Theoretical investigation of the gas-phase Mn+- and Co+-catalyzed oxidation of benzene by N2O

The gas-phase Mn(+)- and Co(+)-mediated oxidation of benzene by N(2)O has been theoretically investigated using density functional theory. The geometries and energies of all the stationary points involved are located. Two different oxidation mechanisms, i.e., mediated by M(+)(benzene) and MO(+), are taken into account. In the former catalytic cycle, benzene initially coordinates to the metal ion affording the M(+)(C(6)H(6)) adduct (M = Mn or Co), then N(2)O coordinates to the nascent benzene complex and gets activated by the metal to yield (C(6)H(6))M(+)O(N(2)). After releasing a molecular nitrogen, through the non-radical and/or O-insertion pathways, the system would be oxidized to phenol and regenerates the active catalyst M(+). This catalytic mechanism is energetically favourable, explaining the efficient Mn(+)- and Co(+)-catalyzed benzene hydroxylation observed in ion cyclotron resonance (ICR) experiments [J. Am. Chem. Soc., 1994, 116, 9565-9570]. For the alternative MO(+)-mediated oxidation mechanism, spin inversion as well as high energy barrier in the course of the N-O activation imply low reaction efficiency of the ground-state reactants, according with the ICR experiment finding that MO(+) was formed from exited M(+)*, thus both Mn(+) and Co(+) are unable to work as a catalyst in this case.