Diphosphene with a phosphineborane tether and its rhodium complex

A diphosphene ligand possessing a PP bond and a phosphineborane moiety in its molecule was synthesized. The reaction of the new bidentate diphosphene-phosphineborane ligand with [Rh(cod)₂]BF₄ provided a cationic diphosphene-rhodium complex with cis-coordination through the η¹-PP and η²-BH₃ moieties. The complex was applied to the coupling reaction of benzimidazole with cyclohexylallene. The complex also underwent a ligand exchange reaction with N-donor reagents such as N-methylpyrrolidine and N,N,N,N-tetramethylethylenediamine. In particular, the addition reaction of pyridine with the rhodium complex provided an equilibrium mixture of the rhodium complex, pyridine, the diphosphene-phosphineborane ligand, and [Rh(pyridine)₂(cod)]BF₄.