Palladium complexes of C2-, C3-, and C4-bridged bis(phospholyl) ligands:: Remarkably active catalysts for the copolymerization of ethylene and carbon monoxide

The C-2-, C-3-, and C-4-bridged bis(2,3,4,5-tetramethylphospholes) [{C(Me)C(Me)C(Me)C(Me)P}(2)X] (1a, X= C2H4; 1b, X= C3H6; 1c, X=(CH2)(2)C6H4) 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 Ic 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 = Ic) 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 Ic is comparable to that based on bis(diphenylphosphino)propane (dppp).