Three classes of bifunctional compounds related to frustrated Lewis pair chemistry were studied. The first class, alkynyl-linked phosphonium borates, was strategically synthesized and the corresponding neutral alkynyl-linked phosphine boranes generated in solution. They were reacted with THF, alkenes and alkynes to undergo either ring-opening or multiple bond addition reactions, giving rise to zwitterionic macrocycles. In two select alkynyl-linked phosphonium borates, thermolysis resulted in unique rearrangements transforming the phosphino- and boryl-substituted alkynyl moieties into C4 chains. The alkynyl-linked phosphine boranes were further demonstrated to coordinate as η3-BCC ligands in Ni(0) complexes. The rigid nature of the coordination was confirmed by dimerization without cleavage of the Ni–B interaction upon the addition of acetonitrile or carbon monoxide. Moreover, reactions with Al-, Zn- and B-based Lewis acids prompted hydride transfer within the alkynyl-linked phosphonium borate and interesting functional group transfer reactions. The second class of the bifunctional systems, a series of gem-substituted bis-boranes, was subjected to reactions with tBu3P and CO2. The O-linked bis-borane was shown to coordinate the phosphino-carboxylate moiety with one B, while the methylene-linked bis-boranes were demonstrated to chelate the carboxyl group. The third bifunctional system class, vinyl-group tethered boranes, was examined to elucidate the mechanism of the frustrated Lewis pair addition reaction to olefins. Using a bis(pentafluorophenyl)alkylborane, the close proximity of the olefinic protons and the ortho-fluorine nuclei were evident by both NOE measurements and DFT calculations. Moreover, its reactions with phosphine bases suggested that an initial interaction between the highly electrophilic borane and the olefinic fragment precedes such frustrated Lewis pair addition reaction. Furthermore, a bis(pentafluorophenyl)alkoxyborane was synthesized and reacted with P-, N-, C- and H-based nucleophiles, demonstrating the wide range of Lewis bases that can be applied in olefin addition reactions with complementary regioselectivity.

The asymmetric synthesis of N-aryl substituted chiral 1,4-aminoalcohols and their applications in asymmetric borane reduction and enantioselective diethylzinc addition to benzaldehyde reactions were performed starting from meso anhydride 51 that is the cycloadduct of cyclopentadiene and maleic anhydride. The desymmetrization of meso-anhydride 51 was achieved by using quinine or quinidine with very high enantiomeric excess value (up to 98% ee) and with high chemicalb yield. The quinine-mediated desymmetrization of meso-anhydride 51 with methanol gave (2S,3R)-(-)-cis-monoester 52. The hemiester was subjected to chemoselective amidation with various types of N-aryl substituted amines and then, it was treated with LAH and followed by hydrogenation in the presence of palladium catalyst to get the chiral 1,4-amino alcohols. The catalytic effectiveness of these chiral 1,4-amino alcohol ligands, (2S,3R)-60, (2S,3R)-61, (2S,3R)-62 and (2S,3R)-63 were examined in asymmetric borane reduction and enantioselective diethylzinc addition to benzaldehyde reactions. Keywords: Amino alcohol, chiral ligand, asymmetric reaction, borane reduction, diethylzinc addition

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.

Amine boranes have recently been considered as solid hydrogen storage materials with high capability of hydrogen storage. Dimethylamine borane is one of the promising amine boranes with high theoretical gravimetric capacity of 16.9 wt%. Dimethylamine borane can undergo dehydrogenation only in the presence of a suitable catalyst at moderate temperature. In this project, throughout the dehydrogenation of dimethylamine borane (DMAB), the catalytic activity of ruthenium(III) acetylacetonate was examined for the first time. During the catalytic reaction, formation of a new in-situ ruthenium(II) species, [Ru{N2Me4}3(acac)H], is observed. Mercury poisoning experiment indicates that the in-situ ruthenium(II) species is a homogeneous catalyst in the dehydrogenation of dimethylamine borane. Kinetics of catalytic dehydrogenation of dimethylamine borane starting with ruthenium(III) acetylacetonate was investigated depending on catalyst concentration, substrate concentration and temperature. As a result, the hydrogen generation rate was found to be first-order with respect to catalyst concentration and zero-order regarding the substrate concentration. Besides, evaluation of the kinetic data yielded that the activation parameters for dehydrogenation reaction: the activation energy, Ea = 85 &plusmn / 2 kJ&bull / mol-1 / the enthalpy of activation, DH# = 82 &plusmn / 2 kJ&bull / mol-1 and the entropy of activation / DS# = -85 &plusmn / 5 J&bull / mol-1&bull / K-1. Additionally, before deactivation, [Ru{N2Me4}3(acac)H] provides 1700 turnovers over 100 hours in hydrogen evolution from the dehydrogenation of dimethlyamine borane. [Ru{N2Me4}3(acac)H] complex formed during the dehydrogenation of dimethylamine borane was isolated and characterized by UV-Visible, FTIR, 1H NMR, and Mass Spectroscopy. The isolated ruthenium(II) species was also tested as homogeneous catalyst in the dehydrogenation of dimethylamine borane.

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.

Because of the growing concerns over the depletion of fossil fuel supplies, environmental pollution and global warming caused by a steep increase in carbon dioxide and other greenhouse gases in the atmosphere, much attention has been given to the development of renewable energy sources that are the only long-term solution to the energy requirements of the world&rsquo / s population, on the way towards a sustainable energy future. Hydrogen has been considered as a clean and environmentally benign new energy carrier for heating, transportation, mechanical power and electricity generation. However, the lack of effective, safe, and low-cost hydrogen storage materials for mobile, portable, and stationary applications is one of the major hurdles to be overcome for the implementation of hydrogen economy. Among various solid state hydrogen storage materials, chemical hydrogen storage materials such as sodium borohydride (NaBH4) and ammonia borane (H3NBH3) have received much attention as promising candidates for fuel cell applications under ambient conditions due to their high gravimetric and volumetric hydrogen storage capacities. Both sodium borohydride and ammonia borane generate hydrogen upon hydrolysis in the presence of suitable metal catalysts. Transition metal nanoclusters can be used as active catalysts to catalyze the hydrolysis reactions of sodium borohydride and ammonia borane for hydrogen generation since they exhibit unique properties that differ from their bulk counterparts. Although the catalytic activity of metal nanoclusters increases with decreasing particle size, they are unstable with respect to agglomeration into the bulk metal leading to a significant decrease in activity in their catalytic applications. Therefore, the exploitation of microporous and mesoporous materials with ordered porous structures as hosts to encapsulate metal nanoclusters has attracted great interest since the pore size restriction of these host materials could limit the growth of nanoclusters leading to an increase in the percentage of the catalytically active surface atoms. In this dissertation, we report the preparation, characterization and the investigation of the catalytic activities of zeolite confined cobalt(0) nanoclusters in the hydrolysis of sodium borohydride and ammonia borane. The zeolite confined cobalt(0) nanoclusters were prepared by the reduction of cobalt(II)-exchanged zeolite-Y by sodium borohydride in aqueous solution at room temperature with no alteration in the framework lattice or loss in the crystallinity. The characterization of zeolite confined cobalt(0) nanoclusters were done by using inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-visible spectroscopy (DR-UV-Vis), infrared spectroscopy (IR), Raman spectroscopy, and N2 adsorption-desorption technique. The catalytic activity of zeolite confined cobalt(0) nanoclusters and the kinetics of hydrogen generation from the hydrolysis of sodium borohydride and ammonia borane were studied depending on catalyst concentration, substrate concentration and temperature. The rate laws and the activation parameters (Arrhenius activation energy, Ea / activation enthalpy, &Delta / H# / and activation entropy, &Delta / S#) for both catalytic hydrolysis reactions were calculated from the obtained kinetic data.

The property transition metal nanoclusters are more active catalysts than their bulk counterparts because of increasing proportion of surface atoms with decreasing paricle size. The development of efficient and economical catalysts to further improve the kinetic properties under moderate conditions is therefore important for the practical application of nanoclusters as catalyst in the hydrogen generation from hydrolysis of ammonia borane this. In this regard, the development of active iron catalysts is a desired goal because it is the most ubiquitous of the transition metals, the fourth most plentiful element in the Earth&rsquo / s crust. In this dissertation, we report the preparation, characterization and investigation of the catalytic activity of the water soluble polymer stabilized iron(0) nanoclusters. They were prepared from the reduction of iron(III) chloride by a mixture of sodium borohydride (NaBH4, SB) and ammonia borane (H3NBH3, AB) mixture in the presence of polyethylene glycol (PEG) as stabilizer and ethylene glycol as solvent at 80 &deg / C under nitrogen atmosphere. PEG stabilized iron(0) nanoclusters were isolated from the reaction solution by centrifugation and characterized by SEM, EDX, TEM, HRTEM, XRD, UV-Vis, ICP-OES and FT-IR techniques. PEG stabilized iron(0) nanoclusters have almost uniform size distribution with an average particle size of 6.3 &plusmn / 1.5 nm. They were redispersible in water and yet highly active catalyst in hydrogen generation from the hydrolysis of AB. They provide a turnover frequency of TOF = 6.5 min-1 for the hydrolysis of AB at 25.0 &plusmn / 0.5 &deg / C. The TOF value is the best ever reported among the Fe catalyst and comparable to other non-noble metal catalyst systems for the catalytic hydrolysis of AB. Kinetics of hydrogen generation from the hydrolysis of AB in the presence of PEG stabilized iron(0) nanoclusters were also studied by varying the catalyst concentration, substrate concentration, and temperature. This is the first kinetic study on the hydrolysis of AB in the presence of an iron catalyst. Moreover, PEG stabilized iron(0) nanoclusters can be separated magnetically from the catalytic reaction solution by using a magnet and show catalytic activity even after tenth run.

Ordered mesoporous silicas have been shown to have a variety of useful applications ranging from adsorbents for containments to supports for catalysts. While these materials have received a good deal of attention in the literature there is still much opportunity for new technologies. We present research describing a novel approach to incorporate functionality onto the pore surfaces of these materials as well as a highly active catalyst for the Suzuki-Miyaura reaction. Our approach to selectively graft functionality on to the pore walls of the mesoporous silicas SBA-15 and MCM-41 involves treating the materials loaded with a structure directing agent (SDA), with hexamethyldisilazane that passivates the external surface through silylation. Once the SDA is removed the mesopores can be functionalized selectively using standard methods. A test designed to look at the passivation layer is also described. The catalyst developed is designated Pd-SBA-15-SH(g) and it is active for the Suzuki-Miyaura reaction. The activity, recyclability and leaching of Pd-SBA-15-SH(g) was found to be superior to related materials. A mechanistic analysis suggests the catalyst is a reservoir for soluble Pd metal. A key challenge that is holding back wide scale application of ammonia borane (NH3BH3) as a hydrogen storage material for mobile applications is the dearth of regeneration strategies. Presented are our forays into the development of an organic hydride based regeneration strategy. The first phase of the project focused on the reaction between Hantzsch esters and B(C6F5)3. N-substituted Hantzsch esters were found to transfer hydride to boron in >90 % yield. Mechanistic analysis of the reaction suggests either a SET mechanism or a highly asynchronous transition state. A novel hydride transfer equilibrium promoted by B(C6F5)3 was observed and it operated at temperatures below -10 ºC. N,N-ditertbutyl-dihydroimidazole is also an effective hydride donor to B(C6F5)3 as well as other Lewis acids that are more relevant mimics to those invoked in regeneration schemes. When the redistribution of B(SPh)3 is carried out with N,N-ditertbutyl-dihydroimidazole in the presence of NEt3 and CH2Cl2 at 50 ºC, BH2(NEt)3(SPh) is formed. CH2Cl2 functions as a thiol scavenger under the reaction conditions. 1-Octene trapping experiments provided indirect evidence for the formation of diborane, a critical component in the regeneration of NH3BH3. / Thesis (Ph.D, Chemistry) -- Queen's University, 2011-09-09 14:51:54.697

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 borohidrido 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] / 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]