Chemistry and photochemistry of selected organometallic ions in the gas phase
Abstract
The chemistry and photochemistry of organotransition metal ions in the gas phase have been explored with Fourier transform mass spectrometry(FTMS). Bond energies obtained from photodissociation thresholds are evaluated by comparing them with values obtained by ligand displacement and competitive collision-induced dissociation(CID) reactions. General agreement is found when comparing these data with theoretical computations and other experimental values. Gas-phase photoinduced reactivity is a largely unexplored area. Here the photoinduced reactivity of RhC$\sb5$H$\sb6\sp+$ with cyclopentane to produce rhodocenium ion, which has been reported earlier, is further investigated along with the photoinduced reactivity of a new system, CoC$\sb5$H$\sb6\sp+.$ The wavelength dependence of these ions show that the photoinduced reactivity competes effectively with the more prevalent photodissociation process. Photodissociation experiments, using either a Hg/Xe arc lamp or one of various lasers, are performed on YL$\sp{n+}$ (n = 1 and 2, L = $\rm C\sb2H\sb2, C\sb2H\sb4, C\sb3H\sb6)$ and YCH$\sb3\sp+$ to determine metal-ligand bond energies. Ion-molecule displacement reactions are carried out in instances where only upper limits could be obtained from photodissociation. The D$\sp\circ$(Y$\sp+$--CH$\sb3)$ = 50$\pm$5 kcal/mol determined is in reasonable agreement with an ion beam determination of D$\sp\circ$(Y$\sp+$--CH$\sb3)$ = 59.5 $\pm$ 1.2 kcal.mol and a theoretical value of 58.6 kcal/mol. Photodissociation studies using lasers to determine the wavelength dependence and the M$\sp+$-benzene bond energies for M = Nb, V, Rh, Fe, Ti, Co show exclusive loss of the ligand except in the case of NbC$\sb6$H$\sb6\sp+$ where NbC$\sb6$H$\sb4\sp+$ (Nb$\sp+$-benzyne) and NbC$\sb6$H$\sb2\sp+$ were observed. Theoretical calculations are found to be in general agreement with these values. The reactivity of Ti$\sp{2+}$ and V$\sp{2+}$ with small linear alkanes show similar behavior to Sc$\sp{2+}.$ Bond insertion reactions were absent and only charge, hydride and methide transfer were observed. The reactivity trends of groups 3, 4 and 5, when analyzed, show unexpectedly high reactivity for group 5 second and third row metal dications and unexpectedly low reactivity for group 3 metal dications.
Degree
Ph.D.
Advisors
Freiser, Purdue University.
Subject Area
Analytical chemistry
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