Phase transformations of H₄4[SiW₁₂0₄₀]xH₂0 in the temperature range 25 - 900 ⁰C have been investigated and characterised by differential thermal analysis (DTA), thermogravimeteric analysis (TGA), X-ray powder diffraction (XRD), ²⁹Si MAS NMR and FT-IR spectroscopy. Dehydration occurs between 25 - 300 °C to give three crystalline hydrated states (x = 24, 14 and 6) and finally an anhydrous form.

The effects on reactions of catalytically-capable trace metal impurities were investigated in the context of two separate reports of iron-catalysed Suzuki reactions. In both cases, the reported reactions were found to irreproducible and the likelihood of palladium contamination was discussed. In one of the cases, it was found that as little as 0.0001 mol% of Pd(OAc)2 could account for the observed activity. As a result of pressure from our group and others, both papers were retracted. The importance of testing for trace impurities and of conducting blank reactions is discussed. The roles of l,2-bis(diphenylphosphino)benzene (dpbz) and l,3-bis(diphenylphosphino)propane (dppp) ligands in the Fe-catalysed Negishi and Suzuki reactions were investigated through a structure/reactivity study. A series of modified dppp and dpbz analogues were prepared and characterised and some of their key structural differences analysed. The ligand library was then investigated in both the Fe-catalysed Suzuki and Negishi reactions. Despite the broad range of structurally-related but significantly different phosphine ligands tested, nearly all were shown to perform well in both of the test-bed reactions. Reasons for the unprecedented high activity of this class of catalysts are discussed and the importance of pre- forming iron complexes before their application to catalysis is highlighted. In parallel with a full kinetic study and the isolation of potential reactive intermediates conducted by other group members, the mechanism of the Fe-catalysed Negishi reaction was investigated. Kinetic analysis identified Fe(l) as the most likely lowest oxidation state in the catalytic cycle and efforts were made to isolate Fe(l) intermediates. A series of Fe(l) complexes had been isolated by other group members and these were tested in a range of representative Negishi reactions. An Fe(l) bromide complex was identified as a likely on-cycle intermediate and the implications of this in catalysis are discussed. The use of boron/zinc transmetallation for the generation of nucleophiles in Fe-catalysed coupling reactions was investigated. It was found that under forcing conditions, the aryl transfer reaction could be made to proceed without the need for additional catalysts. The mechanism of boron/zinc transmetallation was investigated using llB NMR spectroscopy and DFT calculations. It was demonstrated that the degree to which the alkyl groups from the zinc transferred to the boron was far higher than was previously thought and that the addition of stabilising solvents or ligands could dramatically alter the positions of the equilibria in transmetallation reactions. Two examples of 11 tetraarylborate salts formed in transmetallation reactions were isolated and structurally characterised. The implications of these observations on the catalyst-free aryl transfer and other reported aryl transfer reactions are discussed.

This thesis has sought to develop the field of small-molecule activation via the rational evolution of the principle of Frustrated Lewis Pairs. In the first instance, Chapter 1 serves to give a brief introduction into the field of small molecule activation by transition metals and FLPs, with a particular focus on the most challenging and impacting small molecule substrates. Chapter 2 [1] explores the concept of frustrated Lewis pairs and Lewis acidity in more detail and specifically, the structure-reactivity trends of boron Lewis acids in FLP systems with respect to the reversible binding of H2. The motivation for this research was to develop a series of linked phosphino-borinate FLPs with a view to generating systems that may activate hydrogen in a reversible manner, furthering the scope for this class of compounds in hydrogen storage applications. Chapter 3 [2] is a continuation on the previous theme; modifying the Lewis acid component of an FLP system to facilitate previously unseen transformations and address some of the issues of existing systems. More specifically, to address the lack of catalytic systems based on the FLP paradigm. To that end, a series of cationic phosphino-aryl(alky)oxymetallocenes (PAMs) was targeted with the hypothesis that these compounds would behave as transition metal-main group FLPs. Correspondingly, the limit of this semblance to the FLP was investigated in depth in Chapter 4 [3] by demonstrating that a wide range of the reactions reported for main group FLPs could be affected by PAM complexes. In addition, several other novel reactivity patterns were discovered that are so far unprecedented for the main group analogues. In the final chapter [4], the benefits of including the unique properties of the transition metals in PAM complexes is demonstrated by an in depth study into their utility as catalysts for the dehydrogenation of amine-boranes. The fact that this reaction is only known in a stoichiometric sense for the main group systems is testament to the success of the original thesis.

Nano-size metals and alloys are well known to display extremely high catalytic activity for many chemical reactions due to their high percentage of surface atoms. The stability of these nano catalysts is just as, or even more important than activity when used under extreme conditions adopted in industry. Most nano particles undergo surface reconstruction at high temperatures, and are very susceptible to surface poisons. We report a new research, mentioned in this thesis, which clearly demonstrates that encapsulation of a metal nanoparticle with carbon by a simple hydrothermal treatment of glucose is able to offer a protective jacket to the enclosed metal. As a result, 5 nm platinum particle stabilised inside the carbonaceous cage which protects the metal against sintering even at 1000 °C, and after extreme treatments, the material is still active with sufficient surface area for catalytic hydrogenation reactions.

In this thesis, the results of synthesis of chiral ionic liquids (ILs) and an investigation of their application in chiral separation and catalysis are described. The study of the chiral lLs application was performed using liquid-liquid extraction, crystallization and asymmetric catalysis with analysis of substrate content and enantioselectivity by High Performance Liquid Chromatography (HPLC) . A series of chiral lLS with chiral cations or chiral anions were synthesized through alkylation or anion exchange with optical pure starting materials as the •chiral pool", Properties of chiral ILS made in house were studied using various techniques, The structures and configurations of the chiral ILs can be altered easily to meet the required physical properties, such as melting point and viscosity, Chiral! ILs made in house show chiral affinity with a range of racemic compounds, In the liquid-liquid extraction of menthol from chiral lL, good extraction is observed from the chiral lL layer into alkane !layer without visible leaching of the chiral lL into the alkane layer. In the mandelic acid resolution by • Dutch resolution", 22 different ILS were used as additive in the chiral selector, In general, ILS exhibit a equalize effect on both yield and ee of the final product. For the asymmetric catalysis study, both Mukaiyama-aldol reaction and Diels-Alder reaction were investigated with Cu(II)-PhBOX and Zn(II)-PhBOX as catalyst. In the Mukaiyama-aldol reaction, chiral ILS can be applied . as ligand and an increased ee is observed as compared with the reactions in the absence of the Il. In the Diels-Alder reaction, addition of the chiral Il 19 (Il of (1R,2S.5R)- menthol) with Zn(II)-PhBOX led to an increase in the endo ee from 5 % in DCM, 68 % in ether and 57 % in pure (C 2mim][NH 10 91 % under homogeneous reaction condition and 95 % in biphasic system with both high conversion and high endo selectivity. The endo selectivity of biphasic system with the chiral lL 1 g, [C2mim][NTf21 and ether is 99 %, which means nearly all product goes into endo form with 95 % ee.

A redox-neutral catalysis strategy has been designed for the development of phosphorus-mediated substitution and elimination reactions. This new concept has been validated through the development of catalytic Appel halogenation reactions of alcohols, catalytic deoxydichlorination reaction of aldehydes and catalytic dehydration reaction of oximes. In these new catalytic reactions, oxalyl chloride is used as a consumable stoichiometric reagent to generate the chlorophosphonium salts responsible for halogenation or elimination from catalytic phosphine oxides. Therefore, phosphine oxides have been transformed from the stoichiometric waste products in traditional phosphorous-mediated reactions into organocatalysts. The substrate scope, limitations and mechanisms of the new catalytic reactions have been fully explored. Finally, a new cross coupling reaction berween triarylphospbines and aryl boronic acids has been developed for the synthesis of tetraarylphosphoruum salts.

This thesis details investigations into two modes of organocatalytic enolate generation and reactivity. The first is the addition of chiral NHCs to a ketene to form an azolium enolate. Investigations into three different electrophiles within this system will be discussed. The second catalytic system investigated is the formation of a C1-ammonium enolate through the addition of chiral isothioureas to activated carboxylic acids. Studies on one electrophile within this system will be discussed. Chapter 2 investigates the use of bespoke C2-symmetric NHCs in the asymmetric Staudinger reaction: the formal [2+2] cycloaddition between ketenes and imines. A chiral relay mechanism was proposed and experimentally validated with β-lactams prepared in good yields (up to 85%) and moderate enantioselectivity (up to 61% ee). Chapter 3 describes the asymmetric formal [4+2] cycloaddition between alkylarylketenes and γ-substituted-β,γ-unsaturated α-ketocarboxylates. A substrate dependant switch in diastereoselectivity was observed with γ-aryl α-ketocarboxylates giving preferentially the syn-dihydropyranones (up to 70:30 dr syn:anti, up to 98% ee syn) and γ-alkyl α-ketocarboxylates giving preferentially the anti-dihydropyranones (up to 18:82 dr syn:anti, up to 75% ee anti, 97% ee syn). Chapter 4 illustrates the extension of the methodology described in Chapter 3 to include γ-substituted-β,γ-unsaturated α-ketophosphonates. Once more, a substrate dependant switch in diastereoselectivity was observed with γ-aryl α-ketophosphonates giving preferentially the syn-dihydropyranone-phosphonates (up to 72:28 dr syn:anti, up to 98% ee syn) and γ-methyl α-ketophosphonate giving preferentially the anti-dihydropyranone-phosphonates (20:80 dr syn:anti, 71% ee anti, 90% ee syn). Within this system it is also possible to generate the alkylarylketenes in situ with no loss in stereoselectivity but with typically improved yield when compared with the corresponding two-step procedure. Chapter 5 describes the activation of arylacetic acids via the formation of a mixed anhydride followed by C1-ammonium enolate generation with a chiral isothiourea. Asymmetric Michael addition and lactonisation with γ-substituted-β,γ-unsaturated α-ketophosphonates gave the corresponding anti-dihydropyranone-phosphonates (up to 89:11 dr anti:syn, up to 97% ee anti). More conveniently however, in situ ring opening with MeOH gave di-esters with excellent stereocontrol (up to >98:<2 dr anti:syn, up to 99% ee anti) and which can be readily derivatised.

The hypothesis that a model, incorporating appropriate experimentally obtained intrinsic kinetics and the real pore structure of the support, could accurately predict the real kinetic performance of a catalyst pellet was investigated. Four different spherical pellet diameters of platinum supported on gamma alumina (0.1, 0.4, 1.2 and 2.5 mm) were used as a model catalyst and carbon monoxide oxidation was used as a probe reaction to make the connection between the real physico-chemical properties of the catalyst pellets and their real kinetic performance.

No description available.

No description available.