Ligand Attachment Chemistry in the Preparation of PCsp3P and PCsp2P Complexes of Rhodium

Abstract

The attachment of electron-rich PCP pincer ligands bis(2-(dialkylphosphino)phenyl)methane (alkyl = isopropyl, tert-butyl) to rhodium via reactions with [(COE)2Rh(μ-X)]2 (X = Cl, OSO2CF3) through C-H bond activations is reported. The first C-H activation to produce PCsp3P derivatives is facile and favors products wherein the remaining benzylic C-H and the Rh-H hydrogens are trans-disposed across the new Rh-C bond. For the less bulky isopropyl-substituted ligand, chlorido- or triflato-bridged dinuclear products are favored, while for the tert-butyl-adorned ligand, monomers are formed. The favoring of both trans C-H/Rh-H and dinuclear systems hampers the second C-H activation, necessary to form the (more desirable) PCcarbeneP derivatives. Through spectroscopic and structural investigations, the factors that influence the ligand attachment chemistry through successive C-H activations in these ligands are discussed.