Understanding the Reaction Mechanism of anti-Addition of (NHC)Au(I)-H and (NHC)Au(I)-F across Alkyne

Abstract

The experimentally observed anti-addition reactions of (NHC)Au(I)-H with dimethyl acetylenedicarbonxylate (DMAD) MeOOCC≡CCOOMe and (NHC)Au(I)-F with phenylacetylene MeC≡CPh 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 -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.