P I and P III Ions Supported by BZIMPY Ligands

We report a class of compounds in which both P -X and P forms featuring the same ligand are stable and readily cycled with each other. A series of P -X (X=Cl, Br, I) dicationic triflate salts supported by benzyl- and allyl-substituted 2,6-bis(benzimidazole-2-yl)pyridine (BZIMPY) ligands is synthesized. Surprisingly, treatment of these with R PO (R=Et, Oct) results in reduction to BZIMPY-ligated P monocationic triflate salts while treatment with Ph P reduces but also substitutes the compound to produce Ph P-BZIMPY-ligated P dicationic triflate salts. The mechanisms of these surprising reductions are probed experimentally and rationalized computationally. The P -X dications are shown to be strong Lewis acids both experimentally and computationally and to readily behave as X , PX, and P transfer agents in reactions with phosphines, NHCs, and diazabutadienes. The P mono- and dications are shown to be very effective P transfer agents when treated similarly. Oxidation from a monocationic P salt back to the dicationic P -X (X=Cl, Br) salt was achieved by treatment with N-chlorosuccinimide (NCS) or N-bromosuccinimide (NBS). Full characterization is reported using multinuclear nuclear magnetic resonance spectroscopy, elemental analysis, and single-crystal X-ray diffractometry where suitable crystals were isolated.