Ligand and Solvent Effects in the Alternating Copolymerization of Carbon Monoxide and Olefins by Palladium−Diphosphine Catalysis

Abstract

The substitution of two hydrogen atoms by methyl groups in the 1,2 positions of 1,2-bis(diphenylphosphino)ethane (dppe) gives meso- and rac-2,3-bis(diphenylphosphino)butane (meso-2,3-dppb and rac-2,3-dppb). The corresponding Pd(II) complexes Pd(OTs)2(meso-2,3-dppb) and Pd(OTs)2(rac-2,3-dppb) are effective catalyst precursors for the alternating copolymerization and terpolymerization of carbon monoxide with ethene and ethene/propene in MeOH with productivities that are higher than those of the unsubstituted dppe catalyst Pd(OTs)2(dppe) even by a factor of 10 (OTs = p-toluenesulfonate). It has been found that the low productivity of the dppe-based catalyst in MeOH is due to the autoionization of the precursor Pd(OAc)2(dppe) in MeOH to give the catalytically inactive bis-chelate species [Pd(dppe)2](OAc)2 and palladium acetate. In an attempt to evaluate and rationalize the effective ligand control on the intrinsic catalytic activity, the methyl complexes [Pd(Me)(MeCN)(P−P)]PF6have been synthesized and employe...