The reaction mechanism of the hydroamination of alkenes catalyzed by gold(I)-phosphine: the role of the counterion and the N-nucleophile substituents in the proton-transfer step

The reaction mechanism of the gold(I)-phosphine-catalyzed hydroamination of 1,3-dienes was analyzed by means of density functional methods combined with polarizable continuum models. Several mechanistic pathways for the reaction were considered and evaluated. It was found that the most favorable series of reaction steps include the ligand substitution reaction in the catalytically active Ph3PAuOTf species between the triflate and the substrate, subsequent nucleophile attack of the N-nucleophile (benzyl carbamate) on the activated double bond, which is followed by proton transfer from the NH2 group to the unsaturated carbon atom. The latter step, the most striking one, was analyzed in detail, and a novel pathway involving tautomerization of benzyl carbamate nucleophile assisted by triflate anion acting as a proton shuttle was characterized by the lowest barrier, which is consistent with experimental findings.