Herein I describe a model study to determine the feasibility of organic hydride donors as a source of hydride in the regeneration of ammonia borane. Hydride transfer was observed in the model system comprised of Hantzsch ester and several analogues, as the organic hydride donor, and tris(pentafluorophenyl)boron, as the boron-based hydride acceptor akin to BBr3. Side reactions could be minimized by varying the reaction conditions. We determined that a Lewis acid-base adduct was forming between the carbonyls of the donor and the hydride acceptor, that this adduct was dynamic in the case of Hantzsch ester and that it could be inhibited by bulkier ester groups or promoted by reducing the steric bulk at the carbonyl in the case of a methyl ketone. The thermodynamics of the hydride transfer reaction with an N-substituted analogue were probed via variable temperature NMR and compared to two differently substituted analogues. In addition, the scope of the sp2-sp3 Suzuki-Miyaura cross-coupling previously developed in our lab was extended to include 2-(1,2-diaryl)ethane pinacolborane scaffolds. In order to access this asymmetric scaffold, reaction conditions for the cross-coupling of a primary boronic ester in the presence of a secondary one were developed. Yields achieved for the linear cross-coupling were in the 70 % range and varied from 42 % to 69 % for the secondary position. These latter yields are in the same range as the hydroborated styrene scaffolds described in our first account demonstrating the broad scope of these reaction conditions. / Thesis (Master, Chemistry) -- Queen's University, 2011-09-30 14:43:02.652

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Hypergolic hybrid motors are advantageous for rocket propulsion due to their simplicity, reliability, low weight, and safety. Many hypergolic hybrid fuels with promising theoretical performance are not practical due to their sensitivity to temperature or moisture. Ammonia borane (AB) has been proposed and studied as a potential hypergolic hybrid fuel that provides both excellent performance and storability. This study investigates the effect of droplet impact velocity, pellet composition, and storage humidity on ignition delay of AB with white fuming nitric acid as the oxidizer. Most ignition delays measured were under 50 ms with many under 10 ms and some even under 2 ms, which is extremely short for hybrid systems. Higher droplet velocities led to slightly shorter ignition delays, and exposing samples to humidity slightly increased ignition delay. An AB pellet composition of at least 20% epoxy binder was found to minimize ignition delay. The epoxy facilitates ignition by absorbing or adhering the oxidizer and slowing the reaction with the fuel, preventing oxidizer expulsion and holding it close to the fuel. These results emphasize the importance of binder properties in hypergolic hybrids. Pellets varying in composition and storage method were extinguished and reignited with the oxidizer to demonstrate reignition capability.

Hydrogen, nature’s simple and the most abundant element has been in the limelight for the past few decades from the stand point of the so-called hydrogen economy. With a high calorific value (142 MJ/kg) that is three times as large as the liquid hydrocarbons, hydrogen has emerged as a promising and environmentally friendly source of energy for the future generations. However, on-board hydrogen storage is one of the bottlenecks for its widespread usage for mobile applications. Storing hydrogen in liquid or compressed form is extremely difficult because of its low density. One of the best alternatives is to store hydrogen in a chemical form. Despite extensive work in this area, none of the materials seem to satisfy the essential criteria of reversible hydrogen storage with high gravimetric content. With regard to chemical hydrogen storage, apart from metal hydrides, ammonia borane (H3N•BH3, AB) is a promising prospect with a very high gravimetric storage of 19.6 wt% of hydrogen. Objectives 1) Develop cost-effective and active first-row transition metal based catalysts for the generation of hydrogen from AB in protic solvents 2) Study the dehydrogenation of AB in fluorinated alcohols and acids in order to realize compounds that are suitable for regeneration. 3) Study the interaction of Cu2+ with AB in non-aqueous medium using 11B NMR spectroscopy and powder XRD techniques. 4) Generation of highly pure hydrogen from ammonia borane in the solid state under mild conditions in the presence of late first row transition metal salts. 5) Synthesis of highly monodisperse ultrasmall colloidal Mg nanoparticles using the Solvated Metal Atom Dispersion (SMAD) method and digestive ripening technique; study the effect of size on the desorption temperature of MgH2. 6) Synthesize Cu/ZnO and Cu/MgO nanocomposites from the individual metal nanoparticles using co-digestive ripening technique and establish the structure of the composites using TEM, EF-TEM, and powder XRD techniques. Significant results Hydrogen generation from AB in protic solvents was realized using first-row transition metal catalysts. Initial studies were carried out using Cu nanocatalyst synthesized by the solvated metal atom dispersion method (SMAD). The activity order was found to be Cu2O > Cu@Cu2O > Cu. In addition, the late first-row transition metal ions, Co2+, Ni2+, and Cu2+ ions were also found to be highly active towards AB hydrolysis. These ions assisted AB hydrolysis via in-situ formation of metal atoms/clusters. Cu2+ assisted the hydrolysis of AB via the in-situ generation of both H+ and Cu clusters. At higher concentrations of AB, hydrolysis resulted in the evolution of NH3 in addition to H2 whereas, methanolysis afforded pure H2. In the case of methanolysis, for catalyst/AB = 0.2, three equiv of H2 were liberated in 2.5, 4.2, and 1.5 min when Co-Co2B, Ni-Ni3B, and Co-Ni-B nanopowders were used as catalysts, respectively. Dehydrogenation of ammonia borane (AB) was carried out in 2,2,2-trifluoroethanol and trifluoroacetic acid in order to realize compounds that are suitable for regeneration. The final byproduct obtained after the catalytic dehydrogenation of AB in 2,2,2-trifluoroethanol was NH4+B(OCH2CF3)4–. The FTIR data showed that the B-O bond in NH4+B(OCH2CF3)4 is slightly weaker compared to that in boric acid. Dehydrogenation of AB in trifluoroacetic acid in a controlled manner resulted in the formation of [CF3COO]–[BH2NH3]+ as the final by-product. Ammonia-borane was regenerated from [CF3COO]–[BH2NH3]+ by its reaction with LiAlH4, which served as the hydride source. Dehydrogenation of AB in non-aqueous medium and in the solid state were studied in hydrogen storage point of view. Cu2+ was found to activate the B–H bond in amine boranes in non-aqueous medium even at room temperature. As a result of the B–H bond cleavage in AB, [H3N•BH2]Cl species is formed. This compound reacts with unreacted AB via 3 separate pathways one involving hydrogen evolution, a second involving formation of a stable diammoniate of diborane cation [(NH3)2BH2]Cl without hydrogen evolution, and the third involving the formation of [H2NBH2]n and BNHx polymers accompanied by the generation of H2. Mechanisms of these pathways have been elaborated using 11B NMR spectroscopy and powder X-ray diffraction methods. These studies demonstrate that Cu(II) salts can be used as effective initiators for the dehydrogenation of amine boranes. Copper-induced hydrogen generation from AB in the solid state was also studied: for Cu2+/AB = 0.05, two equiv of H2 were liberated in 6.5 h at 333 K, which is equal to 9 wt% of the system. The 11B MAS NMR studies showed that the reaction proceeds through the intermediacy of [NH4]+[BCl4]– which eliminates the formation of borazine impurity, thereby affording pure H2. The cost effectiveness of CuCl2 makes this reaction scheme extremely attractive for real time applications. In the context of hydrogen storage in metal hydrides, highly monodisperse colloidal Mg nanoparticles with a size regime of 2–4 nm were synthesized by using the SMAD method followed by digestive ripening technique. The Mg-HDA nanopowder was fully hydrided at 33 bar and 391 K. Onset of hydrogen desorption from MgH2 nanoparticles was observed at a remarkably low temperature, 388 K compared to > 623 K in the case of bulk MgH2. The present study is a step towards realizing hydrogen storage materials that could operate close to ambient conditions. Colloids of Cu and Zn nanoparticles stabilized by 2-butanone have been prepared by the SMAD method. The as-prepared colloids which are polydisperse in nature have been transformed into highly monodisperse colloids by the digestive ripening process in the presence of hexadecylamine. Using this process, copper nanoparticles of 2.1 ± 0.3 nm and zinc nanoparticles of 3.91 ± 0.3 nm diameters have been obtained. Co-digestive ripening of Cu, Zn and Cu, Mg colloids resulted in the formation of Cu/ZnO and Cu/MgO nanocomposites, respectively. The structures of these nanocomposites were established using UV-visible spectroscopy, TEM, EF-TEM, and powder XRD techniques.

Ammonia borane and ammonium borohydride have been considered extensively as potential hydrogen storage materials. This thesis reports their structure and functional properties, emphasising the key role that dihydrogen bonding plays in both materials. The formation of a 'mobile phase' is considered to be the preliminary step in the decomposition of ammonia borane. The formation of this mobile phase has been studied using neutron diffraction, inelastic neutron spectroscopy and NMR. It has been found that in the mobile phase, 'end-to-end' flipping of the ammonia borane molecule occurs. This is an important precursor to the next step in the decomposition: the formation of the diammoniate of diborane. The dihydrogen bonding networks which occur in both the orthorhombic and the tetragonal phases of ammonia borane, and are the controlling factor in the decomposition process, were investigated using Density Functional Theory Molecular Dynamics (DFT-MD) simulations. It was hence shown that in the high-temperature tetragonal phase of ammonia borane, dihydrogen bonding is still an important stabilising interaction and there is little to distinguish between the three crystallographically distinct dihydrogen bonds. A closely related hydrogen storage material, ammonium borohydride, was also studied using the same techniques. Its low temperature phase progression was examined using variable temperature neutron diffraction. The vibrational modes of ammonium borohydride were assigned by comparing vibrational spectra determined using inelastic neutron spectroscopy with the results of DFT-MD simulations. Quasielastic neutron spectroscopy was used to show that both the ammonium and borohydride groups in ammonium borohydride perform discrete 'hopping' reorientational motions at a wide range of temperatures, and that the ammonium group has a mean residence time approximately 100 times less than that of the borohydride group. Hydrogen atom densities in the ammonium group were determined from DFT-MD simulations, and from refinements of high-resolution neutron diffraction data using cubic harmonic basis functions.

Les matériaux à base de bore et d'azote présentent un grand potentiel et donc un grand intérêt pour des applications énergétique et en particulier dans le domaine du stockage de l'hydrogène. L'ammoniaborane (NH3BH3) s'est révélé, au milieu des années 2000, comme un matériau avec une grande capacité gravimétrique (19,6%m) et volumétrique (140 g.L-1) en hydrogène. Au cours de l'analyse de la bibliographie nous nous sommes aperçus que tous les travaux sur l'ammoniaborane portés sur sa déstabilisation thermique, nous avons donc choisi une approche originale en nous concentrant sur la stabilisation thermique de l'ammoniaborane. Mon travail de thèse a consisté à revisiter la synthèse de l'ammoniaborane pour en dégager les meilleurs paramètres de synthèse (précurseurs de bore et d'azote, solvant et température) possible en vue d'obtenir une température de début de déshydrogénation la plus haute possible. En effet, en faisant varier certains précurseurs nous avons pu observer une modification de la température de début de déshydrogénation et donc de la stabilité thermique de l'ammoniaborane. Après avoir déterminé les meilleurs paramètres de synthèses nous avons entrepris une étude thermique et thermolytique afin de comprendre quel(s) facteur(s) étai(en)t à l'origine de cette différence de stabilisation. Pour cela nous avons effectué une étude d'analyse thermogravimétrique couplée à un spectromètre de masse afin de déterminer le mécanisme de déshydrogénation et une étude en conditions isotherme afin de vérifier la stabilité des ammoniaboranes que nous avons synthétisés. Dans un troisième temps nous avons effectué une étude spectroscopique de surface, grâce à l'XPS et du matériau dans son ensemble, grâce à la RMN-MAS à l'état solide des noyaux de bore 11 et d'azote 15. Ces études nous ont permis de déterminer un nouveau mécanisme de déshydrogénation de l'ammoniaborane pour des expériences en conditions isotherme. / Boron and nitrogen based-materials offer a great potential and interest in energy applications and in particular in the field of hydrogen storage. The ammonia borane (NH3BH3) was revealed, in the mid 2000s, as a material with high gravimetric (19.6%m) and volumetric (140 g.L-1) capacities in hydrogen. During the analysis of the literature we realized that all studies on ammonia borane treated on its thermal destabilization, so we chose an original approach by focusing our work on the thermal stabilization of ammonia borane. My thesis work focused on the synthesis of ammonia borane to identify the best synthesis parameters (boron and nitrogen precursors, solvent, and temperature) for the highest possible onset temperature. Indeed, by varying some precursors we observed a change in the onset temperature and therefore in the thermal stability of the ammonia borane. After determining the best synthesis parameters we undertook thermal and thermolytic studies to understand which factor(s) is(are) responsible for the stabilization's differences. For this, we performed thermogravimetric analysis coupled to mass spectrometer studies to determine the dehydrogenation mechanism and studies in isothermal conditions to verify the stability of our ammonia boranes. Thirdly we performed a spectroscopic study by XPS and solid state MAS-NMR of boron 11 and nitrogen 15. These studies allowed us to identify a new mechanism of dehydrogenation of ammonia borane for experiments in isothermal conditions.

This thesis investigates the chemistry of ammonia borane (NH3BH3) relevant to the development of hydrogen storage systems for vehicular applications. Because of its high hydrogen content and low molecular weight ammonia borane has the potential to meet stringent gravimetric hydrogen storage targets of gt;9 wt%. Two of the three moles of H2 in ammonia borane can be released under relatively mild conditions, with the highest gravimetric yield obtained in the solid-state. However, ammonia borane does not deliver sufficient H2 at practical temperatures and the products formed upon H2 loss are not amenable to regeneration back to the parent compound. The literature synthesis of ammonia borane was modified to facilitate large scale synthesis, and the deuterated analogues ND3BH3 and NH3BD3 were prepared for the purpose of mechanistic studies. The effect of lithium amide on the kinetics of dehydrogenation of ammonia borane was assessed by means of solid-state reaction in a series of specific molar ratios. Upon mixing lithium amide and ammonia borane, an exothermic reaction ensued resulting in the formation of a weakly bound adduct with an H2N...BH3-NH3 environment. Thermal decomposition at or above temperatures of 50eg;C of this phase was shown to liberate gt;9 wt% H2. The mechanism of hydrogen evolution was investigated by means of reacting lithium amide and deuterated ammonia borane isotopologues, followed by analysis of the isotopic composition of evolved gaseous products by mass spectrometry. From these results, an intermolecular multi-step reaction mechanism was proposed, with the rates of the first stage strongly dependent on the concentration of lithium amide present. Compounds exhibiting a BN3 environment (identified by means of solid-state sup1;sup1;B NMR spectroscopy) were formed during the first stage, and subsequently cross link to form a non-volatile solid. Further heating of this non-volatile solid phase ultimately resulted in the formation of crystalline Li3BN2 - identified by means of powder X-ray diffractometry. This compound has been identified as a potential hydrogen storage material due to its lightweight and theoretically high hydrogen content. It may also be amenable to hydrogen re-absorption. The LiNH2/CH3NH2BH3 system was also investigated. Thermal decomposition occurred through the same mechanism described for the LiNH2/NH3BH3 system to theoretically evolve gt;8 wt% hydrogen. The gases evolved on thermal decomposition were predominantly H2 with traces of methane detected by mass spectrometry.

Among the new hydrogen storage materials, ammonia borane (AB) appears to be the most promising one as it has high hydrogen content, high stability, and being environmentally benign. Dehydrogenation of AB can be achieved via hydrolysis, thermolysis or methanolysis. Methanolysis of AB eliminates some drawbacks of other dehydrogenation reactions of AB. The use of colloidal and supported particles as more active catalyst than their bulky counterparts for the hydrolysis of AB implies that reducing the particle size can cause an increase in the catalytic activity as the fraction of the surface atoms increases by decreasing the particle size. Similarly, transition metal nanoclusters can be utilized as catalyst for the methanolysis of AB as well. For this purpose transition metal nanoclusters need to be stabilized to a certain extent. Actually in the catalytic application of transition metal nanoclusters one of the most important problems is the aggregation of nanoclusters into bulk metal, despite of using the best stabilizers. In this regards, the use of metal nanoclusters as catalysts in systems with confined void spaces such as inside mesoporous and microporous solids appears to be an efficient way of preventing aggregation. In this dissertation we report for the first time the use of intrazeolite rhodium(0) nanoclusters as a catalyst in the methanolysis of ammonia borane. Rhodium(0) nanoclusters could be generated in zeolite-Y by a two-step procedure: (i) incorporation of rhodium(III) cations into the zeolite-Y by ion-exchange, (ii) reduction of rhodium(III) ions within the zeolite cages by sodium borohydride in aqueous solution, followed by filtration and dehydration by heating to 550 &deg / C under 10-4 Torr. Zeolite confined rhodium(0) nanoclusters are stable enough to be isolated as solid materials and characterized by ICP-OES, XRD, SEM, EDX, HRTEM, XPS and N2 adsorption-desorption technique. The zeolite confined rhodium(0) nanoclusters are isolable, bottleable, redispersible and reusable. They are active catalyst in the methanolysis of ammonia-borane even at low temperatures. They provide exceptional catalytic activity with an average value of TOF = 380 h-1 and unprecedented lifetime with 74300 turnovers in the methanolysis of ammonia-borane at 25 &plusmn / 0.1 &deg / C. The work reported here also includes the full experimental details of previously unavailable kinetic data to determine the rate law, and activation parameters (Ea, &amp / #916 / H&amp / #8800 / and &amp / #916 / S&amp / #8800 / ) for the catalytic methanolysis of ammonia-borane.

More attention has been paid to find new type renewable energy sources because of increasing concern about the environmental problems arising from the combustion of fossil fuels as energy sources. The development of new storage materials will facilitate the use of hydrogen as a major energy carrier. Several possibilities exist for &lsquo / &lsquo / solid-state&rsquo / &rsquo / storage: the hydrogen can be trapped in metal organic frameworks, carbon nanotubes and certain alloys / or one can use materials in which hydrogen is already present in the composition (e.g., chemical hydrides). The latter option seems to be the most promising since it permits a higher mass ratio of hydrogen. Recently, ammonia-borane complex (NH3BH3, AB) has been considered as solid hydrogen storage material since it possess one of the highest hydrogen contents (19.6 wt. %) and high stability under the moderate conditions. Hydrolysis and methanolysis are the two reactions liberating hydrogen from AB. However, a catalyst is needed for hydrogen generation from methanolysis of AB. In this context, we aim to develop PVP-stabilized palladium(0) and ruthenium(0) nanoclusters as catalyst for the methanolysis of AB. The PVP-stabilized palladium(0) and ruthenium(0) nanoclusters were prepared from the in-situ reduction of palladium(II) acetylacetonate and ruthenium(III) chloride respectively in the methanolysis of AB. The prepared palladium(0) nanoclusters were isolated as solid materials by removing the volatile in vacuum and characterized by using TEM, SAED, XPS, FT-IR, XRD and UV-visible electronic absorption spectroscopy techniques while and ruthenium(0) nanoclusters were characterized by TEM, XPS, XRD, FT-IR and UV-visible electronic absorption spectroscopy techniques. The kinetics of methanolysis of AB catalyzed by palladium(0) and ruthenium(0) nanoclusters were studied depending on the catalyst concentration, substrate concentration and temperature. The activation parameters of the catalytic methanolysis reaction obtained from the evaluation of kinetic data.

The production of transition metal(0) nanoparticles with controllable size and size distribution are of great importance in catalysis since their catalytic activity decreases as nanoparticles aggregate into clumps and ultimately to the bulk metal. Reducing the particle size of heterogeneous catalyst provides a significant rise in its activity as the fraction of surface atoms increases with decreasing particle size. Therefore, transition metal(0) nanoparticles need to be stabilized to certain extend in their catalytic applications by strong stabilizers. In this regard, tert-butylammonium octanoate [(CH3)3CNH3+][CH3(CH2)6COO-] seems to be an appropriate stabilizer for rhodium(0) nanoparticles since octanoate anion and its associated tert-butylammonium cation can provide a sufficient protection for rhodium(0) nanoparticles against aggregation by the combined electrostatic and steric effects. We report herein the preparation and characterization of rhodium(0) nanoparticles stabilized by tert-butylammonium octanoate and their catalytic use in the dehydrogenation of ammonia borane, H3NBH3, which appears to be the most promising hydrogen storage material due to its high hydrogen content (19.6 wt %). Rhodium(0) nanoparticles stabilized by tert-butylammonium octanoate were reproducibly prepared by the reduction of rhodium(II) octanoate dimer with tert-butylamine borane in toluene at room temperature and characterized by EA, XRD, ICP/OES, TEM, HRTEM, STEM, FTIR, XPS, UV-VIS and NMR spectroscopy. The new rhodium(0) nanoparticles is the first example of well-defined, reproducible, and isolable true heterogeneous catalyst used in the dehydrogenation of ammonia borane. They show record catalytic activity in the dehydrogenation of ammonia borane at room temperature with an apparent initial TOF value of 342 h-1 and TTO value of 1100.