Altering molecular weight distributions: Benzyl–phosphinimide titanium complexes as ethylene polymerization catalysts

Abstract

The phosphines and corresponding phosphinimines R2BnPNSiMe3 (R = t-Bu, Cy), p-C6H4(CH2PR2)2 (R = t-Bu (1), Cy (2)), and p-C6H4(CH2PR2NSiMe3)2 (R = t-Bu (3), Cy (4)) were prepared in high yields. Subsequent reaction with Ti precursors afforded (R2BnPN)TiCp*Cl2 (Cp* = η-C5Me5; R = t-Bu (5), Cy (6)), (R2BnPN)TiCpCl2 (Cp = η-C5H5; R = t-Bu (7), Cy (8)), p-C6H4(CH2PR2NTiCp*Cl2)2 (R = t-Bu (9), Cy (10)), and p-C6H4(CH2PR2NTiCpCl2)2 (R = t-Bu (11), Cy (12)). Methylation of the above complexes gave (R2BnPN)TiCp*Me2 (R = t-Bu (13), Cy (14)), (R2BnPN)TiCpMe2 (R = t-Bu (15), Cy (16)), p-C6H4(CH2PR2NTiCp*Me2)2 (R = t-Bu (17), Cy (18)), and p-C6H4(CH2PR2NTiCpMe2)2 (R = t-Bu (19), Cy (20)). The activity of these species as catalyst precursors in ethylene polymerization catalysis was evaluated using Schlenk line and Buchi reactor techniques using activation by methylaluminoxane (MAO) or [Ph3C][B(C6F5)4]. All these catalysts showed good activities and yield polymers with relatively broad molecular weight distributions. The bimodal polymers derived from catalysts generated using MAO are proposed to result from additional active species, possibly as a result of reaction of MAO with the benzylic fragments. X-ray data are reported for 1, 4–8, 10, 12–14, 16, and 18–20.Key words: phosphinimides, polymerization, catalysis, polyethylene, titanium, polymer molecular weight distributions.