http://pubs.acs.org/doi/abs/10.1021/acscatal.5b02201

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

Genping Huang^*† and Peng Liu^*‡

^† Department of Chemistry, School of Science, Tianjin University, and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, People’s Republic of China

^‡ Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States

ACS Catal., 2016, 6, pp 809–820

DOI: 10.1021/acscatal.5b02201

Publication Date (Web): December 21, 2015

Copyright © 2015 American Chemical Society

*E-mail: gphuang@tju.edu.cn. Web: http://genpinghuang.weebly.com., *E-mail: pengliu@pitt.edu.

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 olefin migratory insertion step. Ligand steric contour maps show that, in reactions with large-bite-angle bisphosphine ligands, such as d^Fppb, the steric repulsions between the substrate and the aryl substituents on the ligand lead to complete branched selectivity, and the linear selectivity in reactions with small-bite-angle ligands is due to electronic effects that favor 2,1-olefin migratory insertions.