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Bifunctional catalysis is a well understood phenomenon in nature, with enzymes frequently using two (or more) functional groups to accomplish selective transformations on a suitable substrate. It is becoming clear however, that bifunctional catalysis is not merely of interest to explain or mimic biological efficiency and rate enhancement, but is a viable design principle for the development of new molecular catalysts. In this thesis we have prepared achiral amino-boronic acid compounds with different scaffold structures based on general structures 1 and 2.(^5). although these compounds did not show any reactivity towards the MBH and aza-MBH reaction, they were very successful as catalysts for the aldol reaction. For this reaction it was possible to select the wanted product (aldol or chalcone product) using the same bifunctional catalyst only by changing the solvent. Also with hydroxyacetone some excellent results were gained with yields between 49 to 97% for both aromatic and aliphatic aldehydes in very high regioselectivity.

Initially the perfluoroacylation of a range of commercially available vinyl ethers and conversion of the resulting perfluoroacylated enol ethers to 1-H-pyrazoles via reaction with hydrazine is reported. The selective synthesis of a range of alpha-aryl vinyl ethers using Heck chemistry is then reported. Subsequent perfluoroacylations of the vinyl ethers followed by reaction of the resulting perfluoroacyl enol ethers with hydrazine affords a range of 5-aryl-3-perfluoroalkyl pyrazoles in good yields.;Alternative methodology for the synthesis of 5-aryl-3-perfluoroalkyl pyrazoles is then described in which resin bound esters are converted to vinyl ethers <via a Tebbe reaction. Subsequent perfluoroacylations generate the expected resin bound perfluoroacyl enol ethers and cleavage with cyclisation with hydrazine liberates the desired pyrazoles in acceptable yields for this type of methodology. Finally the microwave mediated Suzuki coupling of 4-iodo-1-methyl-3-trifluoromethyl-1-H-pyrazole with various boronic acids is reported as a general way in which 4-substituted-3-perfluoroalkyl-pyrazoles can be synthesised rapidly in reasonable yields.

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Our interest in developing new ligands for asymmetric catalysis by octahedral metal complexes has led us to consider ways in which tripodal ligands may be used to reduce their symmetry to C₃ and thus provide three homotopic coordination sites for substrate coordination opposite the ligand. Initial attempts at producing our desired coordination mode concentrated on using the system [C(NR)₃]^2- as an isoelectronic analogue of the well established trimethylenemethane ligand. However, although these proved to be interesting chelating and bridging ligands, the distortion from planarity required for the h³-coordination of such Y-shaped ligands is precluded by the energy associated with the in-plane p-bonding in such systems. In order to address this problem we have begun employing ligands centred on tetrahedral rather than planar atoms which effectively have the required distortion built in to the ligand before coordination. The synthesis and characterisation of the phosphonium salts [R'P(CH₂R)₃]Cl and [R'P(NHR)₃]Br as precursors to such ligands is described herein. Studies of the identified phosphonium salts were then carried out in order to prove that a proton can be removed from all three of the potential donor atoms, and that formation of the dilithiates [R'P(CHR)Li₂] and [R'P(NR)Li₂] results on treatment of the phosphonium salts with three equivalents of <i>n-</i>butyllithium. Methylation studies and <i>in-situ</i> NMR proved formation of the dilithiates but attempts to obtain crystallographic evidence of the dilithiate form of the ligand were unsuccessful, with only double deprotonated (monolithiate) species being observed. Reactions of the nitrogen donor ligands [R'P(NR)₃]^2- with various metal precursors are highlighted in Chapter 4. Chromium, ruthenium, rhodium and palladium complexes containing the phosphorous centred nitrogen donor ligands have been crystallographically analysed. All complexes isolated contain the nitrogen donor ligands in a h²-coordination mode. Reactions of the carbon donor ligands [R'P(CHR)₃]^2- with various metal precursors are highlighted in Chapter 5. Chromium, ruthenium, rhodium and platinum complexes containing the phosphorous centred carbon donor ligands have been crystallographically analysed. The complexes isolated have shown the carbon donor ligands to be flexible and versatile chelating ligands, but the desired h³-coordination mode was not observed.

Iridium catalysed C-H borylation has moved from an interesting observation to an efficient catalytic reaction. This work has developed and improved upon some of the key issues associated with the methodology. The one-pot conversion of aryl boronates, generated by C-H borylation, to other functionality has been one area of interest. However, reactions typically require a change in reaction solvent to make this possible. This thesis describes a one-pot, single solvent C-H borylation/Suzuki-Miyaura cross-coupling sequence. The key to this transformation is the use of methyl tert-butyl ether (MTBE). This procedure allows efficient synthesis of biaryls by initial C-H borylation of aromatic substrates followed by addition of water, subsequent reagents and aryl halide to complete the Suzuki-Miyaura cross-coupling without the need for change in reaction solvent. Another issue associated with the C-H borylation reaction is the extended reaction times required for some substrates. This issue was tackled by development of a microwave accelerated C-H borylation reaction. Microwave reactions are conducted at the same temperature as standard heated reactions with accelerations of 2 - 24 times affording comparable product yields. Typically reaction times were reduced from hours to minutes. A microwave accelerated one-pot, single solvent C-H borylation/Suzuki-Miyaura cross-coupling sequence allowed synthesis of biaryls from arene plus aryl halides in reaction times of minutes. Subsequent work focussed on the borylation of novel substrates classes, in particular quinolines. The borylation of substituted quinolines highlighted interesting electronic selectivity of the reaction. The site of borylation can be directed by changing the nature of the substituent on the ring. DFT calculations have been conducted to gain understanding into the causes of selectivity. A link between C-H acidity, calculated by DFT methods, and the borylation site was observed. Preliminary studies into the borylation of azaindoles are discussed. Studies towards a procedure to convert aryl boronates to trifluoromethyl groups are also been introduced.

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Today, bulk silicon is one of the best studied semiconductors. However, in its different nano-modifications, e.g. as porous silicon, totally new properties are exhibited. Despite the fact, that porous silicon is widely known and has been extensively studied since the 1990s, many unique features of this material are still unexplored. In this work, specific functionalities of porous silicon prepared, utilising both solid (via electrochemical or stain etching processes) and gas phase (from silane) syntheses, were investigated. Since this study was in-part industry oriented, the emphasis has been placed upon the investigation of porous silicon nanostructures, made from low cost metallurgical grade polycrystalline silicon powder. It has been previously demonstrated that porous silicon exhibits a very large, hydrogenated internal surface area (up to 500 m2 g−1). It is verified in this work, that morphological properties of this material result in a high reductive potential of its internal surface due to hydrogen passivation. Therefore, in this thesis, we would like to show that porous silicon-based reactive templates are promising for their applications in nanometal-supported catalysis. We used salts of platinum, gold, palladium, silver and their mixtures, which were reduced on the silicon nanocrystalline internal surface, resulting in formation of metal nanoparticles embedded into porous silicon matrix. Various experimental techniques were used to evaluate the morphology, size and composition of metal nanoparticles, as well as their growth rates. Hydrogen effusion experiments proved the crucial difference between porous silicon and other chemically inert supporting templates for the process of metal nanoparticles formation. The catalytic activity of the synthesised materials was evaluated in gas phase conversion of CO to CO2. Furthermore, the new porous silicon-based catalysts were tested in gas/liquid phase reactions as well, using hydrogenation, oxidation, dehalogenation and C-C coupling class reactions. Following the trends of “state of the art” current Si technology, we present the design of the developed flow microreactor, based on patterned Si wafer, which can be implemented in future work to catalyse selected reactions. Results obtained in this work suggest that porous silicon matrices are promising supports for metal nanoparticle based catalysis.

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