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) _<i>n</i> (<i>n</i> = 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 CH₄ <i>a</i> ₁ and <i>t</i> ₂ 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 <i>t</i> ₂ 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) _<i>n</i>=2,3 complexes corresponding, presumably, to the loss of two H₂ molecules.