Synthesis, structure and butadiene polymerization behavior of CoCl2(PRxPh3-x)2 (R=methyl, ethyl, propyl, allyl, isopropyl, cyclohexyl; x=1,2). Influence of the phosphorous ligand on polymerization stereoselectivity

Several cobalt(II) phosphine complexes have been synthesized by reacting cobalt(II) chloride with various mono- and diphenylalkylphosphines (PRxPh3x; R = methyl, ethyl, allyl, propyl, isopropyl, cyclohexyl; x = 1, 2). For some of these complexes single crystals were obtained and their molecular structures were determined by X-ray diffraction method. All the complexes were then used in association with MAO for the polymerization of 1,3-butadiene and they were found to be extremely active. Predominantly 1,2 polymers having different tacticity (predominantly iso- or syndiotactic), depending on the type of phosphine ligand bonded to the cobalt atom, were obtained. An interpretation of this particular behavior, based on the diene polymerization mechanism previously proposed, is reported.