CONCERTED MULTIPLE DEHYDROGENATION OF GAS-PHASE SATURATED CYCLIC C-4-C-8 HYDROCARBONS BY OS+

The gas-phase reactions of laser-generated Os+ with various cycloalkan es, C5H10, C6H12, C7H14, C8H16, C6H10, C6H6, cis-1,2-dimethylhexane, a nd cis-1,3-dimethylhexane, have been examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. In contrast to many t ransition-metal ions, whose reactions with alkanes show extensive clea vage of C-C bonds, dehydrogenation is the major process in all reactio ns. No evidence of C-C insertion is found, and the carbon ring is left intact. Saturated cyclic hydrocarbons exposed to Os+ undergo repeated dehydrogenation to form the complex ions (CnHnOs+, which then react w ith another corresponding neutral hydrocarbon molecule to form [CnHn-O s-CnHn](+). The Os-ligand complex ions may be identified unambiguously from isotopic distributions. Reaction mechanisms for the various reac tion pathways are proposed.