A series of nonalternating ethene/carbon monoxide copolymers with very low carbon monoxide content were synthesized using a neutral palladium catalyst bearing a phosphine-sulfonate ligand. The ratio of the binding affinities of carbon monoxide and ethene to the palladium chelate complex (P ∩SO3)-- PdCH2CH2C(O)CH 3 has been determined by NMR spectroscopy to be ∼50:1 at 25 °C. The migratory insertions of ethene and carbon monoxide into the palladium methyl complex (P∩SO3)-PdCH3(py) have also been examined by NMR spectroscopy, giving the following activation parameters: ΔG‡(25°C) = 21.7kcal mol-1 (ΔH‡ = 17.7(1) kcal mol-1 and ΔS ‡ = -13.6(4) eu) for ethene insertion; ΔG ‡(25°C) = 13.0 kcal mol-1(ΔH ‡ = 16.6(8) kcal mol-1 and ΔS ‡ = 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.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry