Molybdenum Oxide Cluster Ions in the Gas Phase:  Reactions with Small Alcohols

The gas-phase reactions of molybdenum oxide cluster ions Mo x O y + ( 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 Mo x O y + 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 Mo 3 O 9 + ion with more than one CH 3 OH molecule yielding Mo 3 O 9 (C 2 H 5 ) + and Mo 3 O 9 (C 3 H 7 ) + ions. The Mo 3 O 9 CH 3 + 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 Mo x O y proton affinities were estimated as PA(MoO) < 180 kcal/mol, PA(Mo 2 O 4, Mo 2 O 5, Mo 3 O 8 ) = 188 ± 8 kcal/mol, PA(MoO 2 ) = 202 ± 5 kcal/mol, PA(MoO 3, Mo 2 O 6, Mo 3 O 9 ) > 207 kcal/mol.