Nickel-Catalyzed Anti-Markovnikov Hydroarylation of Unactivated Alkenes with Unactivated Arenes Facilitated by non-Covalent Interactions
Anti-Markovnikov additions to alkenes have been a longstanding goal of catalysis, and anti-Markovnikov addition of arenes to alkenes would produce alkylarenes that are distinct from those formed by acid-catalyzed processes. Existing hydroarylations are either directed or occur with low reactivity and low regioselectivities for the linear alkylarene. Herein, we report the first undirected hydroarylation of unactivated alkenes with unactivated arenes that occurs with high regioselectivity for the anti-Markovnikov product. The reaction occurs with a Ni catalyst ligated by a highly sterically hindered N-heterocyclic carbene (NHC, L4 or L5). Catalytically relevant arene- and alkene-bound Ni complexes have been characterized, and the rate-limiting step was shown to be reductive elimination to form the C-C bond. DFT calculations, combined with energy decomposition analysis (EDA), suggest that the difference in activity between catalysts containing large and small carbenes results more from stabilizing intramolecular, non-covalent interactions in the secondary coordination sphere than from steric hindrance.