Infrared Spectroscopy of Au+(CH4)n Complexes and Vibrationally-Enhanced C–H Activation Reactions

Abstract

A combined spectroscopic and computational study of gas-phase Au+(CH4)n (n = 3–8) complexes reveals a strongly-bound linear Au+(CH4)2 core structure to which up to four additional ligands bind in a secondary coordination shell. Infrared resonance-enhanced photodissociation spectroscopy in the region of the CH4a1 and t2 fundamental transitions reveals essentially free internal rotation of the core ligands about the H4C–Au+–CH4 axis, with sharp spectral features assigned by comparison with spectral simulations based on density functional theory. In separate experiments, vibrationally-enhanced dehydrogenation is observed when the t2 vibrational normal mode in methane is excited prior to complexation. Clear infrared-induced enhancement is observed in the mass spectrum for peaks corresponding 4u below the mass of the Au+(CH4)n=2,3 complexes corresponding, presumably, to the loss of two H2 molecules.