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 inve stigated in detail. The stability of the catalytic system is mainly influen ced by the nature of the reaction medium. By virtue of the high stability o f the active species in 2,2,2-trifluoroethanol compared to methanol, no add ition 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 ad ded revealed that (i) phen is a better ligand than bipy and the catalyst ge nerated 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 s tability is enhanced by addition of a mixture of the N-N ligand and the cor responding monoprotonated salt [(N-N)H][PF6]; (iii) a relatively high carbo n monoxide pressure is required to protect the catalyst toward its decompos ition. A correlation between these parameters and the molecular weight of p olyketones produced was also found. In trifluoroethanol, with no benzoquino ne added, CO/styrene polyketones with M-w values as high as 80 000 were syn thesized 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 mo iety. The mechanistic implications deriving from this analysis-are discusse d.