Photoredox Reactions of cis-Dialkylcobalt(III) Complexes with Benzyl and Allyl Bromides

When the photolysis of an acetonitrile solution of cis-dialkylcobalt(III) complexes cis-[R₂CO(bpy)₂]ClO₄(R = Me and Et; bpy = 2,2^/-bipyridine) was carried out in the presence of benzyl or allyl bromide by using visible light, cis-[R₂Co(bpy)₂]C10₄reacted with approximately three equivalent amounts of benzyl or allyl bromide to yield mainly the homocoupling products 1,2-diphenylethane or 1,5-hexadiene as well as a small amount of the cross-coupling product between the alkyl group of cis-[R₂Co(bpy)₂]C1O₄and the benzyl or allyl group of the bromide. On the other hand, in the photoredox reaction of cis-[(PhCH₂)₂Co(bpy)₂] with benzyl or allyl bromide, cis-[(PhCH₂)₂Co(bpy)₂] reacted with an equivalent amount of benzyl or allyl bromide to yield only the homocoupling product in the case of benzyl bromide or comparable amounts of the homocoupling and cross-coupling products in the case of allyl bromide. Reaction schemes of the photoredox reactions are discussed on the basis of ESR measurements to detect the reactive intermediates as well as the quantum yield measurements.