Catalytic reactions with palladium supported on mesocellular foam : Applications in hydrogenation, isomerization, and C-C bond forming reactions

The major part of this thesis concerns the development of catalytic methodologies based on palladium nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF). The catalytic activity of the precursor to the nanocatalyst, PdII-AmP-MCF is also covered by this work. In the first part the application of Pd0-AmP-MCF in Suzuki-Miyaura cross-coupling reactions and transfer hydrogenation of alkenes under microwave irradiation is described. Excellent reactivity was observed and a broad range of substrates were tolerated for both transformations. The Pd0-AmP-MCF exhibited high recyclability as well as low metal leaching in both cases. The aim of the second part was to evaluate the catalytic efficiency of the closely related PdII-AmP-MCF for cycloisomerization of various acetylenic acids. The catalyst was able to promote formation of lactones under mild conditions using catalyst loadings of 0.3 - 0.5 mol% at temperatures of up to 50 oC in the presence of Et3N. By adding 1,4-benzoquinone to the reaction, the catalyst could be recycled four times without any observable decrease in the activity. The selective arylation of indoles at the C-2 position using Pd-AmP-MCF and symmetric diaryliodonium salts is presented in the third part. These studies revealed that Pd0-AmP-MCF was more effective than PdII-AmP-MCF for this transformation. Variously substituted indoles as well as diaryliodonium salts were tolerated, giving arylated indoles in high yields within 15 h at 20 - 50 oC in H2O. Only very small amounts of Pd leaching were observed and in this case the catalyst exhibited moderate recyclability. The final part of the thesis describes the selective hydrogenation of the C=C in different α,β-unsaturated systems. The double bond was efficiently hydrogenated in high yields both under batch and continuous-flow conditions. High recyclability and low metal leaching were observed in both cases.

Diversity in Catalytic Reactions of Propargylic Diazoesters

Abstract Title of Document: Diversity in Catalytic Reactions of Propargylic Diazoesters Huang Qiu, Doctor of Philosophy, 2016 Directed By: Professor Michael P. Doyle, Department of Chemistry and Biochemistry Propargylic aryldiazoesters, which possess multiple reactive functional groups in a single molecule, were expected to undergo divergent reaction pathways as a function of catalysts. A variety of transition metal complexes including rhodium(II), palladium(II), silver(I), mercury(II), copper(I and II), and cationic gold (I) complexes have been examined to be effective in the catalytic domino reactions of propargylic aryldiazoesters. An unexpected Lewis acid catalyzed pathway was also discovered by using FeCl3 as the catalyst. Under the catalysis of selected gold catalysts, propargylic aryldiazoesters exist in equilibrium with 1-aryl-1,2-dien-1-yl diazoacetate allenes that are rapidly formed at room temperature through 1,3-acyloxy migration. The newly formed allenes further undergo a metal-free rearrangement in which the terminal nitrogen of the diazo functional group adds to the central carbon of the allene initiating a sequence of bond forming reactions resulting in the production of 1,5-dihydro-4H-pyrazol-4-ones in good yields. These 1,5-dihydro-4H-pyrazol-4-ones undergo intramolecular 1,3-acyl migration to form an equilibrium mixture or quantitatively transfer the acyl group to an external nucleophile with formation of 4-hydroxypyrazoles. In the presence of a pyridine-N-oxide, both E- and Z-1,3-dienyl aryldiazoacetates are formed in high combined yields by Au(I)-catalyzed rearrangement of propargyl arylyldiazoacetates at short reaction times. Under thermal reactions the E-isomers form the products from intramolecular [4+2]-cycloaddition with H‡298 = 15.6 kcal/mol and S‡298= -27.3 cal/ (mol•degree). The Z-isomer is inert to [4+2]-cycloaddition under these conditions. The Hammett relationships from aryl-substituted diazo esters ( = +0.89) and aryl-substituted dienes ( = -1.65) are consistent with the dipolar nature of this transformation. An unexpected reaction for the synthesis of seven-membered conjugated 1,4-diketones from propargylic diazoesters with unsaturated imines was disclosed. To undergo this process vinyl gold carbene intermediates generated by 1,2-acyloxy migration of propargylic aryldiazoesters undergo a formal [4+3]-cycloaddition, and the resulting aryldiazoesters tethered dihydroazepines undergo an intricate metal-free process to form observed seven-membered conjugated 1,4-diketones with moderate to high yields.

STUDIES OF ELECTROCHEMICAL CATALYTIC REDUCTION REACTIONS OF TETRAPHENYLPORPHINATOCOBALT 1,2-DIBROMOETHANE AND 1,2-DICHLOROETHANE SYSTEMS IN NONAQUEOUS MEDIA

Electrochemical catalytic reactions of tetraphenylporphinatocobalt were studied in DMF and EtCl2 solutions in the presence of 1,2-dibromoethane and 1, 2-dichloroethane utilizing cyclic voltammetry, thin-layer electrochemistry, in situ UV-visible spectroel

A catalytic reactor for the trapping of free radicals from gas phase oxidation reactions

A catalytic reactor for the trapping of free radicals originating from gas phase catalytic reactions is described and discussed. Radical trapping and identification were initially carried out using a known radical generator such as dicumyl peroxide. The trapping of radicals was further demonstrated by investigating genuine radical oxidation processes, e.g., benzaldehyde oxidation over manganese and cobalt salts. The efficiency of the reactor was finally proven by the partial oxidation of cyclohexane over MoO3, Cr2O3, and WO3, which allowed the identification of all the radical intermediates responsible for the formation of the products cyclohexanol and cyclohexanone. Assignment of the trapped radicals was carried out using spin trapping technique and X -band electron paramagnetic resonance spectroscopy. © 2010 American Institute of Physics.

Catalytic transformation of aliphatic alcohols to corresponding esters in O2 under neutral conditions using visible-light irradiation

Selective oxidation of aliphatic alcohols under mild and base-free conditions is a challenging process for organic synthesis. Herein, we report a one-pot process for the direct oxidative esterification of aliphatic alcohols that is significantly enhanced by visible-light irradiation at ambient temperatures. The new methodology uses heterogenerous photocatalysts of gold–palladium alloy nanoparticles on a phosphate-modified hydrotalcite support and molecular oxygen as a benign oxidant. The alloy photocatalysts can absorb incident light, and the light-excited metal electrons on the surface of metal nanoparticles can activate the adsorbed reactant molecules. Tuning the light intensity and wavelength of the irradiation can remarkably change the reaction activity. Shorter wavelength light (<550 nm) drives the reaction more efficiently than light of longer wavelength (e.g., 620 nm), especially at low temperatures. The phosphate-exchanged hydrotalcite support provides sufficient basicity (and buffer) for the catalytic reactions; thus, the addition of base is not required. The photocatalysts are efficient and readily recyclable. The findings reveal the first example of using “green” oxidants and light energy to drive direct oxidative esterification of aliphatic alcohols under base-free, mild conditions.

Reactivity and catalytic activity of layered YBA2CU3O7-delta (123) type defect perovskites

The chemical modifications of structure, reactivity and catalytic properties of layered triple perovskite oxides, related to the YBa2Cu3O7-delta (123) system, have been briefly reviewed. These oxides form a versatile family of materials with wide-ranging chemical and physical properties. The multiple sites available for chemical doping, and the ability to reversibly intercalate oxygen at the defect sites have rendered these oxides important model systems in the area of oxide catalysis. An attempt has been made to comprehend the hitherto known catalytic reactions and correlate them to various factors like structure, oxygen diffusional limitations, different geometries adopted by various substituents, oxidative non-stoichiometry and activation energy for oxygen desorption. In particular, results on the enhanced catalytic activity of cobalt-substituted 123 oxide systems towards the selective catalytic oxidation of ammonia to nitric oxide and carbon monoxide to carbon dioxide are presented.

Noble metal ions in CeO2 and TiO2: synthesis, structure and catalytic properties

In the past four decades, CeO2 has been recognized as an attractive material in the area of auto exhaust catalysis because of its unique redox properties. In the presence of CeO2, the catalytic activity of noble metals supported on Al2O3 is enhanced due to higher dispersion of noble metals in their ionic form. In the last few years, we have been exploring an entirely new approach of dispersing noble metal ions on CeO2 and TiO2 matrices for redox catalysis. In this study, the dispersion of noble metal ions by solution combustion as well as other methods over CeO2 and TiO2 resulting mainly in Ce1-xMxO2-delta, Ce1-x-yTixMyO2-delta, Ce1-x-ySnxMyO2-delta, Ce1-x-yFexMyO2-delta, Ce1-x-yZrxMyO2-delta and Ti1-xMxO2-delta (M = Pd, Pt, Rh and Ru) catalysts, the structure of these materials, their catalytic properties toward different types of catalysis, structure-property relationships and mechanisms of catalytic reactions are reviewed. In these catalysts, noble metal ions are incorporated into a substrate matrix to a certain limit in a solid solution form. Lower valent noble metal-ion substitution in CeO2 and TiO2 creates noble metal ionic sites and oxide ion vacancies that act as adsorption sites for redox catalysis. It has been demonstrated that these new generation noble metal ionic catalysts (NMIC) have been found to be catalytically more active than conventional nanocrystalline noble metal catalysts dispersed on oxide supports.

The Metabolic Core and Catalytic Switches Are Fundamental Elements in the Self-Regulation of the Systemic Metabolic Structure of Cells

19 p.

Heterogeneous catalytic activity on Mn, Fe and Co-based metalloporphyrinic Solid Coordination Frameworks (SCFs)

Comunicación al congreso 1st European Conference on Metal Organic Frameworks and Porous Polymers, celebrado en Postdam del 11 al 14 de octubre de 2015

In situ IR spectroscopic studies on molybdenum nitride catalysts: active sites and surface reactions

Recent IR spectroscopic studies on the surface properties of fresh Mo2N/gamma-Al2O3 catalyst are presented in this paper. The surface sites of fresh Mo2N/gamma-Al2O3, both Modelta+ (0<δ<2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm(-1), due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo2N/gamma-Al2O3 behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo2N/gammaAl(2)O(3) catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo2N/gammaAl(2)O(3) catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites.

Bronsted-Evans-Polanyi relation of multistep reactions and volcano curve in heterogeneous catalysis

Multistep surface processes involving a number of association reactions and desorption processes may be considered as hypothetical one-step desorption processes. Thus, heterogeneous catalytic reactions can be treated kinetically as consisting of two steps: adsorption and desorption. It is also illustrated that the hypothetical one-step desorption process follows the BEP relation. A volcano curve can be obtained from kinetic analysis by including both adsorption and desorption processes.

Catalytic routes to convert saccharides to furanic aldehydes

The conversion of plant biomass-derived carbohydrates (preferably non-edible) into added-value products is envisaged to be at the core of the future biorefineries. Carbohydrates are the most abundant natural organic polymers on Earth. This work deals with the chemical valorisation of plant biomass, focusing on the acid-catalysed conversion of carbohydrates (mono and polysaccharides) to furanic aldehydes, namely 2-furaldehyde (Fur) and 5-hydroxymethyl-2-furaldehyde (Hmf), which are valuable platform chemicals that have the potential to replace a variety of oil derived chemicals and materials. The investigated reaction systems can be divided into two types depending on the solvent used to dissolve the carbohydrates in the reaction medium: water or ionic liquid-based systems. The reaction temperatures were greater than 150 ºC when the solvent was water, and lower than 150 º C in the cases of the ionic liquid-based catalytic systems. As alternatives to liquid acids (typically used in the industrial production of Fur), solid acid catalysts were investigated in these reaction systems. Aiming at the identification of (soluble and insoluble) reaction products, complementary characterisation techniques were used namely, FT-IR spectroscopy, liquid and solid state NMR spectroscopy, TGA, DSC and GC´GC-ToFMS analyses. Complex mixtures of soluble reaction products were obtained and different types of side reactions may occur. The requirements to be put on the catalysts for these reaction systems partly depend on the type of carbohydrates to be converted and the reaction conditions used. The thermal stability is important due to the fact that formation of humins and catalyst coking phenomena are characteristically inherent to these types of reactions systems leading to the need to regenerate the catalyst which can be effectively accomplished by calcination. Special attention was given to fully inorganic nanoporous solid acids, amorphous or crystalline, and consisting of nano to micro-size particles. The investigated catalysts were silicoaluminophosphates, aluminosilicates and zirconium-tungsten mixed oxides which are versatile catalysts in that their physicochemical properties can be fine-tuned to improve the catalytic performances in the conversion of different substrates (e.g. introduction of mesoporosity and modification of the acid properties). The catalytic systems consisting of aluminosilicates as solid acids and water as solvent seem to be more effective in converting pentoses and related polysaccharides into Fur, than hexoses and related polysaccharides into Hmf. The investigated solid acids exhibited fairly good hydrothermal stabilities. On the other hand, ionic liquid-based catalytic systems can allow reaching simultaneously high Fur and Hmf yields, particularly when Hmf is obtained from D-fructose and related polysaccharides; however, catalyst deactivation occurs and the catalytic reactions take place in homogeneous phase. As pointed out in a review of the state of the art on this topic, the development of truly heterogeneous ionic liquid-based catalytic systems for producing Fur and Hmf in high yields remains a challenge.

Synthesis and metal complexes of C2 symmetric ligands obtained from (R)-(+)-Betti and dialdehydes for asymmetric induction reactions

The aim of this master’s research thesis was the employment of an enantiopure 1,3-aminoalcohol, the 1-(α-aminobenzyl)-2-naphthol, known as Betti base, for the synthesis of some novel compounds which show a C2 symmetry. Some of these compounds, after derivatization, were used as ligands in association with transition metals to prepare some catalysts for enantioselective catalytic reactions. Some aminoalcohol (Salan-type) derivatives of these compounds were obtained upon reduction and in some cases it was possible to obtain complexes with transition metals such as Mn, Ni, Co and Cu. Furthermore a novel 6-membered analogue bisoxazoline ligand, 2,6-bis((R)-1-Phenyl-1H-naphtho[1,2-e][1,3]oxazin-3-yl)pyridine, was obtained and from it two Cu-complexes were prepared. The metal complexes were employed in some reactions to test the asymmetric induction, which was in some cases up to discrete values.

The reactions of carbon dioxide with complexes

The studies described in this thesis are concerned with the reaction of carbon dioxide and transition metal complexes of Co, Ir, Rh, Ru. Due to the important role of group VIII transition metals in homogeneous catalytic reactions, the work is mainly concerned with complexes of ruthenium.

Theoretical Study of Heteroatom Doping in Tuning the Catalytic Activity of Graphene for Triiodide Reduction

Graphene with heteroatom doping has found increasing applications in a broad range of catalytic reactions. However, the doping effects accounting for the enhanced catalytic activity still remain elusive. In this work, taking the triiodide electroreduction reaction as an example, we study systematically the intrinsic activity of graphene and explore the origin of doping-induced activity variation using first-principles calculations, in which two typical N and S dopants are tested. The most common graphene structures, basal plane, armchair edge, and zigzag edge, are considered, and it is found that the former two structures show a weak adsorption ability for the iodine atom (the key intermediate in the triiodide electroreduction reaction), corresponding to a low catalytic activity. Doping either N or S can strengthen the adsorption and thus increase the activity, and the codoping of N and S (NS-G) exhibits a synergistic effect. A detailed investigation into the whole process of the triiodide electroreduction reaction at the CH3CN/NS-G interface is also carried out to verify these activity trends. It is found that the zigzag edges which contain spin electrons show a relatively stronger adsorption strength compared with the basal plane and armchair edge, and initial doping would result in the spin disappearance that evidently weakens the adsorption; with the disappearance of spin, however, further doping can increase the adsorption again, suggesting that the spin electrons may play a preliminary role in affecting the intrinsic activity of graphene. We also analyzed extensively the origin of doping-induced adsorption enhancement of graphene in the absence of spin; it can be rationalized from the electronic and geometric factors. Specifically, N doping can result in a more delocalized “electron-donating area” to enhance I adsorption, while S doping provides a localized structural distortion, which activates the nearest sp2-C into coordinatively unsaturated sp3-C. These results explain well the improved activity of the doping and the synergistic effect of the codoping. The understandings are generalized to provide insight into the enhanced activity of the oxygen reduction reaction on heteroatom doped graphene. This work may be of importance toward the design of high-activity graphene based material.