Mechanism-Guided Computational Design of Indium(I) Carbenoid-Promoted Alkene Reduction with Aluminum(III) Hydride

Conventional Al(III) hydrides (e.g., LiAlH₄) effectively reduce C═O and C═N groups but show low reactivity toward unfunctionalized C═C bonds. This work presents a computationally designed and validated cooperative strategy for alkene reduction, which leverages the synergistic interaction between Al(III) hydrides and Group 13 carbenoids. A key conceptual advance is the identification of In(I) carbenoids as the unique partner with Al(III) hydrides. Unlike the lighter Al(I) counterpart, which tends to undergo comproportionation with Al(III) dihydrides, In(I) carbenoids remain stable in the presence of Al(III) dihydrides. This relative stability allows their vacant p-orbital to function as an electrophilic "alkene trap," while the lone pair concurrently facilitates Al(III)-H bond cleavage, enabling C═C bond reduction via a cooperative hydride transfer mechanism. Furthermore, through extensive ligand screening, three readily accessible In carbenoids were identified as promising catalysts for alkene reduction when paired with an amidinate-supported Al(III) dihydride. These Al(III) hydride/In carbenoid pairs mediate alkene reduction with a significantly lower activation free barrier (Δ<i>G</i>^≠ as low as 24.6 kcal mol^-1) than the traditional reductant LiAlH₄. The reduction system is also applicable to a range of monosubstituted, 1,1-disubstituted, and conjugate alkenes, offering a novel and efficient route for preparing various valuable alkyl Al(III) reagents.