Thiolate Bridged Gold(I)-NHC Catalysts: New Approach for Catalyst Design and its Application to Trapping Catalytic Intermediates

New dinuclear N-heterocyclic gold complexes with bridging thiolate ligands have been designed as catalytic precursors with desired properties such as stability, recyclability and that do not require additives. The dinuclear compound [(AuNHC)₂ (μ-SC₆ F₅ )]OTf could slowly release the active catalytic species [Au(NHC)]⁺ and the precursor [Au(SC₆ F₅ )(NHC)] in solution, which means that both species would remain stable throughout the catalytic cycle and the pre-catalyst could easily be recovered. The properties exhibited by the complexes have been taken advantage of to gain new insights on the gold-catalyzed hydroalkoxylation of alkynes, with the aim of clarifying all the steps of the catalytic cycle, together with the characterization of intermediates and final products. Isolation and characterization of the pure final spiroketals and the thermodynamic intermediate have been achieved for the first time. Moreover, the kinetic intermediate has also been detected for the first time.