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

Abstract

The pro-catalysts [V(NAr)(L)(OR)] (Ar = p-tolyl, p-ClC(6)H(4), p-(OMe)C(6)H(4), p-(CF(3))C(6)H(4); R = t-Bu, i-Pr, n-Pr, Et, C(CH(3))(CF(3))(2)) have been prepared in good yields from the reaction of [V(NAr)(OR)(3)] and the bisphenol 2,2'-CH(3)CH[4,6-(t-Bu)(2)C(6)H(2)OH](2) (LH(2)). X-Ray crystal structure determinations for the Ar = p-tolyl, R = t-Bu (1), R = C(CH(3))(CF(3))(2) (2) and Ar = p-ClC(6)H(4), 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)(mu-OR)](2) (R = i-Pr, Ar = p-tolyl (4), p-ClC(6)H(4) (5), p-(CF(3))C(6)H(4) (6), p-(OMe)C(6)H(4) (7); R = n-Pr, Ar = p-tolyl (8), p-(CF(3))C(6)H(4) (9); R = Et, Ar = p-ClC(6)H(4) (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 epsilon-caprolactone polymerisation, mononuclear 1-3 exhibit low conversion (< or = 25%; 0% for 2), whereas use of the dimeric species 4-11 led to higher conversions (41-78%).