The cationic bis(phosphine) cobalt(I) arene complex, [(depe)Co(η6-C7H8)][BAr4F] (depe = 1,2-bis(diethylphosphino)ethane; BAr4F = B[(3,5-(CF3)2)C6H3]4), was investigated as a precatalyst for three-component coupling of arenes, alkenes, and alkynes. Although a sterically attenuated catalyst was targeted with the goal of accelerating C-H functionalization, hydrovinylation derived from the alkene and alkyne was favored over three-component coupling. Remarkably, no catalytic hydrovinylation was observed in the absence of arene, demonstrating the role of C-H activation in the hydrovinylation process and ruling out a mechanism that involves β-H elimination from a cobalt(III) metallacycle. Deuterium labeling supported β-H elimination from a putative cobalt(III)-alkyl,aryl intermediate that forms after C-H activation by a cobalt(III) metallacycle. By varying the arene and alkene coupling partners, factors affecting the selectivity of C(sp3)-C(sp2) reductive elimination versus β-H elimination from the cobalt(III)-alkyl,aryl intermediate were determined.
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