Synthesis, structure, and butadiene polymerization behavior of alkylphosphine cobalt(II) complexes

The synthesis, characterization and behavior in polymerization of 1,3-butadiene of some cobalt(II) phosphine complexes (CoCl2(PEt3)2, CoCl2(PnPr3)2, CoCl2(PCy2H)2, CoCl2(PtBu2H)2, CoCl2(PtBu2Me)2, CoCl2(PCyp3)2, CoCl2(PCy3)2; Et = ethyl, nPr = normal-propyl, Cy = cyclohexyl, tBu = tert-butyl, Cyp = cyclopentyl) are described. The X-ray diffraction studies of CoCl2(PCy3)2 and CoCl2(PCy2H)2 are reported. Treatment of these complexes with methylaluminoxane (MAO) leads to highly active butadiene polymerization catalysts; polymers having different microstructure have been obtained depending on the type of phosphine ligand bonded to the cobalt atom. An interpretation for this particular behavior, based on the 1,3-dienes polymerization mechanism previously proposed, is given.