Understanding the reaction mechanism of anti-addition of (NHC)Au(<sc>i</sc>)-H and (NHC)Au(<sc>i</sc>)-F across alkyne

The experimentally observed anti-addition reactions of (NHC)Au(i)-H with dimethyl acetylenedicarboxylate (DMAD) MeOOCC 00000000000000000 00000000000000000 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 00000000000000000 00000000000000000 CCOOMe and (NHC)Au(i)-F with phenylacetylene MeCCPh are intriguing and deserve more in-depth study. In this work, with the aid of density functional theory (DFT) calculations and intrinsic bond orbital (IBO) analysis, we systematically investigated the addition reactions of (NHC)Au(i)-X (X = H, Me and halides) with different alkynes. We found that the nature of the two anti-addition reactions is different. The addition of (NHC)Au(i)-H is initiated by a direct nucleophilic hydride attack from (NHC)Au(i)-H, followed by migration of the [(NHC)Au(i)]+ moiety to the diagonally opposite side with the aid of the out-of-plane pi-bond of the alkyne. However, in the addition of (NHC)Au(i)-F, the [(NHC)Au(i)]+ moiety functions as a Lewis acid to initially activate the alkyne, followed by the fluoride attack.