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-sBu-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; X=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).

A series of organometallic, monocationic, monochelated Pd(II) complexes with different nitrogen-donor ligands is reported together with thier characterization both in solid state and in solution. The synthesized complexes act as efficient precatalysts for the CO/styrene copolymerization reaction, evidencing the positive effect of trifluorethanol both on productivity and on molecular weight of the obtained polyketones. The role of the fluorinated alcohol is clearly evidenced even in the ethylene homopolymerization, allowing, for the first time, the synthesis of polyethylene in an alcholic medium.Figure optionsDownload as PowerPoint slide