Adaptive Rhodium Catalysis with a Lewis‑Acidic Secondary Sphere for Divergent Hydrogenation of Propargylic Alcohols.

Achieving chemoselective transformations of multifunctional molecules under mild and sustainable conditions remains a central challenge in catalysis. Here, we show that a rhodium complex equipped with a Lewis acidic secondary coordination sphere can mediate condition-dependent, divergent hydrogenation of propargylic alcohols. By tuning the reaction medium, the system selectively yields one of three products-retained alkynes, allylic ethers, or (E)-alkenes-from a single substrate-catalyst pair under hydrogen. Mechanistic studies implicate π-allyl and rhodium hydride intermediates, with solvent polarity and nucleophilicity steering the reaction pathway. Control experiments confirm the critical roles of both molecular hydrogen and the boron Lewis acid in enabling divergent selectivity. These findings demonstrate how rational secondary-sphere design can enable adaptive catalysis and provide a platform for programmable bond transformations in multifunctional substrates.