Abstract
AbstractRelevant steps in the CO/ethene copolymerization reaction, namely the migratory insertion of [Pd(Me)(CO)(P‐P)]BAr′4 and the carbonylation of the β‐keto chelates [Pd(CH2CH2C(O)Me)(P‐P)]BAr′4 have been studied by in situ high‐pressure NMR spectroscopy in CH2Cl2; P‐P = 1,2‐bis[bis(2‐methoxyphenyl)phosphanyl]ethane or 1,3‐bis[bis(2‐methoxyphenyl)phosphanyl]propane. This study, backed by batch catalytic reactions in the same solvent, has contributed to rationalizing the higher catalytic activity of PdII catalysts modified with o‐methoxy‐substituted diphosphane ligands as compared to analogous PdII catalysts with 1,2‐bis(diphenylphosphanyl)ethane (dppe) and 1,3‐bis(diphenylphosphanyl)propane (dppp) ligands. It was found that o‐MeO substituents on the phosphorus aryl rings ease the opening of the β‐chelate ring by CO and affect the kinetics of the overall CO/ethene copolymerization. Indeed, unlike the catalysts with the dppe and dppp ligands, the rate of carbonylation of the o‐MeO‐modified β‐keto chelates is limited by the Pd(alkyl)(CO) migratory insertion, which makes the overall copolymerization process independent of the CO pressure. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
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