Trifluoroethanol: key solvent for palladium-catalyzed polymerization reactions

A series of cationic palladium complexes of general formula [Pd(CH3)(NCCH3)(N–N)][X] (N–N = phen 1, 3-sec -butyl-1,10-phenanthroline (3-s Bu-phen) 2, bpy 3, (−)-(S ,S )-3,3′-(1,2-dimethylethylenedioxy)-2,2′-bipyridine (bbpy) 4, (+)-(R )-3,3′-(1-methylethylenedioxy)-2,2′-bipyridine (pbpy) 5, N ,N ′-bis(2,6-diisopropylphenyl)-2,3-butanediimine (iso-DAB) 6; View the MathML sourceX=PF6-a, OTf (OTf = triflate) b) containing different nitrogen-donor ligands were prepared from the corresponding neutral chloro derivatives [Pd(CH3)(Cl)(N–N)] (1c–6c). They were characterized by 1H NMR spectroscopy and elemental analysis. Single crystals suitable for X-ray determination were obtained for complexes [Pd(CH3)(NCCH3)(bbpy)][PF6] (4a), [Pd(CH3)(NCCH3)(iso-DAB)][PF6] (6a) and [Pd(Cl)2(bbpy)] (4c′). The latter is the result of an exchange reaction of the methyl group, present in complex 4c, with a chloride, that occurred after dissolution of 4c in CDCl3, for 1 week at 0 °C. The catalytic behavior of complexes 1a–5a and 1b–5b in the CO/styrene copolymerization was studied in CH2Cl2 and 2,2,2-trifluoroethanol (TFE) evidencing the positive effect of the fluorinated alcohol both in terms of productivity and molecular weight values of the polymers obtained. Influence of the nitrogen ligand, the anion and the reaction time in both solvents were investigated and is discussed in detail. Encouraging preliminary results were also obtained in the synthesis of polyethylene, in TFE, catalyzed by [Pd(CH3)(NCCH3)(iso-DAB)][PF6] (6a).