Pioneering investigations into organometallic electrochemistry

• Main Author: Dann, Thomas
• Published: University of East Anglia 2014
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614623

Recently there has been a large effort to take advantage of electrochemistry to develop and understand novel chemical processes and reactivity. This thesis contains investigations into the synthesis and electrochemical properties of three diverse organometallic systems. In chapter 2, the first experimental determination of a an unsupported AuII-AuII bond is reported. The electrochemical characterisation of gold(III) hydride, hydroxide and chloride pincer complexes based on a backbone of a doubly cyclometalated 2,6-bis(4’-tert-butylphenyl) pyridine ligand was performed, in which it was determined that upon reduction of the AuIII complexes, an unsupported AuII dimer is formed, confirmed by characterisation of an authentic sample of the dimer. Using digital simulation, the reduction potentials of the hydride and hydroxide along with the oxidation potential of the dimer were determined, allowing the construction of a Hess cycle, from which the bond energy of the gold-gold bond in the dimer and the difference of the Au-OH and Au-H bond energies could be estimated. In chapter 3, the redox non-innocent behaviour of the ligands in zinc(II) bis(formazanate) complexes is investigated. These complexes have been electrochemically characterised by cyclic voltammetry, showing remarkably facile reduction to a radical anion, and further reduction to a dianion. Simulation of the cyclic voltammetry recorded for these compounds yielded optimised values of formal potentials, E0, and electron transfer rate constants, k0. In chapter 4, the synthesis and electrochemical characterisation of the first known examples of triazole-substituted cymantrene and cyrhetrene complexes are reported. The compounds h5-(-phenyltriazol-1-yl)cyclopentadienyl tricarbonyl manganese(I), with a phenyl, 3-aminophenyl or 4-aminophenyl substituent on the 4-position of the triazole ring were prepared via the copper(I)-catalyzed azide-alkyne cycloaddition (1,3-CuAAC) reaction. Cyclic voltammetric characterization of the redox behavior of each of the three cymantrene–triazole complexes is presented together with digital simulations, in-situ infrared spectroelectrochemistry, and DFT calculations to extract the associated kinetic and thermodynamic parameters. The synthesis and characterisation of the rhenium(I) analogues of the phenyl and 4-amino triazole substituted complexes are also reported. In chapter 5, the use of diazirines as carbene precursors for carbon surface modification is investigated, via the synthesis and characterisation of diazirine derivatised cymantrene and cyrhetrene. The surface modification of glassy carbon electrodes was attempted via irradiation of the half-sandwhich diazirine bearing complexes, resulting in oxidation waves visible on the electrode by cyclic voltammetric analysis.