-carbene canonical structure B in the
13
1
29
1
C{ H}, and Si{ H} NMR and IR spectra with those of the authentic
sample that was prepared by a method analogous to that for the preparation
of (t-Bu)Me2SiCH2CN: Furuta, K.; Ishiguro, M.; Haruta, R.; Ikeda, N.;
Yamamoto, H. Bull. Chem. Soc. Jpn. 1984, 57, 2768.
(
10) Filippou, A. C.; Portius, P.; Winter, J. G.; Koiciok-K o¨ hn, G. J.
Organomet. Chem. 2001, 628, 11.

Communications
Organometallics, Vol. 26, No. 18, 2007 4381
silyl-containing five-membered-ring complex Cp*(CO)2W[κ2-
(C,N)-C{CH2Si(p-Tol)3}dN-C(Me)dN(H)] (3). The prepara-
tive-scale reaction of Cp*(CO)2W(NCMe)Me with HSi(p-Tol)3
in acetonitrile (ca. 300 equiv) at 60 °C for 20 h gave 2 as a
major product, but the formation of 3 was considerably inhibited
(2:3 ) 16:1). Isolation of 2 from the reaction mixture was
unsuccessful owing to the difficulty of the separation from minor
products, namely, complex 3 and unidentified byproducts.
Taking into account the NMR-scale reaction in C6D6 that gave
the 1:1 mixture of 2 and 3, we also investigated the preparative-
scale reaction under similar conditions in which acetonitrile was
diluted in toluene, to improve the formation of complex 3. Thus,
the reaction of Cp*(CO)2W(NCMe)Me, HSi(p-Tol)3, and a large
excess (ca. 40 equiv) of acetonitrile in toluene (1:2 volume ratio
of acetonitrile to toluene) at room temperature for 8 days gave
a 1:1.3 ratio of 2 and 3 (Scheme 2). Only complex 3 was isolated
in pure form in 34% yield by recrystallization from the mixture.
The reason for the formation of the 3-type complex only in the
case of (p-Tol)3Si derivative 1b and also the reason for the
alteration in the ratio of products 2 and 3 depending on the
concentrations of acetonitrile in solution are closely related to
the reaction mechanism (Vide infra), but are not clear so far.
The characterization of five-membered-ring complexes 2 and
Figure 2. Molecular structure of 3 (50% probability ellipsoids).
Hydrogen atoms bound to carbon atoms are omitted for clarity.
Selected bond distances (Å) and angles (deg): W-N2 ) 2.112-
(
5), W-C3 ) 2.164(6), N1-C3 ) 1.335(8), N1-C4 ) 1.364(7),
N2-C4 ) 1.303(8); W-N2-C4 ) 119.3(4), W-C3-N1 ) 119.5-
4), N2-W-C3 ) 70.9(2), C3-N1-C4 ) 112.0(5), N1-C4-
N2 ) 118.2(5).
(
3
was performed by analytical, spectroscopic, and crystal-
15-17
lographic methods.
The X-ray crystal structure analysis
Chart 2
established the molecular structure of 3 shown in Figure 2.
Complex 3 adopts a four-legged piano-stool geometry: the
tungsten center possesses one Cp*, two carbonyls, and a
2
κ (C,N)-bidentate ligand. The sum of the interior angles of the
chelate ring is 540(2)°, as expected for a planar five-membered
metallacycle. A similar five-membered ring was structurally
5
2
characterized for the iron complex (η -C5H5)(CO)Fe{κ (C,N)-
19
C(CF3)dN-C(CF3)dN(H)}.18 On the other hand, the bond
N(Et)} [W-C(ring) 2.179(6) Å; W-N 2.160(5) Å]. The
1
3
1
downfield-shifted C{ H} NMR signals of W-C(ring) [273.6
2), 276.1 (3) ppm] also indicate their strong carbene-ligand
lengths of W-C3 [2.164(6) Å] and W-N2 [2.112(5) Å] are
(
comparable to those of the five-membered-ring carbene complex
2
character. The C-N bond distances in the five-membered
chelate ring of 3 are comparable with those in common
π-conjugated heterocycles (1.35 Å), and the difference among
of tungsten Cp*(CO)2W{κ (C,N)-C(NHEt)-C(H)dC(H)-
20
(
15) Data for 2: 1H NMR (300 MHz, C6D6, room temperature): δ
.62 (s, 15 H, Cp*), 2.29 (s, 3 H, NdCMe), 3.18 (s, 3 H, W-CMe), 7.98
1
(
1
(
them is relatively small, implying the π-electron delocalization
within the ring. Thus, we propose considerable contribution of
the amido-carbene canonical structure D as well as the alkyl-
imino canonical structure C (Chart 2).
1
3
1
br, 1 H, NH). C{ H} NMR (75.5 MHz, C6D6, room temperature): δ
0.4 (C5Me5), 21.4 (NdCMe), 40.9 (W-CMe), 102.6 (C5Me5), 177.4
NdC-N), 240.9 (br, CO), 273.6 (JW-C ) 75 Hz, W-CMe). IR (C6D6):
-
1
+
1
940 (s, νCO), 1861 (s, νCO) cm . ESI-MS: m/z 459 (M + H). Anal.
Calcd for C16H22N2O2W: C, 41.94; H, 4.84; N, 6.11. Found: C, 41.45; H,
.97; N, 5.90.
16) We could not get crystals of 2 suitable for a full X-ray analysis,
1
In the H NMR spectrum of 3 in toluene-d8, one broad signal
4
(4.06 ppm) assignable to the CH2 moiety was observed at room
(
but a tentative analysis using a poor-quality crystal of 2 revealed a piano-
stool structure containing a five-membered metallacycle. Crystal data for
temperature, while this signal changed to two inequivalent
doublets (3.85, 4.32 ppm; J ) 14.8 Hz) at 253 K. Furthermore,
2
(
: formula C16H22N2O2W, M ) 458.21, monoclinic, space group P21/c
1
3
1
the CO signals of 3 in C{ H} NMR, which did not appear at
room temperature, were observed as two signals (239.2, 244.3
ppm) at 253 K. These observations suggest the existence of a
dynamic process involving the inversion of the chiral tungsten
No. 14), a ) 19.3351(14) Å, b ) 10.2804(4) Å, c ) 18.4975(13) Å, â )
3
1
10.6676(17)°, V ) 3440.2(4) Å , Z ) 8, R1 (all data) ) 0.158, wR2 (all
data) ) 0.218.
(
17) Data for 3: 1H NMR (300 MHz, C6D6, room temperature): δ 1.55
(
s, 15 H, Cp*), 2.10 (s, 12 H, C6H4Me + NdCMe), 4.12 (br, 2 H, CH2Si),
1
3
1
center on the NMR time scale. The C{ H} NMR spectrum of
2 at room temperature exhibits one broad signal assignable to
CO, which suggests the existence of a dynamic behavior
analogous to that of 3.
7
6
.10 (d, J ) 8.1 Hz, 6 H, Ar-H), 7.42 (br, 1 H, NH), 7.92 (d, J ) 8.1 Hz,
1
H, Ar-H). H NMR (300 MHz, toluene-d8, 253 K): δ 1.54 (s, 15 H,
Cp*), 2.12 (s, 12 H, C6H4Me + NdCMe), 3.85 (d, J ) 14.8 Hz, 1 H,
CH2Si), 4.32 (d, J ) 14.8 Hz, 1 H, CH2Si), 7.10 (d, J ) 7.8 Hz, 6 H,
13
1
Ar-H), 7.39 (br, 1 H, NH), 7.93 (d, J ) 7.8 Hz, 6 H, Ar-H). C{ H}
NMR (75.5 MHz, C6D6, room temperature): δ 10.3 (C5Me5), 21.1
A possible mechanism for the formation of 2 from 1 is
(
NdCMe), 21.4 (C6H4Me), 45.1 (CH2Si), 102.3 (C5Me5), 128.5, 134.7,
2
illustrated in Scheme 3. The coordinated N atom of the η -
1
37.1, 138.4 (aromatic carbons), 176.9 (NdCMe), 276.1 (W-CdN), no
signal assignable to CO was observed because of dynamic behavior.
C{ H} NMR (75.5 MHz, toluene-d8, 253 K): δ 10.3 (C5Me5), 21.3
NdCMe), 21.6 (C6H4Me), 44.8 (CH2Si), 102.2 (C5Me5), 134.5, 137.1, 138.4
1
iminoacyl ligand of 1 is substituted by MeCN to give an (η -
1
3
1
iminoacyl)-nitrile complex 4. The lability of the iminoacyl
nitrogen atom of 1 is attributable to the ring strain. Nucleophilic
attack of the iminoacyl nitrogen on the electrophilic CN carbon
of the acetonitrile ligand results in the C-N bond formation to
(
(
aromatic carbons, one of the signals is overlapped with those of toluene-
29
1
d8), 176.8 (NdCMe), 239.2, 244.3 (CO), 275.7 (W-CdN). Si{ H} NMR
(
59.6 MHz, C6D6, room temperature): δ -12.3. IR (C6D6): 1940 (s, νCO),
-
1
+
1
861 (s, νCO) cm . ESI-MS: m/z 759 (M + H). Anal. Calcd for
C37H42N2O2SiW: C, 58.58; H, 5.58; N, 3.69. Found: C, 58.87; H, 5.57;
N, 3.62.
(19) Filippou, A. C.; V o¨ lkl, C.; Kiprof, P. J. Organomet. Chem. 1991,
415, 375.
(
18) Bottrill, M.; Goddard, R.; Green, M.; Hughes, R. P.; Lloyd, M. K.;
(20) International Tables for X-Ray Crystallography; D. Reidel: Dor-
drecht, The Netherlands, 1985; Vol. III, pp 275-276.
Taylor, S. H.; Woodward, P. J. Chem. Soc., Dalton Trans. 1975, 1150.

4
382 Organometallics, Vol. 26, No. 18, 2007
Communications
Scheme 3. Plausible Mechanism for the Formation of 2
tion or Vice Versa, cannot be ruled out. The resulting ketene
imine can be rearranged to the silyl nitrile R3SiCH2CN, because
the thermal 1,3-rearrangement of ketene imines to nitriles is
known for N-(arylmethyl)diphenylketene imines. The forma-
tion mechanism for 3 is not clear, but the first stage (formation
of a five-membered-ring complex 5) would be the same as that
for 2. In both cases, a possible driving force of the transforma-
tion is the formation of a resonance-stabilized, π-conjugated
ring system.
2
3
In conclusion, we demonstrated a novel reaction sequence
of the insertion and C-N coupling of acetonitrile molecules
via tungsten silyl complexes. The reaction of Cp*(CO)2W-
2
(
NCMe)Me with HSiR3 (R ) Et, p-Tol) gave η -iminoacyl
complexes 1, which are thermally stable in C6D6 at room
temperature. A further reaction of 1 with acetonitrile afforded
complexes 2 and 3, both of them having a five-membered C,N-
chelate ring. The formation of the five-membered metallacycles
2
through incorporation of acetonitrile into the η -iminoacyl
complexes is unprecedented. In contrast, the formation of similar
M-C-N-C-N five-membered metallacycles via the reaction
of low-valent iron and iridium complexes with electrophilic
trifluoroacetonitrile has been explained by the completely
different mechanism involving consecutive electrophilic attacks
1
8
of two trifluoroacetonitrile molecules. Further studies on
formation mechanisms of the five-membered-ring complexes
and reactivity of the isolated iminoacyl complexes 1 are in
progress.
give the five-membered-ring complex 5. As an example of a
similar reaction, Werner et al. have reported the [3+2]-
cycloaddition of the cationic isocyanide-methyl cobalt complex
5
Acknowledgment. This work was supported by Grants-in-
Aid for Scientific Research (Nos. 18350027 and 18064003) from
the Ministry of Education, Culture, Sports, Science and Tech-
nology of Japan.
[
(η -C5H5)(PMe3)Co(CNMe)Me]I with acetonitrile mediated by
1
21
an (η -iminoacyl)-nitrile complex. For the next step, we
propose a concerted reaction between intermediate 5 and an
external acetonitrile molecule via a cyclic transition state that
leads to the formation of complex 2 and a N-silylated ketene
imine molecule. This reaction involves deprotonation of the
acetonitrile molecule by the basic imino nitrogen of the five-
membered ring in 5 and nucleophilic attack of the nitrile nitrogen
on the silicon atom of 5. Legzdins et al. have proposed that the
basic imino nitrogen in the intermediary generated W-C-C-
C-N five-membered-ring complex can deprotonate cyclopen-
Supporting Information Available: Text giving synthetic
procedures and characterization data as a PDF file; X-ray crystal-
lographic data as a CIF file. These materials are available free of
charge via the Internet at http://pubs.acs.org.
OM700514D
2
2
tadiene. However, an alternative pathway from 5 to 2 by a
(
22) Legzdins, P.; Lumb, S. A.; Young, V. G., Jr. Organometallics 1998,
7, 854.
23) (a) Singer, L. A.; Lee, K. W. J. Chem. Soc., Chem. Commun. 1974,
stepwise reaction, namely, desilylation followed by deprotona-
1
(
(
21) (a) Werner, H.; Heiser, B.; K u¨ hn, A. Angew. Chem., Int. Ed. Engl.
962. (b) Lee, K.-W.; Horowitz, N.; Ware, J.; Singer, L. A. J. Am. Chem.
Soc. 1977, 99, 2622. (c) Clarke, L. F.; Hegarty, A. F.; O’Neill, P. J. Org.
Chem. 1992, 57, 362.
1
1
981, 20, 300. (b) Heiser, B.; K u¨ hn, A.; Werner, H. Chem. Ber. 1985, 118,
531.