The carbonylation of alcohols represents a straightforward and atom-efficient methodology for the preparation of carboxylic acids. It is desirable to perform these reactions under precious metal-free and low-pressure conditions, with regioselectivity control. In this work, we present a detailed mechanistic study of a catalytic system based on NiI2, which can carbonylate benzylic alcohols in a highly regioselective manner to the corresponding branched carboxylic acids, core motifs for nonsteroidal drugs. The combination of catalytic amounts of nickel and iodide is crucial for efficient catalytic and regioselective conversion. Quantum-chemical computations were used to evaluate the underlying mechanistic processes. They revealed that a combination of two mechanisms is responsible for the observed reactivity and that the oxidative addition of alkyl halides to the Ni(0) species follows a radical oxidation pathway via two one-electron steps.

The (hydroxy)carbonylation of tertiary aliphatic alcohols and their corresponding olefins with a Ni-based catalyst system is investigated. This study builds on a previous mechanistic investigation into the Ni-catalyzed carbonylation of alcohols. The findings differed from what could be explained with the previously reported mechanisms, prompting this in-depth mechanistic study. Combined experimental and quantum chemical efforts are crucial for the rationalization of the observed reactivities and ultimately help reveal another isobutene-based catalytic pathway, accessible with these substrates. This study further expands the knowledge about Ni-catalyzed carbonylation reactions, which have been known for more than 70 years but were scarcely studied in detail from a mechanistic point of view.