Applications of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry and density functional theory to the studies of gas phase metal ion-ligand structures and reactivities

Quan Chen, Purdue University

Abstract

The gas-phase reactions of a number of interesting ligated metal species have been studied using Fourier transform ion cyclotron resonance mass spectrometry, together with density functional calculations. Both experimental and theoretical results indicate that the structure of $\rm MCF\sb3\sp+$ (M = Fe, Co and Ni) corresponds to a $\rm\lbrack FM\sp+{\...}F\sb2C\rbrack $ ion-dipole complex with electrostatic bonding between $\rm FM\sp+$ and $\rm CF\sb2,$ involving C-F activation. This represents the first case of a gas-phase C-F activation by bare cobalt ions. The reaction mechanisms were further investigated by obtaining the potential energy surfaces of $\rm\lbrack M\sp+,\ C,\ F\sb3\rbrack $ cation systems by density functional calculations. In order to compare the structure and reactivity of the $\rm CF\sb2$ group on $\rm MCF\sb3\sp+,$ the reactions of fluorinated metal-carbene ions $\rm FeCF\sb2\sp+$ and $\rm CoCF\sb2\sp+$ with selected hydrocarbons are studied. The experimental and theoretical results illustrate that the $\rm CF\sb2$ ligand on $\rm MCF\sb2\sp+$ is different from that on $\rm FM\sp+{\...}F\sb2C$ in terms of structure, chemical bonding and reactivity with small hydrocarbons. The ligand effects of formaldehyde and its sulfur-containing analog, thioformaldehyde, on $\rm Fe\sp+$ are investigated. We found distinct differences between the reactivities of $\rm FeCH\sb2O\sp+$ and $\rm FeCH\sb2S\sp+.$ While C-C insertion leading to alkane loss is predominant for the reactions of $\rm FeCH\sb2O\sp+$ with alkanes, C-H insertion is preferred for $\rm FeCH\sb2S\sp+.\ CH\sb2O$ behaves like a spectator ligand. On the other hand, $\rm CH\sb2S$ ligand participates in a rearrangement to form an activated $\rm H\sb2S$-$\rm Fe\sp+$-olefin complex. The reaction mechanisms are proposed and theoretical calculations are fully supportive in explaining the different reaction pathways. Finally, the gas-phase $\rm Fe\sp+$-assisted cycloaddition of cyclopentadiene with small alkenes and alkynes are also studied. $\rm Fe\sp+$-cyclopentadiene is found to react with ethene, propene, ethyne, propyne and allene to generate Diels-Alder reaction products, which further rearrange to $\rm C\sb7$-$\rm C\sb8$ membered ring Fe complex ions.

Degree

Ph.D.

Advisors

Freiser, Purdue University.

Subject Area

Analytical chemistry

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