GAS PHASE ION-MOLECULE REACTIONS OF TRANSITION METAL IONS WITH ORGANIC MOLECULES

GARY DWIGHT BYRD, Purdue University

Abstract

The gas phase reactions of transition metal ions with organics are investigated to provide fundamental information about metal-hydrocarbon interactions. Experiments are performed in ion cyclotron mass spectrometers where metal ions are generated by laser desorption and trapped in the presence of various types of hydrocarbons. Oxidative addition and (beta)-hydrogen elimination are the major steps in the reactions of these metals with alkanes. In general, the behavior of metal ions toward alkanes falls into three different categories: (1) those that selectively cleave C-H bonds, (2) those that cleave both C-C and C-H bonds, and (3) those that cleave neither. Dehydrocyclization is suggested in some cases and evidence is presented for the existence of allyl structures bound to certain metal ions. The presence of an oxygen atom in the hydrocarbon structure can greatly influence the reaction. Overall, the ROR' and RCOR' linkages facilitate cleavage of the molecule. While most transition metal ions appear to directly insert into hydrocarbon bonds, some reactions of Cu('+) are seen to induce cleavage of ketones, esters, and carboxylic acids without direct insertion. The strength of the metal-oxygen bond is a factor in many of the reactions with oxygenated hydrocarbons, especially for Ti('+), V('+), and Nb('+) which exhibit a strong tendency to form metal oxides in the gas phase. Metal ion reactivities toward a particular functional group vary a great deal. With esters and acids, Cu('+) shows very predictable trends in cleaving the RCOOR' group while Co('+) and Rh('+) reveal a variety of competing processes including dehydration and decarbonylation. Atomic metal ions can be used as chemical ionization agents to identify unknown compounds and components in mixtures. By reacting a sample with several different metal ions, a periodic reactivity plot can be rapidly generated which provides a unique fingerprint for a given molecule. The full potential of using atomic metal ions as chemical ionization agents has yet to be realized since these types of reactions are relatively new. Also, the addition of a ligand to the metal ion can alter its behavior which increases the flexibility of this technique and usefulness to analytical mass spectrometry.

Degree

Ph.D.

Subject Area

Analytical chemistry

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