Vanadium-Based Pro-Catalysts Bearing Depleted 1,3-Calix[4]arenes for Ethylene or ε-Caprolactone Polymerization

Reaction of [V(X)(OR)3] (X = O, Np-tolyl, R = nPr, tBu) with 5,11,17,23-tBu-25,27-dihydroxycalix[4]arene (LH2) led to the formation of [V(X)(OR)L]2 X = O, R = nPr (1); X = Np-tolyl, R = nPr (2); X = Np-tolyl, R = tBu (3) as the major product. In the case of X = O, the minor hydrolysis product {[VO(OnPr)]2(μ-O)L}2 (4) has also been characterized. Complexes (1)–(4), in the presence of the co-catalyst dimethylaluminum chloride and the reactivator ethyltrichloroacetate, are highly active (≤16,400 g/mmol h bar), thermally stable pro-catalysts for the polymerization of ethylene. The use of silica supports with (1) and (2) under slurry conditions yielded polymer with activities ≤30 g/mmol h. Complexes (1)–(3) have also been screened as pro-catalysts for the ring-opening polymerization of ε-caprolactone; the conversion rate order (1) (94%) > (2) (46%) > (3) (20%) was observed at 80 °C over 72 h.