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

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journal contribution
posted on 04.03.2022, 18:36 by William G. Whitehurst, Junho Kim, Stefan G. Koenig, Paul J. Chirik
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)]­[BArF4] (dcype = 1,2-bis­(dicyclohexylphosphino)­ethane; BArF4 = 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.