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, [LAuSc]­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 [LAuSc]­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 [ClAuSc], 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 Sc behaves as a carbene.