Theoretical study of the gas-phase ethane C-H and C-C bonds activation by bare niobium cation

The potential energy surfaces for the reaction of bare niobium cation with ethane, as a prototype of the C-H and C-C bonds activation in alkanes by transition metal cations, have been investigated employing the Density Functional Theory in its B3LYP formulation. All the minima and key transition states have been examined along both high- and low-spin surfaces. For both the C-H and C-C activation pathways the rate determining step is that corresponding to the insertion of the Nb cation into C-H and C-C bond, respectively. However, along the C-H activation reaction coordinate the barrier that is necessary to overcome is 0.13 eV below the energy of the ground state reactants asymptote, while in the C-C activation branch the corresponding barrier is about 0.58 eV above the energy of reactants in their ground state. The overall calculated reaction exothermicities are comparable. Since the spin of the ground state reactants is different from that of both H-Nb+-C2H 5 and CH3-Nb+-CH3 insertion intermediates and products, spin multiplicity has to change along the reaction paths. All the obtained results, including Nb+-R binding energies for R fragments relevant to the examined PESs, have been compared with existing experimental and theoretical data. © 2008 Springer-Verlag.