Spectroscopic and electrochemical characterization of group 6 organometallic odd electron complexes

The rational design, synthesis, technique development, and both spectroscopic and electrochemical characterization of transition metal organometallic intermediates is described within this thesis. A systematic variation in ligands attached to the cyclopentadienyl ring was accomplished in order to tailor the electronic characteristics of the intermediate, which consequently alters the reactivity of the intermediate. Incorporation of basic ligands on the cyclopentadienyl ring such methyl, pentamethyl, triisopropanol, and pendant THF onto the cyclopentadienyl ring resulted in significant change of physical properties and the creation of new functionality by altering the electronic distribution in the intermediate, resulting in the shift of the electrochemical reduction potential. The shift in reduction potential is proportional to the increase in the electron-donating property of the ligand. The pendant ligand, tetrahydrofurfurylcyclopentadienyl, allows for a novel reaction mechanism to occur where the transient intermediate reacts with the pendant ligand to form a relatively stable, observable steady state concentration of the 19-electron molecule. Another method for tailoring the reduction potential is by altering the medium in which the compound reacts. Changing the solvent by selecting its electron-donating or -withdrawing ability provides a method to alter the reduction potential. Direct characterization of these intermediates is not only useful as model systems for mimicking the electron and energy transfer in the fixation of carbon monoxide but also allows for the determination of redox potentials of related compounds.; In order to characterize these short-lived intermediates, an effort was undertaken to enhance a novel technique first developed in the laboratories of Wayner and Fox. The technique, photomodulated voltammetry (PMV), allows for the direct electrochemical characterization of the reduction potential of these transition metal organometallic compounds. The theory and physical methodology of PMV are described (Chapter 2). With the basis of this technique developed, the characterization of the parent compound (eta5-C 5H5)2M2(CO)6 was performed using cyclic voltammetry, in order to understand the overall electrochemical reactivity of this family of compounds. Outlined in Chapter 3 is the electrochemical analysis of the intermediate 17-electron radical as a function of group 6 transition metal, substituted cyclopentadienyl ligands, and solvents. This Chapter reports the first utilization of PMV on this family of compounds. (Abstract shortened by UMI.)...