Bulky Aluminum Alkyl Scavengers in Olefin Polymerization with Group 4 Catalysts

The binding of H2O to MeAl(OAr)2 (1:  Ar = 2,6-di-tert-butyl-4-methylphenyl) in THF-d8 at −40 °C provides aquo complex 2, the structure of which was determined by X-ray crystallography. Complex 2 is unstable above 0 °C in THF-d8 and decomposes to form ArOH (major), CH4 (minor), and a methyl aluminoxane of undetermined structure. Decomposition of 2 follows first-order kinetics with k = 3.0 × 10-4 s-1 at 5 °C. The hindered phenol ArOH slowly reacts with [Cp2ZrMe][MeB(C6F5)3] (4) in bromobenzene-d5 solution at 25 °C to furnish CH4 and [Cp2ZrOAr][MeB(C6F5)3] (5), the structure of which was confirmed by X-ray crystallography. This reaction follows second-order kinetics for [ArOH] = [4] = 0.045 M and with k = 2.8 × 10-3 M-1 s-1 at 25 °C. This corresponds to a rate that is >107 × slower than the apparent rate of ethylene insertion for 4 at 25 °C at typical concentrations encountered in olefin polymerization. The kinetic data, as well as control experiments involving the addition of ArOH to active catalyst producing poly(ethylene), demonstrate that ArOH has essentially no effect on polymerization kinetics involving 4.