Redox Reactions of cis-Dialkylcobalt(III) Complexes with Benzyl and Allyl Bromides, Induced by Thermal Cleavage of the Cobalt-Carbon Bond

Article abstract of DOI:10.1246/bcsj.60.563

The thermal cleavage of the cobalt-carbon bond of cis-dialkylcobalt(III) complexes, cis-⁺ (R = Me, Et, and PhCH2; bpy = 2,2'-bipyridine), was enhanced by the presence of benzyl and allyl bromide, inducing the C-C bond formation to yield mainly 1,2-diphenylethane and 1,5-hexadiene, respectively.In the cis-<(PhCH2)2Co(bpy)2>⁺-allyl bromide system, a comparable amount of the cross-coupling product (4-phenyl-1-butene) was obtained together with the homo-coupling products (1,2-diphenylethane and 1,5-hexadiene).The enhancement of the thermal cleavage of the cobalt-carbon bond of cis-+ by the reactions with benzyl and allyl bromides is caused by the high reactivity of the carbanion ligand of ⁺ produced by the homolytic cleavage of the cobalt-carbon bond of cis-⁺, which undergoes the exchange, coupling, and cross-coupling reactions with benzyl and allyl groups of the bromides.Based on the kinetics and the activation parameters, the cobalt-carbon bond dissociation enthalpy of cis-<(PhCH2)2Co(bpy)2>⁺ has been estimated to be 92 kJ mol^-1.