Studies of the Energetics and Mechanisms of Organometallic Reactions in the Gas Phase

Citation

Halle, Linda F. (1983) Studies of the Energetics and Mechanisms of Organometallic Reactions in the Gas Phase. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/29x4-wk61. https://resolver.caltech.edu/CaltechTHESIS:11012019-144753562

Abstract

An ion beam apparatus is used to study reactions of the three first row group 8 atomic metal ions, Fe⁺, C^o+, and Ni⁺, as well as the diatomic FeH⁺ species, with small organic molecules. The kinetic energy dependence of these processes is examined. Analysis of the thresholds for endothermic reactions yields bond strengths of the metal ion to various substituent groups. The thermochemical information derived in this manner and from more qualitative observations is used to assess the mechanisms by which these ions react with small organic molecules.

Chapter I provides a brief summary of some of the organometallic systems previously studied using the ion beam apparatus. Chapter II presents the culmination of our studies of reactions of the first row group 8 metal ions with alkanes in which the extensive use of deuterium and ¹³C-labeled compounds provides further elaboration of the mechanisms by which these ions activate carbon-carbon and carbon-hydrogen bonds.

Chapter III examines the consequences of incorporating a carbonyl group into the hydrocarbon from investigations of the reactions of Co⁺ with aldehydes and ketones. Analysis of products formed at high relative kinetic energies are used in conjunction with thermochemical estimates to infer mechanistic details and construct qualitative reaction coordinate diagrams for the interactions of Co⁺ with carbonyl compounds.

Chapter IV represents an extension of our determinations of metal-carbon bond strengths to include fluorinated substituents. In particular, measurements of the Ni⁺-CH₂ and N⁺-CF₂ bond energies are reported. The implication of these carbene bond strengths for the metathesis of fluorinated olefins is discussed.

Chapter V reports the first ion beam experiment of an organometallic fragment, the FeH⁺ species. Thermochemical information is obtained from reactions involving proton transfer from, and hydride transfer to, FeH⁺. We find that oxidative addition of FeH⁺ to D₂ or hydrocarbons via Fe(IV) or four-centered intermediates is not a facile process, while reversible insertion of olefins into Fe⁺-H occurs with moderate cross section at low energies. Preliminary results for the reactions of FeH⁺ with alcohols, aldehydes, and ethers are also discussed.

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