Exploring the Scope of Nitrogen Acyclic Carbenes (NACs) in Gold-Catalyzed Reactions

The catalytic activity of the recently reported nitrogen acyclic carbene (NAG) complexes of gold(I) has been investigated and compared with the reported activity of other gold(I) and gold(III) complexes. The complexes studied, [AuCl{C(NEt2)(NHTol-p)}], [AuCl{C(NEt2)(NHXylyl)}], and [Au(NTf2){C(NEt2)(NHXylyl)}], are very active in processes such as the rearrangement of homo-propargylsulfoxides, the intramolecular hydroamination of N-allenyl carbamates, the intramolecular hydroalkoxylation of allenes, the hydroarylation of acetylenecarboxylic acid ester, and the benzylation of anisole. Although the NAG ligands have not been optimized for the reactions tested, the yields obtained are usually similar and sometimes better than those reported with other catalysts, showing that the presence of N-H bonds and the wider N-C-N angle in the NAG (as compared to the NHC) complexes are not detrimental for the catalysis. For the hydroarylation reaction (where two competing products can be formed), the NAG complexes allow favoring one over the other. For the benzylation of anisole the selectivity is complementary to that obtained using H[AuCl4] as catalyst, and depending on the substrate, the NAG gold(III) complexes outperform the activity of H[AuCl4]. On average, the reactivity found suggests that the basicity of NACs toward gold(I) is very similar to that of NHCs and higher than that of phosphines.