INTERCONVERSION BETWEEN (C5R5)RU(IV)(ALLYL) AND (C5R5)RU(II)(DIENE) COMPLEXES

When CpRu(eta3-crotyl)Cl2 complex (1a; Cp = eta5-C5H5) was eluted with a silica-gel column, a methyl C-H bond of 1a was activated to give CpRu(eta4-butadiene)Cl (2). Similar activation occurred for CpRu(eta3-prenyl)Cl2 (1b) and Cp*Ru(eta3-crotyl)Cl2 (1c; Cp* = eta3-C5Me5) to give the corresponding diene Ru(II) complexes. This conversion depends on retention time on a silica-gel column, and character of supports. However, the reaction of [Cp*RuCl2]2 with prenyl chloride did not give the expected prenyl complex, but instead gave Cp*Ru(syn-1-chloromethyl-eta3-methallyl)Cl2 (3a). Another 1-chloromethyl-methallyl anti-stereoisomer (4a) was obtained by treatment of [Cp*RuCl3]2 with isoprene. The structures of these two isomeric 1-chloromethyl-methallyl Ru(IV) complexes were determined by X-ray diffraction studies. The analogous 1-chloromethyl-allyl complex (4b) was also obtained by treatment of [Cp*RuCl3]2 with butadiene. In these complexes, irreversible isomerization from the anti-into the more stable syn isomer took place via eta1-allyl intermediates.