Photofragment spectroscopy of covalently bound transition metal complexes: a window into C-H and C-C bond activation by transition metal ions

摘要

Transition metal cations M~+ and metal oxide cations MO~+ can activate C-H and C-C bonds in hydrocarbons. In this review, we discuss our studies of the electronic spectroscopy and dissociation dynamics of the intermediates, reactants and products of these reactions using photofragment spectroscopy. Results are presented on the spectroscopy of the intermediates of methane activation by FeO~+, as well as on the spectroscopy of FeO~+, NiO~+ and PtO~+. Resonance enhanced photodissociation allows us to measure the electronic spectroscopy of FeO+ below the dissociation limit with rotational resolution. Complementary time-dependent B3LYP calculations of excited electronic states of FeO~+ and NiO+ are in surprisingly good agreement with experiment. Dissociation onsets give upper limits to bond strengths for FeCH_2~+, CoCH_2~+, NiCH_2~+, TaCH_2~+ and AuCH_2~+. These results are compared to thermodynamic measurements, and the extent to which rotational energy contributes to dissociation is investigated. The spectroscopy of the π-bonded complexes Pt(C_2H_4)~+ and Au(C_2H_4)~+ is discussed, along with studies of larger systems. Planned studies of the vibrational spectroscopy of covalently bound ions are also discussed.