Highly efficient catalytic system for the CO/styrene copolymerization: Toward the stabilization of the active species

The CO/styrene copolymerization reaction promoted by [Pd(N-N)(2)][PF6](2) (N-N = 2;2'-bipyridine (bpy), 1,10-phenanthroline (phen)) complexes was investigated in detail. The stability of the catalytic system is mainly influenced by the nature of the reaction medium. By virtue of the high stability of the active species in 2,2,2-trifluoroethanol compared to methanol, no addition of 1,4-benzoquinone is required for the reaction. The analysis df the parameters that affect the stability of the catalyst when no oxidant is added revealed that (i) phen is a better ligand than bipy and the catalyst generated by the complex [Pd(phen)(2)]-[PF6](2) is active at least up to 48 h of reaction, yielding a productivity as high Bs 5.4 kg CP/g Pd; (ii) the stability is enhanced by addition of a mixture of the N-N ligand and the corresponding monoprotonated salt [(N-N)H][PF6]; (iii) a relatively high carbon monoxide pressure is required to protect the catalyst toward its decomposition. A correlation between these parameters and the molecular weight of polyketones produced was also found. In trifluoroethanol, with no benzoquinone added, CO/styrene polyketones with M-w values as high as 80 000 were synthesized for the first time. The copolymers were analyzed by MALDI-TOF TOF spectrometry to characterize their end groups. One-of the end groups of the polyketones prepared in trifluoroethanol is always the unsaturated ketone, while the other one is either the saturated ketone or the carboalcohoxy moiety. The mechanistic implications deriving from this analysis-are discussed.