Selective Catalytic Dimerization of Neohexene by [Cp*Ti(NPtBu3)Me][B(C6F5)4

Abstract

The known titanium alkyl cation [Cp*Ti(NPtBu3)Me][B(C6F5)4], supported by a bulky phosphinimide donor, was found to react with 3 equiv of 3,3-dimethyl-1-butene (neohexene) to generate another alkyl cation in which the alkyl group is derived from two dimerized equivalents of the substrate olefin. This species, 1, was characterized in detail by spectroscopic methods and via X-ray crystallographic determinations of two of its derivatives, the THF adduct (2) and the neutral chloride derivative 3 formed upon addition of Cl− to 1. Detailed mechanistic experiments suggest 1 is formed via insertion of neohexene into the Ti−Me bond of [Cp*Ti(NPtBu3)Me][B(C6F5)4] to give a detectable intermediate (4), which was characterized spectroscopically. Cation 4 reacts in a σ-bond metathesis reaction with the olefinic C−H bond trans to the tert-butyl group of another equivalent of neohexene to form an undetected cationic vinyl intermediate, which rapidly inserts a third equivalent of neohexene to generate 1. Deuterium labeli...