Vanadium-based imido-alkoxide pro-catalysts bearing bisphenolate ligands for ethylene and ε-caprolactonepolymerisation?

Dalton Transactions Pub Date: 2009-07-07 DOI: 10.1039/B902402F

Abstract

The pro-catalysts [V(NAr)(L)(OR)] (Ar = p-tolyl, p-ClC6H4, p-(OMe)C6H4, p-(CF3)C6H4; R = t-Bu, i-Pr, n-Pr, Et, C(CH3)(CF3)2) have been prepared in good yields from the reaction of [V(NAr)(OR)3] and the bisphenol 2,2′-CH3CH[4,6-(t-Bu)2C6H2OH]2 (LH2). X-Ray crystal structure determinations for the Ar = p-tolyl, R = t-Bu (1), R = C(CH3)(CF3)2 (2) and Ar = p-ClC6H4, R = t-Bu (3) derivatives revealed monomeric complexes, whereas use of R = i-Pr, n-Pr or Et led to alkoxide-bridged dimeric structures of the form [V(NAr)(L)(μ-OR)]2 (R = i-Pr, Ar = p-tolyl (4), p-ClC6H4 (5), p-(CF3)C6H4 (6), p-(OMe)C6H4 (7); R = n-Pr, Ar = p-tolyl (8), p-(CF3)C6H4 (9); R = Et, Ar = p-ClC6H4 (10), p-tolyl (11)). Complexes 1–11 yield highly active ethylene polymerisation catalysts when treated with DMAC (dimethylaluminium chloride) in the presence of ETA (ethyltrichloroacetate), with activities in the range 38?800 to 75?200 g mmol?1 h?1 bar?1. The molecular weights of the resultant polymers were in the range 37?000 to 411?000 g mol?1, with molecular weight distribution 2.2 to 4.7. The effect of the nature of the para-arylimido substituent and the alkoxide group OR upon the catalytic activity has been investigated. For ε-caprolactone polymerisation, mononuclear 1–3 exhibit low conversion (≤25%; 0% for 2), whereas use of the dimeric species 4–11 led to higher conversions (41–78%).

Graphical abstract: Vanadium-based imido-alkoxide pro-catalysts bearing bisphenolate ligands for ethylene and ε-caprolactone polymerisation
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