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'NiCh (2) (L - bis(l-methylbenzimidazoyl-2-methyl)amine and L' - bis(l-methylbenzimidazoyl-2- methyl)-10-camphorsulfonamide), was found to be temperature-dependent. Mononuclear [LNi(CH₃OH)₂Cl]Cl.2H₂0 (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 a,ß-enones in high yields; in contrast, the same reaction catalyzed by NiCl₂THF or complex 3 was far less effective.