Applications of Fourier transform ion cyclotron resonance mass spectrometry to the studies of isomer differentiation and organometallic distonic ions
Abstract
Fourier transform ion cyclotron resonance (FTICR) mass spectrometry is applied to study MC$\sb7$H$\sb7$ (M = Fe, Co) isomers and to explore organometallic distonic ions. Three MC$\sb7$H$\sb7\sp+$ isomers, presumably, M(tropylium)$\sp+$, M(benzyl)$\sp+$, and M(tolyl)$\sp+$ are generated through different synthetic routes. Of particular interest is the role of the metal in stabilizing the tolyl ligand, given that the unmetallated tolyl ion rearranges to benzyl ion on the time scale of the FTICR experiments. Collision-induced dissociation (CID), photodissociation, and selected ion-molecule reactions readily distinguish Fe(tropylium)$\sp+$ from the other two structures. Fe(benzyl)$\sp+$ and Fe(tolyl)$\sp+$, however, are indistinguishable by CID and photodissociation, but exhibit differences in reactivity with selected reagents including acetone, p-xylene, and methyl iodide. The results show that Fe enhances the stability of tolyl ion. However, upon activation, Fe(tolyl)$\sp+$ rearranges to Fe(benzyl)$\sp+$ prior to dissociation. Bond strengths of Fe$\sp+$-C$\rm\sb7H\sb7$ are also derived. For CoC$\rm\sb7H\sb7\sp+$, CID differentiates the three isomers, particularly Co(tolyl)$\sp+$ and Co(benzyl)$\sp+$. The first example of an organometallic distonic ion, Fe(p-benzyne)$\sp{+}$, is generated and studied together with its isomers, Fe(o-benzyne)$\sp+$ and Fe(ene-1,5-hexadiyne)$\sp+$, by CID and ion-molecule reactions with selected alkenes and halides, as well as dimethyl disulfide and dimethyl diselenide. Fe(p-benzyne)$\sp{+.}$ shows different reactivity toward most of these reagents compared to its isomers. However, its charged metal center is the dominant reaction initiation center, while the radical site is rather inert except for its reaction with allyl iodide. Selected ligands, such as benzene and cyclopentadienyl, are also introduced onto the metal center of Fe(p-benzyne)$\sp{+.}$ to study the ligand effect on the reactivity of the radical center. The generation and investigation of new organometallic distonic species with different metal centers or different structural frames are also attempted.
Degree
Ph.D.
Advisors
Freiser, Purdue University.
Subject Area
Analytical chemistry
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