2,2-Dialkyl-2H-benzimidazoles, the high energy tautomers of the corresponding 1,2-dialkyl-1H-benzimidazoles. Syntheses and their complexes with Cu(I) and Ag(I)

Abstract

Reaction of Cu(1,2-phenylenediamine)₂ (ClO₄)₂ with neat RR'=O (R = methyl and/or ethyl) gives Cu(2,2-dialkyl-2H-benzimidazole)ClO₄, demetallation of which by the action of aqueous ammonia yields pure 2,2-dialkyl-2H-benzimidazoles. These are characterised by NMR. In the X-ray crystal structure, Ag(2,2-methyl-2H-benzimi-dazole)NO₃ is found to be a spiral 1D coordination polymer where the 2H-benzimidazole acts as an N,N bridge between two Ag(I) centers. Although 2H-benzimidazoles are very unstable in the free state, they are quite stable in their Cu(I) and Ag(I) complexes. The 1,2-tautomerisation in imidazole and benzimidazole have been studied by means of transition state calculations at B3LYP/6-311+G(2d,p)* level.