The oxidative addition of organic electrophiles into electrochemically generated Co­(I) complexes has been widely utilized as a strategy to produce carbon-centered radicals when cobalt is ligated by a polydentate ligand. Changing to a bidentate ligand provides the opportunity to access discrete Co­(III)–C bonded complexes for alternative reactivity, but knowledge of how ligand and/or substrate structures affect catalytic steps is pivotal to reaction design and catalyst optimization. In this vein, experimental studies that can determine the exact nature of elementary organometallic steps remain limited, especially for single-electron oxidative addition pathways. Herein, we utilize cyclic voltammetry combined with simulations to obtain kinetic and thermodynamic properties of the two-step, halogen-atom abstraction mechanism, validated by analyzing kinetic isotope and substituent effects. Complex Hammett relationships could be disentangled to allow understanding of individual effects on activation energy barriers and equilibrium constants, and DFT-derived parameters used to build predictive statistical models for rates of new ligand/substrate combinations.

Cobalt complexes have shown great promise as electrocatalysts in applications ranging from hydrogen evolution to C−H functionalization. However, the use of such complexes often requires polydentate, bulky ligands to stabilize the catalytically active Co(I) oxidation state from deleterious disproportionation reactions to enable the desired reactivity. Herein, we describe the use of bidentate electronically asymmetric ligands as an alternative approach to stabilizing transient Co(I) species. Using disproportionation rates of electrochemically generated Co(I) complexes as a model for stability, we measured the relative stability of complexes prepared with a series of N,N-bidentate ligands. While the stability of Co(I)Cl complexes demonstrates a correlation with experimentally measured thermodynamic properties, consistent with an outer-sphere electron transfer process, the set of ligated Co(I)Br complexes evaluated was found to be preferentially stabilized by electronically asymmetric ligands, demonstrating an alternative disproportionation mechanism. These results allow a greater understanding of the fundamental processes involved in the disproportionation of organometallic complexes and have allowed the identification of cobalt complexes that show promise for the development of novel electrocatalytic reactions.

Upon further investigation, we found an error in the calculation of the rate constant for the oxidative addition of benzyl bromide using [LCo(I)(MeCN)Br] ligated by L34. The original manuscript stated, at the end of section 2.8, "By varying the scan rate of the CV, the measured oxidative addition rate constant (k OA = 7430 dm 3 mol −1 s −1 ) was found to be over 3 orders of magnitude greater than the disproportionation rate constant (k disprop = 1.63 dm 3 mol −1 s −1 ) for the same complex."The corrected rate constant is k OA = 68.1 dm 3 mol −1 s −1 , as an average of four new independent measurements with a standard deviation of 5.4 dm 3 mol −1 s −1 . Consequently, the sentence should read as follows:"By varying the scan rate of the CV, the measured oxidative addition rate constant (k OA = 68.1 dm 3 mol −1 s −1 ) was found to be over 1.5 orders of magnitude greater than the disproportionation rate constant (k disprop = 1.63 dm 3 mol −1 s −1 ) for the same complex."These corrections do not affect the conclusions of the original article.