Highly Selective Olefin Trimerization Catalysis by a Borane-Activated Titanium Trimethyl Complex

Reaction of a trimethyl titanium complex, (FI)TiMe_3 (FI = phenoxy-imine), with 1 equiv of B(C_6F_5)_3 gives [(FI)TiMe_2][MeB(C_6F_5)_3], an effective precatalyst for the selective trimerization of ethylene. Mechanistic studies indicate that catalyst initiation involves generation of an active TiII species by olefin insertion into a Ti–Me bond, followed by β-H elimination and reductive elimination of methane, and that initiation is slow relative to trimerization. (FI)TiMe_3/B(C_6F_5)_3 also leads to a competent catalyst for the oligomerization of α-olefins, displaying high selectivity for trimers (>95%), approximately 85% of which are one regioisomer. This catalyst system thus shows promise for selectively converting light α-olefins into transportation fuels and lubricants.