Palladium Complexes of C₂-, C₃-, and C₄-Bridged Bis(phospholyl) Ligands: Remarkably Active Catalysts for the Copolymerization of Ethylene and Carbon Monoxide

Abstract

The C2-, C3-, and C4-bridged bis(2,3,4,5-tetramethylphospholes) (1a, X = C2H4; 1b, X = C3H6; 1c, X = (CH2)2C6H4) and their corresponding palladium complexes [(P-P)PdCl2] (2a−c) have been prepared and characterized. A single-crystal X-ray analysis of [{bis(2,3,4,5-tetramethylphospholyl)-o-xylene}PdCl2] (2c) reveals that 1c forms a seven-membered chelate; the phosphole rings are oriented perpendicular to the PdP2Cl2 plane. Methanol solutions of [(P-P)Pd(OAc)2] (3a, P-P = 1b; 3b, P-P = 1c) and methanesulfonic acid are active for the copolymerization of ethylene and carbon monoxide, generating high-molecular-weight polymers with narrow molecular weight distributions. Under our conditions, the activity of catalyst systems containing 1c is comparable to that based on bis(diphenylphosphino)propane (dppp).