Activation of Methane by Group 11 (Cu, Ag, Au) and Group 9 (Co, Ir) Transition Metal Atomic Anions

Abstract

The interactions of transition metal atomic anions (Cu^–, Ag^–, Au^–, Co^–, Ir^–) with methane were investigated via mass spectrometry, anion photoelectron spectroscopy, and quantum chemical calculations. Anion photoelectron spectra of the anionic metal atom-methane molecular complexes, [MCH₄]⁻, combined with theoretical calculations showed that Cu^– and Co^– formed both chemisorption, HMCH₃^–, and physisorption (solvation), M^–(CH₄), complexes, while Ag^– and Au^– formed only physisorption complexes due to their high activation barriers. Also, the mass spectrum showed Ir^– reacting with methane forming dehydrogenation products [IrCH_n]⁻ (n = 0–3) as well as the parent anion complex [IrCH₄]⁻. While the anion photoelectron spectrum of [IrCH₄]⁻ showed the presence of the physisorption complex, Ir^–(CH₄), and evidence for the intermediates, H₃IrCH^– and H₂IrCH₂^–, the theoretically predicted spectral band for the H₄IrC^– reaction product was outside of our experimental range.