Entrances, Traps, and Rate-Controlling Factors for Nickel-Catalyzed C–H Functionalization

Abstract

A detailed mechanistic investigation of N-heterocyclic carbene-nickel-catalyzed hydroarylation via C–H functionalization is described. These catalysts are complicated, in part, by undesired reactivity stemming from common olefinic ligands such as cyclooctadiene (COD) that stabilize the precatalyst. This reaction adds diversity to the overall reactive landscape by permitting multiple types of ligand-to-ligand hydrogen transfer (LLHT) steps to activate the substrate arene C–H bonds. In one case, stable π-allyl complexes can be formed via LLHT to the olefin, hindering catalysis, and in the other, LLHT to the alkyne substrate leads to productive catalysis. Here, a useful map is built from extensive computational and experimental studies to guide subsequent investigations on the productive use of Ni catalysis. In addition to showing the details of catalyst deactivation, activation, and operating regimes, this article suggests the following: 1. Reductive elimination is rate-limiting and assisted by an additiona...