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

Reaction of a trimethyl titanium complex, (FI)­TiMe₃ (FI = phenoxy-imine), with 1 equiv of B­(C₆F₅)₃ gives [(FI)­TiMe₂]­[MeB­(C₆F₅)₃], an effective precatalyst for the selective trimerization of ethylene. Mechanistic studies indicate that catalyst initiation involves generation of an active Ti^II 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)­TiMe₃/B­(C₆F₅)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.