Nickel-Catalyzed Hydrocarboxylation of Terminal Unactivated Alkenes: Formation of Branched Carboxylic Acids and Competing Catalyst Deactivation from CO2 Reduction to CO

The reductive coupling of CO₂ and alkenes represents a compelling strategy for the synthesis of carboxylic acids. In this study, we show that Ni(OAc)₂ and 6,6′-Me₂bpy (dmbpy) catalyze hydrocarboxylation of terminal unactivated alkenes to afford the branched 2-methyl-substituted carboxylic acids. The nickel/dmbpy speciation in solution is elucidated through electrochemical and UV–visible and NMR spectroscopic methods. A catalyst deactivation process is identified, involving competitive reduction of CO₂ to CO resulting in the formation of an inactive Ni–CO complex. The Ni catalyst may be reactivated by oxidative treatment of the Ni–CO complex to release CO; however, the results highlight an important complication that can arise in reactions of Ni-catalyzed reductive coupling with CO₂.