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Gas phase ion-molecule chemistry of ironcyclopentadienyl and ironcyclopentadiene ions with C1-C4 alcohols by Fourier transform ion cyclotron resonance mass spectometry

University of British Columbia

The gas phase ion-molecule chemistry of organometallic ions CpFe+ (1) and C₅H₆Fe+ (2), shown below, has been examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. [MODEL] These ions, generated by electron impact ionization from organometallic neutral precursors ferrocene and cyclohexadienone iron tricarbonyl, were allowed to react with neutral methanol, ethanol, n-, i-propanol, and n-, i-, f-butanol. Selected isotopologues of employed alcohols were used to infer the reaction mechanism. Abundances of ionic reactants and products were monitored as a function of reaction time to obtain kinetic data. A general trend was observed that the reactivity of ions 1 and 2 with alcohols increases with the increasing length of the alkyl chain. The most important difference in the gas phase chemistry of these two ions was noted for the reactions with methanol. CpFe+ forms only an ion-neutral complex without any bond activation. C₅H₆Fe+ was found to dehydrogenate methanol by a competitive insertion into C-H and H-0 bonds. Taking the ratio of ADO collision rates and the measured reaction rates it was found that ion 2 has a twofold increase in reaction efficiency as compared to ion 1. For the reactions of CpFe+ with higher alcohols the major processes observed were dehydration and loss of alkene. Dehydrogenation of alcohols was a minor reaction. In all C₅H₆Fe+/alcohol systems except for methanol, reductive elimination of water and alkene was always accompanied by loss of a hydrogen molecule. Experiments with labeled alcohols have shown that one of the hydrogen atoms in the eliminated neutrals originates on a cyclopentadiene ring. This was rationalized by proposing that the reacting form of C₅H₆Fe+ ion has a CpFe+-H structure, formed by an intramolecular 6-hydrogen transfer that results in a metal-hydrogen bond.

Thesis/Dissertation

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2009-04-29

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http://hdl.handle.net/2429/7696

Chemistry

University of British Columbia

UBCV

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