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.