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Gas phase ion-moleculae chemistry of an analogous series of aryl transition-metal carbonyl compounds by Fourier transformation ion cyclotron resonance mass spectrometry Taylor, Sandra M.


The gas phase ion-molecule chemistry of an analogous series of five aryl transition-metal carbonyl compounds has been examined using FT-ICR-MS techniques. Under 25 eV (positive ion) and 2.5 eV (negative ion) electron ionisation, ionic fragments of the following compounds were generated: CpV(CO)4; BzCr(CO) 3;CpMn(CO)3; BuFe(CO)3; and CpCo(CO)2; {where Cp=ƞ5-C5H5; Bz=ƞ6-C6H6;Bu=ƞ4-C4H6).Ion-molecule reaction products were temporally monitored. Kinetic analyses showed that reaction pathways for each reactive cation fragment involved interaction with the neutral parent molecule, either by electron or ligand transfer, or by condensation with simultaneous carbonyl ejection. Condensations resulted in generation of higher molecular weight polynuclear ionic cluster fragments such as: (CpV)3(CO)3+; (BzCr)2(CO)3+;and (BuFe)2(CO)+. In general, the reactivity of any cationic species varied directly with electron deficiency and coordination site availability of the central metal core. Some reactive cations exhibited unexpected reactivity patterns, despite their large formal electron deficiency, suggesting possession of unusual bonding configuration within cluster cores. Several reactive cations exhibited excited state behaviour, reacting more rapidly than their ground state counterparts. Reaction rate constants approximated those predicted by Langevin for unpolarised gas phase bimolecular processes. Smaller, highly electron-deficient daughter cations, e.g. CpV+ and BzCrCO+, were reactive with respect to some small molecular addition reagents such as ammonia or dioxygen. Several important hydride adducts were also observed. On the other hand, anion-molecule chemistry was less complicated: anion daughter fragments reacted solely by formation of one or two stable clusters; and were relatively unreactive with respect to addition reagent molecules.

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