Dual Gold Catalysis: Stepwise Catalyst Transfer via Dinuclear Clusters

The interest in and use of dual gold catalysts is forever increasing, but little is known of the mechanism for the catalyst transfer and its effect on the continued high turnover frequency. Herein, we present a computational investigation of the mechanism for the final intermolecular catalyst transfer in the synthesis of dibenzopentalene from 1-ethyny1-2-(phenylethynyl)benzene. Three different scenarios have been explored: a single catalyst transfer from the monoaurated product complex, the analogous water mediated single transfer, and a dual catalyst transfer from the diaurated product complex. Transition structures have been found for each step of the three possible pathways, and a stepwise dual catalyst transfer has proven to be the lowest energy pathway. We here describe a three-step transfer of two gold moieties from one dibenzopentalene to one diyne. This process directly gives the sigma,pi-gold coordinated diyne for the further intramolecular cyclization reaction.