Oxidation or Reduction State of Au Stabilized by an MOF: Active Site Identification for the Three‐Component Coupling Reaction

Abstract

AbstractAs one of the most efficient catalysts for the three‐component coupling reaction of aldehyde, amine, and alkyne (A3 coupling), Au has attracted extensive attention, but there is a debating issue on whether Auδ+ (δ > 0, representing the oxidation state of Au species) or Au0 is the better active site. According to previous reports, both Auδ+ and Au0 can catalyze the A3 coupling reaction. Therefore, the establishment of a suitable comparison model to identify the better active site is highly desired. In this work, an ideal model to identify the efficient active sites for the A3 coupling reaction based on a metal–organic framework (MOF) platform is rationally fabricated. The Auδ+ in oxidation state can be well bound to the MOF, MIL‐101‐NH2, via postsynthetic modification, and the Au0 catalyst with retained MOF skeleton can be formed via a subsequent one‐step reduction, which provide ideal comparison models with the only difference in the Au oxidation state. Strikingly, the two catalysts exhibit significant activity difference in the A3 coupling reaction. The activity of Auδ+ catalyst is 11‐fold higher than that of Au0, which reveals that Auδ+ serves as a much more effective active site in the A3 coupling reaction.