"[(2-Methoxyphenyl)diphenylphosphine]2CoCl2 and [2-(1,1-Dimethylpropyl)-6-(diphenylphosphino)pyridine]2CoCl2: Synthesis, Characterization and Behavior in the Polymerization of 1,3-Dienes

Two novel cobalt diphenylphosphine complexes were synthesized by reacting cobalt(II) chloride with (2-methoxyphenyl)diphenylphosphine and 2-(1,1-dimethylpropyl)-6-(diphenylphosphino)pyridine. For both of them single crystals were obtained and their molecular structures were determined by X-ray diffraction method. The two novel complexes were successively used in association with MAO for the polymerization of 1,3-dienes. Unlike that previously obtained with the catalytic systems based on CoCl2(PRPh2)2-MAO (R = alkyl, cycloalkyl or phenyl group), which provided diene polymers with a predominantly 1,2 structure independently of the Al/Co molar ratio, the new catalytic systems were found able to supply highly cis-1,4 polydienes or predominantly 1,2 polydienes depending on the Al/Co molar ratio value. A plausible interpretation for this unexpected behavior is provided, based on the diene polymerization mechanism previously proposed.