An EPR study of the V(IV) species formed upon activation of a vanadyl phenoxyimine polymerization catalyst with AlR3 and AlR2Cl (R = Me, Et)

Vanadium(IV) complexes formed in the systems L2VIVO/AlR3, L2VIVO/AlR3/ETA, L2VIVO/AlR2Cl, and L2VIVO/AlR2Cl/ETA, where L is a phenoxyimine ligand (Scheme 1), R = Me or Et, and ETA is ethyltrichloroacetate, were monitored by EPR. It was shown, that at 20 °C, V(IV) complexes with proposed structures (L′)VIV(O)(R)(AlR3) are formed in the systems L2VIVO/AlR3 and L2VIVO/AlR3/ETA, whereas complexes with proposed structures (L′)VIV(O)(R)(AlR2Cl) are formed in the systems L2VIVO/AlR2Cl and L2VIVO/AlR2Cl/ETA (L′ is the modified initial ligand). The systems L2VIVO/AlR3/ETA are inert towards polymerization of ethylene, whereas the systems L2VIVO/AlR2Cl/ETA are moderately active in this reaction. The polymerization activity of the systems L2VIVO/AlR2Cl/ETA correlates with the concentration of V(IV) species present in the reaction solution. V(IV) complexes of the type (L′)VIV(O)(R)(AlR2Cl) can be precursors of the active species of polymerization.