Palladium-catalyzed reactions for carbon-carbon bond formation have had a significant impact on the field of organic chemistry in recent decades. Illustrative is the 2010 Nobel Prize, awarded for “palladium-catalyzed cross couplings in organic synthesis”, and the numerous applications of these transformations in industrial settings. This thesis describes recent developments in C(sp2)-C(sp3) bond formation, focusing on alkane arylation reactions and arylative dearomatization transformations. In the first part, our contributions to the development of intramolecular C(sp3)-H arylation reactions from aryl chlorides are described (Chapter 2). The use of catalytic quantities of pivalic acid was found to be crucial to observe the desired reactivity. The reactions are highly chemoselective for arylation at primary aliphatic C-H bonds. Theoretical calculations revealed that C-H bond cleavage is facilitated by the formation of an agostic interaction between the palladium centre and a geminal C-H bond. In the following section, the development of an alkane arylation reaction adjacent to amides and sulfonamides is presented (Chapter 3). The mechanism of C(sp3)-H bond cleavage in alkane arylation reactions is also addressed through an in-depth experimental and theoretical mechanistic study. The isolation and characterization of an intermediate in the catalytic cycle, the evaluation of the roles of both carbonate and pivalate bases in reaction mechanism as well as kinetic studies are reported. Our serendipitous discovery of an arylation reaction at cyclopropane methylene C-H bonds is discussed in Chapter 4. Reaction conditions for the conversion of cyclopropylanilines to quinolines/tetrahydroquinolines via one-pot palladium(0)-catalyzed C(sp3)-H arylation with subsequent oxidation/reduction are described. Initial studies are also presented, which suggest that this transformation is mechanistically unique from other Pd catalyzed cyclopropane ring-opening reactions. Preliminary investigations towards the development of an asymmetric alkane arylation reaction are highlighted in Chapter 5. Both chiral carboxylic acid additives and phosphine ligands have been examined in this context. While high yields and enantiomeric excesses were never observed, encouraging results have been obtained and are supported by recent reports from other research groups. Finally, in part two, the use of Pd(0)-catalysis for the intramolecular arylative dearomatization of phenols is presented (Chapter 7). These reactions generate spirocyclohexadienones bearing all-carbon quaternary centres in good to excellent yields. The nature of the base, although not well understood, appears to be crucial for this transformation. Preliminary results in the development of an enantioselective variant of this transformation demonstrate the influence of catalyst activation on levels of enantiomeric excess.

The last decade has been marked by a large increase of demand for green chemistry processes. Consequently, chemists have focused their efforts on the development of more direct routes toward different classes of targets. In that regard catalysis has played a crucial role at enabling key bond formations that were otherwise inaccessible or very energy and resources consuming. The central theme of this body of work concerns the formation of C–N bonds, either through transition metal catalysis or organocatalysis. These structural units being highly recurrent in biologically active molecules, the establishment of more efficient routes for their construction is indispensable. The first part of this thesis describes a new method for the synthesis of isoquinolines from the oxidative coupling/annulation of alkynes with N-tert-butyl benzaldimines via Rh(III) catalysis (Chapter 2). Preliminary mechanistic investigations of this system pointed to the involvement of Rh(III) in the C–H bond cleavage step as well as in the C–N bond reductive elimination that provides the desired heterocycle. Following this oxidative process, a Rh(III)-catalyzed redox-neutral approach to isoquinolones from the reaction of benzhydroxamic acids with alkynes is presented (Chapter 3). The discovery that an N–O bond contained in the substrate can act as an internal oxidant was found to be very enabling. Indeed, it allowed for milder reaction conditions, broader scope (terminal alkyne and alkene compatible) and low catalyst loadings (0.5 mol%). Mechanistic investigations on this system were also conducted to identify the nature of the C–N bond formation/N–O bond cleavage as well as the rate-determining step. The second part of this work presents mechanistic investigations performed on a recently developed intermolecular hydroamination reaction catalyzed through tethering organocatalysis (Chapter 4). This transformation operates via the reversible covalent attachment of two reactants, a hydroxylamine and an allylamine, to an aldehyde catalyst by the formation of a mixed aminal. This allows a difficult intermolecular Cope-type hydroamination to be performed intramolecularly. The main kinetic parameters associated with this reaction were determined and they allowed the generation of a more accurate catalytic cycle for this transformation. Attempts at developing new families of organocatalysts are also discussed.

Les phosphines jouent un rôle central dans la chimie organique moderne. Dans le domaine de la catalyse, les composés organophosphorés peuvent être appliqués soit en tant qu’organocatalyseurs dans de nombreuses transformations, soit en tant que ligands en catalyse organométallique. Au cours de cette thèse, nous avons utilisé les phosphines dans ces deux applications : en organocatalyse et en catalyse asymétrique à l’or(I). Dans la première partie, nous avons développé une réaction d’addition de Michael/réaction de Wittig intramoléculaire. Nous avons judicieusement choisi la phosphine utilisée ainsi que l’agent réducteur afin de permettre la réduction in situ de l’oxyde de phosphine correspondant. De nombreux dérivés 1,2-dihydroquinolines diversement fonctionnalisés ont pu être isolés avec de bons rendements. Parallèlement à cela, une nouvelle réaction d’oléfination a pu être découverte, donnant accès à des dérivés succinates. Un mécanisme réactionnel a pu être proposé, en se basant notamment sur des expériences de deutération. Dans un deuxième temps, nous nous sommes intéressés au développement de réactions énantiosélectives catalysées par des complexes chiraux d’or(I), et utilisant des substrats énynes. Une première réaction de cyclisation d’énynes-1,5, suivie d’une addition nucléophile a été développée en utilisant des complexes d’or de structure TADDOL-phosphoramidite-AuCl. Ce catalyseur a permis l’obtention de vingt dérivés cyclopentènes avec de bons rendements et des excès énantiomériques atteignant 94% ee. Finalement, des substrats énynes-1,6 correctement substitués ont été utilisés dans une réaction de cyclisation, suivie d’un piégeage intramoléculaire, afin de donner accès à des composés tétracycliques et pentacycliques complexes. Les composés racémiques ont été isolés avec de bons rendements et la version asymétrique a également été développée, par l’utilisation de complexes chiraux d’or(I). / Phosphines play a major role in modern organic chemistry. In the field of catalysis, organophosphorus derivatives can be applied as catalysts in numerous transformations by itself, as organocatalysts, or as ligands in organometallic catalysis. This thesis focused on the application of phosphines both in phosphine organocatalysis and in asymmetric gold(I) catalysis. In the organophosphorus catalysis part, we have developed a phosphine-catalyzed Michael addition/Wittig reaction by using a well-chosen cyclic phosphine catalyst. In this process, silane was used as reducing agent to selectively reduce in situ the phosphine oxide. A series of highly functionalized 1,2-dihydroquinolines were prepared. Besides, a new olefination process was discovered for the synthesis of succinate derivatives. Detailed mechanism research was carried out with H/D exchange experiments. In the asymmetric gold(I) catalysis part, we have developed two new methodologies based on cyclization reactions of 1,n-enyne substrates. A 1,5-enyne cyclization/nucleophilic addition reaction was first developed with an acyclic TADDOL-derived phosphoramidite-Au(I) complex. Twenty examples were carried out with good to excellent yields and up to 94% enantiomeric excess. For the 1,6-enyne cyclization/intramolecular nucleophilic addition sequence, we have synthesized a range of racemic tetracyclic and pentacyclic compounds in high yields. The enantioselective version of this transformation was carried out successfully with both high reactivity and enantioselectivity.

<div>As shale gas exploitation has been developed, production of shale gas in the US has rapidly increased during the last decade. This has motivated the development of techniques to covert shale gas components (mainly C₁ to C₃) to liquid fuels by catalytic conversion. The main goal of the dissertation is to study the geometric and electronic structures of the metal catalysts, which are crucial for understanding the structure-property relationship.</div><div><br></div><div><div>The fi?rst project studies bimetallic Pt-Bi catalyst for non-oxidative coupling of methane. In a recent publication published in ACS catalysis, Pt-Bi/ZSM-5 catalyst</div><div>has been shown to stably convert methane into C2 for 8 hours under non-oxidative conditions. In this thesis, structure of the Pt-Bi/ZSM-5 was shown with HAADF</div><div>imaging, synchrotron XAS and XRD. A new surface cubic Pt₃Bi phase on Pt nanoparticles with Pt-Bi bond distance of 2.80 A was formed. Formation of noble metal intermetallic alloys such as Pt₃M may be the clue for non-oxidative conversion of methane.</div></div><div><br></div><div><div>The second and third project highlight strong metal-support interaction catalysts for propane dehydrogenation. Chemisorption showed partial coverage of the SMSI oxides</div><div>on the surface of the nanoparticles. In situ X-ray absorption near edge (XANES), resonant inelastic X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS)</div><div>have shown that little electronic effect on the metal nanoparticles. The catalyst activity per mol of metal decreased due to the partial coverage of the SMSI oxides on the surface of the catalysts. The catalysts, however, had higher selectivity due to smaller ensembles inhibiting hydrogenolysis.</div></div><div><br></div><div><div>In the fourth project Pt-P catalyst was investigated to understand the promoting effect of P.Pt-P catalysts had much higher selectivity for propane dehydrogenation</div><div>(>95%). These give two types of catalysts, a PtP₂-rich surface on Pt core and full PtP₂ ordered structure, which were con?rmed by scanning transmission electron microscopy (STEM), and in situ methods of EXAFS, synchrotron XRD, XPS, and Resonant Inelastic X-ray Spectroscopy (RIXS). The PtP₂ structure has isolated Pt</div><div>atoms separated by P₂atoms. In addition XANES, XPS and RIXS indicate a strong electronic modi?cation in the energy of the valence orbitals.</div></div><div><br></div><div><div>It can be concluded from the Pt-Bi catalyst that intermetallic alloys might be selective for NOCM. Therefore, promoters with higher reduction temperature, such as Mn and Cr, should be used to have stable catalysts at high temperature. Moreover, both Pt-Bi and Pt/CeO₂suggest that selective catalysts for propane dehydrogenation and NOCM may have some correlation. Further studies would be conducted to understand the correlation between the two reactions.</div></div>

With a few exceptions, all organisms are restricted to the 20 canonical amino acids for ribosomal protein biosynthesis. Addition of new amino acids to the genetic code can introduce novel functionalities to proteins, broadening the diversity of biochemical as well as chemical reactions and providing new tools to study protein structure, reactivity, dynamics and protein-protein-interactions. The site directed in vivo incorporation developed by P. G. SCHULTZ and coworkers, using an archeal orthogonal tRNA/aaRS (aminoacyl-tRNA synthase) pair, allows site-specifically insertion of a synthetic unnatural amino acid (UAA) by reprogramming the amber TAG stop codon. A variety of over 80 different UAAs can be introduced by this technique. However by now a very limited number can form kinetically stable bonds to late transition metals. This thesis aims to develop new catalytically active unnatural amino acids or strategies for a posttranslational modification of site-specific amino acids in order to achieve highly enantioselective metallorganic enzyme hybrids (MOEH). As a requirement a stable protein host has to be established, surviving the conditions for incorporation, posttranslational modification and the final catalytic reactions. mTFP* a fluorescent protein was genetically modified by excluding any exposed Cys, His and Met forming a variant mTFP*, which fulfills the required specifications. Posttranslational chemical modification of mTFP* allow the introduction of single site metal chelating moieties. For modification on exposed cysteines different maleiimid containing ligand structures were synthesized. In order to perform copper catalyzed click reactions, suitable unnatural amino acids (para-azido-(L)-phenylalanine, para-ethynyl-(L)-phenylalanine) were synthesized and a non-cytotoxic protocol was established. The triazole ring formed during this reaction may contribute as a moderate σ-donor/π-acceptor ligand to the metal binding site. Since the cell limits the incorporation of boronic acids, an aqueous protocol for Miyaura borylation using a highly active palladacycle catalyst was established and can be transferred to a selective borylation of proteins. It allows subsequent Suzuki cross coupling and therefore broadens the possibilities for chemical modifications and the establishment of new metalloenzymes. Different metal chelating amino acids were investigated, such as Hydrochinolin-Alanine, Bipyridyl-Alanine, Dipyridine-Lysines and phosphorous containing amino acids.

La catalyse par les métaux de transition a pris une ampleur considérable depuis quelques décennies et est devenue un outil puissant en chimie organométallique. La réaction de CH ortho fonctionnalisation, impliquant une catalyse duale palladium/norbornène, découverte à la fin des années 90, a permis une grande avancée dans le domaine des réactions multi-composantes. Elle permet d’accéder à des structures polycycliques via un mécanisme original, impliquant la formation d’un palladacycle. Elle constitue également la première réaction catalytique incluant trois états d’oxydation du palladium (0, II et IV). Dans un contexte où la chimie tend à être plus éco-compatible, nous souhaitions tirer avantage de cette réaction pour la synthèse de dibenzoazépines. Ils représentent en effet d’intéressants motifs utilisés aussi bien en organocatalyse que comme composés bioactifs, cependant les synthèses existant à ce jour ne permettent pas de diversifier la structure de ces molécules et requièrent souvent des séquences multiples étapes ou des réactifs toxiques. La synthèse de dibenzoazépines a ainsi été réalisée selon une approche à trois composants incluant une bromobenzylamine, un iodure aromatique ortho substitué et une oléfine portant un groupement électro-attracteur via une séquence de CH ortho fonctionnalisation/Heck/aza-Michael. Remarquablement, cette dernière étape présente une diastéréosélectivité totale. L’emploi de bromobenzylamine substituée racémique montre la même sélectivité grâce à un dédoublement cinétique. L’accès à un large panel de molécules, ainsi qu’aux imines correspondantes via un mécanisme de rétro-Mannich par l’emploi d’une oléfine énolisable, démontre la robustesse de la réaction d’ortho CH-fonctionnalisation. La formation de liaison carbone-carbone par les métaux de transition a été largement développée depuis quelques décennies. Cependant elle génère souvent des déchets et l’utilisation de réactifs toxiques à haute température. La catalyse photorédox connaît un vif intérêt depuis peu et a l’avantage d’utiliser la lumière comme source d’énergie couplé à une faible quantité catalytique de métal ou d’organocatalyseur. Nous avons ainsi développé une méthode de couplage biaryalique via une catalyse photorédox médiée par un complexe de ruthénium. Les précurseurs à coupler que sont les arènes diazoniums ont l’avantage de ne générer comme déchets que du diazote, et réalise une réaction de substitution homolytique aromatique sur des accepteurs aromatiques ou hétéroaromatiques. De plus elle se déroule à température ambiante en l’absence de base. Elle constitue donc une alternative pour le couplage biarylique en une chimie éco-compatible. / Catalysis by transition metal has considerably grown these decades and has become a powerful tool in organometallic chemistry. The CH ortho fonctionnalisation reaction, involving a duale palladium/norbornene catalysis, discovered at the end of the 90’s, allowed a breakthrough in the field of multi-component reactions. It provides access to polycyclic structures through an original mechanism, involving a palladacycle formation. It is the first catalytic reaction including three oxidation states of palladium (0, II and IV). In a context where the chemistry is going to be more ecocompatible, we wished taking advantage of this reaction to synthetize dibenzoazepines. They represent interesting scaffold both as organocatalysts and as bioactive compounds, however the existing synthesis don’t allow diversifying the structure of these molecules and often requiring multi-step sequences or toxic reagents. Dibenzoazepines synthesis has been realised according a three components approach from readily available reagents, a bromobenzylamine, an ortho substituted aromatic iodide and an electrowithdrawing olefin via a CH ortho fonctionnlisation/Heck/aza-Michael sequence. Remarquably, this last step presents a total diastereoselectivity. Using racemic substituted bromobenzylamine shows the same selectivity thanks to a parallel kinetic resolution-like mechanism. The access to a wide range of molecules, and the corresponding imine via a retro-Mannich mechanism using an enolisable olefin demonstrates the robustness of the ortho CH fonctionnalisation reaction.  Carbon-carbon bond formation by transition metal has been largely developped since decades. However, it often generate waste and use toxic reagent at high temperature. Photoredox catalysis is a great success recently and have the advantage to use light as energy source and small amounts of metal and organocatalyst. We have developed a method of biarylic coupling via a photoredox catalysis mediated by a ruthenium complex. Arene diazonium, the precursor coupled, have the advantage to generate diazote as waste, and realise an homolytic aromatic substitution on aromatic and heteroaromatic acceptors. Moreover, it takes place at room temperature without base. It is an alternative for the biarylic coupling and an green chemistry.

Zeolites are crystalline microporous solid acids composed of silica-rich frameworks with aliovalent Al heteroatoms substituted in crystallographically-distinct location sand arrangements, which generate anionic lattice charges that can be compensated by protons and extra framework metal cations or complexes that behave as catalytic active sites. Protons that charge-compensate Al are similar in Brønsted acid strength, yet differ in reactivity because their bound intermediates and transition states are stabilized by van der Waals interactions with confining microporous cavities, and by electrostatic interactions with proximal heteroatoms and adjacent protons. A diverse array of framework Al and extra framework H⁺site ensembles are ubiquitous in low-silica and low-symmetry zeolite frameworks (e.g., MFI, MOR), which cause measured turnover rates to reflect the reactivity-weighted average of contributions from each distinct site ensemble. The reactivity of distinct sites can be further masked by diffusion barriers often imparted by microporous domains and secondary reactions of primary products, which become increasingly prevalent as products encounter higher numbers of active sites during diffusion prior to egress from zeolite crystallites. Consequently,catalytic behavior often depends on zeolite material properties at orders-of-magnitude different length scales, which depend on the specific protocols used in their synthesis and crystallization.<div><br></div><div><div>In this work, CHA zeolites that contain only one symmetrically-distinct lattice site for Al substitution are used as model materials to decouple the effects of proton</div><div>location and proximity in vibrational spectra and turnover rates for acid catalysis. Interactions between proximal protons influence their equilibrium distribution among anionic lattice O atoms in AlO⁻_4/2tetrahedra, and result in temperature-dependent changes to vibrational frequencies and intensities of the asymmetric OH stretching region in infrared spectra measured experimentally and computed by density functional theory (DFT). Protolytic propane cracking and dehydrogenation, a catalytic probe reaction of the intrinsic reactivity of Brønsted acid protons, occur with turnover rates (748 K, per H⁺) that are an order-of-magnitude higher on paired protons than isolated protons, resulting from entropic benefits provided to late carbonium ion-pair transition states by proximal protons. These results indicate that cationic transition states can be stabilized entropically through multi-ion interactions with lattice anion and cation sites. Precise interpretation and quantification of the reactivity of different types and ensembles of Brønsted acid protons in zeolites requires that protolytic chemistry prevails in the absence of secondary active sites or other kinetically-relevant processes, a requirement generally met for alkane cracking but not dehydrogenation on H-form zeolites. Propane dehydrogenation activation energies vary widely (by >100 kJ mol⁻¹) among H-form zeolites of different structure (MFI, MOR, CHA) and composition (Si/Al = 10 – 140) because reactant-derived carbonaceous deposits form in situ and catalyze alkane dehydrogenation under non-oxidative conditions through hydride transfer pathways. Contributions of reactant-derived active sites to propane dehydrogenation rates are quantified through a series of transient and steady-state kinetic experiments with co-fed alkene and dihydrogen products, and are found to depend on gradients in product pressures that are present in integral reactors under non-ideal plug-flow hydrodynamics. Propane dehydrogenation rates collected at initial time-on-stream and in the presence of co-fed H₂ solely reflect protolytic reaction events and can be used to interpret differences in the reactivity of distinct proton sites and ensembles for alkane activation catalysis. The reaction conditions identified here can be used to remove or suppress the reactivity of carbonaceous active sites during catalysis, or to engineer the formation of organocatalysts on zeolite surfaces for selective dehydrogenation or hydride transfer reactions.</div></div><div><br></div><div><div>Synthetic strategies to decouple bulk and active site properties at disparate length scales, which are typically correlated in MFI zeolites crystallized hydrothermally, are developed by adding a second heteroatom and organic structure directing agent (SDA) to synthesis media. Crystallite size and morphology are independently varied from Al content by incorporating B heteroatoms into zeolitic frameworks, which generate protons that are catalytically irrelevant compared to those compensating Al, and NH₃ temperature-programmed desorption methods are developed to differentiate between these two types of proton sites. The siting of Al heteroatoms in distinct locations and ensembles is influenced by the decrease in cationic charge density among occluded SDAs, in cases where ethylenediamine is co-occluded with tetra-<i>n</i>-propylammonium cations. The co-occlusion of organic SDAs enables crystallizing MFI zeolites with different bulk properties but similar Al distributions, or with similar bulk properties and different Al distributions. MFI zeolites crystallized with these methods provide model materials that can be interrogated to decouple the effects of bulk and atomicscale properties on acid catalysis, and open opportunities to exploit these material properties by designing active site ensembles and crystallite diffusion properties for catalytic chemistries that depend on coupled reaction-transport phenomena.</div></div>

<div>Carbenes are reactive organic intermediates comprised of a neutral, divalent carbon atom. The reactivity of carbenes is often orthogonal to polar functional groups (nucleophiles and electrophiles), making them valuable intermediates for organic synthesis. For example, carbenes can engage in cheletropic reactions with olefins to form cyclopropane rings or undergo insertions into weak element-hydrogen bonds. The most established strategy for accessing carbene intermediates is through a redox-neutral decomposition of diazoalkanes to form a transient M=CR₂ species. Over the course of nearly a half-century of development, many instrumental synthetic methods have emerged that operate on this basis. Despite the combined utility of these methods, the scope of catalytic carbene transfer reactions remains largely constrained by the inherent instability of the starting materials. Diazoalkanes often require electron-withdrawing groups to provide stability through resonance effects.</div><div>Contrary to redox-neutral methods, reductive carbene transfer reactions utilize non-stabilized 1,1-dihaloalkanes as carbene precursors. The Simmons-Smith cyclopropanation reaction represents the most documented example of this class, and remains today as the most practical method for parent methylene (:CH₂) transfer. Nevertheless, reductive carbene transfer processes have proven to be remarkably resistant to catalysis. Our group is interested in developing first-row transition metal catalysts which can initiate an oxidative addition into 1,1-dihaloalkanes, followed by a two-electron reduction with an outer-sphere reductant to provide access to a M=CR₂ intermediate for carbene transfer.</div><div>The application of this mechanistic hypothesis toward reductive methylene transfer using CH₂Cl₂ as the carbene source and a Ni catalyst is outlined in chapter one. The discovery of an unexpected cyclooligomerization of methylene carbenes is discussed. Mechanistic studies are presented, which are consistent with a pathway in which carbenes are iteratively inserted into an expanding metallacycle. In chapter two, the corresponding activation of 1,1-dichloroalkenes for vinylidene transfer in [5+1]-cycloadditions with vinylcyclopropanes is outlined. Finally, in the third and final chapter, organic reactions catalyzed by complexes which feature metal-metal bonds are reviewed.</div>

<p>Zeolites are microporous crystalline solids with tetrahedrally bonded Si⁴⁺ atoms linked together with bridging oxygens, interconnected in various geometries and arrangements to generate a diversity of microporous topologies. The substitution of Al³⁺ into framework tetrahedral sites (T-sites) generates anionic lattice charges that can be counterbalanced by protons (Brønsted acid sites) or extraframework metal cations and complexes that can act as catalytic active sites. The local arrangement of Al ensembles can be categorized by the size of the (alumino)silicate rings and the number and order of the Al atoms they contain, which are critical structural features that influence their ability to serve as binding sites for extraframework cations of different size and oxidation state. The ability to exercise control over the isomorphic substitution of Al³⁺ into the zeolite framework during hydrothermal crystallization has long been envisioned, but recognized to depend on complex and kinetically-controlled nucleation and crystal growth events that challenge the development of reproducible synthesis routes and predictive synthesis-structure relations. Here, we present the results of extensive experimental and theoretical investigation of the chabazite (CHA) zeolite topology, which contains a single crystallographically distinct T-site that enables studying effects of Al arrangement independent of T-site location. We then extend these findings and methodologies to investigate more complex zeolite topologies with larger numbers of distinct T-sites, including other small-pore (AEI, LEV) and medium-pore zeolites (MFI, MEL), with a specific focus on MFI zeolites because of their versatility in commercial applications. Cationic species are often present during hydrothermal zeolite crystallization, in the form of inorganic and organic structure directing agents (SDAs), to help guide formation of the intended zeolite topology and to compensate charge when Al is incorporated into the lattice. Variations in the type and amount of cationic SDAs have been shown to influence both the Al siting within different void locations of a given zeolite and the local Al arrangement. In order to make quantitative assessments of the number of Al-Al site pairs formed in a given zeolite, experimental protocols to titrate the specific Al-Al site ensembles are required. We specifically explore the use of Co²⁺titrants at saturation uptakes, verifying the sole presence of Co²⁺ cations via spectroscopic identification and a cation site balance that is closed by quantifying residual Brønsted acid sites by NH₃titration. We then investigate the role of the cationic SDA content in the synthesis mixture on the Al arrangement in MFI zeolites. Depending on the specific mixture of the</p><p>organic cation tetrapropylammonium (TPA⁺) or various neutral organic molecules when used together with smaller Na⁺ cations, MFI zeolites can be crystallized over a range of Al content. Moreover, the fraction of Co²⁺-titratable Al-Al pairs correlates with the amount of occluded Na⁺ cations when the total Al content is held approximately constant (Si/Al ~ 50). These results are consistent with our prior reports of CHA zeolites, wherein the occlusion of smaller Na⁺ cations correlates positively with the formation of Al-Al pairs in six-membered ring (6-MR) locations. Unlike the N,N,N trimethyl-1-adamantylammonium (TMAda⁺) cation used to crystallize CHA, which alone does not form Co²⁺titratable Al-Al site pairs, the organic TPA+ alone can form Al-Al site pairs in MFI. DFT calculations of Al siting energies, using a 96 T-site MFI unit cell containing either one or two Al charge-balanced by one or two occluded TPA⁺respectively, reveal the dominant influence of electrostatic interactions between the cationic N of TPA⁺ and the anionic lattice charge. DFT calculations of probable Co²⁺exchange sites are used to identify a subset of Al-Al site pairs with favorable energies when compensated either by Co²⁺ or by two TPA⁺ molecules in adjacent MFI channel intersections. MFI crystallized with one cationic species (TPA⁺ or Na⁺) with a neutral organic species (ethylenediamine, pentaerythritol, or a mixture of methylamine and 1,4-diazabicyclo[2.2.2]octane) contain significantly lower fractions of Co²⁺-titratable Al-Al pairs at similar bulk Al content (Si/Al = 43–58), demonstrating the role of neutral organic species to occupy void spaces without providing the capacity to compensate charge, thus serving to increase the average spatial separation of framework Al sites. The kinetics of methanol dehydration to dimethyl ether can be quantified by first-order and zero order rate constants (415 K, per H⁺) to probe acid strength and confinement effects in solid Brønsted acids. Here, we use this quantitative probe reaction to investigate how Al arrangements in MFI and CHA affect the mechanism and kinetics of this reaction, in order to connect synthetic protocols to structure and to catalytic function. This effort first involved measurement of methanol dehydration kinetics on a suite of commercially sourced MFI samples to benchmark results obtained on our kinetic instruments to prior literature reports. CHA zeolites with 6-MR isolated protons show zero-order rate constants similar to those for commercial MFI zeolites and other topologies previously studied in the literature, reflecting the invariance in Brønsted acid strength with zeolite topology. First-order rate constants on isolated acid sites in CHA are an order of magnitude higher than acid sites in MFI, reflecting the smaller confining environments present in CHA than in the medium-pore zeolite MFI. In contrast, both first-order and zero-order rate constants among CHA samples increase systematically with the fraction of 6-MR Al pairs, even for samples of nominally similar composition (Si/Al ~ 15). DFT provides evidence for lower activation barriers at protons of 6-MR paired Al sites in CHA, which stabilize transition states via H-bonding interactions through co-adsorbed methanol bound at the proximal acid site, in a manner dependent on the specific Al arrangement and ring size and structure. Such favorable configurations are identified for 6-MR paired Al sites in CHA, but were not identified within MFI zeolite, which shows first-order and zero-order rate constants that are invariant with varying Al-Al site pair content. These findings and conclusions demonstrate how quantitative experimental characterization and kinetic data, augmented by theory insights, can aid in the development of more predictive synthesis-structure-function relations for zeolite materials and help transform empirical efforts in active site design and engineering into a more predictive science.</p>

No description available.