Role of Spectator Species for Amine-Surface Chemistry: Reactions of Amines and Alkenes on Pt(111).

This study investigates the roles of ethylene and ethylidyne in the surface chemistry of -methylaniline (NMA) on Pt(111). Using X-ray photoelectron spectroscopy, temperature-programmed desorption, and density functional theory calculations, we demonstrate that ethylidyne is not merely a passive spectator species but actively contributes to hydroamination. It facilitates C-N bond formation by transferring a methyl group to NMA, leading to the formation of ,-dimethylaniline. Additionally, it stabilizes reaction intermediates and suppresses the decomposition of NMA. This works demonstrates, in contrast to the widely accepted notion, that ethylidyne is not just an inert spectator species; rather, it plays a dual role as both an active reaction partner and a stabilizer. In addition, the coadsorption of ethylene on an NMA-precovered surface shows a side reaction of ethylene with the decomposition products of NMA.