Chemical transformations of [MAu(PPh)] (M = Pt, Pd) and [Au(PPh)] in methanol induced by irradiation of atmospheric pressure plasma.

The reaction processes of ligand-protected metal clusters induced by irradiating atmospheric pressure plasma (APP) were investigated using optical spectroscopy, mass spectrometry, and density functional theory (DFT) calculations. The target clusters were phosphine-protected gold-based clusters [MAu(PPh)] (M = Pt, Pd) and [Au(PPh)], which have a crown-shaped M@Au (M = Pt, Pd, Au) core with an unligated M site at the central position. The APP irradiation of [MAu(PPh)] (M = Pt, Pd) in methanol resulted in the selective formation of [PtAu(PPh)CO] and [PdAu(PPh)CN] via the addition of a CO molecule and AuCN unit, respectively, generated in situ by the APP irradiation. In contrast, the APP irradiation of [Au(PPh)] in methanol yielded [Au(PPh)(CN)] and [Au(PPh)(CN)] as the main products, which were produced by sequential addition of AuCN to reactive [Au(PPh)] formed by dissociation equilibrium of [Au(PPh)]. DFT calculations predicted that a unique chain-like {-(CNAu)-PPh} (n = 1, 2) ligand was formed via the sequential insertion of -CNAu- units into the Au-PPh bond of [PdAu(PPh)] and [Au(PPh)]. These findings open up a new avenue for developing novel metal clusters via the chemical transformation of atomically defined metal clusters by APP irradiation.