H
H
R1
R2
C
C
4
R2
H
R1
R2
R1
R1
H
H
N2
C
CH2
Ru(η-C5H5)
C
C
C
C
(η-C5H5)Ru
R2
R2 = H
H
2
H
C
(η-C5H5)Ru
Ru(η-C5H5)
C
O
N
O
room temp., < 5 min
C
(η-C H )Ru
5
5
Ru(η-C H )
5
5
H
C
O
C
O
Me
1
C
C
O
O
3
7
2
–N2
R1
rotation slow
R1
C
H
R1
R2
R1
R2
H
H
C
C
H2C
η-C5H5)Ru
C
H2C
R2 = H
H
C
C
(
Ru(η-C5H5)
(η-C5H5)Ru
Ru(η-C5H5)
R2
(η-C5H5)Ru
Ru(η-C5H5)
C
C
O
C
C
O
H
O
C
O
C
O
O
8
9
Ru
Ru
3′ (not detected)
7′
R1 = SiMe3, R2 = H
H
H
H
H
C
C
C
Me3Si
C
H
(
η-C5H5)Ru
Ru(η-C5H5)
Me3Si
Ru
H
C
O
C
O
Ru
c′
7
6
5 5
Scheme 3 Ru = Ru(h-C H ); 8 = coordinatively unsaturated site
2 2 2
); IR (in CH Cl
) 1961, 1913 cm21. 3b (major
The specific alkylidene coupling and rearrangement can be
interpreted in terms of the reaction mechanisms summarized in
Scheme 3, involving the coordinatively unsaturated alkene spe-
cies 7 as a key intermediate. Oxidative addition of a C–H bond
in 7 would lead to the m-alkenyl complex 3, while in the case of
the reaction with disubstituted diazoalkane (2f, g), the alkene 4
may be eliminated from the diruthenium centre due to the steric
repulsion. The absence of the regioisomer 3A and the results of
the labelling experiments indicate that the C–H oxidative
addition giving 3 must take place before the unsymmetrical
structural information of 7 is lost (e.g. via rotation of the alkene
ligand leading to 7A). Because (i) the di(m-alkylidene) complex
(t, J 156 Hz, m-CHNCH
isomer), d (in C ) 8.34 (1 H, d, J 11.7 Hz, m-CHNCH), 4.76, 4.47 (5 H
2, s 3 2, C ), 3.54 (1 H, dq, J 5.9, 11.7 Hz, m-CHNCH), 1.61 (3 H, d,
J 5.9 Hz, CH
(in CDCl
2, C 3 2), 2.55 (1 H, d, J 13.9 Hz, m-CHNCH), 214.83 (1 H, s, m-H);
IR (in CH
H
6 6
D
H
5 5
3
2
1
3
), 214.44 (1 H, s, m-H); IR (in CH
2 2
Cl ) 1954, 1911 cm . 3c,
d
H
3
) 8.78 (1 H, d, J 13.9 Hz, m-CH = CH), 5.06, 4.89 (5 H 3 2, s
3
5 5
H
21
2
Cl
2
H 6 6
) 1958, 1908 cm . 3d (major isomer), d (in C D ) 9.36 (1
H, d, J 12.5 Hz, m-CHNCH), 7.2–7.0 (5 H, m, Ph), 4.80, 4.26 (5 H 3 2, s 3
2, C H 3 2), 4.64 (1 H, d, J 12.5 Hz, m-CHNCH), 214.43 (1 H, s, m-H); IR
5
5
2
1
(in CH
2
Cl
2
) 1958, 1915 cm . 3e (major isomer), d
H
(in CDCl
3
) 10.04 (1
3 2), 4.18
), 3.55 (1 H, d, J 11.7 Hz, m-CHNCH), 1.29 (3
), 215.04 (1 H, s, m-H); IR (in CH Cl ) 1973, 1923,
H, d, J 11.7 Hz, m-CHNCH), 5.20, 4.91 (5 H 3 2, s 3 2, C
2 H, q, J 6.8 Hz, OCH CH
H, t, J 6.8 Hz, OCH CH
2
5 5
H
(
2
3
2
3
2
2
1
1
700 cm ..
5
does not undergo C–C coupling under the present reaction
‡
Complex 3 (except for 3c) is composed of two isomers arising from the
and CO ligands) with
conditions and (ii) the symmetrical structure of 5 cannot explain
5 5
different configurations of the Ru auxiliaries (C H
respect to the Ru (m-CHNCHR )(m-H) core.
1
the results of the labelling experiments, the unsymmetrical h -
1
5
2
alkylidene-m-alkylidene species 8 and the dimetallacyclobutane
9
are plausible precursors of 7. The different reactivities of
References
complexes 8 and 5, which have the same composition, may be
attributed to the relative facility of migratory insertion cf.
reductive elimination. Finally, thermolysis of the b-silylethenyl
derivative 3c is proposed to occur via reductive elimination to
regenerate 7 with subsequent rotation of the alkene ligand (7cA)
followed by oxidative addition of the Si–C bond giving rise to
the silyl–ethenyl complex 6.
1
See, for example: J. P. Collman, L. S. Hegedus, J. R. Norton and Finke,
Principles and Applications of Organotransition Metal Chemistry,
University Science Books, Mill Valley, CA, 1987; G. W. Parshall and
S. D. Ittel, Homogeneous Catalysis, 2nd edn., Wiley-Interscience, New
York, 1992.
2
3
(a) H. Berke and R. Hoffmann, J. Am. Chem. Soc., 1978, 100, 7224; (b)
B. E. R. Schilling, R. Hoffmann and D. L. Lichtenberger, J. Am. Chem.
Soc., 1979, 101, 585; (c) N. M. Kostic and R. F. Fenske, J. Am. Chem.
Soc., 1982, 104, 3879.
W. A. Herrmann, (a) Adv. Organomet. Chem., 1982, 20, 159; (b)
J. Organomet. Chem., 1983, 250, 319; (c) R. J. Puddephatt, Polyhedron,
1988, 7, 767; (d) S. A. R. Knox, J. Organomet. Chem., 1990, 400, 255;
(e) P. M. Maitlis, H. C. Long, R. Quyoum, M. L. Turner and Z.-Q. Wang,
Chem. Commun., 1996, 1. See also: (f) G. A. Somorjai, Introduction to
Surface Chemistry and Catalysis, Wiley-Interscience, New York,
The present study reveals that alkylidene units on a
polynuclear system can be coupled with each other in a quite
specific manner under very mild reaction conditions, if they are
incorporated into the metal system in an appropriate way. In the
present case, the C–C coupling is most probably realized via
1
migratory insertion of the h -alkylidene-m-alkylidene species 8.
A similar alkylidene coupling leading to an alkenic intermediate
may occur on a heterogeneous catalyst surface, and, recently, a
vinyl species has been proposed as an initiator of the carbon-
chain propagation.3
1
994.
4
5
6
N. M. Doherty, J. A. Howard, S. A. R. Knox, N. J. Terril and M. I. Yates,
J. Chem. Soc., Chem. Commun., 1989, 638.
R. E. Colborn, A. F. Dyke, S. A. R. Knox, K. Mead and P. Woodward,
J. Chem. Soc., Dalton Trans., 1983, 2099.
(a) R. E. Colborn, D. L. Davis, A. F. Dyke, S. A. R. Knox, K. A. Mead
and A. G. Orpen, J. Chem. Soc., Dalton Trans., 1989, 1799; (b) M. Akita,
R. Hua, T. Oku and Y. Moro-oka, Organometallics, 1996, 15, 2548.
e
Footnotes
†
1
Spectroscopic data: 3a (major isomer), d
2.7 Hz, m-CHNCH ), 5.01, 4.84 (5 H 3 2, s 3 2, C
(cis)], 2.58 [1 H, d, J 12.7 Hz, m-CHNCH
(in C ) 203.5, 202.4 (s 3 2, CO), 144.4 (d, J 147
), 84.1 (d, J 176 Hz, C ), 83.5 (d, J 178 Hz, C ), 53.2
H
(in CDCl
3
) 8.48 (1 H, dd, J 7.8,
3 2), 4.51 [1 H, d,
(trans)],
2
5 5
H
J 7.8 Hz, m-CHNCH
2
2
2
14.95 (1 H, s, m-H); d
C
6 6
D
Hz, m-CHNCH
2
5
H
5
5
H
5
Received, 23rd September 1996; Com. 6/06525B
52
Chem. Commun., 1997