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

Transition metal cations Mþ and metal oxide cations MOþ 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 FeOþ, as well as on the spectroscopy of FeOþ, NiOþ and PtOþ. Resonance enhanced photodissociation allows us to measure the electronic spectroscopy of FeOþ below the dissociation limit with rotational resolution. Complementary time-dependent B3LYP calculations of excited electronic states of FeOþ and NiOþ are in surprisingly good agreement with experiment. Dissociation onsets give upper limits to bond strengths for FeCH2 , CoCH þ 2 , NiCH þ 2 , TaCH þ 2 and AuCH þ 2 . These results are compared to thermodynamic measurements, and the extent to which rotational energy contributes to dissociation is investigated. The spectroscopy of the p-bonded complexes Pt(C2H4) þ and Au(C2H4) þ is discussed, along with studies of larger systems. Planned studies of the vibrational spectroscopy of covalently bound ions are also discussed.