Reactivity studies of metal halide ions, niobium cluster ions and thermochemistry of selected cationic cobalt (aromatic heterocycles) using Fourier transform ion cyclotron resonance mass spectrometry

Vajira Kumara Nanayakkara, Purdue University

Abstract

The gas-phase reactions of halogen substituted first row transition metal ions with small and cyclic alkanes, photochemistry of Co$\sp{+}$ substituted with aromatic heterocycles (pyrrole, furan, thiophene and selenophene) and the unique reactivity of Nb$\sp{+}$ as well as Nb$\rm\sb {n}\sp{+}\ (n=2-13)$ cluster ions towards CH$\sb3$I have been studied using Fourier transform mass spectrometry. Several gas phase techniques have been used to gather information on reaction mechanisms and thermochemistry of each of these systems. Reactions of CoI$\sp{+}$ with alkanes revealed that CoI$\sp{+}$ inserts exclusively into the C-H bonds of small linear and cyclic alkanes. A generalized mechanism involving C-H insertion followed by $\beta$-hydrogen transfer is proposed as preceeding steps for dehydrogenation processes. Unlike bare metal ions, the resultant CoI(alkene)$\sp{+}$ complex does not isomerize to a hydrido $\pi$-allyl complex ion. Literature cited bond energy data have been used to explain the absence of HI loss. The unique 2,3-dehydrogenation of n-butane with CoI$\sp{+}$ was further examined for several other metal halide ions (MX$\sp{+})$ where M = Fe, Cr, V and X = Cl, Br, I. Nb$\sp{+}$ has shown unique reactivity towards CH$\sb3$I. This unique reactivity of Nb$\sp{+}$ is explained on the basis of multiple bond formation between Nb$\sp{+}$ and C. In a related study of the reactivity of Nb$\rm\sb{n}\sp{+}\ (n = 2-13),$ saturation limits have been used to probe the structures of some of the niobium cluster ions. Photodissociation methods have been employed to measure the bond energies of CoL$\sp{+}$ and CoL$\sb2\sp{+}$ systems (L = pyrrole, furan, thiophene and selenophene). These bond energy measurements are further corroborated by ligand displacement reactions and competitive collision-induced dissociation experiments. The CO loss product ion, obtained from the reaction of Co$\sp{+}$ with furan, is explained by using respective literature cited thermochemical data.

Degree

Ph.D.

Advisors

Freiser, Purdue University.

Subject Area

Analytical chemistry|Chemistry

COinS