Influence of promoters on the catalytic cycles of the CO-ethene copolymerization catalyzed by [Pd(dppb)(TsO)2]

Perfectly alternating CO-ethene copolymerization, catalyzed by “cationic” (diphosphine)-Pd(II) in MeOH, yields a mixuture of polyketones (PKs), CH3CH2(COCH2CH2)nCOOMe, MeO(COCH2CH2)nCOOMe and CH3CH2(COOCH2CH2)nCOCH2CH3, named KE, EE, KK, respectively. The nature of the ending groups depends on the termination/initiation steps. Termination occurs through methanolysis or protonolysis of the species Pd-CO-P or Pd-CH2CH2P (P = growing chain), which gives copolymers with at least one COOMe (E) or COCH2CH3 (K) ending group and the initiators Pd-H or Pd-OMe, respectively. Insertion of ethene or of CO into the initiators, followed by multiple alternating insertion of the monomers and by the termination/initiation steps, yields the above copolymers. The catalytic cycles leading to EE or KK are interconnected, so, ideally, they occur at the same rate and consequently the K/E ratio should be 1/1. We studied the influence of the promoters TsOH, H2O and benzoquinone (BQ) on the K/E ratio and the activity of [Pd(dppb)(TsO)2] (dppb = 1,4-bis(diphenylphosphino)butane). GC, 13C CPMAS, 13C DEMAS NMR and DSC analysis were used to measure K/E ratio, molecular weight and crystallinity. The ability of the PKs to act as a support and a stabilizer of metal nanoparticles for heterogeneous catalysts will be also shown.