Ligand enabled disproportionation of 1,2-diphenylhydrazine at a P(V)-center

We present herein the synthesis of a nearly square pyramidal chlorophosphorane supported by the tetradentate bis(amidophenolate) ligand, N,N’-bis(3,5-di-tert-butyl-2-phenoxy)-1,2-phenylenediamide. After chloride abstraction the resulting phosphonium cation efficiently catalyzes the disproportionation of 1,2-diphenylhydrazine to aniline and azobenzene. Mechanistic studies, spectroscopic analyses and theoretical calculations suggest that it is the combination of high electrophilicity at the cationic P(V)-center, which originates from the geometry constraints imposed by the rigid pincer ligand, and the ability of the o-amidophenolate moieties to act as electron reservoir what leverages this unprecedented reactivity mode for P(V)-centres. This study illustrates the promising role of cooperativity between redox-active ligands and phosphorus for the design of organocatalysts able to promote redox processes.