Computational Exploration of the Nature of Li+-Ureide Anion Catalysis on Formation of Highly Reactive Vinyl Carbocations and Subsequent C-C Bond Forming Reactions.

Abstract

The mechanisms of the C-H insertion reactions of vinyl carbocations formed by heterolysis of vinyl trifluoromethanesulfonates (triflates) by catalytic lithiated 1,3-bis[3,5-bis(trifluoromethyl)phenyl]urea (Li+-ureide) have been studied with ωB97X-D density functional theory. The ionization promoted by the Li+-ureide forms a metastable intimate ion pair complex of Li+-ureide-triflate anion and vinyl cation. The relative thermodynamic stabilities of isomeric alkyl cations are impacted by ion-pairing with the Li+-ureide-triflate anion. We show that the C-H insertion reaction of the vinyl cation intermediate is the rate-determining step and explain the effect of the aryl substituents on the formation of the vinyl cation and its C-H insertion reactivity as well as the regioselectivity of C-H activation by the vinyl cation.