Cationic Ir–H as an Active Regulator: Mechanistic Origins of Reactivity and Selectivity in Ir-Catalyzed Asymmetric Hydroalkylation

Metal hydride intermediates play a central role in transition-metal catalysis, yet the intrinsic reactivity modes and selectivity-governing features of cationic Ir-H species remain poorly understood. Herein, a comprehensive density functional theory (DFT) study is reported to elucidate the mechanism and stereochemical origins of an Ir(I)-catalyzed asymmetric hydroalkylation of alkenes. The calculations reveal that the active cationic Ir-H intermediate preferentially undergoes a concerted β-H elimination rather than charge-separated H-transfer pathways, despite the inherent polarity of the Ir-H bond. Subsequent alkene difunctionalization proceeds through a sequence of migratory insertion steps, among which the Ir-C/C═O migratory insertion is identified as both the rate-determining and stereochemistry-determining step. Distortion/interaction-activation strain analyses show that unfavorable interaction energies associated with polarized Ir-H/C═O insertion disfavor competing pathways, while sterically guided Ir-C/C═O insertion is kinetically preferred. Detailed transition-state analyses and steric contour maps demonstrate that the Ir-H-centered chiral environment acts as an active steric regulator, governing both enantio- and diastereoselectivity. These findings provide a unified mechanistic framework for Ir-H-mediated hydrofunctionalization reactions and highlight the critical role of cationic Ir-H species in controlling reactivity and selectivity.