The Effect of ZnII Coordination on the Addition of 2-(Aminomethyl)benzimidazole to Acrylonitrile

The effects of N[RIGHTWARDS ARROW]Zn coordination, solvent, and pH on the aza-addition reaction between 2-(aminomethyl)benzimidazole (HL) and acrylonitrile were studied. In the absence of ZnII ion, the aza-addition reactions between HL and acrylonitrile (in aqueous media) depended on pH and were not selective. The mono-addition compound {3-[(1H-benzimidazol-2-ylmethyl)amino]propanenitrile} was always obtained in a greater proportion than the di-addition products [3,3?-[(1H-benzimidazol-2-ylmethyl)imino]dipropanenitrile and 3-(2-{[(2-cyanoethyl)amino]methyl}-1H-benzimidazol-1-yl)propanenitrile]. Acrylonitrile selectively reacted at the amine group in the [ZnCl3(H2L)] and [ZnCl2(HL)] complexes in aqueous solutions. Moreover, [ZnCl(HL)2]Cl and [Zn(H2O)2(HL)2]Cl2 complexes yielded mixtures of mono- and di-addition products. In contrast, Zn complexes formed with HL did not react with acrylonitrile in solution in DMSO. The synthesis of mono- and di-addition compounds was studied by 1H and 13C NMR spectroscopy and X-ray diffraction crystallography. Quantum theory of atoms in molecules (QTAIM) computations were used to demonstrate the probable presence of a mono-addition chelate complex.