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.

This dissertation presents the preparation and characterization of rhodium(0) nanoparticles supported on hydroxyapatite, and investigation of their catalytic activity in hydrogen generation from the hydrolysis of hydrazine-borane and ammonia-borane. Rh+3 ions were impregnated on hydroxyapatite by ion-exchange / then rhodium(0) nanoparticles supported on hydroxyapatite were formed in-situ during the hydrolysis of hydrazine-borane at room temperature. The rhodium(0) nanoparticles supported on hydroxyapatite were isolated as black powders by centrifugation and characterized by ICP-OES, SEM, TEM, EDX, XRD, XPS, and N2 adsorption-desorption spectroscopy. Rhodium(0) nanoparticles supported on hydroxyapatite have a mean particle size of 2.7&plusmn / 0.7 nm. The catalytic activity of rhodium(0) nanoparticles supported on hydroxyapatite was tested separately in the hydrolysis of hydrazine-borane and ammonia-borane. The hydrolysis of hydrazine-borane was started by adding the precatalysts, Rh+3-exchanged hydroxyapatite into the aqueous solution of hydrazine-borane / whereas, the hydrolysis of ammonia-borane was initiated by adding the catalyst rhodium(0) nanoparticles supported on hydroxyapatite which have been isolated from the first run of hydrolysis of hydrazine-borane. Rhodium(0) nanoparticles supported on hydroxyapatite provide a turnover frequency value of 6700 h-1 in the hydrolysis of hydrazine-borane at room temperature. The reuse experiments reveal that these supported nanoparticles are isolable, bottlable, and redispersible in solution. Furthermore, they retain 62 % of their initial activity at the fifth run in the hydrolysis of hydrazine-borane with release of 3 equivalents hydrogen. Activity of rhodium(0) nanoparticles supported on hydroxyapatite is maintained after the redispersion of the sample and 3 equivalents hydrogen generation from the hydrolysis of ammonia-borane confirms the activity of preformed catalyst. Rhodium(0) nanoparticles supported on hydroxyapatite provide a turnover frequency value of 3990 h-1 in the hydrolysis of ammonia-borane at room temperature.

<p dir="ltr">Reported herein is a brief summary regarding the previous syntheses of borane-amines, newly developed protocols to synthesize borane-amines, and the material and synthetic applications utilizing borane-amines. Methods to generate borane-amines typically relied on a metathesis-dehydrogenation reaction between ammonium salts and metal borohydrides in organic solvent, typically hazardous tetrahydrofuran (THF). However, due to the poor solubility of inorganic salts in organic solvent, stirring of the reaction mixture becomes difficult and, in turn, scalability is made challenging. We report two new methods to generate borane-amines that both rely on the hydroboration of sodium borohydride and a carbonyl activator, followed by the S_N2-type reaction with the amine to form the requisite borane-amine. The activator for our procedures are either 1) gaseous carbon dioxide or 2) water/ethyl acetate system. The CO₂ mediated protocol was applied to a variety of 1°-, 2°-, 3°-, and heteroaromatic amines as well as phosphines to form the corresponding borane adducts (73-99%). Water was also found to be a green, compatible activator. Interestingly, we had swapped environmentally and health hazardous THF with ethyl acetate (EtOAc) and found the reaction had still proceeded with competitive conversion of amines to the borane-amines (72-97%). The robustness of this reaction was demonstrated with a 1.1 mol scale synthesis of borane pyridine with 87% yield. With increased accessibility of borane-amines established, we sought to investigate their potential applications, including testing their hypergolic properties. Additionally, we utilized borane-ammonia for a sequential reduction/Friedel-Crafts alkylation of benzyl carbonyls. Traditionally an alkyl halide, the scope of the electrophilic aromatic substitution reaction has widened to include alcohols and carbonyls as potential Friedel-Crafts reactants. Few reports exist for the arylation of aldehydes and ketones, while no precedence exists for the arylation of carboxylic acids and esters. Our group previously reported that TiCl₄ is capable of eliminating oxygen from benzyl alcohols, forming a carbocation intermediate. Theoretically, the carbocation formed from TiCl₄ and benzyl alcohols would be vulnerable from attacks from other nucleophiles, including pi bonds from arenes. This was indeed proven to be the case when benzyl alcohol was reacted in 1 equiv. TiCl₄with benzene as the solvent and diphenylmethane was obtained as the sole product. By including borane-ammonia as a hydride source, various aryl carbonyls and aryl carbinols were also reduced to the corresponding alcohol <i>in situ</i>, enabling these substrates to participate in Friedel-Crafts alkylation.</p>

The synthesis and characterisation of a series of novel borane, boryl and borylene complexes of electron rich group 8 and 9 metal centres are described in this thesis. Chapter 3 reports on the properties of a highly nucleophile tolerant borylene system, [CpFe(dmpe)(BNMe₂)]⁺, together with its surprising formation via an unprecedented spontaneous halide ejection process. The incorporation of strongly electron releasing ancillary phosphine ligands is reflected by an Fe-B distance (ca. 1.80 Å) which is more akin to alkyl/aryl substituted borylene complexes, and perhaps more strikingly, by the very low exothermicity associated with the binding of pyridine to the two-coordinate boron centre (∆H = -7.4 kcal mol⁻¹ cf. -40.7 kcal mol⁻¹ for BCl₃). Despite the strong π electron release from the metal fragment implied by this suppressed reactivity and short Fe-B bond, the barrier to rotation about the Fe=B bond in the asymmetric variant [CpFe(dmpe){BN(C₆H₄OMe-4)Me}]⁺ is very small (ca. 2.9 kcal mol⁻¹). This apparent contradiction is rationalised by the orthogonal orientations of the HOMO and HOMO-2 orbitals of the [CpML2]⁺ fragment, which mean that the M-B π interaction does not fall to zero even in the highest energy conformation. The reactivities of the aminoboryl complexes, CpFe(CO)₂B(NR₂)Cl (R = Me, Cy), towards electrophiles (H⁺, Me⁺) are discussed in Chapter 4, with a view to probing potential modification of the boryl ligand substituents. The reaction of CpFe(CO)₂B(NCy₂)Cl with [Me₃O][BF₄] leads to the formation of CpFe(CO)₂B(NCy₂)F. Subsequent reactivity with Brookhart’s acid results in the formation of the known difluoroboryl system CpFe(CO)₂BF₂. Reaction of the dimethylaminoboryl complex CpFe(CO)₂B(NMe₂)Cl with [Me₃O][BF₄] generates CpFe(CO)₂BF₂ directly; however, reaction of CpFe(dmpe)B(NMe₂)Cl with [Me₃O][BF₄] is limited to the formation of CpFe(dmpe)B(NMe₂)F, presumably on steric grounds. Additionally, given the enhanced stability of the bis(phosphine) ligated systems, [CpM(PR₃)₂(BNR2)]⁺ compared to related dicarbonyl ligated complexes, it has also proved possible to synthesise other borylene complexes e.g. [CpFe(dmpe)(BOMes)]⁺ which are otherwise unstable under ambient conditions. Chapter 5 reports the coordination and B-H bond activation of aminoboranes at ruthenium and iridium metal centres. Reaction of aminoboranes, H₂BNR₂, with 14-electron fragments of the type [Cp*RuL]⁺, leads to κ² coordination. The interaction with 16- electron fragments, [CpRu(PR₃)₂]⁺, has also been probed. In contrast to side on-binding of isoelectronic alkene donors, an alternative κ¹-(σ-BH) mode of aminoborane ligation has been established, albeit with binding energies only ~ 8 kcal mol⁻¹ greater than for those for analogous dinitrogen complexes. Variations in ground-state structure and exchange dynamics as a function of the phosphine ancillary ligand set are consistent with chemically significant back-bonding into an orbital of B-H σ* character. By contrast, simple borane coordination compounds prove difficult to isolate on addition of aminoboranes, H₂BNR₂, to <m>in situ</m> generated sources of [(p-cymene)Ru(PR₃)Cl]⁺; spontaneous loss of HCl to generate a rare class of primary hydridoboryl complexes is witnessed instead. Attempts to synthesise boryl complexes via simple oxidative addition of monomeric aminoboranes have also proved successful, through the use of electron rich iridium precursors containing the [Ir(PMe₃)₃] fragment. This step results in the synthesis of novel amino(hydrido)boryl complexes, Ln(H)M{B(H)NR₂}; subsequent conversion (on loss of an ancillary ligand) to a borylene dihydride system proceeds via a novel B-to-M α hydride migration. The latter step is unprecedented for group 13 ligand systems and is remarkable in offering α-substituent migration from a Lewis acidic centre as a route to a two-coordinate ligand system.

This thesis explores the reactivity of amine-boranes with the {Rh(Xantphos)}+ fragment, with the aim of gaining mechanistic insight into the catalytic dehydropolymerisation of the amine-borane H₃B∙NMeH₂ to yield the polyaminoborane [H₂BNMeH]_n. Chapter 2 describes the synthesis of suitable Rh^III and Rh^I Xantphos precursors to be used in this investigation. Moreover, the first example of the dehydrogenative B—B homocoupling of the tertiary amine-borane H₃B∙NMe₃ to form H₄B₂•2NMe₃ is reported. The synthesis of the Rh^I precatalyst introduced in Chapter 2 entails the hydroboration of tert-butylethylene by H₃B∙NMe₃. In Chapter 3, the ability of the {Rh(Xantphos)}+ fragment to mediate this hydroboration in a catalytic manner is explored, and a mechanism is presented in which reductive elimination is proposed to be turnover-limiting. Other alkenes and phosphine-boranes are also trialled to determine the scope of the hydroboration. Chapter 4 investigates the catalytic dehydrocoupling of H₃B∙NMe₂H and H₃B∙NMeH₂ with {Rh(Xantphos)}+ to form the dehydrocoupling products [H₂BNMe₂]₂ and [H₂BNMeH]_n, respectively, and the dehydrocoupling mechanisms are shown to be similar. Both involve an induction period in which the active catalyst is formed (thought to involve N—H activation), and saturation kinetics operate during the productive phase of catalysis. H₂ is shown to inhibit the dehydrocoupling, and lead to production of shorter chain [H₂BNMeH]_n. Conversely, using THF as the dehydropolymerisation solvent instead of C₆H₅F results in longer chain [H₂BNMeH]_n. Finally, Chapter 5 presents new dicationic {Rh(Xantphos)}-based dimers, the formation of which involves loss of a phenyl group from the Xantphos ligands by P—C activation. The dimers are produced by routes involving either dehydrogenative homocoupling of H₃B∙NMe₃, or dehydrocoupling of H₃B∙NMe₂H. One of these dimers was tested as a catalyst for the dehydrocoupling of H₃B∙NMe₂H, and the reaction kinetics appear closely related those obtained using {Rh(Xantphos)}+, suggesting that the active catalysts in each system may be related.

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No description available.

As new technological tasks arise, electroless coatings on the basis of cobalt have come into use in microelectronics and micromechanics in order to form a protective layer against copper migration in integral schemes. Copper possesses a low specific resistance, however it also has some disadvantages, such as a low corrosion resistance and a high diffusion coefficient into So and SiO2 as well as into other substances. These problems can be diminished by using a thin barrier layer protecting from copper diffusion. The barrier properties of CoP and CoB layers which can be further improved by addition of tungsten would be suited for this purpose. At present, investigations of this kind are being carried out in many countries. Recently much attention is given to the search of new substances, which could be used in direct borohydride fuel cells as catalysts for the borohydride oxidation reaction. The aim of our work was to investigate the peculiarities of electroless cobalt coatings deposition in glycine solutions using sodium hypophosphite and morpholine borane as reducing agents, as well as to determine the composition of the coatings obtained and the possibilities of their employment for the formation of barrier layers on copper and application for fuel cells production. It has been determined that using hypophosphite as a reducing agent the rate of CoP and CoWP coatings deposition and the quantity of P in them increases with increase in solution pH. After appropriate... [to full text] / Iškilus naujiems technologiniams uždaviniams, chemines dangas kobalto pagrindu, pradėta naudoti mikroelektronikoje ir mikromechanikoje siekiant sudaryti apsauginį sluoksnį vario migracijai integralinėse schemose. Varis turi mažą specifinę varžą, tačiau turi ir keletą trūkumų, tokių kaip blogas korozinis atsparumas ir aukštas difuzijos koeficientas į Si ir SiO2, bei kitas medžiagas. Šios problemos gali būti sumažintos naudojant ploną barjerinį sluoksnį, apsaugantį nuo vario difuzijos. Tam tiktų CoP bei CoB sluoksnių barjerinės savybės, kurias galima pagerinti įvedant volframą. Šiuo metu tokie tyrimai vyksta daugelyje šalių. Taip pat pastaruoju metu skiriamas didelis dėmesys naujų medžiagų paieškai, kurios būtų taikomos tiesioginiuose borohidrido kuro elementuose katalizatoriais borhidrido oksidacijos reakcijai. Mūsų darbo tikslas ištirti kobalto dangų cheminio nusodinimo glicininiuose tirpaluose ypatumus, reduktoriais naudojant natrio hipofosfitą ir morfolino boraną, bei nustatyti gaunamų dangų sudėtį ir jų panaudojimo galimybes barjerinių sluoksnių formavimui ant vario bei taikymui kuro elementų gamybai. Nustatyta, kad naudojant reduktoriumi hipofosfitą didinant tirpalų pH, CoP ir CoWP dangų nusėdimo greitis ir P kiekis jose didėja. Parinkus tinkamas sąlygas buvo gautos kokybiškos kobalto dangos, į kurias patenka nuo 2,9 iki 6,3 at.% P ir nuo 3 iki 5 at.% W. Nustatyta, kad dikarboninės rūgštys gerina tirpalų buferines savybes, pagreitina kobalto dangų nusėdimą ir didina... [toliau žr. visą tekstą]

Ces travaux de doctorat se concentrent sur le développement d’une technologie originale et innovante de pile à combustible alimentée directement à l’anode par une solution alcaline contenant de l’hydrazine borane (HB), celui-ci intervenant comme combustible (technologie notée DHBFC pour direct hydrazine borane fuel cell). Thermodynamiquement, il est possible d’atteindre une tension de pile avoisinant 1.6 V avec une DHBFC alors que la technologie la plus commercialisée et mature, à membrane échangeuse de protons (PEMFC), ne peut offrir au mieux que 1.23 V (en pratique cette valeur est même inférieure à 1 V). En outre, la DHBFC permet de répondre à plusieurs problèmes rencontrés par la PEMFC (tels que le coût des électrodes contenant du platine et leur faible durabilité) et le choix de l’HB comme alternative chimique au stockage de l’hydrogène, sous la forme d’une poudre blanche soluble et stable en milieu alcalin, rendra le stockage plus simple, sûr et commode que celui de l’hydrogène gazeux sous pression.Ensuite, ces travaux démontrent que la réaction d’électrooxydation de l’HB (HBOR) en milieu alcalin est possible et efficace sur des métaux nobles tels que le palladium (moins cher que le platine) et sur des matériaux non nobles à base de nickel. Pour tous ces matériaux, la HBOR démarre à des potentiels inférieurs à 0 V vs. RHE, ce qui permet d’espérer des valeurs élevées de tension de pile pour les DHBFC. Aussi, cette solution permet-elle de diminuer le cout général de la technologie (en termes de matériaux d’électrode et de stockage de l’hydrogène) pour rivaliser économiquement avec les PEMFC ; il est important de rappeler que de tels électrocatalyseurs métalliques non nobles (à base de nickel) ne seraient pas stables dans des technologies acides telles que la PEMFC.Dans ce cadre, ces travaux apportent des résultats surprenants sur l’instabilité des électroctalyseurs de platine (et de palladium) largement utilisés dans les PEMFC. En effet, les particules de platine (et de palladium) supportées sur carbone sont très significativement dégradées (dans une moindre mesure pour le palladium) après une centaine de cycles dans une fenêtre de potentiel classique dans une solution légèrement alcaline. Il semble donc que les électrocatalyseurs à base de nickel soient des matériaux plus appropriés pour une utilisation industrielle comme anode dans des DHBFC au vu de leur activité électrocatalytique et de leur grande stabilité.Enfin, ces travaux soulignent l’importance du choix du combustible sur les performances de tels systèmes alcalins. Parmi les composés de la famille des boranes testés, l’HB présente les performances les plus intéressantes, en comparaison avec l’ammonia borane (AB) ou le dimethylamine borane (DMAB). L’étude du mécanisme de la réaction d’électrooxydation du fragment borane (BH3OR) est menée sur des électrocatalyseurs de palladium (car bien que ceux-ci subissent une dégradation non négligeable en milieu alcalin, ils restent néanmoins des matériaux nobles et modèles permettant de mieux comprendre le mécanisme de la BH3OR). Cette étude permet d’observer l’impact négatif de la présence des fragments d’ammoniac et de dimethyl amine contenus dans l’AB et le DMAB sur la BH3OR. En revanche, le fragment « hydrazine » de l’HB n’empoisonne pas le palladium et peut quant à lui être complétement valorisé en produisant 4 électrons échangés qui s’ajoutent aux 6 électrons échangés issus de la BH3OR, rendant alors la technologie alcaline DHBFC encore plus attrayante du point de vue de la densité énergétique.Ainsi, ces travaux soulignent l’intérêt de l’hydrazine borane pour les piles à combustible directes et alcalines, en particulier pour les applications nomades pour lesquelles le stockage d’hydrogène gazeux sous pression est délicat. Enfin, l’anode des DHBFC pourrait être composée d’électrocatalyseurs métalliques à base de nickel, garantissant une durabilité satisfaisante et diminuant le coût général de la technologie. / The present PhD work focusses on the development of an original and innovative technology of direct liquid alkaline fuel cell (DLAFC) using hydrazine borane as a fuel for the anode. Thermodynamically, a direct hydrazine borane fuel cell (DHBFC) system can have an operating voltage value around 1.6 V when the most commercialized and mature proton membrane exchange fuel cell (PEMFC) technology can only reach 1.23 V (and in practice this value is even lower than 1 V). In principle, a direct alkaline fuel cell technology such as the DHBFC addresses most of the issues encountered in acidic PEMFC systems (such as the cost of the platinum-containing electrodes and their poor durability) and hydrazine borane is a relevant alternative to store chemically the hydrogen in the form of a white powder that is stable in alkaline solutions; this chemical hydrogen storage is easier, safer and more user-friendly than compressed H2 gas.This PhD work demonstrates that the HB electrooxidation reaction (HBOR) in alkaline medium is possible and efficient on noble metals such as palladium (cheaper than platinum) and more importantly on noble-free nickel-based materials. For those materials, the HBOR onset potential is measured below 0 vs. RHE, which enables to expect promising operating voltage if they are used as anode electrocatalysts in DHBFC systems. This solution allows to diminish the technology’s cost (both in terms of fuel storage and electrocatalyst materials) and could enable to rival industrially PEMFC systems, if the anode durability is demonstrated.On this prospect, whereas non-noble metals (such as nickel) can generally not be used as anode electrocatalysts in acidic PEMFC systems because of their instability, this work demonstrates that they are stable in alkaline environment. Surprisingly, “state-of-the-art” platinum (and palladium) electrocatalysts, generally used in PEMFC, are unstable in alkaline medium: indeed, platinum (and palladium) carbon-supported nanoparticles are highly degraded (and in lesser extent for palladium) in alkaline solution, after 150 potential cycles in a usual potential window; so, these “state-of-the-art” noble electrocatalysts are not suitable for real DHBFC system applications. Therefore, the nickel-based electrocatalysts (both active and stable) are found to be the most suitable electrocatalyst materials for the DHBFC anode.Finally, it is also demonstrated that the nature of the borane fuel is critical for a utilization in DALFC system; hydrazine borane is found to be the most promising fuel against ammonia borane (AB) or dimethyl amine borane (DMAB). The borane electrooxidation reaction (BH3OR), carried out on palladium electrocatalysts (despite its relative instability for real systems, palladium is a suitable noble and model electrocatalyst to get a better understanding of BH3OR mechanism), using these various fuels sheds light on the detrimental (poisoning) role of the counter-borane fragments of AB and DMAB (ammonia and dimethyl amine, respectively); on the contrary, the counter-borane fragment of HB (hydrazine) is found to have no detrimental effect on the BH3OR. Interestingly, the hydrazine moiety is completely electrooxidized on palladium, leading to 4 exchanged electrons in addition to the 6 exchanged electrons generated by the BH3OR.To conclude, this PhD work underlines the interest of hydrazine borane for the DHBFC systems, in particular for nomad applications, where the hydrogen storage can be a problem. HB is a relevant fuel to store chemically the hydrogen and to be valorized on noble-free materials, diminishing the overall system cost while ensuring a sufficient durability for the DHBFC anode.

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.