The paper investigates the oxidative metal-catalyzed hydrogen atom transfer (MHAT) of alkenes to form C–N and C–O bonds using cobalt complexes supported by salen ligands. The authors characterized relevant cobalt complexes and their reactions with alkenes, silanes, oxidants, and solvents. They found that a cobalt(III) aquo complex, rather than a cobalt(III) fluoride complex, is more active under catalytic conditions. Water addition speeds up the catalytic reaction, and kinetic studies show that water enables catalytic product formation in 2 hours at −50 °C in acetone. The addition of water also stabilizes the cobalt(III) resting state, which is observed by UV-vis spectrophotometry. The mechanism involves the formation of a transient cobalt(III)-hydride complex, which transfers H+ to the alkene to form an alkyl radical. This radical can be trapped to form a cobalt(III) alkyl complex, which then undergoes HAT to form the final product. The rate of the catalytic reaction follows a power law that depends on the concentration of cobalt, while the degradation reaction follows a different power law. Lowering the catalyst loading improves the yield by reducing the rate of unproductive silane/oxidant consumption. These findings provide insights into the mechanism of oxidative MHAT and lay the groundwork for improving catalytic reactions.The paper investigates the oxidative metal-catalyzed hydrogen atom transfer (MHAT) of alkenes to form C–N and C–O bonds using cobalt complexes supported by salen ligands. The authors characterized relevant cobalt complexes and their reactions with alkenes, silanes, oxidants, and solvents. They found that a cobalt(III) aquo complex, rather than a cobalt(III) fluoride complex, is more active under catalytic conditions. Water addition speeds up the catalytic reaction, and kinetic studies show that water enables catalytic product formation in 2 hours at −50 °C in acetone. The addition of water also stabilizes the cobalt(III) resting state, which is observed by UV-vis spectrophotometry. The mechanism involves the formation of a transient cobalt(III)-hydride complex, which transfers H+ to the alkene to form an alkyl radical. This radical can be trapped to form a cobalt(III) alkyl complex, which then undergoes HAT to form the final product. The rate of the catalytic reaction follows a power law that depends on the concentration of cobalt, while the degradation reaction follows a different power law. Lowering the catalyst loading improves the yield by reducing the rate of unproductive silane/oxidant consumption. These findings provide insights into the mechanism of oxidative MHAT and lay the groundwork for improving catalytic reactions.