<div><p>Nitrenes are reactive intermediates that are known to generate high interest organic molecules. Due to their inherent instability, nitrenes are often stabilized by introducing them to transition metal complexes. Many transition metal stabilized nitrenes (M=NR₂) have been reported and some of these complexes have been shown to control nitrene reactivity and selectivity. Transition metal nitrene reactivity can be categorized into two main groups: bond-insertion and group transfer reactions. In the reference to the former, chapter one of this dissertation highlights using unique dinuclear Nicatalysts to generate nitrenes from aromatic azides. These Ni₂ nitrenes are used towards selective C(sp²)−H bond amination in order to generate indole and carbazole derivatives. This work highlights the unique properties of the Ni₂ imide that enable a 1,2-addition pathway, which contrasts known bimetallic nitrene insertion reactions. A detailed mechanistic study, primarily using density functional theory (DFT) is the focus of this chapter.</p> <p>Chapter two of this dissertation focuses on nitrene group transfer. In particular, this chapter highlights the ability of the dinuclear Nicatalyst [<i>ⁱ</i>^-PrNDI]Ni₂(C₆H₆) to react with aromatic azides to perform N=N coupling. A large scope of functional groups are tolerated in high yield with short reaction times. Catalyst comparison studies, studies on relevant catalytic intermediates for N=N coupling and reaction kinetics are shown in this chapter. Lastly, chapter three showcases the expansion of the nitrene group transfer ability of [<i>ⁱ</i>^-PrNDI]Ni₂(C₆H₆) to generate high molecular weight azopolymers from aromatic diazides. These azopolymers are generated from monomers often used in organic semi-conducting materials. End group control and post polymer functionalization are highlighted in this chapter. Lastly, this work showcases a new polymer, polyazoisoindigo, as the first organic semiconducting material that reversibly transitions from a colored to colorless state upon reduction.</p><br></div>

<p> Metal-stabilized carbenes, most commonly formed through the decomposition of  diazoacetates, are extensively employed in organic synthesis. However, several classes of carbenes,  such as vinylidenes, are challenging to utilize in transition metal catalysis due to the instability of  the required diazo precursors. To overcome this challenge, most transition metal-catalyzed  vinylidene transfer and insertion methods rely on alkynes as vinylidene precursors. Only catalysts  that form stable M=C multiple bonds and weak M(π-C≡C) interactions can promote this alkyne  isomerization, and the resultant metal(vinylidene) species is often less reactive compared to free  vinylidenes. The discovery of 1,1-dihaloalkenes as precursors to transition metal vinylidene  complexes has significantly expanded the scope of vinylidene transfer and insertion reactions.  Dinuclear catalysts were found to promote the reductive cyclization of 1,1-dichloroalkenes  containing pendant alkenes to form methylenecycloalkenes, and mechanistic studies are consistent  with the formation of a Ni2(vinylidene) species. Furthermore, these catalysts promote reductive  three-component cycloaddition reactions with 1,1-dichloroalkenes and aldehydes to generate  methylenedioxolanes, which upon treatment with aqueous acid provides access in one step to new,  unsymmetrical aliphathic α-hydroxy ketones that would be difficult to access with existing  methods. Under dilute conditions, an enone byproduct is formed and a DFT model is presented  that accounts for concentration-based reaction selectivity.</p>

<p>This work studies propene aromatization reaction on H-MFI (Si/Al = 40) and physical mixtures of H-MFI (Si/Al = 40) and PtZn/SiO2 (2 wt% Pt, 3 wt% Zn) at 723 K - 823 K and 3 kPa C3H6. The influence of PtZn alloy (dehydrogenation function) is investigated on the product distribution and selectivity of metal-acid catalyzed propene aromatization. Typical product distribution consists of methane, ethane, ethene, propane, C4-C6 alkanes and alkenes, and benzene, toluene, xylene (BTX). On comparing the BTX carbon selectivity over the two catalysts at first equivalent space velocity and then equivalent propene conversion, higher BTX selectivities are observed on PtZn+H-MFI than H-MFI in both the cases. The higher BTX selectivities were previously attributed in the literature to the dehydrogenation pathway on the metal function. However, space velocity is an inadequate descriptor of reaction progress because the conversion of reactants can be different at same space velocity. Similarly, propene conversion is an incomplete descriptor for reaction progress because intermediates such as ethene and C4-C6 hydrocarbons react to form higher molecular weight hydrocarbons and subsequent aromatics as the reaction progresses. Such reactive hydrocarbons were lumped together as reactive intermediates and the remaining hydrocarbons were classified as non-reactive species or products. When BTX selectivities over PtZn-H-MFI and H-MFI are compared at equivalent temperature and equivalent conversion of all the reactive intermediates, both the catalysts exhibit similar BTX selectivities, suggesting that the presence of the dehydrogenation metal function doesn’t influence the selectivity towards BTX products. Further, we hypothesize cyclohexene as an intermediate in aromatic formation and use cyclohexene conversion as a probe reaction to understand how aromatics are formed over Brønsted acid sites and PtZn alloy. Cyclohexene conversion results at 723 K and 823 K shows the presence of an alternate route of aromatic formation via dehydrogenation of cycloalkenes, and this dehydrogenation pathway has an order of magnitude higher rates than the hydride transfer route on Brønsted acid sites. Further, we propose dominant reaction pathways of C1 – BTX hydrocarbon formation on H-MFI and bifunctional PtZn+H-MFI. Finally, we discuss the implications of using PtZn+H-MFI on developing a commercial propylene aromatization process and provide our recommendations for chemical and fuel production. In summary, these findings reveal previously unknown mechanistic details of metal bifunctionality for propene aromatization catalysis.  </p>

<p>An original palladium-catalyzed ring opening carbonylative lactonization of synthetic available hydroxycyclopropanols was reported to efficiently synthesize tetrahydrofuran (THF) and tetrahydropyran (THP)-fused bicyclic γ-lactones, two unique scaffolds often found in quite a few natural products. This new developed reaction features mild reaction conditions, good functional group tolerability, and the scale-up abilities. The synthetic application was demonstrated in a short total synthesis of (±)-Paeonilide. The THF-fused bicyclic γ-lactone products can be readily diversified into some medicinally important structures, which further broadens the application of this new carbonylation approach.</p> <p>The first total synthesis of Phleghenrine A was reported. This synthesis features an unprecedented inverse electron-demand Diels-Alder reaction and Tiffeneau-Demjanov ring expansion to rapidly construct bicyclo[3,2,2]-nonane core structure of Phleghenrine alkaloids. Two Diels-Alder adducts were synthesized, which were the synthetic precursors for divergent synthesis of Phleghenrine A and B, respectively.</p>

<p>Thermal, non-catalytic conversion of light olefins (C2= - C4=) was originally utilized in the production of motor fuels at several U.S. refineries in the 1920-30’s. However, the resulting fuels had relatively low-octane number and required harsh operating conditions (T > 450 oC, P > 50 bar), ultimately leading to its succession by solid acid catalytic processes. Despite the early utilization of the thermal reaction, relatively little is known about the reaction products, kinetics, and initiation pathway under liquid-producing conditions. </p> <p>In this thesis, thermal ethylene conversion was investigated near the industrial operating conditions, i.e, at temperatures between 320 and 500 oC and ethylene pressures from 1.5 to 43.5 bar. Non-oligomer products such as propylene and/or higher odd carbon products were observed at all reaction temperatures, pressures, and reaction extents. Methane and ethane were minor products (< 1 % each), even at ethylene conversions as high as 74 %. The isomer distributions revealed a preference for linear, terminal C4 and C5. The reaction order was found to be 2nd order with a temperature dependent activation energy ranging from 165 to 244 kJ/mol. The importance of diradical species in generating free radicals during a two-phase initiation process was proposed. The reaction chemistry for ethylene, which has only strong, vinyl C-H bonds starkly contrasted propylene, which possesses weaker allylic C-H bonds and showed preference for dimeric C6 products over C2-C8 non-oligomers. </p> <p>Extending this work further, the thermal oligomerization of ethylene was enhanced using high surface area supports such as silica and alumina. Both supports resulted in order of magnitude rate increases compared to the gas phase reaction, however the ethylene conversion rate with alumina was superior to silica by a factor of between 100 and 1,000. Additionally, the alumina evidently confers a catalytic function, resulting in altered product distributions, notably an increase in branched products such as isobutene and isopentenes. The oligomerization chemistry with alumina appears to reflect the involvement of Lewis acid sites rather than traditional Brønsted acid or transition metal catalysis, which operate via carbenium ion and metal-alkyl intermediates, respectively. </p>

<p dir="ltr">Ring strain is the driving force for numerous ring-opening reactions of three- and four-membered heterocycles. By comparison, five-membered heterocycles lack this thermodynamic driving force. As a result, only a few methods exist for the ring-opening of five-membered heterocycles using transition metal catalysts. For unstrained and unactivated 2,5-dihydrofurans this is achieved via a β-O elimination process, wherein, gaining selectivity over a competing β-H elimination is challenging. We report a novel strategy for the asymmetric ring-opening of 2,5-dihydrofurans with dichloroalkenes utilizing an earth-abundant cobalt catalyst. We propose that the dichloroalkenes form reactive vinylidene intermediates with the chiral catalyst, followed by a [2+2] cycloaddition with the heterocyclic alkene. This cobaltacyclobutane exclusively undergoes an outer-sphere β-O elimination assisted by zinc halide. Alternative inner-sphere β-O and β-H elimination pathways are inaccessible from this four-membered metallacycle. This is followed by a transmetallation step to form a zinc metallacycle, which subsequently gives rise to homoallylic alcohols, upon quenching, with high diastero- and enantioselectivity. Additionally, the organozinc intermediate can be trapped in situ by various electrophiles for further derivatizations. DFT model predicts the origin of the high diastereo- as well as enantioselectivity observed in the reaction.</p><p dir="ltr">Furthermore, the cobaltacyclobutane intermediate serves as a dynamic platform, facilitating access to a diverse array of products depending on the alkene partners employed. Utilizing chiral allylic alcohols as alkene partners leads to the translation of stereochemical information enabling the stereospecific synthesis of both <i>E</i>- and <i>Z</i>-isomers of alkenes. Alkenes are important motifs found in various natural products and bioactive compounds. A catalytic approach for the precise control of the alkene geometry is highly valuable since the stereochemistry of alkenes plays a pivotal role in determining the properties of molecules. Our strategy provides access to organozinc dienes which could be functionalized further to form highly substituted 1,4-skipped dienes. Additionally, meso-diols can undergo a desymmetrizing β-O elimination from the cobaltacyclobutane intermediate yielding chiral cyclopentenols with contiguous stereocenters</p>

<p> Brønsted acid zeolites can be synthesized in a wide range of topologies, each characterized by diverse void sizes, shapes, and micropore connectivity. The location of Brønsted acid sites (H+-sites) within microporous voids of different size and shape, and the relative proximity of H+-sites influences their reactivity. Additionally, the diffusion of reactant and product molecules through a given zeolite topology depends on micropore size, tortuosity, and connectivity. The coupled influences of reaction kinetics and intrazeolite reactant and product diffusion govern rates and selectivity for a plethora of zeolite-catalyzed reactions and underlie the well-established effects of “shape-selectivity”. The independent effects of reaction and diffusion on rates and selectivity for a given reaction are often obfuscated by concomitant changes in the zeolite properties governing diffusion (e.g., crystallite size) and reactivity (e.g., H+-site density or proximity) in zeolite materials synthesized with conventional methods. Herein, we develop synthetic methods to decouple H+-site density, proximity and crystallite size in medium-pore, 10-membered ring (10-MR) zeolites, and evaluate the independent effects of these material properties on the kinetic and transport phenomena that govern propene oligomerization catalysis. </p> <p>Among synthetic methods to influence H+-site proximity in zeolites, varying the charge-density and ratio of structure directing agent (SDA) cations that compensate anionic charges in frameworks at Al centers has been reported to influence H+-site proximity in MFI and CHA zeolites of fixed H+-site density. Changes in H+-site proximity can be evaluated using Co2+ cations to selectively titrate and quantify subsets of proximal H+-sites (H+-site pairs); conditions to perform such titrations were identified for MEL zeolites. The fraction of paired H+-sites changed concurrently with changes in framework Al content in MEL zeolites synthesized using a single organic SDA (OSDA), tetrabutylammonium hydroxide (TBA+). Synthesis of MEL with mixtures of TBA+ and Na+ as an inorganic SDA (ISDA), at fixed total SDA and Al content, allowed the fraction of paired H+-sites to be systematically varied in MEL zeolites of fixed H+-site density, reflecting changes in the location and quantity of charge-balancing SDAs with Na+/TBA+ ratio. The energetic favorability of SDA occlusion in MEL was also evaluated with density functional theory (DFT). In contrast to MEL, occluded SDA content in TON zeolites crystallized with varied OSDA (1,6-diaminohexane, or 1,8-diamooctane) and K+ content, at fixed total SDA content, was invariant with K+/OSDA ratio, reflecting a different mechanism of SDA occlusion in TON. These findings provide an approach to influence H+-site pairs in 10-MR zeolites of fixed H+-site density and demonstrate the dependence of SDA occlusion on zeolite topology.</p> <p>The independent influences of H+-site and crystallite properties on rates and selectivity of propene oligomerization to heavier alkenes in a representative medium-pore zeolite topology (MFI) were explored by interrogating suites of samples crystallized with independently varied H+-site density (0.3–5.7 H+/u.c.), proximity, and crystallite size (0.03–2.65 μm) over a wide range of reaction conditions (483–523 K, 7–615 kPa C3H6). Dimerization rates (per H+) decreased with increasing crystallite size among MFI materials synthesized with fixed H+-site density (0.3 or 1.3 H+/u.c.), revealing the strong and ubiquitous influence of intrazeolite diffusion limitations on measured dimerization rates. Weisz-Prater criterion analyses, in conjunction with dimerization rate transients upon step-changes in reaction conditions, indicate that these intrazeolite diffusion limitations arise from a product-derived organic phase occluded within zeolitic micropores during propene oligomerization catalysis, which restricts intrazeolite diffusion by lowering the effective diffusivities of propene and product alkenes. This occluded organic phase becomes heavier in composition at higher propene pressures and lower reaction temperatures, which favor chain growth over β-scission, resulting in more severe intrazeolite diffusional constraints. The composition of the occluded organic phase was also found to depend on H+-site density in MFI zeolites. Rate constants (per H+) of dimerization and trimerization were higher on MFI samples of dilute H+-site density, resulting in faster growth of heavier oligomer products and consequently lower effective diffusivities compared to MFI samples of higher H+-site density. The convoluted influences of reaction and diffusion on measured propene oligomerization rates result in apparent reaction orders that deviate from the first-order dependence of rates on propene pressure expected in the limit of strict kinetic control. Accounting for the coupled influences of reaction and diffusion on propene oligomerization rates and the influence of H+-site density on intrazeolite diffusion, rationalizes contradictory conclusions among prior reports about the dependence of oligomerization rates on H+-site density, proximity, and crystallite size, which did not identify or consider the influences of intrazeolite diffusion in their interpretations of rate data. </p> <p>Finally, we explore the consequences of zeolite pore size and connectivity for reactivity and intrazeolite diffusion during propene oligomerization by interrogating H-zeolites of different topologies. Intrazeolite diffusional constraints are imposed by an occluded organic phase and influence dimerization rates among medium-pore zeolite topologies (MFI, MEL, TON), but such constraints are alleviated on large-pore zeolite topologies (FAU, MOR, *BEA), reflecting the slower growth and faster diffusion of heavy oligomer products in large-pore zeolites. Among medium-pore zeolites, the composition of the occluded organic phase, and consequently the effective diffusivities of propene and product alkenes, is influenced by void size. Analysis of product selectivity on zeolites of different pore size and connectivity (TON, MOR, MFI) reveals that TON restricts the growth of heavier oligomer products, resulting in effective diffusivities that are higher on TON compared to MFI, and are relatively invariant with propene pressure and H+-site density. Together, the findings herein demonstrate the ability of slow-diffusing products to impose intrazeolite diffusional constraints on other products during alkene oligomerization catalysis, and reveal the critical influence of reaction conditions, H+-site density, and micropore size on the composition of this occluded organic phase, and consequently intrazeolite diffusional constraints. Ultimately, this work demonstrates how kinetic studies performed on well-defined zeolite materials can reveal important changes in reaction and diffusion phenomena, which are otherwise inextricably convoluted, and provides a framework through which such effects can be assessed for other zeolite-catalyzed molecular chain-growth reactions. </p>

<p dir="ltr">Nature moves small things by chemical energy. Inspired by this, catalytic reactions driven microswimmers have been designed and believed to be promising to help transport drugs and other cargos at microscales. However, decorating the microswimmers with drugs and cargos would make them heavy and hard to move. An alternative solution to this would be designing self-pumping devices that can pump the fluid and things carried by the fluid all together without external resources. In this work, we have presented the first full numerical model of electrochemically-powered self-pumping in the Pt-Au coated polycarbonate membrane reported by Jun and Hess [1]. The simulations demonstrate that autonomous flow in self-pumping membranes is an electro-osmotic flow driven by a self-generated electric field. The injection and consumption of H⁺ on Pt and Au respectively lead to a charge asymmetry and an associated electric field that acts on the electric double layers (EDL) coating the pore walls driving fluid move, i.e. self-electro-osmosis. Key parameters controlling the performance of self-pumping are pore radius and background pH values, as they affect the EDL overlap and ionic strength. Other parameters such as porosity and pore length can both be tuned to find the local optimum for a membrane design. By tuning these parameters, the trade-off between increased ionic current and increased ionic strength could be balanced, contributing to an optimum self-pumping performance. When inclination or deformation occurs in cylindrical pores, the self-pumping flow does not significantly deviate from the trend. Membranes with complicated shape of contracting/expanding pores and cross-linked connecting pores should follow same pattern as cylindrical pores with similar pore size. In addition, if we replace the Pt/Au catalytic pairs by TiO₂/Au photocatalytic pairs, self-pumping membrane could be driven by light. The geometry of pore enhances the light absorption, enabling self-pumping membrane achieving high flow rate at large porosity with relatively large pores. At the end, we provide experimental evidence of self-pumping flow on TiO₂-Au plates as well as self-pumping membrane driven by light.</p>

<p>A fundamental understanding of heterogeneous catalysis requires analysis of model catalytic surfaces in tandem with complex technical catalysts. This work was divided in three areas, 1- preparation and characterization of model surfaces synthesized by vapor deposition techniques, 2- kinetic evaluation of model catalysts for formic acid decomposition and dry methane reforming, 3- characterization and kinetic evaluation of technical catalysts for the water gas shift reaction.</p> <p>In the first project, model PdZn intermetallic surfaces, a relevant catalyst for propane dehydrogenation, were prepared using an ALD approach. In this work, model surfaces were synthesized by exposing Pd(111) and Pd(100) surfaces to diethylzinc at ca. 10^-6mbar. Several different surface structures were identified by careful control of the deposition temperature of the substrate. Modifications in the adsorption properties of these surfaces towards carbon monoxide and propylene coincided with the structure of the PdZn surface layer. </p> <p>In the second project, formic acid decomposition kinetics were evaluated on model Pt catalysts. Formic acid decomposition was found to be structure-insensitive on Pt(111), Pt(100), and a polycrystalline foil under standard reaction conditions. CO selectivity remained < 1% for conversions <10%. Additionally, inverse Pd-Zr model catalysts were prepared by ALD of zirconium-t-butoxide (ZTB). Depending on treatment conditions, either ZrO_xH_y or ZrO₂ overlayers or Zr as sub-nanometer clusters could be obtained. The activity of the model catalyst surface towards dry reforming of methane if the initial state of the zirconium is metallic. </p> <p>In the third project, Au/Fe₃O₄ heterodimer catalysts were characterized for their thermal stability. In-situ TEM and XPS characterization demonstrates that the gold nanoparticles transform into gold thin films that wet the Fe₃O₄ surface as the reduction of the oxide proceeds. DFT calculations show that the adhesion energy between the Au film is increased on a partially reduced Fe₃O₄ surface. Additionally, Pt/Nb₂CT_x catalysts were characterized and kinetics evaluated for the water gas shift reaction. XPS and TEM characterization indicates that a Pt-Nb surface alloy is formed under moderate reduction temperatures, 350^OC. Water-gas shift reaction kinetics reveal that the alloy-MXene interface exhibit high H₂O activation ability compared to a non-reducible support or bulk niobium carbide. </p>

The Bayer process for the production of alumina (A1203) from bauxite involves a perennial gibbsite (y-Al(OH)3) precipitation step, relating to an inherently slow crystal growth from supersaturated sodium aluminate solutions (pregnant Bayer liquors). The kinetics and mechanisms involved in the transformation of the tetrahydroxo, Al(III)-containing species in solution into octahedrally-coordinated Al(OH)3 crystals in the presence of NA+ and excess of ions, are as yet not fully known. To gain further knowledge and better understanding of the nature of solution species, their specific interaction and participation in the gibbsite crystallization mechanisms, the role alkali ions play in the kinetic behaviour and mechanisms of nucleation, growth and aggregation/agglomeration from caustic aluminate solutions of industrial strength has been investigated.