Molybdenum oxide cluster ions in the gas phase: Reactions with small alcohols

The gas-phase reactions of molybdenum oxide cluster ions MoxOy+ (x = 1-3, y =;1-9) with small alcohols have been investigated using Fourier transform ion cyclotron resonance mass spectrometry. The product branch ratios are reported. The reactions of MoxOy+ with alcohols can be envisioned as proceeding via metal insertion into C-H and C-O bonds. C-H bond insertion leads to alcohol dehydrogenation and aldehyde elimination, whereas insertion into the C-O bonds results in alcohol dehydration and formation of metal-alkyl groups. Moreover, an increase of the chain length and branching lead to C-C bond cleavage. The most intriguing process is the reaction of the Mo3O9+ ion with more than one CH3OH molecule yielding Mo3O9(C2H5)(+) and Mo3O9(C3H7)(+) ions. The Mo3O9CH3+ ion was found to be the key intermediate of the polymerization process. Molybdenum oxides are protonated in the presence of alcohols. The upper and lower limits for the MoxOy, proton-affinities were estimated as PA(MoO) < 180 kcal/mol, PA(Mo2O4, Mo2O5, Mo3O8) = 188 +/- 8 kcal/mol, PA(MoO2)= 202 +/- 5 kcal/mol, PA(MoO3, Mo2O6, Mo3O9) > 207 kcal/mol.