Controlling hydrogen transfer dynamics in adaptive semihydrogenation of alkynes: Unveiling and directing outer- vs. inner-sphere mechanisms

<h2>Summary</h2> This research presents an adaptive catalyst engineered to optimize hydrogen activation and transfer, demonstrated through its application in the semihydrogenation of alkynes. The catalyst is distinguished by a unique ligand pocket that precisely manipulates H₂ dynamics and substrate interactions. Its ability to adjust to solvent variations ensures the selective synthesis of <i>cis-</i> and <i>trans-</i>alkenes directly from alkynes without reliance on selectivity-altering additives. Our extensive mechanistic study sheds light on the critical influence of the solvent in guiding hydrogen transfer mechanisms, revealing an unconventional outer sphere hydrogenation process. The reversible nature of the catalyst and its robust performance over repeated cycles represent a significant advancement in controlled hydrogen catalysis. This progress highlights the feasibility of selectively producing both kinetic and thermodynamic products, setting a new standard for efficiency and versatility in catalytic processes.