Photocatalytic hydrogenation of alkenes using ammonia-borane

<h2>Summary</h2> Alkene hydrogenation is one of the most widely used reactions for producing high-value materials. Traditional methods rely on H₂ gas under transition metal catalysis, which presents challenges related to cost, safety, waste management, and undesired reactivity. An ideal hydrogenation method would circumvent both components by employing a hydrogen storage material under mild, metal-free conditions. Herein, we introduce a photocatalytic strategy for alkene hydrogenation using H₃N-BH₃. Our system harnesses visible light with a diaryl ketone photocatalyst to convert H₃N-BH₃ into its corresponding boryl radical. This open-shell species undergoes a complex sequence of transformations, including a key halogen-atom transfer with the solvent, <i>in situ</i> generation of alkyl borane intermediates, H-atom transfer to generate an aminyl radical, and subsequent β-fragmentation to engage with a thiol co-catalyst. This H₂- and metal-free approach enables the transformation of a broad range of alkenes, tolerating functional groups typically incompatible with standard protocols.