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

• Published in: European journal of inorganic chemistry Vol. 2014; no. 31; pp. 5415 - 5423
• Main Authors: Falcón-León, Martha P., Tapia-Benavides, Antonio R., Tlahuext, Hugo, Galán-Vidal, Carlos, Suarez-Castillo, Oscar R., Tlahuextl, Margarita
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.11.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Aqueous solutions; Michael addition; N ligands; Nitrogen heterocycles; Zinc
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201402346

The effects of N→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. The aza additions of 2‐(aminomethyl)benzimidazole (HL) to acrylonitrile depend on pH and are not selective. However, the N→Zn coordination bonds in HL increase the selectivity of the aza addition to acrylonitrile because the ZnII protects the imidazolic nitrogen atoms. Moreover, the aza addition of ZnII complexes requires an aqueous medium.