Thermal Rearrangement via P–C Bond Cleavage of a Tridentate Diphosphine–N-Heterocyclic Carbene Ligand System Coordinated to Rhodium

The synthesis of a series of rhodium complexes, [PCP]RhX, where X = Cl, H, CH3 and PCP is a tridentate ligand that contains a central, saturated NHC donor flanked by two o-phenylenediisopropylphosphino groups, is described. These complexes were characterized by NMR spectroscopy (1H, 13C, and 31P) and, in the case of the X = Cl derivative, by X-ray crystallography. Investigation of the thermal reactivity of these complexes uncovered an unexpected ligand rearrangement process (for X = H, CH3) resulting from intramolecular P–C bond cleavage between one of the phosphine donors and the aryl linker of the ligand backbone. The structures of the P–C activation products are confirmed through X-ray diffraction analysis, and preliminary rate data in the case of the rhodium hydride are presented.