Efficient palladium catalysts for the copolymerization of carbon monoxide with olefins to produce perfectly alternating polyketones

A class of highly efficient homogeneous palladium catalyst systems has been developed for the production of perfectly alternating copolymers of carbon monoxide with ethylene. Mixtures of carbon monoxide, ethylene and propene are converted into the corresponding alternating carbon monoxide/olefin terpolymers in which C3 units randomly replace ethylene units along the chain. The essential features of the new catalyst systems are that they are formed by the combination of an equimolar quantity of a suitable bidentate phosphine ligand with a palladium(II) species in which the counter anions are weakly coordinating. For a series of diphenylphosphinoalkanes of general formula Ph2P(CH2)mPPh2 the most efficient catalyst system for the production of high-molecular-weight polyketones is that with m = 3. High rates with conversions of more than one million molecules of carbon monoxide and ethylene per palladium center are obtained. In methanol, the majority of the polymer chains produced are polyketo-esters of general formula H(CH2CH2CO)nOMe; analyses of methanol-soluble oligomer fractions shows that diesters MeOCO(CH2CH2CO)nOMe and diketones H(CH2CH2CO)nCH2CH3 are also formed. Two interlinked catalytic cycles are invoked to account for the formation of polyketones with keto-ester, diester and diketone end groups.