Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 307-324). Also available for download via the World Wide Web; free to University of Oregon users.

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Our aim was to develop the synthetic potential and reaction chemistry of Ir3+ and Ru2+ electrophiles by preparing well-characterized complexes whose properties are controllable by modification of the ancillary ligand environment Specifically, we prepared a series of ruthenium complexes to serve as selective hydrogenation and hydrogenolysis catalysts of furan derivatives. We also expanded the synthesis of electrophilic Ir3+ di-thiolate complexes. These types of compounds could eventually serve as catalysts precursors for the addition of weak nucleophiles to alkynes and nitriles.

The binding of molecular hydrogen to a metal center leads to the elongation of the H−H bond and subsequently to its cleavage along the reaction coordinate for the oxidative addition of H2. There has been considerable interest in the study of the activation of dihydrogen and map out the reaction coordinate for the homolysis of H2 on a metal center. A large number of H2 complexes reported to date possess H−H distances ranging from 0.8 to 1.0 Å. A relatively fewer examples of elongated dihydrogen complexes wherein the H−H distances fall in the range of 1.0 to 1.5 Å, are known. Study of the elongated dihydrogen complexes is of great significance because of its relevance in important catalytic processes such as hydrogenation, hydrogenolysis, and hydroformylation. Objectives The objectives of this work are as follows: (a) Synthesis and characterization of elongated dihydrogen complexes with chelating phosphine coligands by varying the electron donor ability. (b) Trap the various intermediate states in the process of oxidative addition of H2 to a metal center. (c) Map the reaction coordinate for the oxidative addition for the oxidative addition of H2 to a metal center. Results We have synthesized and characterized two new elongated dihydrogen complexes cis-[Ir(H)(η2-S2CH)(η2-H2)(PR3)2][BF4] (PR3 = PCy3, PPh3) wherein hydrogen atom undergoes site exchange between the H2 and the hydride sites. The dynamics of the exchange was studied using NMR spectroscopy. In addition, a series of ruthenium dihydrogen complexes of the type trans-[Ru(Cl)(η2-H2)(PP)][BF4] (PP = 1,2- Synopsis bis(diarylphosphino)ethane) has been synthesized and characterized wherein the aryl group is a benzyl moiety with a substituent (p-fluoro, H, m-methyl, p-methyl, p-isopropyl); in this series of complexes, a small increment in the electron donor ability (decrease in Hammett substituent constants) of the chelating phosphine ligand resulted in an elongation of the H−H bond by a small, yet significant amount. We also synthesized a series of 16-electron dicationic dihydrogen complexes bearing elongated dihydrogen ligand. In addition, we prepared a series of dihydrogen complexes of the type [RuCp/Cp*(PP)(η2-H2)][OTf] (PP = 1,2-bis(diarylphosphino)ethane, 1,2-bis(diarylphosphino)methane, 1,2-bis(dialkylphosphino)methane) bearing elongated H2 ligand (dHH = 1.0 to 1.17 Å); in this series of complexes as well, we found that the H−H bond distances increased as the donor ability of the chelating phosphines increased in small increments, along the reaction coordinate for the oxidative addition of H2 to a metal center. This investigation therefore, has established a very nice correlation between the H−H bond lengths and the Hammett substitutent constants (donor properties) resulting in the construction of dihydrogen complexes along the reaction coordinate for the oxidative addition of H2 to a metal center.

The bite angle of a diphosphine ligand plays an important role in determining the reactivity of a transition metal complex. The coordinated dihydrogen on a transition metal center can be activated toward homolysis or heterolysis depending upon the nature of the metal center and the ancillary ligand environment. The present work deals with our investigations on the effect of the bite angle of the chelating diphosphine ligands in the chemistry of certain ruthenium hydride and dihydrogen complexes. Protonation of the ds-[Ru(H)2(dppm)(PPh3)2] (dppm = Ph2PCH2PPh2) using HBF4-Et2O resulted in the dihydrogen/hydride complex trans-(Formula). This species shows dynamic exchange of the H-atom between the dihydrogen and the hydride ligands. The H-atom site exchange was studied by NMR spectroscopy. Attempts to prepare the ruthenium dihydride complexes, cis-[Ru(H)2(dppe)(PPh3)2] (dppe = Ph2PCH2CH2PPh2) and cw-[Ru(H)2(dppp)(PPh3)2] (dppp = Ph2PCH2CH2CH2PPh2) with larger bite-angled diphosphines dppe and dppp were unsuccessful. Earlier work in our group on the effect of trans nitrile ligands in a series of complexes of the type (Formula)howed that the properties of the bound H2 are almost invariant with a change in the R group of the nitrile. hi an effort to compare those results with analogous ruthenium complexes bearing smaller bite-angled diphosphine, dppm, we synthesized and characterized a series of complexes of the type (Formula). We found that the properties of the bound H2 were once again invariant with a change in the R group of the nitrile. In an effort to compare the effect of having two diphosphine ligands of different bite angles with systems containing symmetrical diphosphine ligands reported by our group,3 we synthesized a series of complexes of the type (Formula). These complexes exhibit hybrid properties in comparison to systems with symmetrical diphosphine ligands in terms of spectroscopic features and chemical reactivity. Thus, the bite angle of the diphosphine ligand has a definite influence on the properties of the bound H2 ligand.

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Non-covalent interactions taking place in solution are essential in chemical and biological systems. The solvent environment plays an important role in determining the geometry and stability of interactions. This thesis examines aromatic stacking interactions, alkyl-alkyl interactions, edge-to-face aromatic interactions, halogen bonds and hydrogen…hydrogen interactions in solution. Chapter 1 briefly introduces the different classes of non-covalent interactions, in addition to the state-of-the-art models and methods for investigating these weak interactions. The chapter finishes with a focus on dispersion interaction in alkanes and arenes. Chapter 2 investigates dispersion interactions between stacked aromatics in solution using a new class of complexes and thermodynamic double mutant cycles (DMCs). In extended aromatics, dispersion was detected as providing a small but significant contribution to the overall stacking free energies. Chapter 3 concerns the experimental measurement of alkyl-alkyl dispersion interactions in a wide range of solvents using Wilcox torsion balances. The contribution of dispersion interactions to alkyl-alkyl association was shown to be very small, with DMC, QSPR method and Hunter's solvation model. Chapter 4 studies edge-to-face aromatic interactions in series of solvents. In the open system, edge-to-face aromatic interactions were found to be sensitive to the solvent environment. The solvent effects were complicated and cannot be rationalised by a single parameter. Further analysis is needed. Chapter 5 describes a preliminary approach to investigate organic halogen…π interactions in solution using supramolecular complexes and torsion balances. Chapter 6 is a preliminary investigation of the ability of hydrogen atoms to act as H bond acceptors in silane compounds. Computations and 1H NMR demonstrated a weak interaction between silane and perfluoro-tert-butanol.

L’électrochimie devient incontournable dans les nouvelles technologies de stockage et de conversion de l’énergie. La réaction de dégagement de dihydrogène constitue aujourd’hui une réaction à fort intérêt sociétal qui est au cœur des nouvelles technologies permettant l’élaboration de systèmes pour la conversion de l’énergie. Cependant, des problématiques liées à l’utilisation de certains métaux nobles (le platine notamment) en tant que catalyseurs restent encore à résoudre. Ce travail de thèse s’inscrit dans les thématiques scientifiques de l’équipe de Recherche et d’Innovation en Electrochimie pour l’Energie (ERIEE) qui s’intéresse depuis plusieurs années à la substitution de ces métaux nobles par l’utilisation de catalyseurs moléculaires constitués de composés organiques contenant des métaux de transition comme centre électro-actif pour application dans les électrolyseurs industriels. Ce travail de thèse se focalise sur l’étude d’une famille de complexes moléculaires à base de métaux de transition (Co ou Fe), les clathrochélates, caractérisés par différentes structures chimiques. Le choix des ligands de ces complexes ainsi que l’étude des processus de fonctionnalisation sur des substrats ad hoc, sont des éléments déterminants dans l’appréhension des performances électro-catalytiques obtenues.Ces électro-catalyseurs ont été étudiés à la fois en solution (phase homogène) et fonctionnalisés à la surface d’électrodes solides. Leurs propriétés physico-chimiques ainsi que leurs performances électro-catalytiques vis-à-vis de la réaction de dégagement d’hydrogène, ont été caractérisés de façon systématique.La microscopie électrochimique à balayage (SECM) a notamment permis d'effectuer une caractérisation à l’échelle locale des propriétés électro-catalytiques des électrodes modifiées. / Electrochemistry is becoming a major field in new energy storage and conversion technologies. Nowadays, the hydrogen evolution reaction (HER) is a reaction of great societal interest, which is at the heart of new technologies enabling the development of systems for the conversion of energy. However, some issues related to the use of noble metals (platinum, in particular) as catalysts have not been solved yet. This thesis is part of the scientific approach of the Research and Innovation in Electrochemistry for Energy (ERIEE) research group which has been interested for several years in the substitution of these noble metals by the use of transition metal based electro-catalysts. These molecules consist of organic compounds containing transition metals as an electro-active center for application in industrial electrolysers. This thesis focuses on the study of a family of molecular complexes based on transition metals (Co or Fe), the so-called clathrochelates, characterized by different chemical structures. The choice of the ligands constituting these complexes as well as the study of their functionalization processes on ad hoc substrates, constitute key elements in the apprehension of the resulting electro-catalytic performances.These electro-catalysts were studied both in solution (homogeneous phase) and functionalized at the surface of solid electrodes. Their physico-chemical properties as well as their electrocatalytic turnover for the hydrogen evolution reaction, have been systematically characterized.In particular, scanning electrochemical microscopy (SECM) allowed for the characterization of the electrocatalytic properties of modified electrodes at the local scale.

Humankind’s tremendous industrial and technological progress over the last two centuries has been driven by the natural abundance and availability of fossil fuels. As those reserves deplete, the prudent course of action would be to develop other readily available fuel sources. Some research efforts using biomolecules involve the hydrogenases and nitrogenases with the goal of evolving dihydrogen. At the nitrogenase active site, the iron-molybdenum cofactor (FeMo-co) catalyzes the reduction of dinitrogen and protons to form ammonia and dihydrogen. Toward the goal of producing dihydrogen passively as an alternative fuel, a novel advanced material has been developed. CdSe nanoparticles complexed with FeMo-co, in both aqueous and organic solvent systems showed complex formation. When the system was interrogated by EPR spectroscopy, evidence of electron transfer was observed. The CdSeMSA●NafY●FeMo-co system when illuminated with visible light evolved dihydrogen consistently in four different experimental sets under the same reaction conditions. NifEN protein plays an important role in the biosynthesis of FeMo-co in addition to the involvement of NifU, NifS, NifB, NifX, NifH and NafY. After NifB synthesizes a FeMo-co precursor, 6-Fe NifB-co, NifEN further incorporates additional Fe, S, Mo, and (R)-homocitrate to complete the synthesis of FeMo-co. Molybdenum is provided to NifEN as its oxoanion, Mo(VI)O4 2- ; however, in FeMo-co molybdenum is in the oxidation state of Mo(IV). EPR spectroscopic investigation of NifEN turnover samples showed a signal at g = 2.00 that was dependent on molybdate concentration. Power and temperature profiles gave evidence that the g iv = 2.00 EPR signal was distinct from the Fe-S clusters in NifEN. The species observed at g = 2.00 was assigned to the reduction of Mo(VI) to Mo(V). How to utilize the effectiveness of FeMo-co and complex it to photoactive materials for the purpose of evolving dihyrogen upon illumination, thus providing a sustainable alternative energy source is one subject of this dissertation. A related subject is to gain an understanding of the biosynthetic pathway of FeMo-co by investigation of NifEN turnover experiments. This understanding should contribute towards the development of improved catalysts for meeting future energy demands.