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.