Thesis (Ph. D.)--Lund University, 1997. / Published dissertation.

Thesis (Ph. D.)--Lund University, 1997. / Published dissertation.

Dehydrogenation is the catalytic process of removing hydrogen from a saturated hydrocarbon to produce an olefin. Olefins are important feedstocks for the petrochemical industry and can potentially be used to produce fuels through oligomerization. Alloys containing an active metal such as platinum and palladium and a non-catalytic metal offer improved selectivity towards the olefin. This body of work seeks to further the understanding of how heteroatomic bonds in alloys change the rate and selectivity of alloy catalysts used for dehydrogenation.In the first study, a series of Pt-V bimetallic catalysts are synthesized, which are highly selective propane dehydrogenation catalysts. The bimetallic nature of the nanoparticles was verified by in-situX-ray Absorption Spectroscopy(XAS)and the formation of the Pt3V alloy phase was shown by in-situ synchrotronX-ray Diffraction(XRD). A reduction-oxidation differenceXASmethod was used to examine the surface stoichiometry and found that a shell layer of the alloy phase forms when the particles are platinum rich. Electronic modification of Pt was studied by Pt L3edgeX-ray Absorption Near Edge Structure(XANES),X-ray Photoelectron Spectroscopy(XPS), Resonant Inelastic X-ray Scattering (RIXS)andDensity FunctionalTheory(DFT). The spectral changes observed were shown to be due to changes in the energy of the filled and unfilled 5d density of states, and not due to electron transfer. The electronic modifications cause a weakening of adsorbate binding and destabilization of deeply dehydrogenated hydrocarbons, which contributes to the dehydrogenation selectivity.In the second study, alloys between palladium and five different promoters were synthesized and tested as propane dehydrogenation catalysts.The structure ofthe alloy catalysts was characterized by in-situ XAS and in-situ synchrotron XRD.Zinc and indium form alloy structures with site isolated palladium, while gallium, iron and manganese do not. All of the alloys have improved propane dehydrogenation selectivity compared to monometallic palladium. The propylene production turnover rate of the alloys increased by almost an order of magnitude compared to monometallic Pd, but among the alloys the turnover ratesonly varied by a factor of two despite the different structures and electronic modifications inherent to each phase. The site isolated alloys had higher propylene selectivity than those that were not site isolated. The site isolated alloys showed strongerelectronic modification: both in binding strengths and in Pd projected Density of States (pDOS)by DFT than did the non-site isolated alloys. The commonly used computational selectivity descriptor for dehydrogenation, which is the difference in energy between alkene desorption and alkene C-H bond activation energy correctly predicts that the site isolated alloys will have high selectivity but shows weaker trends for alloys without site isolation. A modified selectivity descriptor, involving the C-C bond breaking barrier in the adsorbed alkyne more accurately reflects the high selectivity of the non-site isolated alloys.In a third study,RIXS and XPSare used to examine trends in the electronic modification of platinum alloys with transition metal and post transition metal promoters. All alloys show an increase in the energy transfer maximum, showing that alloying modifies energy the filled and unfilled density of states. The increase in the energy transfer maximum in platinum alloys with 3d metals islargerfor early transition metals, which by DFT show larger shifts in the d-band center. The post transition elements showsignificantlylarger shifts than to the transition elements, partially due to the lack of orbital overlap between the valence p orbitals and Pt 5d orbitals. Platinum has the same number of valence d electrons regardless of promoter or structure, and redistribution of the 5d electron energy brought about by heteroatomic bonds leads to the observed electronic modifications. The positive binding energy shifts measured by XPS reflect these energy changes, which occur due to changes in the Fermi energy of the alloy, initial state effects and intra and extra atomic relaxation (final state effects). The calculated initial state effect shift is correlated to descriptors of the valence d band, such as the d band center.

The synthesis of cyclopenta[c]thiophenes has been sparsely reported in the literature owing to several difficulties involved in their synthesis. The present work involves the proposed synthesis of cyclopenta[c]thiophenes and their precursors using activated methylene. Cyclopenta[c]thiophene compounds show promise in the field of polymer and catalysis chemistry. These substituted polythiophenes are potential organic semiconductors and anti-tumor agents. The research presented shows the successful and novel conversion of 3,4-bis(chloromethyl)-2,5-dimethylthiophene and 3,4-bis(bromomethyl)-2,5-dimethylthiophene to a fused 5,5'-fused membered ring which is the precursor to cyclopenta[c]thiophene the sulfone ester, 5-carbomethoxy-5- phenylsulfonyl-1,3-dimethyl-5,6-dihydro-4H-cyclopenta[c]thiophene, in just two steps as compared to four steps previously reported in the literature. This valuable precursor intermediate currently made and proven by characterization is one synthetic step away from a substituted cyclopenta[c]thiophene. A paper has been submitted to Letters in Organic Chemistry to report our work.

This thesis documents the development of rhodium-catalyzed traceless chelation-controlled hydroacylation reactions for the synthesis of a variety of ketone products. <strong>Chapter 1</strong> provides an overview of rhodium-catalyzed hydroacylation chemistry, focusing on the origin of chelation-controlled strategies and the benefits thereof. <strong>Chapter 2</strong> describes a sequential reaction involving alkene hydroacylation, sulfide elimination and boronic acid conjugate addition, which affords products with the initial sulfide coordinating group replaced by a stereochemically defined aryl group. <strong>Chapter 3</strong> demonstrates a sequential process involving alkyne hydroacylation, boronic acid conjugate addition and sulfide elimination, which provides enantioenriched β'-arylα,β-unsaturated ketones in a highly efficient and selective manner. <strong>Chapter 4</strong> illustrates a versatile chelating group, triazene, for hydroacylation reactions. Subsequent functionalization of aromatic C-H bonds, promoted by the same chelating unit, offers highly substituted phenyl ketone products. <strong>Chapter 5</strong> documents experimental procedures and data.

A brief summary of the use of palladium as a catalyst, the characteristic reactivity of palladium complexes and the commonly used palladium-catalysed cross coupling reactions is given, with a special focus on the palladium-catalysed α-arylation of enolates and its application to the synthesis of aromatic heterocycles. The synthesis of aromatic heterocycles via both traditional methods and more recent metal-catalysed approaches is discussed in the context of isoquinolines. The palladium-catalysed oxidation of dihydrofurans bearing an ortho-bromophenyl group at the 2-position to the corresponding 2-phenyl furans is disclosed along with some preliminary mechanistic investigations. A novel synthetic route to isoquinolines is detailed involving the palladium-catalysed α-arylation of ketone enolates with an appropriate ortho-substituted aryl halide to furnish a protected 1,5-dicarbonyl intermediate. The versatility of these intermediates is demonstrated with their conversion into isoquinolines, isoquinoline N-oxides and naphthols. The scope of the synthetic procedure is fully exemplified across more than 30 different scaffolds covering the full spectrum of electron-rich to electron-deficient moieties. The intermediates were shown to be amenable to functionalisation with electrophiles, leading to isoquinolines bearing additional substitution at the C4 position. Sequential one-pot procedures were developed allowing three and four component couplings to directly deliver highly-substituted isoquinolines from commercially available starting materials. This methodology was utilised in the total synthesis of the natural product berberine in 26% overall yield and a longest linear sequence of six steps.

<strong>Introduction – Dearomatisation of Heteroaromatic Compounds</strong> The introduction provides a survey of dearomatisation reaction of heteroaromatics, with a particular focus on pyridines/pyridinium salts and furans. The mechanism, scope, and limitations of various approaches are covered, along with the goals of this project. <strong>Results and Discussion – Dearomatisation of Electron-Deficient Heteroaromatics</strong> This chapter initially explores the asymmetric addition of organometallic nucleophiles to pyridinium salts bearing a chiral counterion. Unfortunately, this approach ultimately proved unsuccessful, due to low observed enantioselectivities, and the low solubility of such salts. The second part of this chapter concerns the attempted asymmetric addition of dicarbonyl nucleophiles to electron-deficient furans, under conditions of chiral phase-transfer catalysts, affording bicyclic products in moderate enantioselectivity. Various alternative routes were also explored for the dearomatisation of furans and benzenoid systems. <strong>Introduction – Hydrogen Borrowing Alkylation Reactions with Alcohols</strong> The introduction surveys the range of methods available for the alkylation of various nucleophiles with alcohols under transition metal-catalysed conditions. Related methodologies are also explored, along with methods for the dehydrogenation of methanol. <strong>Results and Discussion - Rhodium-catalysed Methylation of Ketones Using Methanol</strong> This chapter describes the development of a novel ketone α-methylation using methanol. The development of reaction conditions is explored, followed by expansion of the substrate scope, including limitations of the methylation reaction. Mechanistic investigations support a methanol oxidation, aldol reaction/elimination, conjugate reduction pathway. Investigations into the role of O2 in the methylation reaction proved inconclusive. The utility of the reaction was also expanded via one-pot dialkylation reactions (work by Di Shen), Baeyer-Villiger oxidation of the products, and an attempted asymmetric transfer-hydrogenation. <strong>Results and Discussion - Interrupted Hydrogen Borrowing Reactions of Methanol</strong> This chapter looks to intercept intermediates from the α-methylation reaction. The selective methylenation of ketones is described, and a range of nucleophiles are screened for further functionalisation of ketones. Finally, a number of nucleophiles, including nitroalkanes, amines, peroxides and boronic acids are applied to one pot methylenation/conjugate addition protocols, affording complex products after two steps in one reaction vessel. <strong>Experimental</strong> Full experimental procedures and spectroscopic characterisation of compounds are provided.