The work presented in this dissertation describes the prepartion and characterisation of various strapped porphyrin compounds which are designed to model cytochrome P450 and the charge separation in photosynthesis. The major part of this work is concerned with models of cytochrome P450. After a brief introduction to the philosophy of modelling, there follows a review of work on the enzyme and various compounds which are designed to reproduce the enzymic characteristics. The synthesis of two singly bridged porphyrins is reported. These incorporate a pendent methyl ester in the centre of the strap and aim to mimic the proposed acylation step in the catalytic cycle. Evaluation as models was performed by a series of experiments involving the addition of potassium superoxide to the manganese complexes of these compounds. Characterisation of the mode of reactivity required the use of many physical techniques and necessitated the synthesis of a radio-labelled sample of one of the porphyrins. The results obtained suggest that superoxide binds preferentially to the bridge-free face of the macrocycle. Doubly bridged analogues of the above models were prepared which force the two faces of the porphyrin to be equivalent. Superoxide binding studies indicated a different mode of reactivity to the singly bridged models, for one of the compounds, and experiments to distinguish between possible interpretations of the results are suggested. A crown ether thiolate doubly bridged porphyrin was prepared as a model for the carbon monoxide complex of the enzyme. This was characterised by ultraviolet spectroscopy and attempts to produce a stable crystalline adduct are described. The remaining part of this work concerns a model for the charge separation process in photosynthesis. A discussion of natural systems and previous models is followed by a description of a tetraene pyromellitimide doubly bridged porphyrin, which shows significant quenching of the porphyrin fluorescence.

The preparation and physical properties of the estertin halides X 4-nSn[ (CH2)mCO2R]n, where n = 1 or 2, m = 1, 2 or 3 and R is a alkyl or aryl substituent are reported. During the course of this work the molecular structures of Cℓ3SnCH 2CH2CO2Pri and Cℓ3SnCH 2CH2CO2CO2Et were determined. The preparations of Ph3Sn(CH2)3R compounds, where R is a functional group, are reported. The reactions of these compounds with electrophiles were investigated as a route to organotin halides. Explanations on their reactivity are postulated. The preparation of Ph3Sn[CHRR'] compounds where R and R' are the same or different functional groups, from the reaction of (Ph3Sn) 2S with Hg[CHRR']2 is also reported along with the physical properties and evidence for their particular structures. Investigations into the Lewis acidity of estertin halides were undertaken. Chloride ion acceptor strengths, adduct formation with nitrogen bases and catalysis of allylic rearrangement were used as a basis for the evaluation of the Lewis acidity. Explanations are offered for the various observations made during these studies. Finally the preparations of estertin mercaptides, [Et02C(CH 2)]n Sn(SCH2CO2C8H 17)4-n, where n = 1 or 2 are reported. Comparisons of the P.V.C. stabilising ability of these estertin mercaptides were made with the commercially available octyltin tris-mercaptide. Explanations are offered for the apparent difference in stabilising ability of each of these compounds in thermally processed P.V.C. during oven testing.

A general review on macrocyclic ligands with particular emphasis to dibenzocryptand 222 and dibenzo 18 crown 6 is given in the first part of the thesis (Chapter 1). This is followed by an exhaustive literature survey on the stability constants (hence free energies of complexing), enthalpies and entropies of metal cations with cryptands (dibenzocryptand 222, benzocryptand 222, cryptand 222) and crown ethers (dibenzo 18 crown 6, benzo 18 crown 6, 18 crown 6) in water and in non-aqueous solvents at 298.15 (Chapter 2). The experimental part (Chapter 3) also includes a detailed description of the principals involved in calorimetry as well as the methods used for the calculation of reaction enthalpies. Stability constant data for alkali-metal and silver cations with dibenzocryptand 222 in five dipolar aprotic solvents (N,N dimethyl-formamide, dimethylsulphoxide, acetonitrile, propylene carbonate and nitromethane) at 298.15 K are reported. These data are used to calculate the standard free energies of the complexation process involving metal(I) cations and dibenzocryptand 222 in the dipolar aprotic solvents. Free energy data are combined with enthalpy data obtained in this work in order to evaluate the entropies of complexation of these cations with dibenzocryptand 222 in these solvents. A linear correlation previously shown for metal(I) cations and cryptand 222 in DMF, Me2SO, AN, PC and NM between entropies of complexing and entropies of solvation of metal(I) cations in dipolar aprotic solvents is also found for dibenzocryptand 222. The results obtained in this thesis provide further evidence that the complexation process with metal (I) cations and cryptands is mainly controlled by the state of solvation of the cation in the solvent. Enthalpies of solution of dibenzocryptand 222 in the dipolar aprotic solvents are reported and the thermodynamic parameters for the extraction process in the water + nitromethane solvent system as described by M+(H2O) + 22B2B(NM) → M+22B2B (NM) are calculated (Chapter 4). Thermodynamic parameters of solution and transfer of dibenzo 18 crown 6 are discussed with respect to corresponding data for dibenzocryptand 222. The transfer free energies of metal ion dibenzocoronates from water to a number of solvents are calculated and it is shown that, unlike cryptates, there is an interaction between the complexed cation and the solvent in metal ion dibenzocoronates in dipolar aprotic media. Thermodynamic parameters of complexation for alkali-metal and dibenzo 18 crown 6 in acetonitrile are reported. The complexation process seems to be enthalpically and entropically controlled (Chapter 5). Synthesis of crown compounds and heats of solution of 18 crown 6 carried out at several temperatures as well as DeltaCp values in water are presented in Chapter 6.

No description available.

Allylic substitution is an important procedure for carbon-carbon, carbon-nitrogen and carbon-oxygen bond formation, and palladium-mediated allylic substitution reactions have previously been employed in the synthesis of a range a physiologically active and natural products. 2,5-Dicarbon substituted 2,5-dihydrofurans have not to date been synthesised by palladium-mediated allylic substitution reactions. It was found in the first part of the work that allylic substitution reactions of 2,5-diacetoxy-2,5-dihydrofuran with a tertiary carbon nucleophile did not result in the desired mono-substitution product due to the elimination of acetic acid from the product, to form the aromatised furan derivative. In an attempt to differentiate between the two potential leaving groups on the dihydrofuran, one of the acetate groups was displaced in a palladium-mediated allylic substitution reaction. This approach was also intended to inhibit the aromatisation reaction. The desired product 2-acetoxy-5-phenoxy-2,5-dihydofuran was obtained. The palladium-mediated allylic substitution reactions of this product with a range of tertiary carbon nucleophiles provided the desired mono-substituted dihydrofuran products in good yield with minimal by-products being detected. The substitution of the phenoxy-leaving group with a carbon nucleophile, however, was not achieved under a range of reaction conditions. Other more electrondeficient phenol derivatives were used in the initial substitution reactions but due to time constraints the work could not be completed in the current study. This would hopefully have increased the leaving group ability of the phenoxy group and the desired disubstituted dihydrofuran would have been achieved, and this will be the subject of further work in this regard. Milder reaction conditions were applied to 2,5-diacetoxy-2,5-dihydrofuran in its reaction with a tertiary carbon nucleophile. The desired mono-substituted mono acetoxy products were obtained in reasonable yields when column chromatography was performed at –15 °C and the silica was neutralised with Et3N. These mono-acetoxy products were reacted with a range of tertiary carbon nucleophiles and the desired disubstituted dihydrofurans could be prepared in reasonable yields. One-pot reactions were investigated by using three equivalents of nucleophile and in most cases the desired symmetrical dihydrofuran was achieved. This result prompted the investigation into the synthesis of disubstituted dihydrofurans in a one-pot reaction by successive addition of two carbon nucleophiles with 2,5- diacetoxy-2,5-dihydrofuran. The disubstituted dihydrofurans were isolated in higher yields than the two-pot procedure and the complex purification procedure developed was not necessary. This study, therefore, allowed for the synthesis of a range of symmetrical and unsymmetrical dicarbon substituted dihydrofurans. This methodology will later be applied to the synthesis of a range of natural products. / Prof. D.B.G. Williams

Signal Amplification by Reversible Exchange (SABRE) is a hyperpolarization technique that utilizes parahydrogen for the NMR signal enhancement of nuclear spins. SABRE is related to Parahydrogen Induced Polarization (PHIP), another means of hyperpolarization using parahydrogen; PHIP achieves hyperpolarization via chemical reduction. Although PHIP and SABRE share many similarities in experimentation, PHIP ultimately requires the presence of an unsaturated chemical bond as well as pairwise-addition of parahydrogen. No permanent chemical change occurs during SABRE, and instead may be considered as a merely physical exchange between molecules with sites on a catalyst. PHIP and SABRE may be compared to Dynamic Nuclear Polarization (DNP), arguably the most well-known and researched method for hyperpolarization; despite all that has been achieved with DNP, PHIP and SABRE offer vastly more-rapid, less-expensive, and more-simplified approaches for achieving hyperpolarization. The focus of this work is experimentation with SABRE processes and methods designed to overcome certain experimental challenges associated with this technique.

The successful application of Tppts, and its derivatives, in biphasic transition metal-catalysed reactions opened up a new field of chemistry requiring a rational design of water-soluble ligands. The main objective of the research described in this dissertation was the preparation and the application of new water-soluble phosphine ligands. The ligands were prepared by the use of carbon nucleophiles and chlorophenylphosphine derivatives. The carbon nucleophiles included malonate derivates, which were subsequently reduced to the di-alcohols and were transformed into water-soluble phosphines by the reaction with 1,4-butanesultone. Secondary and tertiary malonate nucleophiles were used and the steric demands of compounds containing more than one malonate group were investigated. Various attempts to obtain water-soluble compounds from dimalonate phosphine oxides failed. TBDMS-protected aryl halides were also used as nucleophiles. One (or two) of these silyl ethers was reacted with chlorophenylphosphine derivatives and after deprotection with TBAF the compounds were made water-soluble by a reaction with 1,4-butanesultone. The hydrogenation of arylphosphine oxides to form cyclohexylphosphine oxide derivatives was also investigated. However, these cyclohexylphosphines were more easily obtained by the reaction between the previously mentioned carbon nucleophiles and chlorocyclohexylphosphine derivatives, which were freshly prepared. A series of cyclohexyl-containing water-soluble phosphines was prepared in this way. The oxygen sensitive nature of phosphines lead to two different approaches in the reaction route: the phosphines were either borane protected followed by a subsequent deprotection step, or the phosphines were allowed to oxidise and were reduced back to the free phosphine at a later stage. The efficiency of both approaches in the reaction routes was examined. The deprotection of phosphine-boranes was performed using various “new” deprotecting reagents and the borane-species and free phosphines were separated using water/organic extractions. The various extraction coefficients of the amine-borane complexes were determined. The newly prepared ligands were used in a variety of palladium-catalysed reactions as well as in the hydroformylation of 1-octene employing rhodium. The reactions were performed in both neat organic solvents as well as mixtures between water and DMF or toluene and the results were compared to the use of Tpp and Tppts. It was found that many of the new ligands afforded superior yields compared to those of Tpp and Tppts. In the last part of the study, various diphenylphosphinic amides were used as DoM-groups. Sec- and tert-BuLi were used together with a variety of electrophiles to facilitate ortho-substitution on either one or two rings on the amides. This was seen as a start of a new approach towards functionalised phosphine ligands. / Prof. D.B.G. Williams

The use of bidentate ligands in organometallic chemistry is best illustrated by the successful application in homogeneous catalysis1 and bio-medical2 systems. For catalytic systems the use of bidentate phosphines have revolutionised the way in which homogeneous catalysis is viewed, with the use of functionalised organic ligands to induce favourable catalytic product formation such as the production of L-Dopa3. To this end, the investigation of tropolone type ligands and complexes will be discussed further in this chapter. The possible application of tropolone systems will be investigated in the context of possible catalytic and bio-medical applications. In 1945 Dewar4 predicted that 2-hydroxy-2,4,6-cycloheptatrien-one (Tropolone, Eq. 1.1.I), would show certain aromatic properties; he specifically referred to the natural products known at that time, stipitatic acid and colchicine5 as representative of this class of compounds. Thus Dewar was the first person to point to a new field in organic chemistry, which to date has not been fully explored due to the diversity of uses of tropolone and its derivatives. / Prof. A. Roodt

Water is an important resource. It is used for domestic, industrial, agricultural and recreational purposes. The quality of water is, however, significantly deteriorating due to the accumulation of organic species in aqueous system. Domestic, industrial and commercial activities comprise the biggest source of organic pollutants in municipal water. The increase of water pollution by these organics has led to the development of several water purification measures. Among others, water treatment technologies that are in place consist of ion exchange, activated carbon adsorption, reverse osmosis, molecular sieves and zeolites. However, none of these techniques have been reported to remove organic pollutants to parts-per-billion (ppb) or microgram-per-litre (ìg/L) levels. Recently, it has been reported that cyclodextrin nanoporous polymers are capable of absorbing these pollutants from water to such desirable levels. Cyclodextrins (CDs), basically starch derivatives, are cyclic oligomers consisting of glucopyranosyl units linked together through á-1,4-glycosidic linkages. They behave as molecular hosts capable of interacting with a range of guest molecules in a noncovalent manner within their cylindrical hydrophobic cavities. These interactions are a basis for the inclusion of various organic species. However, the high solubility of cyclodextrins in aqueous medium limits their application in the removal of organic pollutants from water. To make them insoluble, they are converted into highly cross-linked polymers. This is achieved by polymerizing the cyclodextrins with suitable difunctional linkers. In this project, a wide variety of monofunctionalized CDs have been effectively prepared using efficient modification strategies and successfully characterized by Infra-red (IR) and Nuclear Magnetic Resonance (NMR) spectroscopy. From these monofunctionalized CDs and corresponding linkers, insoluble nanoporous polymers with different physical properties were synthesized (Scheme 1). / Dr. B.B. Mamba

Rules which correlate structure and insecticidal activity of pyrethroids have evolved over the last thirty years from the results obtained in the testing of various synthetic pyrethroids. The major portion of these rules have dealt either with the development of new alcohol moieties or variations in the unsaturated side chain of the cyclopropane ring. There has been very little work done concerning modifications of the cyclopropane ring. This study was initiated to discover the affect of substituting an aziridin ring for the cyclopropane ring found in pyrethroids.