Studies of Ligand and Solvent Effects in the Alternating Copolymerization of Carbon Monoxide and Ethene by Palladium-Diphosphine Catalysis

Abstract

The Pd(II) methyl complexes [Pd(Me)(MeCN)(P−P)]PF6 are effective catalyst precursors for the alternating copolymerization of carbon monoxide with ethene in CH2Cl2 (P−P = 1,3-bis(diphenylphosphino)propane (dppp), meso-2,4-bis(diphenylphosphino)pentane (meso-bdpp), rac-2,4-bis(diphenylphosphino)pentane (rac-bdpp)). The productivity in high molecular weight polyketones within 30 min follows the ligand order dppp > meso-bdpp > rac-bdpp. All the methyl precursors exhibit comparable values of both intrinsic activity and energy barriers to migratory insertions [Pd(Me)(CO), Pd(COMe)(C2H4)] as well as opening of β-chelates [Pd(CH2CH2C(O)Me)(P−P)]+ by CO. It is concluded that the presence and/or stereochemistry of methyl groups in the 1,3-positions of dppp do not exert a significant influence on the propagation rate of the copolymerization reaction in CH2Cl2. High-pressure NMR studies under catalytic conditions show the occurrence of chain transfer by protonolysis with adventitious water to give μ-hydroxo compounds...