Gold(I) Complexes with Normal 1,2,3-Triazolylidene Ligands: Synthesis and Catalytic Properties

1,2,3-Triazolylidenes as versatile, strong donor ligands have currently experienced a boost in complex synthesis as well as catalytic applications. Although many examples of abnormal 1,2,3-triazolylidenes have been described, their normal congeners have been barely examined to date (for abnormal carbenes the resonance structures of the carbenes cannot be drawn without adding additional charges, but this is possible for normal carbenes). Furthermore, no instance of utilization of this new ligand class in homogeneous catalysis can be found. Therefore, this work presents a variety of potential precatalysts descending from normal 1,2,3-triazolylidene Au chloride complexes. Synthesis and thorough characterization of the new compounds are presented, together with special ligand features such as buried volume and suspected anagostic interactions. The activity of the isolated precatalysts is examined in the intramolecular hydroamination of alkynes and compared with that of a popular imidazolylidene system. It is found that the activity of the best-performing normal 1,2,3-triazolylidene systems is quite similar to that of the imidazolylidene systems. However, mercury drop poisoning experiments suggest that improvements in ligand design are required to enhance catalyst stability.