Three-Component Coupling of Arenes, Ethylene, and Alkynes Catalyzed by a Cationic Bis(phosphine) Cobalt Complex: Intercepting Metallacyclopentenes for C–H Functionalization

A cobalt-catalyzed intermolecular three-component coupling of arenes, ethylene, and alkynes was developed using the well-defined air-stable cationic bis­(phosphine) cobalt­(I) complex, [(dcype)­Co­(η⁶-C₇H₈)]­[BAr^F₄] (dcype = 1,2-bis­(dicyclohexylphosphino)­ethane; BAr^F₄ = B­[(3,5-(CF₃)₂)­C₆H₃]₄), as the precatalyst. All three components were required for turnover and formation of ortho-homoallylated arene products. A range of directing groups including amide, ketone, and 2-pyridyl substituents on the arene promoted the reaction. The cobalt-catalyzed method exhibited broad functional group tolerance allowing for the late-stage functionalization of two drug molecules, fenofibrate and haloperidol. A series of control reactions, deuterium labeling studies, resting state analysis, as well as synthesis of substrate- and product-bound η⁶-arene complexes supported a pathway involving C­(sp²)–H activation from a cobalt­(III) metallacycle.