An experimental study of ligand exchange and bond insertion in the reactions of dimanganese carbonyl ions with alcohols in the gas phase

The gas-phase reactions of dimanganese carbonyl ions (Mn2(CO)n+; n = 1-5) with methanol have been studied with the use of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The predominant reaction of the Mn2(CO)n+ ions with up to four CO ligands involves the incorporation of methanol and the loss of one or more CO ligands, whereas the Mn2(CO)5+ ion reacts by the successive addition of two alcohol molecules. The efficiency of the overall reaction with methanol decreases with the number of CO ligands present in the manganese containing ion. In addition, the reactions of the Mn2(CO)4+ ion with ethanol and n-propanol have been examined and observed to be less efficient than the reaction with methanol. The efficiency of the reaction of the Mn2(CO)4+ ion with CD3OH, C2D5OH or n-C3D7OH is significantly lower than of the reaction with the related unlabelled species revealing the occurrence of a significant isotope effect on the overall process. The primary product ions of the reactions of Mn2(CO)4+ with an alcohol react further with the formation of Mn2(CO)n(ROH)2+ (n = 0-2) ions. These latter ions react with an alcohol molecule with the formation of collision complexes that expel a hydrogen or alkane molecule together with the CO ligands. Based upon experiments with CD3OH, C2D5OH and n-C3D7OH, respectively, the loss of a hydrogen molecule is concluded to involve insertion into the OH bond, whereas alkane elimination is a result of insertion into the CO bond of the alcohol.