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) catalyzes 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 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 Ni-catalyzed reductive coupling reactions with CO2.