Cyclization of 2-Alkynyldimethylaniline on Gold(I) Cationic and Neutral Complexes

The cyclization reaction of 2-(1-hexynyl)dimethylaniline (S) on gold(I) has been studied by NMR spectroscopy, in order to characterize the ion pair structure of the product, [LAuS_c]BF₄. The latter is a good model for the catalytic intermediate between the nucleophilic attack and the protodeauration step of a typical gold catalytic cycle. ¹⁹F, ¹H HOESY NMR results demonstrate that in [LAuS_c]BF₄, with L being three different ligands, the anion mainly interacts with the ammonium moiety of the substrate, thanks to its formal positive charge, even if the ligand can tune the exact position of the anion. Furthermore, also gold chloride is able to promote the cyclization of S, forming [ClAuS_c], which is the first example of a new class of precatalysts with potentially interesting catalytic properties. Preliminary data on its catalytic performances and a detailed DFT characterization of its electronic properties are presented, both of which indicate that S_c behaves as a carbene.