Palladium-Catalyzed Nonalternating Copolymerization of Ethene and Carbon Monoxide: Scope and Mechanism

摘要

A series of nonalternating ethene/carbon monoxide copolymers with very low carbon monoxide content were synthesized using a neutral palladium catalyst bearing a phosphine-sullonate ligand. The ratio of the binding affinities Of Carbon monoxide and ethene to the palladium chelate complex ((PSO3)-S-boolean AND)-PdCH2CH2(O)CH3 has been determined by NMR spectroscopy to be similar to 50:1 at 25 degrees C. The migratory insertions of ethene and carbon monoxide into the palladium methyl complex ((PSO3)-S-boolean AND)-PdCH3(py) have also been examined by NMR spectroscopy, giving the Following activation parameters: Delta G double dagger (25 degrees C) = 21.7 kcal mol(-1) (Delta H double dagger = 17.7(1) kcal mol(-1) and Delta S double dagger = -13.6(4) eu) for ethene insertion; Delta G double dagger (25 degrees C) = 13.0 kcal mol(-1) (Delta H double dagger = 16.6(8) kcal mol(-1) and Delta S double dagger = 20(434) eu) for carbon monoxide insertion. Our study suggests that the Unusually small difference in ethene and carbon monoxide binding affinities plays an important role in determining the copolymer composition.