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.