An EPR Study of the V(IV) Species Formed Upon Activation of a Vanadyl Phenoxyimine Polymerization Catalyst with AlR 3 and AlR 2 Cl (R = Me, Et)

Vanadium(IV) complexes formed in the systems L 2 V IV O/AlR 3 , L 2 V IV O/AlR 3 /ETA, L 2 V IV O/AlR 2 Cl, and L 2 V IV O/AlR 2 Cl/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′)V IV (O)(R)(AlR 3 ) are formed in the systems L 2 V IV O/AlR 3 and L 2 V IV O/AlR 3 /ETA, whereas complexes with proposed structures (L′)V IV (O)(R)(AlR 2 Cl) are formed in the systems L 2 V IV O/AlR 2 Cl and L 2 V IV O/AlR 2 Cl/ETA (L′ is the modified initial ligand). The systems L 2 V IV O/AlR 3 /ETA are inert towards polymerization of ethylene, whereas the systems L 2 V IV O/AlR 2 Cl/ETA are moderately active in this reaction. The polymerization activity of the systems L 2 V IV O/AlR 2 Cl/ETA correlates with the concentration of V(IV) species present in the reaction solution. V(IV) complexes of the type (L′)V IV (O)(R)(AlR 2 Cl) can be precursors of the active species of polymerization.