Synthesis, characterization of new triazaphosphinine-2-oxide derivatives, and elucidation of the mechanism using DFT study

We have developed an efficient synthesis of novel bis-benzo[4,5]imidazo[1,2-c]-1,3,5-triaza-2λ4-phosphinine derivatives bearing various substituents through the reaction of imidates with diamine derivatives. In the first step, N′-(1H-benzimidazol-2-yl)-N-alkyl amidines were obtained as key intermediates. Subsequently, the resulting bis-amidines reacted with hexamethylphosphoramide (HMPA) or methylphosphonic bis(dimethylamide) to afford the corresponding bis-triazaphosphinine oxide derivatives in good yields. The reaction mechanism leading to the formation of the bis-triazaphosphinine framework was elucidated and rationalized by a thermodynamic DFT study.