Activation of metal-involved halogen bonds and classical halogen bonds in gold(I) catalysis.

In gold(I) catalysis, the activation of Au(I) chloride catalysts chloride abstraction and noncovalent interactions has become a research focus in organometallic catalysis. In this work, taking halogen bond donors (CHINO, CFI, CHOI) as activators for a Au(I) chloride catalyst (PhPAuCl), the mechanism of the cyclization reaction of propargylic amide was investigated. It was found that there are two activation modes as design principles to obtain the catalytically active species PhPAu: the halogen bond donors activate the Cl atoms of PhPAuCl to form X-I⋯Cl (X = C, N) classical halogen bonds and activate the Au atoms of PhPAuCl to form X-I⋯Au (X = C, N) metal-involved halogen bonds. For the two activation modes, the mechanism of the cyclization reaction of propargylic amide has pathways: the chloride abstraction process of the first step and the 5-/6- cyclization process of the second step. Both activation modes show good activity for the cyclization reaction with the activation ability of classical halogen bonds being slightly stronger than that of the metal-involved halogen bonds, which is consistent with the strength of the X-I⋯Cl halogen bonds being slightly stronger than that of the X-I⋯Au halogen bonds. Therefore, both metal-involved halogen bonds and classical halogen bonds have important development prospects for the activation of catalysts in gold(I) catalysis.