Mechanistic investigations of gas phase ion-molecule reactions using Fourier transform ion cyclotron resonance mass spectrometry.

摘要

Studies of the mechanisms and energetics of a variety ion-molecule reactions involving organometallic and organic ions, have been performed using Fourier transform ion cyclotron resonance mass spectrometry (FTMS). The bond activation processes of V⁺, VO⁺, VOH⁺, and VOCH₃⁺ with water and methanol were investigated in detail. All ions are observed to preferentially activate the C-O bond in methanol, however C-H and O-H bond cleavage are also observed. The addition of the oxo, hydroxo, and methoxo ligands is found to significantly effect the intrinsic reactivity of the ions, relative to V⁺. The reactions of V(CO)₅⁻ with a wide variety of molecules have revealed mechanistic details of the oxidative addition and ligand switching reactions. Steric effects are proposed to account for the selective reactivity of V(CO)₅⁻ with alcohols and amines. Studies of ligand substitution reactions support an electron transfer initiated mechanism, implying that V(CO)₅⁻ has a triplet ground state and a trigonal bipyramidal structure. The chlorine atom transfer reactions of V(CO)₅⁻ with chloromethanes display a correlation with C-CI bond strength, suggesting the mechanism is initiated by oxidative addition of the C-C1 bond or involves a direct chlorine atom transfer. The decomposition of metallocarboxylate anions ([M(CO)ₓ₋₁CO₂]⁻) was studied in an effort to understand the production of CO₂ by metal carbonyl compounds, proposed as intermediates in the Water-Gas shift reaction. The nascent [M(CO)ₓ₋₁C0₂]⁻*, formed by nucleophilic addition of 0⁻ to M(CO)ₓ (M=Pe, Cr, V), is observed to undergo exclusive loss of CO₂ without subsequent decomposition of the product metal carbonyl anion (M(CO)ₓ₋₁⁻) The reaction of P AHs with O⁻ and O₂⁻ were studied, to investigate the potential of isomer differentiation by chemical ionization. These reactions are characterized by a number of reactive pathways, demonstrating the ability to distinguish isomers which cannot be differentiated by other ionization techniques. Kinetic energy release measurements of the S(N)2 reactions of F⁻ with CH3CI, C₆H₅CI, and CH₃COCl have been made using KEICR. The F⁻/CH₃Cl reaction results in a non-statistical energy disposal. The reaction is proposed to proceed by a direct mechanism.