Osmium Tetroxide and Its Fragment Ions in the Gas Phase: Reactivity with Hydrocarbons and Small Molecules

Article abstract of DOI:10.1021/ja00183a014

Gas-phase ion-molecule reactions of OsOn(1+) (n=0-4) with a number of hydrocarbons and small molecules, including CH4, C2H4, C2H6, C3H8, C4H10, H2, CO, NH3, and SiH4, have been investigated by Fourier transform ion cyclotron resonance spectrometry.Anion chemistry was briefly investigated.Thermochemical quantities derived include D(Os(1+)-O)=100+/-12, D(OsO(1+)-O)=105+/-12, D(OsO2(1+)-O)=105+/-12, D(OsO3(1+)-O)=71+/-12, D(OsO3-O)=78+/-14, D(OsO4(1+)-H)=132+/-3 kcal/mol, D(OsO3(1+)-OH)=101+/-16 kcal/mol, and PA(OsO4)=161+/-2 kcal/mol.Many diverse and novel reactions are observed.Among them are <2_s+2_s> cycloaddition with H2, bond metathesis, oxo transfer, and hydrogen atom abstraction.These ions are also extraordinarily active dehydrogenation reagents; the most dramatic example is the sequential, complete dehydrogenation of SiH4 to mono-, di-, and trisilicides.Another intriguing process is the double bond metathesis with NH3, in which one or two oxo ligands are exchanged for imido groups.The number of oxo ligands is found to have a striking effect on the chemistry; mechanisms are discussed for the reactions observed.For example, the relative inertness of OsO3(1+) is attributed to a failure of the Os(+7) center to undergo oxidative addition.OsO2(1+) emerges as a potential model catalyst for the conversion of methane and dioxygen to aldehydes.