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 ]BF ₄ provided a cationic diphosphene-rhodium complex with cis -coordination through the η ¹ -PP and η ² -BH ₃ 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)]BF ₄ .