Vanadium(III) phosphine complexes: synthesis, characterization and behavior in the polymerization of 1,3-butadiene

In recent years several papers on the polymerization of conjugated dienes with catalysts based on transition metal phosphine complexes were reported1. In general these systems were found to be extremely active, giving polymers with different structure (cis-1,4; 1,2 (3,4); mixed cis-1,4/1,2 (3,4) structure with variable 1,2 (3,4) content) from the different monomers depending on the type of transition metal, the type of phosphine ligand coordinated to the metal, and the monomer nature. To cite some examples, the systems CoCl2(PRPh2)/MAO (R = Me, Et , nPr, iPr, Cy) gave syndiotactic 1,2 polymers from butadiene and terminally substituted butadienes (e.g., 1,3-pentadiene, 1,3-hexadiene, 5- methyl-1,3-hexadiene, 1,3-heptadiene, 1,3-octadiene), the syndiotactic degree increasing with increasing the steric hindrance of the phosphine; the same catalysts gave instead isotactic 1,2 polymers from 3-methyl-1,3-pentadiene, the isotactic degree increasing with decreasing the phosphine steric hindrance. Chromium (II) complexes with bidentate phosphine ligands in combination with MAO gave highly 1,2 polybutadienes, isotactic or syndiotactic depending on the nature of the phosphine ligand. Keeping on this research topic, we have now synthesized and characterized a series of vanadium (III) complexes bearing monodentate phosphine ligands of type VCl3(PRnPh3-n)2 (n = 0, 1, 2,3; R = Me, Et, iPr, Cy) and VCl3(PR3) (R = nPr, tBut, Cyp, Cy). For some of them single crystals were obtained and their crystalline molecular structures determined . The behaviour in the polymerization of 1,3-butadiene of all the above complexes was examined. Upon activation with d-MAO (prepared by removing toluene and unreacted free AlMe3 from commercially MAO), they exhibited a quite good activity, giving polybutadienes with mixed 1,4/1,2 structure. The catalyst activity as well as the stereoselectivity were found to be affected by the nature of the phosphine ligand. 1 G. Ricci, A. Sommazzi, F. Masi, M. Ricci, A. Boglia, G. Leone "Well Defined Transition Metal Complexes with Phosphorus and Nitrogen Ligands for 1,3-Dienes Polymerization" Coord. Chem. Rev. 2010, 254, 661-676