Intramolecular C–H Bond Activation in Bridged Dicyclopentadienyl Dimethyl Dinuclear Complexes

Photolysis
of the doubly bridged dicyclopentadienyl dimethyl dinuclear
complexes [(η5-C5H2R)2(SiMe2)2]­M2(CO)4Me2 (M = Ru, R = H (2a), tBu (2b); M = Fe, R = H (2c)) in benzene
yields the corresponding methylene-bridged complexes [(η5-C5H2R)2(SiMe2)2]­M2(CO)2(μ-CO)­(μ-CH2) (3a–c) and the M–M-bonded
complexes [(η5-C5H2R)2(SiMe2)2]­M2(CO)4 (1a–c). Irradiation of the analogous diethyl
complex [(η5-C5H2R)2(SiMe2)2]­Ru2(CO)4Et2 (4) affords only 1a. Unlike the
case for the doubly bridged complexes, photolysis of the singly bridged
dicyclopentadienyl dimethyl diruthenium complexes [(η5-C5H4)2(EMe2)]­Ru2(CO)4Me2 (E = C (5a); E
= Si (5b)) in benzene yields the corresponding “twisted”
ruthenium methyl complexes with a cyclopentadienyl–Ru σ
bond (η5,η5:η1-C5H4(EMe2)­C5H3)­[Ru­(CO)2]­[Ru­(CO)2Me] (6a,b) and
the similar phenyl complexes (η5,η5:η1-C5H4(EMe2)­C5H3)­[Ru­(CO)2]­[Ru­(CO)2Ph] (7a,b), from reaction with the benzene solvent.
Plausible mechanisms for the formation of the different types of products
are proposed involving intramolecular C–H bond activation.
The molecular structures of 2a,c, 3a,c, 4, 5a, 6a, and 7b, determined by X-ray diffraction,
are also presented.