High-resolution pulsed beam Fourier Transform Microwave Spectroscopy (PBFTMS) technique has been used to investigate the rotational spectra, molecular structures and electronic charge distribution of organometallic and organic molecules. The thesis reports high-resolution rotational spectral findings for nine different asymmetric-top molecules in the singlet electronic ground state including: Cyclopentadienyltungstentricarbonylhydride, Bis-(cyclopentadienyl)tungstendihydride, Tetracarbonylethyleneosmium, two substituted Ferrocenes and an organic keto-enol tautomeric system, Z-2-Hydroxypyridine and 2-Pyridone. Moreover, gas-phase rotational constants and distortion constants have also been reported for an excited vibrational state of Cyclopentadienylnickelnitrosyl complex using a high-resolution Fourier Transform Spectrometer (FTS) system at Kitt Peak Arizona, (KPNO). Preliminary microwave results for a fluxional molecule, Cyclopentadienyliridiumdicarbonyl are also presented in this work. Extensive Density Functional Theory (DFT) calculations have been performed in conjunction with the experiments to provide additional insight toward further understanding the equilibrium structures, structural isomers and electric field distributions of these molecules. These calculations were not only helpful in predicting the preliminary structure and rotational constants of the molecules of interest, but also advantageous in analyzing the observed spectra.

Epidemiological studies have linked exposure to elevated levels of airborne particulate matter with increased incidences of several types of respiratory disease, hospital admissions and morbidity. Millions of tons of airborne particulate matter are generated and released into the atmosphere each year. However, particulate matter resulting from the combustion of fuel oil and coal are of particular concern, because they are generally composed of small particles that can easily penetrate deep into the lungs, and can contain significant concentrations of toxic transition metals, such as zinc, iron and vanadium. Pulmonary toxicity (i.e. damage caused to lung tissues) of particulate matter is currently evaluated via time-consuming in-vivo testing, or via in-vitro testing. Compared to in-vivo testing, in-vitro testing offers significant advantages in terms of time savings and sample throughput. Unfortunately, the number of in-vitro testing methods are currently very limited, and do not allow a thorough investigation of the mechanisms of particulate matter toxicity. In light of these issues, the goals of the study described here were three-fold: *To adapt several in-vitro toxicity assays currently used in other applications to use in measuring particulate matter toxicity on lung cell layers; *To use these adapted assays to quantify the toxicity of numerous types of oil and coal ashes with varying particle sizes and transition metal concentrations, and; *To use the same assays to quantify the toxicities of several transition metals found in coal and oil ashes to better understand their relative contributions to overall particulate matter toxicity. Three colorimetric in-vitro assays were chosen for adaptation, and proved effective in measuring adverse cellular response to particulate matter exposure. Particle size was shown to have a large effect on the overall cytotoxicity of particulate matter; fine (less than 2.5 μm aerodynamic diameter) particles proved substantially more toxic than coarse (larger than 2.5 μm aerodynamic diameter) particles. Dose-response experiments measuring the toxic effects of the transition metals zinc, vanadium and iron revealed that zinc was the most toxic; a concentration of 0.6 mM caused a 50% drop in cellular metabolism, compared to 3 mM and 4 mM for vanadium and iron respectively.

Controlling the absolute stereochemistry of molecules is a major challenge to contemporary chemists. Achieving high enantioselectivity with catalytic amounts of a chirality transfer (or inducing) agent, and the ease of regenerating such catalysts is yet another challenge. Due to the involvement of various transition metal complexes, the relatively young field of enantioselective catalysis has emerged as a powerful tool for organic chemistry. In our efforts towards the synthesis of a universal catalyst, O'Donnell Schiff base derived tetradentate ligands were shown to catalyze dialkylzinc additions to aldehydes in high selectivity. The three pot synthesis of bifurcated dipeptides in very good yields and the mechanistic aspects of diethylzinc additions to aromatic aldehydes are described in this dissertation. The chiral Lewis acidic behavior of these ligands was supported by a mechanistic study done examining the nonlinear effect. Unlike bidentate ligands such as (-)-3-exo-N,N-dimethylaminoisoborneol (DAIB), the tetradentate ligands in this study show strictly linear behavior. Also, the linear free energy relationships studied by observing the enantioselectivity with respect to electron donating or withdrawing substituents on the benzaldehyde substrates supported a Lewis acid role for the zinc complexes. A negative slope was obtained when ee's were plotted against sigma values of the substituted benzaldehydes. Since they bind to various bivalent transition metal cations, these ligands can be viewed as privileged structures, and may potentially become catalysts for various asymmetric reactions. As catalyst screening can be greatly facilitated by heterogeneous catalysis, solid phase ligands were synthesized using Wang and Merrifield resin supports. The synthetic methodology was developed using a diarylketimine linker with the aid of on-bead characterization techniques such as 13C NMR and UV-VIS spectroscopy. The ligands were shown to asymmetrically catalyze the alkenylzinc additions to aromatic aldehydes. In situ generation of alkenylzinc reagents by boron to zinc transmetalation followed by the addition to benzaldehyde in the presence chiral zinc complexes resulted in enantiomerically enriched allylic alcohols. The preliminary results for this transformation resulted in 3:1 selectivity in favor of S-isomer.

No description available.

In the last decade N-heterocyclic carbene (NHC) ligands have become important in organometallic chemistry and homogeneous catalysis, rivalling the well established phosphines. Most of the current attention to date has focused on the NHC complexes of the platinum group metals (rhodium, palladium and nickel) plus ruthenium based system, but the chemistry of NHC systems of iron which is relatively inexpensive and environmentally friendlier is considerably less developed. Thus, this project involves the design, synthesis, characterization and application in catalytic transfer hydrogenation of NHC ligands and their iron(II) complexes. The motivation for the choice of NHC as a ligand stems from the ability to systematically tune the ligand both electronically and sterically in addition to the stability and robustness of the ligand to stabilize metal centres in various environments. In this research imidazolium based NHCs are generated. Thus, three different series of imidazolium salts were synthesized and their iron(II) complexes was obtained. All the compounds were characterized by spectroscopic and crystallographic methods. These are: (a) 1,3-dialkylimidazolium salts (b) 1,3-diarylimidazolium salts and (c) ferrocenylimidazolium salts bearing methyl and phenyl spacers between the ferrocenyl and the imidazolium moieties. A total of 20 novel compounds were synthesized and are reported in this thesis. Furthermore, the application of the new compounds as transfer hydrogenation catalysts was investigated using 17 saturated and unsaturated ketones as substrates, in the presence of KOH as the base and 2-propanol as the hydrogen source. The dialkylated NHC iron(II) complexes showed excellent yields, and TON values of up to 200 were achieved under the optimized reaction conditions. Without complexation with iron, the 1,3-diarylimidazolium and ferrocenylimidazolium series of salts were also found to be active catalysts for the transfer hydrogenation reaction of ketones in alcoholic media. In the case of ferrocenylimidazolium salts a TON value up to 1880 was achieved. Notably, two of the unsaturated ketones were successfully converted at a high yield with a high selectivity to the corresponding saturated ketones only. In addition, the stability of NHC ligands to moisture was investigated, since an understanding of the stability of various deprotonated NHC-based imidazolium cations to attack by moisture resulting in hydrolysis products is very important to understanding the coordination chemistry of the ligands on to metal centres. Four novel ionic diamino aldehyde compounds were obtained by moisture attack on saturated NHC ligands. The route to the formation of the hydrolysed compounds is formulated to occur via an imidazolinium ring opening process. On the other hand the unsaturated counterparts were more stable towards hydrolysis yielding adducts with the iron(II) precursors. Finally, the electrochemical properties of the ferrocenylimidazolium salts were investigated using cyclic voltametry. By comparing the relative shifts in the formal electrode potentials of the ferrocene/ferrocenium coupled with the ferrocenylimidazolium salts, it was easy to evaluate the influence of the substituents on the carbene containing imidazolium moiety on the electrochemical properties of the iron centres. The formal electrode potential of the ferrocenylimidazolium salts shifted to higher positive potentials as compared to ferrocene, indicating a high electron withdrawing effect of the imidazolium salts. This makes the metal centres more vulnerable to attack by nucleophiles. The electrochemical studies have enabled a structure-activity correlation to be drawn for the various ferrocenylimidazolium salts. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

No description available.

This thesis describes a series of calix[n]arene polynuclear transition metal and lanthanide complexes. Calix[4]arenes possess lower-rim polyphenolic pockets that are ideal for the complexation of various transition metal and lanthanide centres. Surprisingly however, with only a few exceptions, the coordination chemistry of p-tBucalix[ 4]arene (TBC[4]), p-tBu-calix[8]arene (TBC[8]) and p-tBuhomotrioxacalix[ 3]arene (TBOC[3]) with paramagnetic transition metal ions for the purpose of making and studying magnetically interesting molecules is unknown. Chapter two describes the reaction of TBC[4] with manganese salts in the presence of an appropriate base (and in some cases co-ligand) resulting in the formation of a family of calixarene-supported [MnIII 2MnII 2] clusters (1-7) that behave as Single-Molecule Magnets (SMMs). These are: [MnIII 2MnII 2(OH)2(TBC[4])2(DMF)6]·2MeOH (1), [MnIII 2MnII 2(OH)2(TBC[4])2(DMF)4(H2O)2]·4MeOH·2DMF (2), [MnIII 2MnII 2(OH)2(TBC[4])2(DMF)6]·2.8MeOH (3), [MnIII 2MnII 2(OH)2(TBC[4])2(DMF)4(EtOH)(H2O)] (4), [MnIII 2MnII 2(OH)2(TBC[4])2(DMSO)6]·2MeOH·2DMSO (5) , [MnIII 2MnII 2(OH)2(TBC[4])2(DMSO)6] (6) and [MnIII 2MnII 2(OH)2(C[4])2(MeOH)6]·4MeOH (7). Variation in the alkyl groups present at the upper-rim of the cone allows for the expression of a degree of control over the self-assembly of these SMM building blocks, whilst retaining the general magnetic properties. The presence of various different ligands around the periphery of the magnetic core has some effect over the extended self-assembly of these SMMs. Chapter three describes how the combination of complementary cluster ligands; sodium phenylphosphinate and the N,O-chelate 2-(hydroxy-methyl)pyridine (hmpH) with TBC[4] results in the formation of two new calixarene-supported clusters. This being an unusual [MnIIIMnII]2 dimer of dimers [MnIIIMnII(O2P(H)Ph)(DMF)2(MeOH)2]2 (8) and a ferromagnetic [Mn5] cage that displays the characteristic bonding modes of each support [MnIII 3MnII 2(OH)2(TBC[4])2(hmp)2(DMF)6](TBC[4]-H)·xDMF ·xH2O (9). Chapter four details how using oxacalix[3]arenes can tune the nature of the metal binding site, by introduction of ≥ 1 ethereal bridge. This results in Mn(II) rather than Mn(III) bonding in the phenolic pocket, and that these components self-assemble with additional Mn(II) and Mn(III) ions to form a [Mn10] supertetrahedron with an unusual oxidation state distribution, [MnII 6MnIII 4O4(TBOC[3])4(Cl)4(DMF)3]∙3.3H2O ∙ 1.5DMF (10). Chapter five introduces a family of lanthanide complexes formed using TBC[8]. Variation in the experimental conditions employed in the reaction of TBC[8] with lanthanide salts (LnX3) provides access to Ln1, Ln2, Ln4, Ln5, Ln6, Ln7 and Ln8 complexes, [Gd(TBC[8]-2H)Cl(DMSO)4]·MeCN·H2O·(DMSO)2·hex (11), [CeIV 4(TBC[8]-6H)2(μ3- O)2(DMF)4]·(DMF)5·hex·MeCN (12), [TbIII 5(TBC[8]-5H)(μ4-O)(μ3- OH)4Cl(DMSO)8(H2O)3]Cl3·(DMSO)2(hex)2 (13), [CeIV 6(TBC[8]-6H)2(μ4-O)2(μ2-OMe)4(μ2- O)2(DMF)4]·(DMF)6·hex (14), [Dy7(TBC[8]-7H)(TBC[8]-6H)(μ4-O)2(μ3-OH)2(μ2- OH)2(DMF)9]·(DMF)3 (15) and [Gd8(TBC[8]-7H)2(μ4-CO3)2(μ5-CO3)2(μ2-HCO2)2(DMF)8] (16), with all polymetallic clusters containing the common bi-nuclear lanthanide fragment. Closer inspection of the structures of the polymetallic clusters reveals that all but one (Ln8) are in fact based on metal octahedra or the building blocks of octahedra.

This Thesis describes the synthesis and characterisation of titanium imido compounds supported by pendant arm functionalised amidinate ligands. Reactivity studies of cyclopentadienyl amidinate-imido compounds with CO2 are presented. Chapter 1 introduces transition metal imido chemistry, with a particular emphasis on imido complexes of titanium. Chapter 2 describes recent developments in the chemistry of functionalised amidinate ligands. The synthesis and characterisation of new titanium imido compounds with pendant amine functionalised amidinate ligands is described. The preparation of an amidinate ligand with a pendant propyl arm is reported. Reactions of a selection of these complexes with small molecules are presented. Chapter 3 reviews recent developments in the chemistry of cyclopentadienyl amidinate-imido compounds. The preparation of cyclopentadienyl-supported titanium imido compounds bearing pendant arm amidinate ligands is described andthereactionsofthesecompoundswithCC>2arediscussed. Kineticanddensity functional theory studies of these reactions are presented. Chapter 4 describes the synthesis and characterisation of alkyl and aryloxide titanium amidinate-imido compounds. The preparation of cationic derivatives is also described and reactions of these cationic derivatives with small molecules are discussed. Chapter 5 presents full experimental procedures for all of the syntheses and reactivity studies outlined in Chapters 2 to 4. Chapter 6 contains characterising data for all of the new compounds reported. Appendices A - K contain tables of selected crystallographic data for all new crystallographically characterised complexes described in this Thesis. Appendices L - O contain kinetics data relating to work discussed in Chapter 3.

This thesis deals with the applications of organopalladium and organochromium chemistry to the functionalisation of the benzopyran ring system, at a variety of oxidation levels. Section I demonstrates the functionalisation of 3-, 6-, and 8-bromochromones via palladium (0) insertion into the C-Br bond. The resultant arylpalladium species are shown to undergo addition to the least substituted end of a variety of olefins including methyl acrylate, acrylonitrile and styrene. Subsequent palladium-hydride elimination leads to overall palladium catalysed vinylation of the chromone and the synthesis of a number of novel compounds. Vinylation occurs regiospecifically at the site of chromone bromination and is shown to allow clean substituent introduction into each of the three sites. The palladium catalysed reaction of 3,6-dibromo-chromone with methyl acrylate leads to vinylation at both the C3 and C6 positions. Carbonylation of the 6-bromochromone in ethanol or butanol leads to the 6-ethyl or 6-butyl esters respectively. The palladium catalysed vinylation of the 6-bromochromone with ethyl vinyl ether leads to a mixture of products from addition of the chromone to either end of the olefin. With p-bromophenol or p-bromo-N,N-dimethylaniline the reaction gives exclusively the acetylated product arising from addition to the more substituted end of the olefin. This change in orientation is rationalised by considering the polarisation of the olefin and the arylpalladium species. Section II demonstrates the functionalisation of chroman and 4-chromanol via coordination to the Cr(CO)₃ moiety. (η⁶-Chroman)Cr(CO)₃ is synthesised and is shown to undergo regiospecific ring deprotonation at C8 under kinetic conditions or regiospecific benzylic deprotonation at C4 under thermodynamic conditions. The resultant anions are quenched with alkyl halides, aldehydes, Eschenmoser's salt and methyl disulphide resulting in selective functionalisation of either site. No mixed products are observed. The uncomplexed arene is shown to be totally unreactive under identical conditions. (η⁶-4-Chromanol)Cr(CO)₃ is synthesised and is shown to undergo regiospecific C8 ring deprotonation by comparison with authentic samples of the C5 and C8 methylated alcohols. Protection of the hydroxyl group as its methyl, t-butyldimethylsilyl or methoxymethyl ethers is found not to alter the regiochemistry of deprotonation. The 4-chromanol t-butyldimethylsilyl and tri-i-propylsilyl ethers are synthesised and coordinated to the metal unit. Cleavage of the silyl ethers is shown to proceed with loss of stereochemistry, indicating C-0 bond cleavage.

Despite the great abundance of C–H bonds in readily available starting materials, their use in synthesis of functionalized molecules has been hampered by the high bond strengths, rendering them inert to common organic reagents. However, recent progress in the field has addressed this issue, enabling selective C–H bond functionalizations to be performed using catalytic transition metal mediated processes. Herein, the use of sulfonyl chlorides as versatile reagents for C–H bond functionalizations is reported. Using chelation assistance, the regioselective conversion of C–H bonds to either C–S, C–Cl or C–C bonds was achieved. The methodology development, substrate scope determination and mechanistic investigations will be discussed.