Syntheses of a number of chiral and non-chiral sulphoxides and corresponding Ru(II) sulphoxide compounds are described, as well as significant reactions of some of these complexes with molecular hydrogen, olefins, and carbon monoxide. The new sulphoxides presented are: (S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide, (MBMSO), (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(methyl sulphinyl)butane‧H₂0, (Dios), and (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(benzyl sulphinyl)butane‧H₂0, (BDios). These sulphoxides are prepared as mixtures of diastereomers. Other sulphoxides discussed are: dimethyl (DMSO), methyl n-propyl, (MeⁿprS0), methyl phenyl, (MPSO), and R-(+)-methyl p-tolyl sulphoxide, (MPTSO) and (2R,3R)-2,3-dihydroxy-l,4-bis(methyl sulphinyl)butane, (DDios). The previously unknown complexes, [NH₂Me₂][RuCl₃(DMSO)₃], [NH₂Me₂][RuCl₃(MeⁿprS0)₃], [RuCl₂(MBMSO)₂]₃, [RuCl₂(MPTSO)₂]₃, [RuCl₂(MPS0)₂]n, RuCl₂(DDios)₂‧2H₂0, RuCl₂(Dios)(DDios) and RuC1₂(DDios)(DMSO)(MeOH) have been prepared using newly developed synthetic routes. The previously prepared compounds, RuCl₂(DMS0)₄ and RuBr₂(DMSO)₄ are more fully described and in collaboration with A. Mercer and J. Trotter of this department the structures of the chloro-complex and the [NH₂Me₂][RuC1₃(DMSO)₃] compound were determined by x-ray crystallography. Both [NH₂Me₂][RuCl₃(DMSO ₃] and RuC1₂(DMSO)₄ react readily with molecular hydrogen in N,N'-dimethylacetamide (DMA) in the presence of a strong base, proton sponge R . The net heterolytic cleavage of H₂ results in hydride species which although not well characterized have anomalously high *H n.m.r. hydride chemical shifts at least for Ru(II). The anionic DMSO complex catalyses the hydrogen reduction of activated olefins in DMA at 60°C under 1 atm and kinetic and spectral studies indicate the following mechanism: [equation omitted] Activation of H₂ is thought to occur by net heterolytic cleavage of molecular hydrogen and this and an olefin insertion step are considered to be rate determining, (k₃ and k₄). Reduction proceeds by two pathways, one olefin-dependent and the other olefin-independent; the final step involves protonolysis of a σ-alkyl complex. Catalytic hydrogenation of acrylamide in DMA at 70°C using [RuCl₂(MBMSO)₂]₃ is described and the postulated mechanism is summarized below [equation omitted]. As with the anion system a two-path reduction occurs, one olefin-dependent and one olefin-independent, with the H₂-activation steps rate determining, (k₁ and k₄); however, H₂ activation is this time via oxidative addition. Asymmetric hydrogenation studies using the catalysts [RuCl₂(MBMSO)₂]₃, [RuCl₂ (MPTSO) ₂]₃, RuCl₂ (DDios) ₂•2H₂0, RuCl₂ (Dios)(DDios), and RuCl₂(DDios)(DMSO)(MeOH) are presented. The largest optical purities obtained are 25 and 15%, for the RuCl₂(Dios)(DDios)-itaconic acid and [RuCl₂(MBMSO)₂]₃-itaconic acid systems, respectively. The preparation of carbonyl derivatives of [RuCl₂(MBMSO)₂]₃ and [RuCl₂ (MPTS0) ₂]₃ are described; these derivatives have anomalously high v(C0) values. / Science, Faculty of / Chemistry, Department of / Graduate

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Thesis advisor: Jeffery A. Byers / Chapter 1. Overview of Carbon Dioxide Hydrogenation for the Production of Formic Acid As the world’s energy demands increase, our resources dwindle and the need for a sustainable energy source is pertinent. Our current energy infrastructure is dominated by fossil fuel use. Hydrogen, on the other hand, is potentially an ideal energy carrier as it is emissions-free when burned and can be used in fuel cells. Significant advances are still needed to develop more efficient ways to produce and store H2. The hydrogenation of CO2 to formic acid and/or methanol provides an encouraging and reversible approach for a hydrogen storage material. The first example of homogeneously catalyzed hydrogenation of carbon dioxide was in 1976. Over the past 40 years, there has been excellent progress in the development of catalysts for CO2 hydrogenation. Typically, homogenous catalysts found to be effect are 2nd and 3rd row transition metals of groups 8-10. In recent years, base-metals (common and inexpensive metals) have demonstrated promising results. This chapter is designed to highlight important discoveries throughout the history of carbon dioxide hydrogenation. Chapter 2. Development of a Transition Metal / N-Heterocyclic Carbene Cooperative System for the Hydrogenation of Carbon Dioxide to Formic Acid Over the past few decades, the conversion of small molecules such as H2, N2, O2, CH4, C2H4, CO, and CO2 have attracted considerable attention. Many of these molecules are thermodynamically or kinetically stable and their usefulness depends on overcoming significant barriers. Frustrated Lewis pairs and N-heterocyclic carbenes have become common strategies to activate unreactive small molecule likes CO2 and H2. However, a hybrid approach utilizing both a transition metal and an activator has only recently been investigated for the transformation of small molecules to more useful and complex compounds. A novel method for these transformations is the use of a bifunctional catalyst system that incorporates a Lewis basic N-heterocyclic carbene and a Lewis acidic transition metal. This chapter highlights our serendipitous discovery that small quantities of bicarbonate and other inorganic salts enhanced the productivity of formic acid in CO2 hydrogenation reactions. The phenomenon was general for many noble-metal catalysts and for one of the most efficient base-metal hydrogenation catalysts. Additionally, the synthesis of a transition metal complex bearing a pendant dihydroimidazolium salt is described. Stoichiometric and catalytic applications of the newly designed complex were explored in investigate our Lewis base / transition metal approach to small molecule activation. Chapter 3. Chemistry of Iron N-Heterocyclic Carbene Complexes N-heterocyclic carbenes are one of the most versatile ligands in organometallic chemistry due to their unique properties as ancillary ligands. Although NHCs are typically potent σ-donors (a) with minor contributions from π*-backdonation (b), they also have the ability to accept electron density from the metal center as two-electron (c) or one-electron (d) interactions. Since the first examples of metal–NHC complexes were reported in the 1960’s, numerous studies have been devoted to the synthesis of new NHCs, to their characterization, and to their use as ligands in transition metal complexes. The coordination chemistry of NHCs with late transition metals has been studied extensively. However, the chemistry of iron–NHC complexes has not been developed to the same extent as other late transition metals. This chapter highlights important discoveries throughout the history of iron–NHC complexes, while emphasizing the nature of the metal–carbene bond. Chapter 4. Reactivity of Bis(amidinato)-N-Heterocyclic Carbene Iron Complexes Over the past few decades, the development of highly active and selective transition metal catalysts has attracted considerable attention. While the metal employed largely influences the expectations for catalytic activity, the importance of supporting ligands in tuning the reactivity of any given complex is vital. Our group recently synthesized a bis(amidinato)-N-heterocyclic carbene complex of iron as an analogy to the highly active bis(imino)pyridine iron complexes. We hypothesized that having an N-heterocyclic carbene as the central donor instead of pyridine could have significant impacts on the reactivity of such iron complexes. This chapter highlights the synthesis of iron bis(amidinato)-N-heterocyclic carbene complexes spanning multiple oxidation states previously described by our group. Through a combination characterization techniques, the bis(amidinato)-N-heterocyclic carbene was discovered to have unique interactions with the iron center, which change depending on the oxidation state of the metal. Additionally, we undertook investigations into the reactivity of these complexes with azides, hydrides, alkyl reagents, and ethylene. The results of which supported the capability of the bis(amidinato)-N-heterocyclic carbene ligand to act as a redox and chemical non-innocent ligand. / Thesis (MS) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This work is an investigation of the mechanism by which norbornadiene, methyl oleate and methyl linoleate are hydrogenated in acetone at 30[sup]oC, 1 atmosphere or 3 atmospheres pressure, using rhodium complexes of the type [Rh(diene)L[sub]n][sup]+A[sup]-(where diene = norbornadiene , L = tertiary phosphine, phosphite, A = CIO[sup]-[sub]4 or PF[sup]-[sub]6). The results were interpreted assuming three active catalyst species, (Rh(diene)L[sub]2)[sup]+, (RhH[sub]2L[sub]2)[sup]+ and RhHL[sub]2. Also investigated were the effects of adding acid (HClO[sub]4) or base (Net[sub]3) and how this altered the equilibrium (RhH[sub]2L[sub]2)[sup]+<--> H[sup]+ + RhHL[sub]2. At atmospheric pressure, the rate of hydrogenation of norbornadiene and norbornene varies with ligand in the order PPh[sub]3 < PPh[sub]2Me < PPhMe[sub]2, suggesting that oxidative addition of hydrogen is an important first stage of the catalysis. The addition of acid, slowed the rate of hydrogenation for catalysts containing more electron donating ligands (relative to triphenyl phosphine), indicating that the monohydride was a more active specie than the dihydride. With triphenylphosphine or less electron donating ligands in the catalyst, the rate remains constant or increase slightly, indicating that an "unsaturate route" emanating from a diene complex is probably important. The catalyst containing cyclohexylphosphine ligands which are strongly electrondonating but sterically crowded is ineffective in hydrogenation, suggesting that steric crowding may cause an alternative route to operate. Higher pressure (3 atm.) causes faster hydrogenation and provided other mechanistic insights. For methyl oleate at atmospheric pressure, the rate of hydrogenation varies with ligand in the order PPh[sub]3 > PPh[sub]2Me > PPhMe[sub]2, but this order is reversed at 3 atm. pressure. The rate of isomerisation of methyl oleate varies with ligand in the order PPh[sub]3 < PPh[sub]2Me < PPhMe[sub]2, at both pressures. The rate of isomerisation of methyl oIeate and methyl linoleate is lowest, when there is no or a slight excess of acid present but is highest in presence of a base (especially for the catalyst containing diphenylmethylphosphine ligand). Mechanistic interpretations were made.

High surface area catalysts have been studied and applied in a wide range of chemical reactions and processes. The related microscopic details of surface chemistry are important and can be effectively explored employing surface science techniques. My dissertation focuses on investigations of catalytic properties of gold, primarily using vacuum molecular beam techniques, temperature programmed desorption (TPD) measurements, reflection-absorption infrared spectroscopy (RAIRS), and density functional theory (DFT) calculations. I conducted fundamental studies of hydrogenation reactions on a H atoms pre-covered Au(111) single crystal surface with co-adsorption of various chemical compounds, including acetaldehyde (CH₃CHO), acetone (CH₃COCH₃), propionaldehyde (CH₃CH₂CHO), water (H₂O), and nitrogen dioxide (NO₂). These studies allow better understanding of hydrogenative conversions facilitated by gold catalysts, which show great promise in hydrogenation applications but for which relevant fundamental studies are lacking. The experimental results unravel the unique and remarkable catalytic activity of gold in hydrogenation reactions: i) H atoms weakly absorb on the Au(111) surface and have a low desorption activation energy of ~ 28 kJ/mol; ii) acetaldehyde can be hydrogenated to ethanol at a low temperature of < 200 K; iii) propionaldehyde can be hydrogenated to 1-proponal (CH₃CH₂CH₂OH) on H pre-covered Au(111) whereas 2-propanol (CH₃CH(OH)CH₃) cannot be formed in the reaction of acetone with hydrogen atoms; iv) a coupling reaction of aldehyde-aldehyde or aldehyde-alcohol is observed on the H pre-covered Au(111) surface at temperatures lower than 200 K and this reaction can produce various ethers (symmetrical or unsymmetrical) from aldehydes and alcohols with the corresponding chain length; v) co-adsorbed H atoms have a strong interaction with water on the gold model surface and induce the dissociation of the O-H bond in water, which cannot be dissociated on the clean surface; vi) we observed a facile reaction of NO₂ reduction on H covered Au(111) and NO is produced at 77 K, yielding high NO₂ (100 %) conversion and selectivity towards NO (100 %) upon heating the surface to ~ 120 K. These studies indicate the exceptional catalytic activity of gold and enhance the understanding of surface chemistry of classical supported Au-based catalysts at the molecular scale. / text