Application of Fourier transform ion cyclotron resonance mass spectrometry to the characterization of selected transition metal imido and acetylene complexes and metal carbon clusters

Don Rufus Anthony Ranatunga, Purdue University

Abstract

The gas-phase reactivity of group 3 transition metal imido ions and metal-carbon cluster ions, and the photochemistry of selected metalacetylene ions have been studied using Fourier transform ion cyclotron resonance mass spectrometry. A variety of gas-phase techniques have been employed to probe reaction mechanisms, ion structures and thermochemistry of these systems. Due to the d$\sp0$ electronic configuration of the metal center, MNH$\sp+$ (M = Sc and Y) provide an opportunity to study alternative mechanisms of C-C and C-H activation other than the most commonly observed oxidative addition. The reactivity of these metal imido ions with simple alkenes is reported. A general reaction mechanism involving the formation of a four-centered 2-azametallacyclobutane key intermediate followed by a $\beta$-hydrogen transfer to the metal center is proposed to explain the reactions observed. Proposed mechanisms for the observed reactions are discussed in light of the condensed-phase early-transition metal cyclometallation chemistry.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)The reactivity of Nb$\sb4$C$\sb4\sp+$ generated from the secondary reaction of Nb$\sb4\sp+$ with ethylene is investigated to provide experimental evidence for the theoretically calculated 2x2x2 cubic crystallite structure. The results are compared with the previously reported reactivity of Nb$\sb4$C$\sb4\sp+$ generated in a supersonic source by seeding the expansion gas with methane. Finally, gas-phase photodissociation of metal-acetylene ions is studied to provide experimental evidence for the trends in bonding observed in ab initio calculations. From the photoappearance thresholds of the simple cleavage product M$\sp+$, experimental bond energy values are assigned. Ion-molecule reactions and competitive CID are used to obtain complementary information.

Degree

Ph.D.

Advisors

Fresier, Purdue University.

Subject Area

Analytical chemistry

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