Mechanism and Origins of Ligand-Controlled Linear Versus Branched Selectivity of Iridium-Catalyzed Hydroarylation of Alkenes

Abstract

The iridium-catalyzed carbonyl-directed hydroarylation of monosubstituted alkenes developed by Bower and co-workers [Crisenza, G. E. M.; McCreanor, N. G.; Bower, J. F. J. Am. Chem. Soc. 2014, 136, 10258–10261] provides an efficient strategy for highly branched-selective hydroarylation of both aryl- and alkyl-substituted alkenes. Density functional theory calculations in the present study revealed that the unique regiochemical control in this reaction is due to an unconventional modified Chalk–Harrod-type mechanism. Instead of the commonly accepted Chalk–Harrod-type mechanism of transition metal-catalyzed hydroarylation that involves C–H oxidative addition, olefin migratory insertion into the Ir–H bond, and C–C reductive elimination, the Ir-catalyzed reaction occurs via migratory insertion of the olefin into the Ir–aryl bond and C–H reductive elimination. The experimentally observed ligand-controlled selectivity is attributed to a combination of electronic and steric effects in the selectivity-determining ...