REACTIONS OF GAS-PHASE TRANSITION-METAL ATOMS WITH SMALL HYDROCARBONS

We compare the chemistry of gas phase transition metal atoms with alkanes and alkenes, surveying the different charge states M, M+, and M2+. Most monopositive cations are highly reactive, dehydrogenating or demethanating linear alkanes in exothermic reaction at room temperature. The dipositive cations abstract electrons or hydride anions from alkanes if the radii of long-range curve crossings permit. If not, M2+ can approach the hydrocarbon to close range, and the same kinds of H-2 and CH4 elimination reactions occur as observed in M+. The neutral atoms are inert to alkanes, but Sc, Ti, V, Ni, Zr, Nb, and Mo react with alkenes. The interplay of the energetics of low-lying metal states of different electron spin and electron configuration; the size of valence d and s orbitals; and the character of long-range forces determines chemical reactivity.