Divergent Mechanisms in the Addition of (NHC)Au(I)–H and (NHC)Cu(I)–H across Alkynes

Copper(I) hydride complexes are widely recognized as reactive intermediates in numerous transformations and typically undergo syn-addition across alkynes. Although copper and gold both belong to Group 11, (NHC)Au(I)–H displays a contrasting anti-addition behavior. In this work, we systematically investigate the reactivity differences between (NHC)Cu(I)–H and (NHC)Au(I)–H using density functional theory. Our results reveal that the observed stereoselectivity originates from the relative stability of the three-coordinated metal-alkyne intermediates. Specifically, the distortion required for (NHC)Au(I)–H to engage in syn-addition is energetically very unfavorable compared to its copper(I) counterpart, destabilizing the corresponding gold-alkyne intermediate and thus favoring anti-addition.