N-Heterocyclic Carbenes and Imidazole-2-thiones as Ligands for the Gold(I)-Catalysed Hydroamination of Phenylacetylene

Gold(I) complexes of 1-[1-(2,6-dimethylphenylimino)alkyl]-3-(mesityl)imidazol-2-ylidene (C boolean AND ImineR), 1,3-dimesitylimidazol-2-ylidene (IMes) and of the corresponding thione derivatives (S boolean AND Imine(R) and IMesS) were prepared and structurally characterised. The solid-state structure of the C boolean AND Imine(R) and S boolean AND Imine(R) gold(I) complexes showed monodentate coordination of the ligand and a dangling imine group that could bind reversibly to the metal centre to stabilise otherwise unstable catalytic intermediates. Interestingly, reaction of C boolean AND Imine(tBu) with [AuCl(SMe2)] led to the formation of [(C boolean AND Imine(tBu))AuCl], which rearranges upon crystallisation into the unusual complex cation [(C boolean AND Imine(tBu))(2)Au](+), with AuCl2- as the counterion. The activity of the gold complexes in the hydroamination of phenylacetylene with substituted anilines was tested and compared to control catalyst systems. The best catalytic performance was obtained with [(C boolean AND Imine(tBu))AuCl], with the exclusive formation of the Markovnikov addition product in excellent yield (>95?%) regardless of the substituents on aniline.