Catalytic Linear Oligomerization of Ethylene to Higher α-Olefins: Insight into the Origin of the Selective Generation of 1-Hexene Promoted by a Cationic Cyclopentadienyl-Arene Titanium Active Catalyst

Abstract

A detailed theoretical investigation is presented of crucial elementary steps of the selective linear ethylene oligomerization to 1-hexene by the cationic [(η5-C5H4-(CMe2)-bridge)-C6H5)TiIV(CH3)2]+ precatalyst, employing a gradient-corrected DFT method. The essential aspects of the originally proposed mechanism have been confirmed and supplemented by novel insights into how the selective ethylene oligomerization operates. This includes the examination of the ability of titana(IV)cycle intermediates to grow and/or to decompose affording α-olefins as a function of their size, the prediction of the favorable route for precatalyst activation, and the exploration of the cycloalkane production as a possible side process. After the TiIV−Me2 precatalyst is smoothly converted into the active TiII−(ethylene)2 catalyst complex, the two ethylene moieties readily undergo oxidative coupling to afford first the titana(IV)cyclopentane species. Metallacycle growth through bimolecular ethylene uptake and subsequent inserti...