L’utilisation des acides de Lewis dérivés du bore tels que les boranes, les acides boroniques et les acides boriniques a émergée récemment comme une alternative intéressante aux métaux de transitions dans le domaine de la catalyse. Lors des travaux précédemment effectués au laboratoire par Tharwat Mohy El Dine, la synthèse d’acides boriniques originaux a été effectuée. Ces catalyseurs ont montrés une activité remarquable et supérieure aux dérivés boroniques correspondants pour la synthèse catalytique de dipeptides et la réaction de formylation d’amines. Au cours de nos travaux, il nous a été possible d’évaluer l’apport des acides boriniques pour la catalyse de la réduction des amides dans des conditions douces avec une bonne compatibilité fonctionnelle, le mécanisme réactionnel a également pu être rationnalisé. Nous avons ensuite évalué l’activité du même acide borinique pour la réaction de réduction des oxydes de phosphines, des sulfoxydes et des N-oxydes d’amines. Après une étude mécanistique portant sur le transfert d’hydrure d’un hydrosilane vers un acide borinique, l’apport des acides boriniques pour l’hydrosilylation des cétones, aldéhydes et imines a également été étudié. Une méthodologie coopérative entre un hydrosilane et un acide borinique pour la catalyse de la réaction d’amidation a été développée. Enfin, une étude théorique utilisant la RMN et la DFT a permis de rationnaliser la relation structure activité de nos catalyseurs. L’ensemble de ces travaux confirme le potentiel des acides boriniques en tant que catalyseurs efficaces pour de nombreuses réactions. / Boron based Lewis acid such as borane, boronic and borinic acids, has recently emerged as a strong alternative to transition metal catalysts for catalysis. During Tharwat Mody El Dine thesis, a range of original borinic acids have been synthetized. These catalysts have been used to investigate catalytic peptides synthesis and amines formylation. This thesis work with aimed the association between borinic acids and hydrosilanes for organic synthesis. In the first part a borinic acid catalyzed amides reductions have been developed, our methodology work in mild conditions and displayed high chemoselectivities. In a second chapter, we will study the activity of borinic acids for the reduction of phosphine oxides, sulfoxides and amine N-oxide. After a study on the formation of previously observed amine-borane, a borinic acid mediated ketones, aldehydes and imines hydrosilylation have been demonstrated in the third chapter. In the fourth chapter a cooperative borinic acid-hydrosilane mediated amide bond formation has been developed, the mild conditions and the absence of racemization appear as the keys elements of this methodology. Finally, RMN and DFT instruments have been used to understand the relationship between structure and reactivity of borinic acids.All this study confirms the potential of borinic acids as efficient metal-free catalysts in many organic transformations.Mots clés : catalyse, acide borinique, hydrosilane, réduction, amides.

Thesis advisor: Chia-kuang Tsung / Thesis advisor: Dunwei Wang / Coating porous materials is a potential pathway to improve Catalytic performance of heterogeneous catalysts. The unique properties of Metal organic frameworks (MOFs) like huge surface area, long range order and high tenability make them promising coating materials. However, two traditional MOF encapsulation methods have their own issues. Herein, we synthesized Pt/Pd metal nanoparticles @UiO-66-NH2 via a one-pot in situ method which has good control of nanoparticles size while avoids the introduction of capping agent. The catalytic performance of synthesized Pt@UiO-66-NH2 is tested via selective hydrogenation of Crotonaldehyde. And the selectivity of our desired product achieves 70.42% which is much higher than merchant Pt catalysts. A step further, we used linker exchange to replace the original NH2-BDC linker of which amine group plays an important role in the coating process. After linker exchanging, the significant decreasing in selectivity of our target product demonstrates that the interaction between Pt and amine group does have some positive impacts on their catalytic performance. We hope our research could provide some insights of the MOFs and nanoparticles interface and help rational design of catalysts with high performance. / Thesis (MS) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

The selective catalytic reduction (SCR) of NO_X (x = 1,2) using Cu-exchanged zeolites is used commercially for the abatement of NO_X from on-road lean-burn diesel engines. At the low exhaust temperatures during cold-start and idle operation (<523 K), the SCR reaction proceeds via a Cu²⁺/Cu⁺ redox cycle of NH₃-solvated and mobilized Cu ions. Reduction of Cu²⁺ species proceeds via NO-assisted reduction of isolated NH₃-solvated Cu²⁺ ions. To complete Cu⁺ to Cu²⁺ oxidation, two [Cu(NH₃)₂]⁺ species react together with O₂ to form a dimeric O₂-bridged Cu²⁺ species that is subsequently reduced by NO and NH₃ to complete the SCR catalytic turnover. NH₃-solvated Cu ion species are nominally isolated under <i>ex-situ</i> conditions, however, motivating the critical research question studied in this work regarding how Cu ion mobility and dynamic interconversion of mononuclear and binuclear active sites facilitate SCR chemistry. In particular, this work focuses on understanding how active site proximity, zeolite pore connectivity and dimensionality, and catalyst poisons impact the number and reactivity of active Cu sites.<br> Steady-state SCR kinetics (473 K) measured at fixed gas conditions (10 kPa O₂) on a series of Cu-chabazite (CHA) zeolites with varied density of isolated Cu ions (0.078-0.35 Cu per 10³ ų) exhibit non-single site behavior because of changes in the kinetic relevance of Cu⁺ oxidation and Cu²⁺ reduction half-cycles, and the non-mean field nature of the Cu⁺ oxidation process. Measurement of SCR rates at dioxygen pressures (1-60 kPa O₂) far removed from typical operating conditions (3-17 kPa O₂) allows isolating the kinetic behavior under primarily Cu⁺ oxidation-limited and Cu²⁺ reduction-limited conditions, and estimating rate parameters for these two regimes by regressing SCR rates as a function of O2 pressure to an empirical Langmuirian rate expression. Apparent rate constants that are first-order in O₂ (k_first) increase systematically with Cu density, consistent with the dual-site Cu⁺ oxidation mechanism. Apparent rate constants that are zero-order in O2 (k_zero) show a weak dependence on Cu density, similar to the fraction of Cu that can be oxidized by O₂ at 473 K in transient experiments, suggesting that changes in k_zero reflect changes in the fraction of active Cu given the single-site nature of Cu²⁺ reduction mechanisms. The measured apparent activation energy in the Cu⁺ oxidation limit (E_app,first) increases systematically with Cu density, highlighting the non-mean field nature of Cu⁺ oxidation over the range of Cu densities studied. The measured apparent activation energies in the Cu²⁺ reduction limit are constant above a threshold Cu density (0.17 Cu per 10³ ų), consistent with mean-field behavior, but begin to deviate at lower densities (0.084-0.10 Cu per 10³ ų).<br> A series of Cu-zeolites with 2D (LEV, FER) and 1D (MOR) pore connectivity were synthesized to quantify how the framework topology and pore structure influences the mobility and reactivity of Cu ions during SCR. When compared to Cu-CHA, a 3D pore structure, values of k_first and k_zero (per total Cu) were several factors lower on the 2D and 1D zeolites, indicating that decreasing the effective volumetric footprint of Cu ions during SCR decreases both the rate of dual-site Cu⁺ oxidation and the fraction of Cu⁺ that oxidizes. When compared to other 3D double-six membered ring (d6r) zeolites with different pore shape (AEI) and size (AFX), rates (per total Cu) were generally a factor of 1.5 to 2 times higher on Cu-CHA, indicating that the open pore structure of cylindrical cages in CHA are favorable for low-temperature SCR reactivity.<br> The arrangement and density of framework Al atoms in CHA influences low-temperature SCR, as the framework Al atoms mediate Cu ion mobility and the arrangement of Al in the framework determines the chemical identity of the Cu active site precursors as either [CuOH]⁺ exchanged at an isolated framework Al center or Cu²⁺ exchanged at paired framework Al in a six-membered ring (6-MR). Synthesis of CHA zeolites with mixtures of Na⁺ and TMAda⁺ provides a strategy to alter the amount of Al centers in 6-MR paired configurations, because Na+ co-occludes in 6-MR voids adjacent to TMAda⁺ occluded within the cha cage. In contrast, synthesis of CHA zeolites with mixtures of K⁺ and TMAda⁺ results in primarily 6-MR isolated Al configurations because K⁺ cations displace TMAda⁺ from residing in cha cages. Thus, the use of different mixtures of organic and inorganic structure directing agents (SDAs) provide routes to synthesize CHA zeolites that favor the formation of either [CuOH]⁺ or Cu²⁺ species. The Cu speciation influences both hydrothermal stability and resistance to sulfur poisoning. SO₂ is a catalyst poison ubiquitous in automotive exhaust and is found to bind to [CuOH]⁺ sites more strongly than Cu²⁺ sites, both before and after high-temperature de-sulfation treatments. <br> Together, these findings reveal several of the important structural and active site requirements for low-temperature NO_X SCR with NH₃ on Cu-zeolites. The non-mean field nature of the SCR redox cycle on Cu²⁺/Cu⁺ ion sites, and the requirement for Cu ions to be located in proximal and accessible locations of zeolite void spaces becomes more favorable in 3D highly connected pore structures, highlighting a primary reason why low-temperature SCR rates (per Cu) are higher on Cu-CHA than on other Cu-zeolites. The synthetic procedures presented here to influence the Al arrangement in CHA zeolites provide new strategies to alter the speciation and density of isolated Cu ion sites, even among Cu-CHA zeolites of nominally identical elemental composition, which have implications for the stability and resistance to poisons of the catalyst under realistic operating conditions. Together, synthetic strategies to manipulate the proximity of active sites, methods to quantify transient and steady-state kinetics, and <i>in situ</i> and <i>operando</i> characterization are invaluable tools to study and understand the non-mean field dynamic interconversion of isolated and multinuclear sites during low-temperature SCR catalysis.<br>

Converting solar energy into useful chemical bonds via photocatalysis is a growing field aimed at addressing global challenges. The research disclosed describes heterogeneous photocatalysis as a nanophotoelectrochemical cell as photocatalysts enable both reduction and oxidation reactions using the local charge separation of photo-excited carriers. Herein, experimental and theoretical results of nanoscale electrolysis of water on the surface of CrOx/Pt/SrTiO3 showed that ohmic losses are negligible when the anode and cathode are within nanometer distances from each other. Additionally, increasing the photocatalytic rate of water splitting by increasing the light intensity demonstrated that pH gradients can still form at the nanoscale. These pH gradients can be minimized by the incorporation of buffers. Typically, photocatalysts decorated with noble-metal nanoparticles can be used for overall water splitting, but generally suffer from low yields due to the water-forming back reaction. The unwanted water-forming back reaction was successfully suppressed by coating Pt nanoparticles on the surface of SrTiO3 with a 2nm CrOx layer that block O2 gas from reaching the surface of the Pt nanoparticle. The back reaction can also be suppressed without the use of a protective layer material by changing the intrinsic nature of the Pt nanoparticle from a metallic state to an oxidized state. The Pt nanoparticles were able to maintain an oxidized state by reducing the particle size below 2 nm. Oxidized Pt particles are less likely to bind to H2, O2, and CO gas, unlike metallic Pt, thereby making it selective for hydrogen generation. Finally, CdS was found to be perform the direct trifluoromethylation of heteroarenes in a single step as opposed to the current multi-step synthetic procedures. The trifluoromethylation of organic compounds is relevant to the field of medicinal chemistry for the synthesis of pharmaceutical drugs. By improving overall water splitting via photocatalysis significantly, artificial photosynthesis may be achieved leading to a solution to the global energy security dilemma. By improving photoredox catalysis of organic compounds via photocatalysis, high value organic compounds (such as pharmaceuticals) can be synthesized more readily under milder conditions.

The RNA World hypothesis describes a period of time during the origins of life in which RNA molecules performed all catalysis and were the only form of information storage. A great deal of evidence has been obtained in support of this hypothesis, however a few key demonstrations are lacking. The first demonstration is of a molecule capable of self-replication that could have plausibly arisen from the prebiotic soup. Previously in the Lehman Laboratory, a 198-nucleotide RNA was discovered that could be fragmented into as many as four pieces ranging from 39 - 63 nucleotides in length. When these pieces were incubated together in a test tube, they re-formed the necessary covalent bonds to regenerate the full-length 198-nucleotide RNA. Furthermore, the full-length RNAs were catalytically active and made copies of themselves from the remaining pieces in solution, providing a model system of self-replication. I was able to remove >10% of the total length of the RNA, which substantially reduced the catalytic activity of the full-length molecule. I discovered several mutations that restored catalytic activity by improved folding and increased catalytic rates using in vitro selection. A subset of these mutations was found to aid in the assembly of the shortened full-length RNA from smaller fragments than were possible in the original system, enhancing the prebiotic relevance of this system. A second demonstration to bolster the RNA World hypothesis would be showing that RNA is capable of harvesting energy from its environment by performing oxidation and reduction reactions. Again using in vitro selection, I have completed five rounds of selection geared towards identifying a ribozyme that reduces benzoic acid to benzaldehyde using Zn2+ and NADH. Results to date suggest the selection is working and it should be continued for another five to ten generations. Finally, I have discovered an RNA sequence that forms knots during transcription, a phenomenon heretofore undocumented in RNA. This new topology has implications for RNA stability by rendering RNA more resistant to hydrolysis, and could impact catalysis through formation of more complex, knotted active sites. Taken together, these findings have improved our understanding of RNA folding and catalysis, and the plausibility of the RNA World.

In the last centuries, transition metal chemistry beсome one оf the mоst іmportant tооls for synthesis of valuable organic compounds and different chemical transformations. In particular, transition metal catalysis are capable of forming novel cross coupling bonds. In this background, photocatalysis was developed later to create new chemical transformations by the irradiation with visible light. In this regard, the combination of transition metal catalysis and photochemistry is a breakthrough in catalysis that has provided impossible transformations in organochemistry. One of the widely available reactants in synthesis are alkyl chlorides. However, it is hard to activate chemically stable C(sp3 )-Cl bond at room temperature. In this study, we overcome this limitation by excited-state palladium catalysis under mild conditions. The reaction goes through the hybrid alkyl-Pd radical as a key intermediate. The procedure provides the synthesis of oxindole and isoquinolinedione derivatives mainly from alkyl chlorides via annulation overcoming its chemical limitations. This work will focus on the generation of alkyl radicals from unactivated C(sp3 )-Cl using simple palladium catalysis

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Alternative energy sources have been investigated for utilization in various applications to mitigate carbon dioxide emissions. The transportation sector is one of the major sectors that require the adaptation of renewable energy storage technologies for onboard applications. Formic acid is a liquid energy carrier that has the potential of replacing current fuels and mitigating carbon dioxide emissions through a circular carbon economy. The production of energy from formic acid can be achieved by homogenous catalysis to extract hydrogen from formic acid. The most promising metals for formic acid dehydrogenation in aqueous solution have been mainly ruthenium and iridium. While iridium has mostly surpassed ruthenium, further exploration of ruthenium is necessary because it is more economical. This work presents the synthesis and catalytic performance of a N,N-bidentate Ru(II) complex. X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and Mass spectrometry (MS) were used to confirm the structure of the catalyst. The title complex was found to be an efficient system for formic acid dehydrogenation to hydrogen gas and carbon dioxide in the aqueous phase. The highest TOF achieved is 656 h-1 in the presence of two equivalents of sodium formate to formic acid in water at 90 °C. There was no detection of carbon monoxide throughout the reaction process, suggesting the high selectivity of this catalytic system.

The objective of this research is to synthesize, fully characterize, and investigate the catalytic properties of a series of rhodium(II) acetate derivatives. On its own, rhodium(II) acetate possesses the ability to catalyze the formation of cyclopropanes—strained, three-carbon rings that are a defining structural feature of the group of insecticides known as permethrins (found naturally in chrysanthemum flowers). Alone, though, the rhodium(II) acetate ‘paddlewheel’ structure does not selectively catalyze the formation of the biologically active version of the cyclopropane product; a mix of products is created that must then be separated. The separation process is expensive in time and % yield. With every step in the purification of the permethrin mixture, a significant amount of product is sacrificed. Thus, the permethrins in their commercial pure form are prohibitively expensive for most desired applications. Extracted permethrins are only used in the treatment of head lice and as flea/tick treatment of pets. With the goal of enhancing the catalytic complex’s selectivity for the biologically active cyclopropane confirmation (atomic arrangement), a p-tolunitrile ligand (molecular ‘adduct’) has been attached to rhodium(II) acetate. The complexes thus synthesized have been characterized by Single Crystal X-ray Crystallography, IR, NMR and UV-visible spectroscopies and elemental analysis. The catalytic properties of such nitrile adducts of rhodium(II) acetate are currently under investigation.