Includes bibliographical references. / The interests in an alternative, sustainable power generation method has greatly increased in the past decade due to increases in greenhouse gases and its impact on global climate change. The use of fuel cells as a form of energy generation is extremely promising as it converts chemical potential energy directly to electrical energy, bypassing the Carnot cycle limitations. Various types of fuel cells have been developed, with the proton exchange membrane fuel cell (PEMFC) being most promising for mobile and small-scale stationary uses under transient conditions. The PEMFC uses hydrogen and oxygen to generate electrical energy. While oxygen can be obtained from air, hydrogen does not exist in its elemental form; hence a process train is required to refine fuels (such as fossil fuels and bio-fuels) into pure hydrogen. This has been successfully achieved by large-scale industrial plants. A typical fuel processing train consists of a steam reforming stage converting the fuel into syngas. This is followed by a water-gas shift (WGS) stage to convert carbon monoxide, which is a poison for the platinum catalysts within fuel cells, into carbon dioxide. If the CO concentration required is extremely low, a methanation or preferential oxidation stage can be used subsequent to the WGS stage. This study focuses on the water-gas shift stage of the fuel processing train. Industrial base metal WGS catalysts are not suitable for a miniaturized fuel processing train due to the catalysts being developed for continuous operations, as miniaturized fuel processing trains are expected to operate at transient conditions. A slow and controlled reduction process is also required prior to operation, as well as the pyrophoricity of industrial catalysts after reduction. These can pose safety issues with non-technical personnel in household applications (e.g. CHP). PGM-based catalysts have shown high activities for the water-gas shift reaction in literature, are not pyrophoric and do not require lengthy and sensitive reduction processes prior to operation. The objective of this study was to investigate and compare two base metal catalysts (high temperature (HT) shift Fe₃O₄/Cr₂O₃ and low temperature (LT) shift CuO/ZnO/Al₂O₃ catalyst) with a PGM based counterpart, as well as to investigate whether the catalysts are able to achieve a required 1 vol% CO via the water-gas shift reaction. For these investigations a synthetic feedstock was used, based on typical exit concentrations of a steam methane reformer.

The Low Temperature Fischer-Tropsch (LTFT) synthesis involves the catalytic hydrogenation of carbon monoxide with the aim to produce long-chained hydrocarbons. Commercial cobalt-based catalysts incorporate oxidic supports that are known to negatively affect the reducibility and hinder formation of the active phase. Consequently, reduction promoters such as Pt are introduced to facilitate the reduction of cobalt during catalyst pretreatment. However, synergistic and adverse effects of the promoter have been reported under reaction conditions including a higher site-time yield and higher selectivity towards hydrogenated products. The perspective on the operation of the Pt promoter is polarised between 'Hydrogen spillover', which is a so-called remote-control effect that could otherwise occur in the absence of Pt-Co contact, and 'ligand/electronic effects' that require direct Pt-Co coordination. The objective of this study was to explicate the operation of Pt and Au as promoters of the Co/Al2O3 catalyst by decoupling hydrogen spillover from effects that require direct promotercobalt coordination. The analysis was subdivided into the reduction process and the Fischer- Tropsch reaction, which are the two arenas in which the actions of these promoters have been claimed. The employment of model 'hybrid' catalysts, which are mechanical mixtures of the monometallic constituents of the promoted catalyst, presents a novel way to investigate the role of spillover hydrogen in the Pt-Co and Au-Co catalyst systems. Thus far, no systematic investigation of the hydrogen spillover phenomenon using these catalyst systems during both reduction and under commercially relevant LTFT conditions has been encountered in the published literature. Furthermore, this study serves to contribute to the limited body of literature on the role of Au as a potential promoter for the commercial cobalt-based catalyst.

Density functional theory (DFT) calculations have been performed to gain insight into the role of defects present on the surface of graphene and TiO₂ based supports on supported metal clusters. The clusters considered are a Pt₃₈ cluster and a bimetallic Pt₃₂Pd₆ alloy. The defects considered on graphene based supports are monovacancy defective graphene, OH and COOH functionalised graphene. The defects considered on TiO₂ based supports are a partially reduced TiO₂(110) surface with a surface oxygen bridge vacancy and hydroxylated TiO₂(110) surface with surface OH groups. The defect free graphene and TiO₂ surfaces were also considered. For both the Pt₃₈ and Pt₃₂Pd₆ cluster, and on both defect containing graphene and TiO₂ (except on hydroxylated TiO₂(110) surface) the binding of the clusters is enhanced relative to binding on the defect free supports. Enhanced binding at the defects imply that the clusters are bound strongly to the support and thus less likely to detach from the support material relative to binding on the defect free supports. Therefore, the defects may improve the durability of the catalyst by limiting particle detachment. The electronic properties of the cluster are modified differently depending on the identity of the defect present on the support. On the graphene based supports, OH functionalisation is expected to result in weaker binding energy of adsorbate molecules, whereas COOH functionalisation is expected to result in stronger binding energy of adsorbates for the supported Pt₃₈ cluster. This is due to different shifts in d-band centre of the facets on the cluster supported on these supports. Therefore, it can be expected that the Pt₃₈ cluster supported on OH functionalised graphene will be more tolerant to poison molecules. This is due to reduced binding strength of adsorbates on OH functionalised graphene compared to adsorption on COOH functionalised graphene. For the Pt₃₂Pd₆ cluster the OH and COOH functional groups do not appreciably modify the d-band centre of the facets available to reactants, and thus is expected not to significantly modify the binding strength of adsorbate molecules relative to binding on the free unsupported Pt₃₂Pd₆ cluster. The binding energy of adsorbate molecules on the Pt₃₈ cluster supported on defect containing TiO₂ is expected to be stronger than on the Pt₃₈ cluster supported on defective graphene based supports, due to higher extent of upward shift of the d-band centre of the exposed facets. The enhanced binding energy of adsorbates on the Pt₃₈ cluster supported on TiO₂ supports may be detrimental to catalyst durability and activity. This can be due to strong binding of poison molecules and reaction intermediates which maybe too strongly bound on the surface such that they cannot participate in further reaction steps. Overall it might turn out that the functionalised graphene based supports are better support materials over the TiO₂ based materials for particular reactions. The Nb-doped partially reduced TiO₂(110) surface attaches the Pt₃₂Pd₆ cluster strongly to the support compared to the functionalised graphene supports. Furthermore, the binding energy of adsorbate molecules is expected to be weaker on the Pt₃₂Pd₆ cluster supported on the Nbdoped partially reduced TiO₂(110) surface compared to the functionalised graphene supports. This might be beneficial as poison molecules may be weakly bound to the cluster resulting in high resistance to poisoning which can also have a positive effect on catalyst activity. In addition to enhancing binding of the cluster to the support and affecting the binding energy of adsorbates on the supported clusters, some of the defects can also alter the ordering pattern of Pd and Pt atoms within the Pt₃₂Pd₆ cluster. OH functionalised graphene and Nbdoped partially reduced TiO₂(110) surface result in segregation of Pd towards the clustersupport interface, thereby exposing more Pt atoms at the surface facets of the cluster. The modified arrangement of Pt and Pd atoms may result in modification of the reactivity of the Pt₃₂Pd₆ cluster. The results of this study indicate that the defects can play a vital role in determining the activity and durability of the catalyst. By having the right combination of defects on the support material, the durability and catalytic activity of the catalyst can be fine-tuned simultaneously. This can lead to better design of catalysts.

The synthesis and characterization of the first series of tetra-NHC-Ag(I)-X cubane clusters are reported. The clusters were characterized with 1H and 13C NMR spectroscopy, ESI-TOF MS, and single crystal X-ray diffraction. Crossover experimental data were consistent with intramolecular exchange, which can be visualized by a molecular rotating type mechanism. Additionally, -NHC Zr(IV) pincer type complexes were synthesized and characterized with 1H and 13C NMR spectroscopy, CHN combustion analysis, and X-ray crystallography. A large rate effect was observed based on the halogen and metal center for the hydroamination/cyclization of unactivated aminoalkenes. Zirconium based pincers provided faster reaction rates than their hafnium counterparts (Zr>Hf). Precatalysts with iodide ligands provided faster reaction rates than their bromide and chloride counterparts (I>Br>Cl). The mechanism of hydroamination for Zr(IV) -NHC complexes was also investigated for bis(iodide) and bis(amido) ligand classes. A full kinetic analysis of substrate and precatalyst have been identified along with the formation of small amounts of an oxidized product. The proposed mechanism contains an imido-type intermediate whose formation depends greatly on which set of ligand class is used.

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Thesis advisor: X. Peter Zhang / Thesis advisor: Shih-Yuan Liu / Recent advancements have witnessed the deployment of radical chemistry for the construction of diverse vital molecular structures. Among these advances, metalloradical catalysis (MRC) has been continuously demonstrated as a practical and unique approach whereby open-shell metal-centered catalysts are exploited to initiate and regulate homolytic radical processes. As stable 15e-metalloradicals, Co(II) porphyrin complexes have been proven effective in activating multifarious precursors to forge unprecedented metal-stabilized organic radicals and are capable of conducting various homolytic processes with well-confined reactivity and selectivity thanks to the support of D2-symmetric chiral porphyrin ligands. Nevertheless, the detailed mechanistic studies of the metalloradical activation of precursors, H atom abstraction (HAA), radical addition, and asymmetric induction have been largely underdeveloped. Therefore, this dissertation mainly focuses on the mechanistic investigations of radical amination and hydroxylation reactions via Co(II)-based MRC with routine experimental methods and powerful computational tools. Chapter 1: Developments on Asymmetric N-Heterobicyclization Reactions of Alkenes via Enantioselective Transition Metal Catalysis. We have viewed recent developments of asymmetric N-heterobicyclization of alkenes rendered by enantioselective transition metal catalysis incorporating first-row, second-row, and third-row transition metals. Chapter 2: Enantioselective Radical N-Heterobicyclization with A New Mode of Asymmetric Induction. We have developed asymmetric radical N-heterobicyclization of allyl sulfamoyl azides with the support of a D2-symmetric chiral bridged amidoporphyrin HuPhyrin ligand. We also revealed a new mode of asymmetric induction that the chirality of a kinetically stable chiral radical center directs the enantioselectivity of the resulting aziridines. The stable chiral radical center was formed from highly challenging enantiofacial selective radical addition and underwent subsequent stereospecific ring closure. Chapter 3: Catalytic Radical N-Heterocyclization by Metalloradical C–H Amination involving 1,7-Hydrogen Atom Abstraction. We have examined intramolecular HAA reaction and pushed its boundary from well-explored 1,5-HAA and 1,6-HAA to unusual 1,7-HAA executed by α-Co(III)-aminyl radicals, which led to the discovery of 1,7-C–H amination and 1,7-HAA triggered indirect 1,5-C–H amination with sulfamoyl azides. Chapter 4: Metalloradical Activation of Alkyl Hydroperoxides for Catalytic Radical C−H Hydroxylation. We have presented comprehensive studies on the metalloradical activation of oxidants, especially cumene hydroperoxide. We have identified ∞-Co(III)-hydroxide cumyloxyl radical species and utilized it for the development of radical C–H hydroxylation with cumyl alcohol as the byproduct. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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Polystyrene bis(salicylaldehyde)-propylene-1,3-diiminato Cobalt (II) [salen] and Polystyrene bis(2,4-pentanedione)-propylene-1,3-diiminato Cobalt (II) [BAE] were prepared stepwise from chloromethylated polystyrene. In addition, a new preparation of a Schiff base was attempted resulting in Polystyrene bis(salicylaldehyde)-isobutylene-1,3-diiminoato Cobalt (II) being produced. Optimum reaction conditions were determined with regard tot ime, temperature, reaction ratios and solvent for each step for the reaction. The ability of the above named Cobalt (II) Schiff bases to oxidize 3-methyl indole to give the corresponding o-formylaminoacetophenone was also studied. One polymer-bound Schiff base cobalt catalyst (co-salen) demonstrated a very small amount of catalytic activity resulting in a minimum amount of o-formylaminoacetophenone being produced.

This PhD thesis project was concerned with the use of alkali metal amide Brønsted bases and alkali metal alkoxide Lewis bases in (asymmetric) catalysis. The first chapter deals with formal allylic C(sp3)–H bond activation of aromatic and functionalized alkenes for subsequent C–C and C–H bond formations. The second chapter is focused on C(sp3)–Si bond activation of fluorinated pro-nucleophiles in view of C–C bond formations. In the first chapter, a screening of various metal amides, hydrides, and alkyl reagents resulted in the observation that alkali metal amides were effective Brønsted bases to trigger allylic C(sp3)–H bond activation of aromatic alkenes at room temperature. Sodium hexamethyldisilazide was found to be most efficient compared with other s-, p-, d-, and fblock metal amides. This unique transition metal-free methodology was exploited to activate a variety of alkene pro-nucleophiles, which were shown to undergo γ-selective C–C bond formation with various aromatic aldimines as well as one aliphatic substrate. The corresponding homoallylic amine derivatives were obtained in high yields with excellent E:Z ratios. The reaction mechanism was investigated and attempts to detect and/or isolate key intermediates were undertaken. Importantly, it was shown that metal-free superbases of the Schwesinger or Verkade type were not apt to catalyse this challenging C–C bond formation. The asymmetric version of this rare sodium amide catalysis has been achieved by using a commercially available enantiopure bisoxazoline ligand (46% ee). Subsequently, the catalytic use of sodium and potassium amides was applied to the isomerization of terminal aromatic alkenes to generate the thermodynamically more stable internal olefins in excellent yields with high E:Z ratios. Furthermore, functionalized metalloid (B, Si) and metal-free alkenes were found to undergo alkali metal amide-triggered (chemoselective) allylic C(sp3)–H bond activation in view of isomerization and/or C–C bond formation with aldimines. In the second chapter, the catalytic C–Si bond activation of an important difluoromethylation reagent, HCF2SiMe3, was investigated. Here, alkali metal alkoxides were shown to be more effective Lewis base triggers than other metal alkoxides or metal-free superbases. This novel method was successfully used to transfer the nucleophilic difluoromethyl fragment to electrophiles such as a variety of amides and lactams, whereas unsaturated amides failed to undergo the intended conjugate C–C bond formation. In this context, it is noted that the α-hydrogen of certain amides was tolerated. This unprecedented catalytic difluoromethylation of unactivated carbonyl electrophiles was achieved using potassium tert-butoxide at room temperature, and the corresponding fluorinated ‘hemiaminal’ products were obtained in high yields.