Temperature-Dependent Nuclearity in Bis(benzimidazoyl) Nickel Complexes and Their Catalysis toward Conjugate Addition of Thiophenols to α,β-Enones

The nuclearity of two previously prepared nickel complexes, [LNiCl(μ-Cl)]2·2CH3OH (1) and L′NiCl2 (2) (L = bis(1-methylbenzimidazoyl-2-methyl)amine and L′ = bis(1-methylbenzimidazoyl-2-methyl)-10-camphorsulfonamide), was found to be temperature-dependent. Mononuclear [LNi(CH3OH)2Cl]Cl·2H2O (3) and dinuclear [L′NiCl(μ-Cl)]2 (4) were obtained as crystals at −20 °C. It is noteworthy that complex 2 can catalyze the conjugate addition of thiophenols to α,β-enones in high yields; in contrast, the same reaction catalyzed by NiCl2·THF or complex 3 was far less effective.