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Monodisperse Pd nanocubes of 20 nm rib length and Pd nanospheres of 3 nm diameter deposited on corundum were used as efficient tool to reveal structure sensitivity of three-phase hydrogenations of unsaturated alcohols. For an olefin alcohol hydrogenation in the kinetic regime, surface (100) atoms of the cubes displayed lower activity than other surface atoms of the spheres. Apparent activation energies of 23 kJ/mol for the cubes and 17 kJ/mol for the spheres confirmed the reaction structure sensitivity. In an acetylenic alcohol hydrogenation, the cubes showed higher selectivity to an olefinic product than the spheres. Apparent activation energy was found as 38 kJ/mol for the cubes and 24 kJ/mol for the spheres. The apparent structure sensitivity in this case was attributed to liquid-solid mass transfer limitations governing the sphere-catalyzed reactions. The study shows the applicability and limitations of the use of nanoparticles for structure sensitivity studies in catalysis. / Chemical Engineering

abstract: Metal hydride materials have been intensively studied for hydrogen storage applications. In addition to potential hydrogen economy applications, metal hydrides offer a wide variety of other interesting properties. For example, hydrogen-dominant materials, which are hydrides with the highest hydrogen content for a particular metal/semimetal composition, are predicted to display high-temperature superconductivity. On the other side of the spectrum are hydrides with small amounts of hydrogen (0.1 - 1 at.%) that are investigated as viable magnetic, thermoelectric or semiconducting materials. Research of metal hydride materials is generally important to gain fundamental understanding of metal-hydrogen interactions in materials. Hydrogenation of Zintl phases, which are defined as compounds between an active metal (alkali, alkaline earth, rare earth) and a p-block metal/semimetal, were attempted by a hot sintering method utilizing an autoclave loaded with gaseous hydrogen (< 9 MPa). Hydride formation competes with oxidative decomposition of a Zintl phase. The oxidative decomposition, which leads to a mixture of binary active metal hydride and p-block element, was observed for investigated aluminum (Al) and gallium (Ga) containing Zintl phases. However, a new phase Li2Al was discovered when Zintl phase precursors were synthesized. Using the single crystal x-ray diffraction (SCXRD), the Li2Al was found to crystallize in an orthorhombic unit cell (Cmcm) with the lattice parameters a = 4.6404(8) &Aring;, b = 9.719(2) &Aring;, and c = 4.4764(8) &Aring;. Increased demand for materials with improved properties necessitates the exploration of alternative synthesis methods. Conventional metal hydride synthesis methods, like ball-milling and autoclave technique, are not responding to the demands of finding new materials. A viable alternative synthesis method is the application of high pressure for the preparation of hydrogen-dominant materials. Extreme pressures in the gigapascal ranges can open access to new metal hydrides with novel structures and properties, because of the drastically increased chemical potential of hydrogen. Pressures up to 10 GPa can be easily achieved using the multi-anvil (MA) hydrogenations while maintaining sufficient sample volume for structure and property characterization. Gigapascal MA hydrogenations using ammonia borane (BH3NH3) as an internal hydrogen source were employed in the search for new hydrogen-dominant materials. Ammonia borane has high gravimetric volume of hydrogen, and additionally the thermally activated decomposition at high pressures lead to a complete hydrogen release at reasonably low temperature. These properties make ammonia borane a desired hydrogen source material. The missing member Li2PtH6 of the series of A2PtH6 compounds (A = Na to Cs) was accessed by employing MA technique. As the known heavier analogs, the Li2PtH6 also crystallizes in a cubic K2PtCl6-type structure with a cell edge length of 6.7681(3) &Aring;. Further gigapascal hydrogenations afforded the compounds K2SiH6 and Rb2SiH6 which are isostructural to Li2PtH6. The cubic K2SiH6 and Rb2SiH6 are built from unique hypervalent SiH62- entities with the lattice parameters of 7.8425(9) and 8.1572(4) &Aring;, respectively. Spectroscopic analysis of hexasilicides confirmed the presence of hypervalent bonding. The Si-H stretching frequencies at 1550 cm-1 appeared considerably decreased in comparison with a normal-valent (2e2c) Si-H stretching frequencies in SiH4 at around 2200 cm-1. However, the observed stretching modes in hypervalent hexasilicides were in a reasonable agreement with Ph3SiH2- (1520 cm-1) where the hydrogen has the axial (3e4c bonded) position in the trigoal bipyramidal environment. / Dissertation/Thesis / Ph.D. Chemistry 2013

The research described in this thesis is directed toward the efficient, enantioselective synthesis of chiral products that have useful functionality. This goal was pursued through catalytic asymmetric hydrogenation, a reaction class that selectively introduces one or two stereocenters into a molecule in an atom-efficient step. This reaction uses a small amount (often &lt;1 mol%) of a chiral catalyst to impart stereoselectivity to the product formed. Though catalytic asymmetric hydrogenation is not a new reaction type, there remain many substrate classes for which it is ineffective. The present thesis describes efforts to extend the reaction to some of these substrates classes. Some of the products synthesized in these studies may eventually find use as building blocks for the production of chiral pharmaceuticals, agrochemicals, or flavouring or colouring agents. However, the primary and immediate aim of this thesis was to develop and demonstrate new catalysts that are rapid and effective in the asymmetric hydrogenation of a broad range of compounds. Paper I describes the design and construction of two new, related chiral iridium compounds that are catalysts for asymmetric hydrogenation. They each contain an N,P-donating phosphinooxazoline ligand that is held together by a rigid bicyclic unit. One of these iridium compounds catalyzed the asymmetric hydrogenation of acyclic aryl imines, often with very good enantioselectivities. This is particularly notable because acyclic imines are difficult to reduce with useful enantioselectivity. The second catalyst was useful for the asymmetric hydrogenation of two aryl olefins. In Paper II, the class of catalysts introduced into Paper I is expanded to include many more related compounds, and these are also applied to the asymmetric hydrogenation of prochiral imines and olefins. By studying a range of related catalysts that differ in a single attribute, we were able to probe how different parts of the catalyst affect the yield and selectivity of the hydrogenation reactions. Whereas iridium catalysts had been applied to the asymmetric hydrogenation of imines and largely unfunctionalized olefins prior to this work (with varied degrees of success), they had not been used to reduce fluoroolefins. Their hydrogenation, which is discussed in Paper III, was complicated by concomitant defluorination to yield non-halogenated alkanes. To combat this problem, several iridium-based hydrogenation catalysts were applied to the reaction. Two catalysts stood out for their ability to produce chiral fluoroalkanes in good enantioselectivity while minimizing the defluorination reaction, and one of these bore a phosphinooxazoline ligand of the type described in Papers I and II. Enol phosphinates are another class of olefins that had not previously been subjected to iridium-catalyzed asymmetric hydrogenation. They do, however, constitute an attractive substrate class, because the product chiral alkyl phosphinates can be transformed into chiral alcohols or chiral phosphines with no erosion of enantiopurity. Iridium complexes of the phosphinooxazoline ligands described in Papers I and II were extremely effective catalysts for the asymmetric hydrogenation of enol phosphinates. They produced alkyl phosphinates from di- and trisubstituted enol phosphinate, β-ketoester-derived enol phosphinates, and even purely alkyl-substituted enol phopshinates, in very high yields and enantioselectivities.

Asymmetric hydrogenation has emerged as a versatile methodology to obtain a wide range of chiral precursors. This thesis focused on the synthesis of new chiral ligands and the expansion of the substrate scope of asymmetric hydrogenations. Paper I described the synthesis and evaluation of N,P-ligands for the Ir-catalyzed hydrogenations of unfunctionalized olefins. The substrate scope of Ir-catalyzed asymmetric hydrogenations is limited to a narrow range of “test” olefins. The foremost focus of this thesis was to expand the substrate scope of Ir-catalyzed asymmetric hydrogenations. Papers II and III disclosed the potential of the N,P-ligated Ir complexes in hydrogenation of the enol phosphinates. This substrate class is attractive because the hydrogenated products are chiral alkylphosphinates that can be transformed into chiral alcohols and chiral phosphines without sacrificing enantiopurity. A wide range of enol phosphinates were hydrogenated to excellent conversions and enatioselectivities. The hydrogenation of purely alkyl-substituted enol phosphinates in very high conversions and ee values was emphasized in these studies. Paper IV described the investigation of unfunctionalized enamines as substrates in Ir-catalyzed hydrogenation studies. The hydrogenation results and structural limitations of the substrates are presented. Paper V described the asymmetric hydrogenation of diphenylvinylphosphine oxides, di- and trisubstituted vinyl phosphonates. The hydrogenation of diphenylvinylphosphine oxides gives direct access to protected chiral phosphines. The hydrogenated products of vinylphosphonates are highly synthetically useful in pharmaceutical and material chemistry. Hydrogenation of E/Z mixtures of carboxyethyl vinylphosphonates with perfect enantioselectivities was striking in these studies. In paper VI, we have reported the development of a new, highly enantioselective synthetic route to building blocks with CF3 at the chiral center. Several functionalized and unfunctionalized CF3-substituted olefins were hydrogenated with varied degree of success. This methedilogy is useful in the formation of chiral fluorine-containing molecules for a wide range of applications. Paper VII described the hydrogenation of imines using the phosphine-free Cp*Ru/diamine complexes. Chiral version of this reaction was also examined. Despite the modest results, this is the first study to use phosphine-free Cp*Ru/diamine complexes as catalysts for the reduction of C=N double bonds.