M.Sc. (Chemistry) / Please refer to full text to view abstract

A lack of methods for the separation and determination of air-sensitive Cr(II) and stable Cr(III) complexes in aqueous and organic phase motivated this study. The formation of kinetically stable Cr(III) complexes with common anions was studied using ion chromatography coupled to inductively-coupled plasma emission spectrometry (ICP-OES). Distribution diagrams for the complex species were determined from the results. Estimations of the stability constants were made from these diagrams and compared with stability constants published in the literature. Separation and determination of Cr(II) and Cr(III) and their complexes with PDCA and EDTA in aqueous phase was investigated using ion chromatography. ICP-OES was used for detection purposes. The separation and determination of Cr(II) and Cr(III) complexes with a ligand, bis-(2-decylsulphanyl-ethyl)amine, developed by Sasol Technology (Pty) Ltd., was attempted. The study was undertaken as the Cr(III) complex is used as a catalyst in the trimerisation of ethylene to 1-hexene. The mechanism is still unknown and determining which species are present in the catalytic cycle could clarify which oxidation-reduction couple is involved during the cycle. Reversed phase HPLC was investigated as a possible method for the separation of these complexes. No separation of the species was, however, achieved. / Prof. P.P. Coetzee

Studies have been made of the reactions which take place when zirconium compounds and vegetable tannins react with chromium tanned leather, in order to elucidate the mechanisms of the reactions which occur on retannage. Statistical procedures have been used in all investigations because of the variable nature of the substrate, and computer techniques have been applied to the repetitive statistical computations. Although chromium and vegetable tannages are well understood, further information on the reaction of zirconium with collagen was necessary before attempting to interpret the results of the studies of combination tannages with chromium, and this has been obtained by a comparative study of the reactions of chromium and zirconium with modified collagen. It is concluded that the mechanism of the reaction of basic zirconium sulphate with collagen is multipoint attachment of the tanning material by residual valency forces, although charge effects with basic groups may be supplementary. Zirconyl chloride reacts with carboxyl groups but does not form satisfactory, stable cross-links with collagen. Further evidence for this theory was obtained from the investigation of the reaction of zirconium compounds with chromium tanned collagen. Zirconyl sulphate does not interfere with effective chromium tannage and therefore can have little affinity for the carboxyl groups on the protein, but it displaces chromium complexes loosely held by auxiliary valencies without reducing the shrinkage temperature of the chromium leather Zirconyl chloride, although only fixed to a limited extent, apparently forms co-ordination compounds with the carboxyl groups, disrupting the chromium tannage because there is an over-all loss of hydrothermal stability. There is no evidence that zirconium co-ordinates with, or releases acid from chromium-collagen complexes, since combination chromium/zirconium tanned leathers are stable on storage. Retannage of chromium tanned leather with vegetable tanning materials generally results in loss of strength and a product which tends to deteriorate on ageing. Lower initial strength is probably due to the increased avidity of chromium tanned pelt for vegetable tannins, resulting from the liberation of internally neutralised reactive sites which are not normally available in vegetable tannage, and from the co- ordination of vegetable tannins and non-tannins to the chromium complex with the displacement of sulphate radicals. From a study of the retannage of chromium tanned modified collagen, it appears that basic groups probably play an important part in the rapid absorption of vegetable tannin. These reactions result in overloading of the fibre and an increased number of cross-links, both of which tend to produce weak leather. Deterioration with age is primarily a hydrolytic degradation of the protein which is catalysed by acid liberated from the chromium complexes by the entry of vegetable tannins, those factors which favour the formation of acid causing greater and more rapid deterioration.

Some properties of soluble chromium complexions containing coordinated aliphatic acids have been studied. The work falls naturally into two sections. In the first, the coordination of a series of ⊄, β and⊁amino acids by chromium chloride has been studied by physical methods. The tanning action of chromium chloride in the presence of these amino acids has also been studied. The absorption spectra of the complexes were similar to those reported previously for trivalent chromium solutions, having two pronounced maxima in the visible region. From the variations in these absorption maxima, it is suggested that the absorption maximum in the 580 m u region is influenced by coordination of the chromium with the ligand, while the maximum in the 420 m u region is also affected by the olation of the basic chromium salts. The spectrophotometric evidence indicates that raising the pH or the concentration of the ligand in the solution increases the amount of coordination, and further, that the tendency for coordination increases as the hydrocarbon chain separating the carboxyl and amino groups becomes longer. This suggests that tho stability of the complex is not dependent on chelate ring formation, but is influenced by the pK₁ value of the carboxyl group of the . ligand. Potentiometric titrations support the hypothesis that only the carboxyl group is coordinated, to an extent depending on its pK₁ value, since the curves have shown that the amino group is still free to titrate. Paper electrophoresis has shown that all the complexes prepared were cationic, indicating that the amino acids were coordinated as dipolar ions. The tanning action of the masked chromium solutions has confirmed the deductions made from the physical measurements. Increasing the amount of amino acid added to the solution lowered the chromium fixation and the hydrothermal stability of the leather, and further, that for solutions at the same pH containing the same amount of masking agent, tanning action was least for the ⊁ amino acid and greatest for the ⊄ amino acids. Comparison of the present data with the corresponding results obtained with chrome alum solutions showed that coordination of the amino acids was greater in the case of the chromium chloride solutions. The second section of the experimental work was an investigation of the coordination of substituted acetic and propionic acids by chromium chloride and chromium sulphate. Spectrophotometric and potentiometric methods were applied and the various solutions were also used in miniature tanning experiments. Certain difficulties were encountered in the preparation of some of the complexes, and it was not possible to carry the work to a point where conclusive results could be obtained. Nevertheless, the work reported suggests that chelate ring formation occurs in the coordination of hydroxy-carboxylic acids, resulting in exceptionally high stability of the complex. In the case of the other ligands, containing amino, chloro and bromo groups, as well as with acetic and propionic acids, the results suggest that coordination involves the carboxyl group only, and that the pY value of this group is an important factor determining the stability of the complexes.

No description available.

Ng, Tsz Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 86-98). / Abstracts in English and Chinese. / Acknowledgements --- p.i / Abstract --- p.ii / Table of Contents --- p.vii / List of Figures --- p.xiii / List of Plates --- p.XV / List of Tables --- p.xxi / Abbreviations --- p.xxii / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- "Pollution, toxicity and environmental impact of azo dye" --- p.1 / Chapter 1.2 --- Common treatment methods for dyeing effluent --- p.2 / Chapter 1.2.1 --- Physicochemical methods --- p.2 / Chapter 1.2.1.1 --- Coagulation/ flocculation --- p.2 / Chapter 1.2.1.2 --- Adsorption --- p.3 / Chapter 1.2.1.3 --- Membrane filtration --- p.4 / Chapter 1.2.1.4 --- Fenton reaction --- p.4 / Chapter 1.2.1.5 --- Ozonation --- p.5 / Chapter 1.2.1.6 --- Photocatalytic oxidation --- p.6 / Chapter 1.2.2 --- Biological treatments --- p.7 / Chapter 1.2.2.1 --- Degradation of azo dyes by bacteria --- p.8 / Chapter 1.2.2.1.1 --- Anaerobic conditions --- p.8 / Chapter 1.2.2.1.2 --- Aerobic conditions --- p.9 / Chapter 1.2.2.1.3 --- Combined anaerobic and aerobic conditions --- p.10 / Chapter 1.2.2.2 --- Decolourization of azo dyes by fungi --- p.11 / Chapter 1.2.2.3 --- Mechanisms of azo dye reduction by microorganisms --- p.12 / Chapter 1.3 --- "Chromium species, toxicity and their impacts on environment" --- p.14 / Chapter 1.4 --- Common treatment methods for chromium --- p.16 / Chapter 1.4.1 --- Chemical and physical methods --- p.16 / Chapter 1.4.2 --- Biological methods --- p.17 / Chapter 1.4.2.1 --- Chromium reduction by aerobic bacteria --- p.17 / Chapter 1.4.2.2 --- Chromium reduction by anaerobic bacteria --- p.18 / Chapter 1.5 --- Studies concerning azo dye and Cr(VI) co-treatment --- p.19 / Chapter 1.6 --- Response surface methodology --- p.21 / Chapter 1.6.1 --- Response surface methodology against one-factor-at-a-time design --- p.22 / Chapter 1.6.2 --- Phases of response surface methodology --- p.25 / Chapter 1.6.3 --- 2 - level factorial design --- p.26 / Chapter 1.6.4 --- Path of steepest ascent --- p.27 / Chapter 1.6.5 --- Central composite design --- p.28 / Chapter 2. --- Objectives --- p.30 / Chapter 3. --- Materials and Methods --- p.31 / Chapter 3.1 --- Isolation of bacterial strains --- p.31 / Chapter 3.1.2 --- Azo dye decolourization --- p.33 / Chapter 3.1.3 --- Chromate reduction --- p.34 / Chapter 3.2 --- Identification of selected bacterial strains --- p.35 / Chapter 3.2.1 --- Gram stain --- p.35 / Chapter 3.2.2 --- Sherlock® Microbial Identification System --- p.35 / Chapter 3.2.3 --- 16S ribosomal RNA sequencing --- p.37 / Chapter 3.3 --- Optimization of dye decolourization and chromate reduction efficiency with response surface methodology --- p.38 / Chapter 3.3.1 --- Minimal-run resolution V design --- p.38 / Chapter 3.3.2 --- Path of steepest ascent --- p.40 / Chapter 3.3.3 --- Central composite design --- p.41 / Chapter 3.3.4 --- Statistical analysis --- p.43 / Chapter 3.3.5 --- Experimental validation of the optimized conditions --- p.43 / Chapter 3.4 --- Determination of the performance of the selected bacterium in different conditions --- p.43 / Chapter 3.5 --- Determination of azoreductase and chromate reductase activities --- p.44 / Chapter 3.5.1 --- Preparation of cell free extract --- p.44 / Chapter 3.5.2 --- Azoreductase and chromate reductase assay --- p.45 / Chapter 3.6 --- Determination and characterization of degradation intermediates --- p.45 / Chapter 3.6.1 --- Isolation and concentration of the purple colour degradation intermediate --- p.45 / Chapter 3.6.2 --- Mass spectrometry analysis --- p.47 / Chapter 3.6.3 --- Atomic absorption spectrometry analysis --- p.48 / Chapter 4. --- Results --- p.49 / Chapter 4.1 --- Azo dye decolourizing and chromate reducing ability of the isolated bacterial strain --- p.49 / Chapter 4.2 --- Identification of selected bacterium --- p.50 / Chapter 4.3 --- Optimization of dye decolourization and chromate reduction efficiency with response surface methodology --- p.50 / Chapter 4.3.1 --- Minimal-run resolution V design --- p.50 / Chapter 4.3.2 --- Path of the steepest ascend --- p.54 / Chapter 4.3.3 --- Central composite design --- p.55 / Chapter 4.3.4 --- Validation of the predicted model --- p.62 / Chapter 4.4 --- Performance of the selected bacterium in different conditions --- p.62 / Chapter 4.4.1 --- Chromate and dichromate --- p.62 / Chapter 4.4.2 --- Initial pH --- p.63 / Chapter 4.4.3 --- Low and high salt concentration --- p.63 / Chapter 4.4.4 --- Initial K2CrO4 concentration --- p.63 / Chapter 4.4.5 --- Initial Acid Orange 7 concentration --- p.63 / Chapter 4.4.6 --- Nutrients limitation --- p.64 / Chapter 4.5 --- Chromate reductase and azoreductase activities --- p.67 / Chapter 4.6 --- Determination of degradation intermediates --- p.67 / Chapter 4.6.1 --- Mass spectrum of the degradation intermediate --- p.68 / Chapter 4.6.2 --- Chromium content of the degradation intermediate --- p.70 / Chapter 5. --- Discussion --- p.71 / Chapter 5.1 --- Characteristic of Brevibacterium linens --- p.71 / Chapter 5.2 --- Optimization of dye decolourization and chromate reduction with response surface methodology --- p.72 / Chapter 5.3 --- Performance of Brevibacterium linens under different culture conditions --- p.75 / Chapter 5.4 --- Postulation of mechanisms --- p.76 / Chapter 5.4.1 --- Possible reasons of unexpected results of the effect of initial Acid Orange 7 and K2CrO4 concentration --- p.76 / Chapter 5.4.2 --- Properties of the purple colour degradation intermediate --- p.78 / Chapter 5.4.3 --- Mechanisms likely responsible for the chromate reduction --- p.80 / Chapter 5.4.4 --- Explanation of the unexpected results --- p.80 / Chapter 6. --- Conclusions --- p.83 / Chapter 7. --- References --- p.86 / Chapter 8. --- Appendices --- p.99 / Chapter 8.1 --- Definition and calculation of different terms in 2-level factorial design --- p.99 / Chapter 8.2 --- Definition and calculation of different terms in ANOVA table --- p.100 / Chapter 8.3 --- Aliases of terms and resolution --- p.103 / Chapter 8.4 --- Moving of factors in path of steepest ascent --- p.105 / Chapter 8.5 --- Estimation of the parameters in linear regression models --- p.106 / Chapter 8.6 --- Definition and calculation of different terms in test of fitness --- p.109

Cai, Qinhong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 142-166). / Abstracts in English and Chinese. / Acknowledgements --- p.i / Abstract --- p.ii / Table of contents --- p.viii / List of figures --- p.xv / List of plates --- p.xix / List of tables --- p.xxi / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Pollution generated from dyeing industry --- p.1 / Chapter 1.2 --- Occurrence and pollution of chromium azo dyes --- p.2 / Chapter 1.3 --- Common treatment methods for dyeing effluents --- p.7 / Chapter 1.3.1 --- Physicochemical methods --- p.7 / Chapter 1.3.2 --- Chemical methods --- p.9 / Chapter 1.3.2.1 --- Ozonation --- p.10 / Chapter 1.3.2.2 --- Fenton reaction --- p.11 / Chapter 1.3.2.3 --- Sodium hypochlorite (NaOCl) --- p.12 / Chapter 1.3.2.4 --- Photocatalytic oxidation (PCO) --- p.13 / Chapter 1.3.3 --- Physical methods --- p.14 / Chapter 1.3.3.1 --- Adsorption --- p.14 / Chapter 1.3.3.2 --- Membrane filtration --- p.15 / Chapter 1.3.4 --- Biological treatments --- p.16 / Chapter 1.3.4.1 --- Decolorization of azo dyes by bacteria --- p.16 / Chapter 1.3.4.1.1 --- Under anaerobic conditions --- p.18 / Chapter 1.3.4.1.2 --- Under anoxic conditions --- p.19 / Chapter 1.3.4.1.3 --- Under aerobic conditions --- p.21 / Chapter 1.3.4.2 --- Mechanisms of azo dye reduction by bacteria --- p.23 / Chapter 1.3.4.3 --- Decolorization of azo dyes by fungi and algae --- p.27 / Chapter 1.4 --- Chromium species and their impacts on environment --- p.27 / Chapter 1.4.1 --- Chromium toxicology and speciation --- p.28 / Chapter 1.4.2 --- Common treatment methods for chromium --- p.31 / Chapter 1.5 --- Studies concerning treatment of chromium azo dyes --- p.32 / Chapter 1.6 --- Response surface methodology (RSM) --- p.33 / Chapter 1.6.1 --- RSM vs. one factor-at-a-time (OFAT) design --- p.36 / Chapter 1.6.2 --- Phases of RSM --- p.39 / Chapter 1.6.3 --- Two level factorial design --- p.40 / Chapter 1.6.4 --- Path of steepest ascent (PSA) --- p.43 / Chapter 1.6.5 --- Central composite design (CCD) --- p.44 / Chapter 1.6.6 --- Estimation of the parameters in linear regression models --- p.45 / Chapter 1.6.7 --- Test of fitness --- p.47 / Chapter 2. --- Objectives and significance of the project --- p.49 / Chapter 3. --- Materials and methods --- p.50 / Chapter 3.1 --- Chemicals --- p.50 / Chapter 3.1.1 --- Chemicals for preparation of bacterial culture media --- p.50 / Chapter 3.1.2 --- Chemicals for identification of bacteria --- p.50 / Chapter 3.1.3 --- Chemicals for chromium speciation --- p.51 / Chapter 3.1.4 --- Chemicals for immobilization of bacterial cells --- p.52 / Chapter 3.2 --- Sludge samples --- p.53 / Chapter 3.3 --- Characterization of Acid Yellow 99 --- p.54 / Chapter 3.4 --- Monitor of azo dye decolorization --- p.55 / Chapter 3.5 --- "Isolation of bacterial strains, which can degrade Acid Yellow 99" --- p.55 / Chapter 3.6 --- Identification of selected bacterial strains --- p.58 / Chapter 3.6.1 --- Gram stain --- p.58 / Chapter 3.6.2 --- Sherlock® microbial identification system --- p.58 / Chapter 3.6.3 --- Biolog® microstation system --- p.59 / Chapter 3.6.4 --- Selection of the most effective bacterial strains --- p.59 / Chapter 3.6.5 --- 16S ribosomal RNA sequencing --- p.60 / Chapter 3.7 --- Chromium speciation with interferences of chromium organic complexes --- p.60 / Chapter 3.7.1 --- Instrumentation --- p.60 / Chapter 3.7.2 --- Column preparation --- p.61 / Chapter 3.7.3 --- Determination of percentage retained and recovery --- p.62 / Chapter 3.7.4 --- "Speciation of Cr(VI), ionic Cr(III) and chromium azo dye" --- p.63 / Chapter 3.7.4 --- Preparation of Cr(III)-organic complexes --- p.65 / Chapter 3.7.5 --- Preparation of a microbial degraded chromium azo dye sample --- p.65 / Chapter 3.8 --- Chromium distribution in a treated solution --- p.66 / Chapter 3.9 --- Distribution of AY99 in a treated solution --- p.68 / Chapter 3.10 --- Optimization of decolorization process with response surface methodology (RSM) --- p.70 / Chapter 3.10.1 --- Correlation of cell mass and cell density of selected bacteria --- p.70 / Chapter 3.10.2 --- Preliminary investigation of the optimum conditions --- p.70 / Chapter 3.10.3 --- Minimal run resolution V (MR5) design --- p.71 / Chapter 3.10.4 --- Path of steepest ascent (PSA) --- p.74 / Chapter 3.10.5 --- Central composite design (CCD) and RSM --- p.75 / Chapter 3.10.6 --- Statistical analysis --- p.76 / Chapter 3.10.7 --- Experimental validation of the optimized conditions --- p.77 / Chapter 3.11 --- Immobilization of bacterial cells --- p.77 / Chapter 3.11.1 --- Immobilization by polyvinyl alcohol (PVA) gels --- p.77 / Chapter 3.11.2 --- Immobilization by polyacrylamide gels --- p.78 / Chapter 3.11.3 --- Performance of immobilized cells and free cells --- p.79 / Chapter 3.11.5 --- Storage stabilities of immobilized cells and free cells --- p.80 / Chapter 3.12 --- Performance of a laboratory scale bioreactor --- p.80 / Chapter 3.12.1 --- Chromium distribution in the bioreactor --- p.82 / Chapter 3.12.2 --- Distribution of AY99 in the bioreactor --- p.82 / Chapter 3.12.3 --- Fourier transform infrared spectroscopy (FT-IR) analysis of suspended particles in the treated solution --- p.84 / Chapter 4. --- Results --- p.85 / Chapter 4.1 --- Characterization of AY99 --- p.85 / Chapter 4.2 --- Identification of isolated bacterial strains --- p.86 / Chapter 4.3 --- Selection of the most effective bacterial strains --- p.89 / Chapter 4.4 --- Chromium speciation with interferences of chromium organic complexes --- p.91 / Chapter 4.4.1 --- Effect of pH --- p.91 / Chapter 4.4.2 --- Speciation of Cr(VI)，ionic Cr(III) and chromium azo dye --- p.92 / Chapter 4.4.3 --- Effect of other Cr(III)-organic complexes --- p.93 / Chapter 4.4.4 --- Limit of detection --- p.94 / Chapter 4.4.5 --- Capacity of Amberlite XAD-4 resin --- p.94 / Chapter 4.4.6 --- Determination of Cr(VI) in a microbial degraded chromium azo dye solution --- p.95 / Chapter 4.5 --- Chromium distribution in a free cells treated solution --- p.95 / Chapter 4.6 --- Distribution of AY99 in free cells treated solution --- p.96 / Chapter 4.7 --- Optimization of decolorization process with RSM --- p.98 / Chapter 4.7.1 --- Correlation of cell mass and cell density of selected bacteria --- p.98 / Chapter 4.7.2 --- MR5 design --- p.100 / Chapter 4.7.3 --- Path of steepest ascent (PSA) --- p.102 / Chapter 4.7.4 --- Central composite design (CCD) and RSM --- p.103 / Chapter 4.8 --- Immobilization of bacterial cells --- p.106 / Chapter 4.8.1 --- Performance of immobilized cells and free cells --- p.106 / Chapter 4.8.2 --- Storage stabilities of immobilized cells and free cells --- p.108 / Chapter 4.9 --- Performance of the laboratory scale bioreactor --- p.108 / Chapter 4.9.1 --- Treatment efficiencies of the bioreactor --- p.108 / Chapter 4.9.2 --- Performance stability of the bioreactor in 5 consecutive runs --- p.111 / Chapter 4.9.3 --- Chromium distribution in the bioreactor --- p.114 / Chapter 4.9.4 --- Distribution of AY99 in the bioreactor --- p.115 / Chapter 4.9.5 --- FT-IR analysis of suspended particles in the treated solution --- p.115 / Chapter 5. --- Discussion --- p.117 / Chapter 5.1 --- Chromium speciation with interferences of chromium organic complexes --- p.117 / Chapter 5.2 --- Chromium distribution --- p.117 / Chapter 5.3 --- Distribution of AY99 --- p.122 / Chapter 5.4 --- Optimization of decolorization process with RSM --- p.124 / Chapter 5.4.1 --- MR5 design --- p.124 / Chapter 5.4.2 --- Path of steepest ascent (PSA) --- p.125 / Chapter 5.4.3 --- Central composite design (CCD) and RSM --- p.126 / Chapter 5.5 --- Immobilization of bacterial cells --- p.126 / Chapter 5.5.1 --- Performance of immobilized cells and free cells --- p.126 / Chapter 5.5.2 --- Storage stability of immobilized cells and free cells --- p.128 / Chapter 5.6 --- Performance of the laboratory scale bioreactor --- p.130 / Chapter 5.6.1 --- Treatment efficiencies of the bioreactor --- p.130 / Chapter 5.6.2 --- Performance stability of the bioreactor in 5 consecutive runs --- p.131 / Chapter 5.6.3 --- FT-IR analysis of suspended particles in the treated solution --- p.132 / Chapter 5.6.4 --- Post treatments of bioreactor treated effluents / Chapter 6. --- Conclusions --- p.136 / Chapter 7. --- References --- p.142

Thesis (Ph. D.)--University of California, San Diego, 2004. / Vita. Includes bibliographical references.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

This thesis describes the application of (arene)Cr(CO)3 methodology to the Stereoselective and enantioselective synthesis of substituted arenes. Chapter one reviews the main methods of preparation and decomplexation of (arene)Cr(CO)₃ complexes and the electronic and steric influences of the Cr(CO)₃ unit on the arene. Chapter two demonstrates that the benzylic oxygen directing effect in complexation reactions operates via a direct oxygen bond to the incoming metal unit. Attachment of bulky ft-acceptor groups, such as t-butyldimethylsilyl, to the benzylic oxygen overrides this directing effect. Chapter three describes the regioselective Cl functionalisation of the cryptopine skeleton. Complexation of dihydrocrytopine gives only a single product, the relative configuration of the product being determined using an X-ray crystal structure analysis. Subsequent alkylation of the O-methyl derivative gives Cl alkylated products. Chapter four describes the regioselective ortho functionalisation of ephedrine and pseudoephedrine derivatives. Treatment of (1S,2R)-(N,O-dimethylpseudoephedrine) Cr(CO)₃ with n-butyllithium leads to exclusive removal of the pro-(R) ortho proton. The observed stereoselectivity arises via</em deprotonation from cyclic bidentate five-membered chelates. Chapter five describes the regioselective C4 and C5 functionalisation of (hydrocotarnine)Cr(CO)₃. Complexation of 1-methylhydrocotarnine occurs to give exclusively the exo-1-methyl derivative. Further functionalisation to give the 1,5- and 4,5-dimethyl products is also described. Chapter six describes the synthesis of ortho substituted (benzaldehyde)Cr(CO)₃ complexes. Chiral material is available via preferential kinetic hydrolysis of, or classical separation of, the L-valinol derived imines. Chapter seven describes the Stereoselective addition of nucleophiles to (o-anisaldehyde) Cr(CO)₃ and (o-trialkylsilylbenzaldehyde)Cr(CO)3. With (o-anisaldehyde)- Cr(CO)₃ the additions are completely stereoselective giving the (RR,SS) diastereoisomer. With (o-trialkylsilylbenzaldehyde)Cr(CO)₃ the ratio of products is influenced by the nature of Lewis acidic species present. Chapter eight describes the Stereoselective benzylic elaboration of (o-methoxybenzyl methyl ether)Cr(CO)₃ achieved via selective removal of the exo benzylic proton from transition states with the methoxy groups anti to each other.