Chemistry Letters Vol.32, No.1 (2003)
15
When the reactivity of 2a toward thiophene was examined in
C6D6, similar decomposition products were only observed.
Interestingly, however, the decomposition was slowed compared
to that in the absence of thiophene, suggesting that thiophene
might interact with 2a to restrain the decomposition.
To get information on the interaction, 2a was treated with
neat 3-methylthiophene (30 equiv) to minimize the decomposi-
tion (Scheme 3). After 3 days at room temperature, thienyl
exchange products 2b (16%) and free thiophene (16%) were
formed in addition to unchanged 2a (47%), although decomposi-
tion was not completely suppressed as shown by the formation of
This work was supported by a Grants-in-Aid for Scientific
Research from the Ministry of Education, Science, Sports, and
Culture of Japan.
References and Notes
1
For recent reviews, see: a) R. J. Angelici, Polyhedron, 16, 3073 (1997). b) W.
D. Jones, D. A. Vicic, R. M. Chin, J. H. Roache, and W. Myers, Polyhedron,
1
6, 3115 (1997). c) R. J. Angelici, Organometallics, 20, 1259 (2001).
2
C. Bianchini, J. A. Casares, R. Osman, D. I. Pattison, M. Peruzzini, R. N.
Perutz, and F. Zanobini, Organometallics, 16, 4611 (1997) and the
references cited therein.
3
A. L. Sargent and E. P. Titus, Organometallics, 17, 65 (1998) and the
references cited therein.
4a (11%) and minor unidentified products. Reversibility of the
4
a) H. Sakaba, K. Ishida, and H. Horino, Chem. Lett., 1998, 149. b) H. Sakaba,
M. Tsukamoto, T. Hirata, C. Kabuto, and H. Horino, J. Am. Chem. Soc., 122,
11511 (2000).
exchange reaction is demonstrated by the reaction of 2b with
thiophene (30 equiv) to give 2a (33%) and free 3-methylthio-
phene (32%) along with unchanged 2b (49%) and decomposition
5
In the following NMR data, 2-thienyl and 4-methyl-2-thienyl ligands are
abbreviated as T and MT, respectively. Satisfactory elemental analyses were
obtained for 3 and 4a,b, but could not for air-sensitive 2a,b. 2a,b-d3 were
ꢀ
10
products including Cp W(CO)3(2-C4H2S-4-Me) (4b) (6%)
under the same conditions. In contrast to the fairly clean reaction
of 1 with the thiophenes, the reactions of 2a,b suffered from the
formation of decomposition products probably due to the lesser
reactivity caused by steric hindrance of the thienyl ligands. The
higher yields of the exchange products and the lower yields of
decomposition products in the reaction of 2b with thiophene
compared to the reaction of 2a with 3-methylthiophene can be
related to the higher reactivity of thiophene compared to 3-
methylthiophene toward C–H bond activation by 1. In the
1
obtained by dissolving 2a,b in CD3CN. 2a: H NMR (400 MHz, C6D6) d
ꢀ
1
.08 (s, 3H, MeCN), 1.70 (s, 15H, Cp ), 7.35 (dd, J ¼ 4:9, 3.2Hz, 1H, T),
7.49 (dd, J ¼ 3:2, 0.7 Hz, 1H, T), 7.62(dd, J ¼ 4:9, 0.7 Hz, 1H, T). 2a-d :
3
13
C NMR (100 MHz, CD3CN) d 4.7 (septet, JCD ¼ 21 Hz, CD3CN), 10.6
C5Me5), 104.9 (C5Me5), 129.3 (T), 130.3 (T), 137.2 (T), 140.3 (CD3CN),
(
1
3
(
1
49.3 (T), 251.4 (CO), 257.8 (CO). 2b: H NMR (400 MHz, C6D6) d 0.97 (s,
ꢀ
H, MeCN), 1.72(s, 15H, Cp ), 2.33 (s, 3H, MT-Me), 7.19 (s, 1H, MT), 7.37
13
s, 1H, MT). 2b-d3: C NMR (100 MHz, CD3CN) d 4.8 (septet,
JCD ¼ 21 Hz, CD3CN), 10.7 (C5Me5), 15.3 (MT-Me), 105.0 (C5Me5),
1 26 .2(MT), 139.9 (MT), 140.2(CD 3CN), 140.5 (MT), 150.2(MT), 25 1.4
(CO), 258.0 (CO).
competitive reaction of 1 with a 1 : 1 mixture of the thiophenes
ꢂ
6
The reaction of 2a with PMe3 in C6D6 exclusively afforded cis-3, which
subsequently underwent slow isomerization to form an equilibrium mixture
with its trans isomer. An equilibrium ratio of cis-3 : trans-3 ¼ 4:6 : 1 was
obtained after 2days at room temperature. Cis-3 was isolated as yellow
(
2
10 equiv each) in toluene-d8 from ꢁ78 C to room temperature,
a and 2b were formed in a 2:8 : 1 ratio.
1
crystals in 46% yield in a preparative reaction. cis-3: H NMR (400 MHz,
ꢀ
S
S
C6D6) d 0.95 (d, JPH ¼ 8:8 Hz, 9H, PMe3), 1.73 (s, 15H, Cp ), 6.99 (dd,
W
+
W
+
JHH ¼ 3:1 Hz, JPH ¼ 2:4 Hz, 1H, T), 7.12(dd, JHH ¼ 4:9, 3.1 Hz, 1H, T),
OC
OC
NCMe
OC
OC
NCMe
13
7
1
1
.48 (dd, JHH ¼ 4:9 Hz, JPH ¼ 1:8 Hz, 1H, T); C NMR (100 MHz, C6D6) d
1.4 (C5Me5), 18.0 (d, JPC ¼ 31:4 Hz, PMe3), 103.1 (C5Me5), 131.1 (T),
S
S
31.2(T), 136.5 (d, JPC ¼ 29:2 Hz, T), 140.6 (d, JPC ¼ 7:5 Hz, T), 238.5 (br,
2a
2b
CO), 250.2 (br, d, JPC ¼ 24 Hz, CO). trans-3: H NMR (400 MHz, C6D6) d
1
ꢀ
Scheme 3.
1.16 (d, JPH ¼ 8:8 Hz, 9H, PMe3), 1.60 (s, 15H, Cp ), 7.24 (dd, JHH ¼ 4:9,
3
13
.2Hz, 1H, T), 7.52(d, JHH ¼ 4:9 Hz, 1H, T), 7.61 (d, JHH ¼ 3:2 Hz, 1H, T);
Similarly to the case of 1-d3, in CD3CN 2a-d3 and 2b-d3 are
stable and did not react with 3-methylthiophene and thiophene,
C NMR (100 MHz, C6D6) d 11.0 (C5Me5), 19.5 (d, JPC ¼ 31:4 Hz, PMe3),
102.3 (C Me ), 128.9 (T), 131.8 (d, J ¼ 9:7 Hz, T), 132.0 (T), 140.6 (d,
5
5
PC
ꢀ
respectively,
suggesting
Cp W(CO)2(2-C4H3S)
and
JPC ¼ 2:2 Hz, T), 237.3 (d, JPC ¼ 20:1 Hz, CO).
Crystal data for cis-3: C O PSW, monoclinic, space group P2 =a
ꢀ
7
8
19 27
H
2
1
Cp W(CO)2(2-C4H2S-4-Me) for the intermediates to activate
the C–H bonds of the thiophenes in the thienyl exchange
reactions. In the reaction of 2a with thiophene in C6D6, the
corresponding process would reproduce 2a and thiophene to
prevent the decomposition to some extent. Thus, acetonitrile
tungsten complexes 1 and 2 were found to undergo C–H bond
activation of thiophenes, and provide rare examples of tungsten
complexes active for C–S and/or C–H bond cleavage of
[
1
No. 14], a ¼ 16:016ð1Þ, b ¼ 8:4880ð8Þ, c ¼ 16:517ð3Þ Aꢀ , ꢁ ¼
ꢂ
ꢀ 3
ꢁ1
15:725ð2Þ , V ¼ 2022:8ð4Þ A , Z ¼ 4, m(Mo Ka) = 59.08 cm , Rigaku/
MSC Mercury CCD diffractometer, R ¼ 0:019 (RW ¼ 0:022) for 3284
observed reflections [I > 3:00sðIÞ].
For X-ray analyses of 2-thienyl complexes, see: a) L. Dong, S. B. Duckett, K.
F. Ohman, and W. D. Jones, J. Am. Chem. Soc., 114, 151 (1992). b) M.
Paneque, M. L. Poveda, V. Salazar, S. Taboada, E. Carmona, E. Guti e´ rrez-
Puebla, A. Monge, and C. Ruiz, Organometallics, 18, 139 (1999).
s-Bond metathesis might be conceivable as another possible mechanism.
4a,b were identified by spectral comparison with authentic samples prepared
9
1
1
1
thiophenes.
0
1
C–H bond activation of thiophene is often accompanied by
C–S bond activation, but 1 and 2 lack the latter reactivity. One
reason for this seems to be larger steric crowding at their metal
centers compared to those of complexes showing C–S bond
by the reactions of 2a,b with CO (1 atm) in benzene. 4a: H NMR (400 MHz,
ꢀ
C6D6) d 1.52(s, 15H, Cp ), 7.11 (dd, J ¼ 5:1, 3.4 Hz, 1H, T), 7.30 (dd,
13
J ¼ 3:4, 0.7 Hz, 1H, T), 7.43 (dd, J ¼ 5:1, 0.7 Hz, 1H, T); C NMR
(
1
100 MHz, C6D6) d 10.1 (C5Me5), 104.9 (C5Me5), 125.6 (T), 129.8 (T),
34.0 (T), 141.2 (T), 222.0 (CO) 232.5 (CO). 4b: H NMR (400 MHz, C6D6)
ꢀ
13
1
ꢀ
activation reactivity: Cp W(CO)2R (R = Me, 2-C4H3S, 2-
d 1.55 (s, 15H, Cp ), 2.19 (s, 3H, MT-Me), 7.01 (s, 1H, MT), 7.15 (s, 1H,
MT); C NMR (100 MHz, C6D6) d 10.2(C 5Me5), 15.2(MT- Me), 104.9
(C5Me5), 126.1 (MT), 130.0 (MT), 140.2 (MT), 143.8 (MT), 221.9 (CO),
ꢀ
C4H2S-4-Me) from 1 and 2 vs Cp Rh(PMe3) from a typical C–S
ꢀ
12
bond activator Cp Rh(PMe3)(Ph)H, for example. It has been
suggested that large steric crowding at a metal center favors C–H
bond activation, although the change of electron density on a
2
32.7 (CO).
1
1
a) C–S and C–H bond activation: W. D. Jones, R. M. Chin, T. W. Crane, and
D. M. Baruch, Organometallics, 13, 4448 (1994). b) C–S bond activation: R.
C. Mills, K. A. Abboud, and J. M. Boncella, Chem. Commun., 2001, 1506.
2
metal center also affects the reactivity. Further reactivity studies
of 2 are now under way.
12W. D. Jones and L. Dong, J. Am. Chem. Soc., 113, 559 (1991).