This thesis is concerned with the problems of sample preparation arising in the study of lead isotope abundances. The importance of this study to geophysics has been amply shown by R.D. Russell, R.M. Farquhar, F.G. Houtermans, J.T. Wilson, H.F. Ehrenberg and many others. Chapter 1 gives an outline of lead isotope measurement techniques, including types of mass spectrometers generally used and some of the problems encountered. The mass spectrometer used in the present research was designed and constructed by R.D. Russell and F. Kollar and descriptions of it will be found in their publications and in F. Kollar's Ph.D. thesis. The present techniques of producing lead tetramethyl for isotopic analysis from ore samples are discussed in Chapter 2. The remaining chapters deal with the purification of lead tetramethyl for mass spectrometer analysis, using vapour phase chromatography. This technique has found immediate application in the precise intercomparison of lead samples recently carried out in the Geophysics Laboratory at the University of British Columbia by F. Kollar and others (F. Kollar, R.D. Russell and T.J. Ulrych, in press). The long range object for developing this technique is to purify lead tetramethyl prepared by free methyl radicals reacting with metallic lead (cf. A.J. Surkan 1956) prior to isotopic analysis. The presence of impurities in samples prepared this way has discouraged the development of this method in the past. The final chapter deals with this aspect of the proposed problem. This thesis is intended as a preliminary to the writer's Ph.D. research which will also deal with isotopic lead analysis. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The redox behavior of a series of organometallic complexes containing Cp'M(NO) groups (Cp' = ƞ⁵-C₅H₅(Cp) or ƞ⁵-C₅Me₅(Cp*) ; M = Mo or W) has been investigated both by cyclic voltammetry and by chemical means. The neutral 16-electron Cp'Mo(N0)X₂ compounds (X = CL, Br or I) undergo a single, essentially reversible, one-electron reduction in CH₂CL₂/O.1M [n-Bu₄N]PF₆ at relatively low potentials (<-0.1 V vs SCE). The electrochemically observed reductions can be effected on a preparative scale by employing CP₂C0 as the chemical reductant. The isolable 17-electron [Cp'Mo (NO)X₂]•⁻ radical anions are cleanly reconverted to their 16-electron neutral precursors by treatment with [Cp₂Fe]BF₄. In contrast, the Cp'W(NO)I₂ compounds undergo rapid decomposition to their [Cp'W(NO)I]₂ monohalo dimers upon electrochemical reduction. Electrophiles NE⁺ (E = O or ϱ-O₂NC₆H₄N) undergo unprecedented insertions into the Cr-C ϭ-bonds of CpCr(NO)₂R complexes (R = Me, CH₂SiMe₃ or Ph) to afford [CpCr(N0)₂{N(E)R}]⁺ cationic complexes. Present evidence is consistent with these insertions occurring via charge-controlled, intermolecular attacks by NE⁺ at the Cr-R groups in classical SE2 processes. The newly-formed N(E)R ligands function as Lewis bases through nitrogen atoms toward the formally 16-electron [CpCr(NO)₂]⁺ cations and may be displaced from the chromium's coordination sphere by the more strongly coordinating CL⁻ anion. The resulting CpCr(NO)₂CL can be reconverted to CpCr(NO)₂R. thereby completing a cycle by regenerating the initial organometallic reactant. The entire sequence of stoichiometric reactions forming the cycle thus constitutes a selective method for the formation of new carbon-nitrogen bonds, the net organic conversions mediated by the CpCr(NO)₂ group being NE⁺ + R⁻ → N(E)R. The electrophilic [Cp'M(NO)₂]⁺ cations (Cp'=Cp or Cp* ; M = Cr, Mo or W) condense with methyl propiolate and 2,3-dimethyl-2-butene to afford cationic organometallic lactone complexes. These complexes undergo facile ⍜-dealkylation to yield the neutral Cp'M(NO)₂(ƞ¹-lactone) derivatives. Furthermore, the neutral Cp'W(NO)₂(ƞ¹-lactone) compounds decompose in air to their Cp'W(O)₂(ƞ¹-lactone) dioxo products. / Science, Faculty of / Chemistry, Department of / Graduate

This thesis describes the synthesis and chemistry of alkyl 2,3-bis(trimethylstannyl)-2-alkenoates ((78) and (83)). It was shown that these compounds could be readily transformed into useful intermediates for the synthesis of functionalized, stereochemically defined tetrasub-stituted alkenes (87) and tricyclic dienes of general structure (322A). The synthesis and chemistry of compounds (277) and (278) is also described. The palladium(O)-catalyzed addition of hexamethylditin to a variety of α,β-acetylenic esters (90), afforded in a stereoselective manner, the corresponding alkyl (Z)-2,3-bis(trimethylstannyl)-2-alkenoates (83). Subsequent thermolysis of these compounds afforded the corresponding alkyl (E)-2 , 3-bis(trimethylstannyl)-2-alkenoates (78). It was found that treatment of alkyl (E)- and (Z)-2,3-bis(tri-methylstannyl)-2-alkenoates with methyllithium at low temperature, followed by reaction of the resultant nucleophilic intermediate with a variety of alkylating agents, afforded the trisubstituted vinylstannanes (80). On the other hand, successive treatment of methyl w-halo-2,3-bis-(trimethylstannyl)-2-alkenoates (202) with methyllithium and HMPA provided a facile route to cyclic β-trimethylstannyl α,β-unsaturated esters (203). Compounds (80) were readily converted into vinyl iodides of general structure (219) in which W is a functionalized group derived from the CO₂R moiety. These latter compounds served as useful intermediates for the synthesis of functionalized, stereochemically defined tetrasubstituted alkenes (87). For example, treatment of compounds (219) with 1.1 or 2.2 equiv of n-butyllithium at -78°C afforded the corresponding vinyllithium species (86) , which could either be alkylated directly or further transposed into the organocopper(I) reagent (263A) and then alkylated, to afford in each case, the tetrasubstituted alkenes (87). The Pd(0)-catalyzed addition of tri-n-butylstannyltrimethylgermane (276) to a variety of α,β-acetylenic esters (90) afforded the corresponding compounds (277) and (278) in a ratio of approximately 3:1, respectively. Treatment of the (E) isomers (277) with n-butyllithium at -98°C, followed by alkylation of the resultant nucleophilic intermediate afforded the corresponding trisubstituted vinylgermanes (293). One of these latter compounds was readily converted into the iodo bromide (308), which is potentially synthetically equivalent to the d,a synthon (310). When the enolate anion of compounds (203) was successively treated with HMPA and compound (308) the esters (311) were obtained. The Pd(0) catalyzed intramolecular coupling of the vinylstannane-vinyl iodide moieties of (311) provided a facile route to the bicyclic triene esters (312). Similarly, alkylation of the enolate anion of compounds (203) with (325) (which was readily obtained from (203), in which n - 1), followed by the Pd(0)-catalyzed coupling of the resulting alkylated material afforded the tricyclic diene esters (322A). [Formula Omitted] / Science, Faculty of / Chemistry, Department of / Graduate

Although hydrides of metal carbonyls are widely known, the number of hydrides in the related family of metal nitrosyls is extremely small. The preparation of a series of nitrosyl hydrides from the treatment of [CpW(NO)I₂]₂ (Cp=ƞ⁵-C₅H₅) with Na[H₂Al(OCH₂CH₂OCH₃)₂] is described. The addition of one or two equivalents of the aluminum reagent results in the formation of [CpW(NO)IH]₂ or [CpW(NO)H₂]₂ respectively. The reaction of [CpW(NO)IH]₂ with a Lewis base (L=P(OPh)₃, P(OMe)₃, PPh₃ or PMe₃) gives the monometallic CpW(NO)IHL, while [CpW(NO)H₂]₂ reacts with P(OPh)₃ or P(OMe)₃ to yield [CpW(NO)HL]₂ which undergoes further reaction to give CpW(NO)H₂L. Proton NMR spectroscopy shows that all bimetallic species contain bridging hydride ligands and are therefore best, formulated as [CpW(NO)1]₂(µ-H)₂, [CpW(NO)H]₂(µ-H)₂ and [CpW(NO)L]₂(µ-H)₂. The ¹H NMR spectrum of [CpW(NO)H]₂(µ-H)₂ shows that there is no hydride ligand exchange on the NMR time scale and that ¹jH(terminal)W ≃ ¹jH(bridging)w > ²jHW. From this finding, it is possible to develop new criteria for assessing the static or fluxional nature of hydride ligands for several families of organotungsten hydrides (Cp₂W, CpW(CO)₃, W(CO)₃ and CpW(NO)x (x=l or 2)). Within each family, the magnitude of ¹JHW strongly reflects the type of metal hydride bonding, i.e. [Formula Omitted] and suggests that bridge bonding involves all the atoms in the bridge and therefore the "fused" notation is introduced. Treatment of CpW(NO)(CH₂SiMe₃)₂ with low pressures of H₂ (60-80 psig) in the presence of Lewis bases (L=P(0Ph)₃, PMePh₂) gives the unusually stable alkyl hydride compounds CpW(NO)(H)(CH₂SiMe₃)L. This chemistry is then extended to the Cp* (Cp*=ƞ⁵ -C₅Me₅) analogues, including the preparation of the appropriate starting materials. Upon thermolysis of Cp*W(NO)(H)(CH₂SiMe₃)(PMe₃) in C₆H₆, the intermolecular C-H activation product Cp*W(N0)(H)(C₆H₅)(PMe₃) is cleanly formed. However, intermolecular activation of CH₄, C₆H₁₂ or n-C₆H₁₄ does not occur under similar experimental conditions. Hydrogenolysis of Cp*W(NO)(CH₂SiMe₃)₂ at high pressures (≃920 psig) with no Lewis base present results in the formation of isolable [Cp*W(NO)H]₂(µ-H)₂ and [Cp*W(N0)H](µ-H)₂[Cp*W(N0)(CH₂SiMe₃)]. The latter is a new example of the rare class of dinuclear alkyl hydride complexes. Proton NMR spin tickling experiments on this compound allow the complete assignment of all couplings in the spectrum and show that ¹jH(terminal)W' ¹JH(bridging)W and ²jHW have the same sign. / Science, Faculty of / Chemistry, Department of / Graduate

The nitrosyl complex CpW(NO)R₂ (R = CH₂SiMe₃) forms 1:1 adducts via isonitrosyl linkages to Lewis acids such as AlMe₃ and Cp₃Er, i.e. CpWR₂(NO→A) (A = AlMe₃, ErCp₃). These adducts regenerate the starting dialkyl complex when treated with water. Protonation of CpW(NO)R₂ by HBF₄⋅0Me₂ can also be effected. Whether the site of protonation is the nitrogen or the oxygen atom of the nitrosyl ligand is not known with certainty, although O-protonation is postulated by analogy with the other Lewis-acid adducts of CpW(NO)R₂. In these adducts, the nitrosyl stretching frequency is shifted to lower wavenumbers relative to that of the parent dialkyl, to an extent which increases as harder Lewis acids are employed. The colour of the adducts also ranges from red to orange to yellow as progressively harder acids are used. Treatment of CpW(NO) (CH₂SiMe₃)₂ with [Ph₃C]⁺ PF₆⁻ in Ch₂CL₂ results in electrophilic cleavage of a carbon-silicon bond to yield the mixed dialkyl CpW(NO)(CH₂SiMe₃)(CH₂CPh₃), which has been fully characterized by spectroscopic methods and by a single-crystal X-ray crystallographic study. The formation of Me₃SiF and PF₅ (coordinated to Lewis bases in the reaction mixture) as by-products of this reaction has been confirmed by ³¹P and ¹⁹F NMR spectroscopy of the reaction mixture in CD₂CL₂. Preliminary attempts to extend this novel reaction of a silicon-containing ligand by using other carbocations were unsuccessful. This is attributed to the high reactivity of the required carbocations and the large number of possible reaction sites on the metal complex. Some reactions of the mixed dialkyl CpW(NO)RR¹ (R = CH₂SiMe₃ R¹ = CH₂CPh₃) were found to be analogous to those of the parent CpW(NO)R₂, while other reactions followed a different course because of the ability of the CH₂CPh₃ ligand to orthometallate. Thus, CpW(NO)RR¹ is much less thermally stable than CpW(NO)R₂. As a solid or a solution in non-coordinating solvents, it decomposes in a matter of days at room temperatures to a mixture of products which were not identified. In acetonitrile solution, an orthometallated complex derived from CpW(NO)RR¹ can be trapped by coordination of solvent. The product CpW(NO)(CH₂C(C₆H₄)Ph₂)(NCMe) has been isolated and crystallographically characterized. Cyclic voltammograms of CpW(NO)R₂ and CpW(NO)RR¹ show that both complexes undergo an apparently chemically reversible reduction and an irreversible oxidation. The mixed dialkyl CpW(NO)RR¹ is somewhat easier both to reduce and to oxidize than CpW(NO)R₂. Like CpW(NO)R₂, CpW(NO)RR¹ reversibly forms a 1:1 adduct with PMe₃. Also analogously to CpW(NO)R₂, it reacts with 0₂ to form a 5:1 mixture of dioxoalkyl complexes CpW(0)₂R and CpW(0)₂R¹, and with NO(g) to form 2 CpW(NO)R¹(ƞ² -0₂N₂R). In this product, insertion of NO has occurred exclusively in the W-CH₂SiMe₃ bond. Upon photolysis, both complexes CpW(NO)R¹¹(ƞ²-0₂N₂R) (R¹¹ = CH₂SiMe₃ or CH₂CPh₃) form dioxo alkyls CpW(O)₂R¹¹ in an unprecedented reaction. The ability of CpW(NO)RR¹ to orthometallate also results in the formation, when this complex is treated with sulphur, of CpW(O)(CH₂C(C₆H₄)Ph₂)-(SR). No analogue to this compound can be obtained from reaction of CpW(NO)R₂ with sulphur. The sequence of reactions leading to the formation of this product is not known. / Science, Faculty of / Chemistry, Department of / Graduate

Thesis (MSc. (Chemistry)) -- University of Limpopo, 2015 / Alkyne-quinoxaline compounds were successfully synthesised form the cross-coupling of 2-benzenesulfonyloxyquinoxaline with terminal alkynes. The current study demonstrates the ability of benzenesulfonyloxy as a good leaving group in Sonogashira coupling reaction, generating a number of alkyne-quinoxaline compounds. The structures of the synthesised compounds were characterised through the comprehensive analysis of spectroscopic data from NMR, HPLC-MS and others selected compounds with IR. Several alkyne-quinoxaline compounds were synthesised in moderate to good yields. During analysis, it was observed that the highest yield was obtained when using 4-(trifluoromethyl)phenylacetylene 4e and the lower yield was obtained when using the 3-ethynylthiophene 4s as a substrate. The alkyne-quinoxaline compounds were investigated for 1,3-dipolar cycloaddition which was done from 2-ethylquinoxaline 6. The 1,3-dipolar cycloaddition reactions were successful and the compounds were obtained in good yields. The in vitro analysis on anti-tubercular screening against H37RvMA strains of M tb reveals that compounds 5e and 5o which contained a trifluoroanisole moiety showed promising activity amongst all the synthesised compounds. The compounds were having MIC90 values 11.8 μM and 12.7 μM respectively, however, they were found to be less active than rifampicin. Compounds 5a, 5b, 5e, 5g, 5h, 5i, 5I, and 5r were evaluated for anti-cancer activity on A549 cells. The results have showed that 5i was able to retard the migration of A549 cells in the Wound-Healing Migration Assay. / National Research Foundation (NRF) Sasol Inzalo Foundation

This thesis involves reactions of cyclam with Mn(III), Ni(II) and Fe(II). The chemistry of each metal with cyclam will be presented in sections discussing each metal. The initial intent of this thesis was to examine and compare the structures and electronic spectra of a series of trans monomeric first row transition metal cyclam compounds. Both Mn(III) and Ni(II) form such trans monomeric complexes with cyclam and their structural and electronic characteristics are, indeed, examined in this thesis. However, in the course of our study, we found that Fe(II) and cyclam in acetonitrile in the presence of oxygen form a di-macrocycle shown here: [See PDF]

Part I. Diels-Alder cycloadditions of 1,2,3,4,9,9-hexachloro-1α,4α,4aα,8aβ-tetrahydro-l,4-methanonaphthalene (32) and 1,2,3,4,9,9-hexachloro-lα,4α,6,7- tetrahydro-l,4-methanonaphthalene (33) to 4-methyl- and 4-phenyl-l,2,4-triazoline-3,5-dione [MTAD and PTAD, respectively] and to N-methylmaleimide (NMM) have been studied. The structures of several of the resulting cycloadducts were determined by X-ray crystallographic methods. The observed stereoselectivity of each of these Diels-Alder reactions was further investigated via application of theoretical methods. Thus, semiempirical (AMI) and ab initio molecular orbital calculations were used to calculate relative energies. Ab initio calculations were employed to perform frontier molecular orbital analyses of diene-dienophile interactions.

Includes bibliographical references. / X-ray crystallographic studies have been used to elucidate the structures of two new Werner clathrates. ... The chloroform molecule is disordered, lying on a two-fold axis. Stoicheiometric characterization of the clathrates was determined using various chemical techniques, including mass spectroscopy, proton nuclear magnetic resonance and complex iometric titration. The clathrating phase of the second clathrate was investigated by guest-loss studies on a McBain balance followed by X-ray powder photography. Host-quest non-bonded interactions of both clathrate compounds were studied using atom-pair potentials.

Includes bibliographical references. / The crystal structures of trans-9, 10-dihydroxy-9, 10-diphenyl-9, 10- dihydroanthracene with various guest molecules have been determined by X-ray diffraction. The guests were 2-butanone, 4-vinylpyridine, 4-methylpyridine and 2-methylpyridine. The host to guest ratios were determined by microanalysis and density measurements. The change of the overall host lattice structure upon guest release was studied by X-ray powder diffraction. The thermal characteristics of the compounds were studied using thermogravimetric analysis and differential scanning calorimetry. Guest desorption from three of the four compounds occurred in a single step whereupon the host framework collapsed back to the guest-free structure. The compound containing 4-methylpyridine, released the guest molecules in a two-step process. Evidence of a new host phase was identified from the XRD pattern of this intermediate phase. On further guest release, the intermediate phase converted to the guest-free host structure. In an attempt to reconcile thermodynamics with structure, the correlation between hydrogen bond length and guest desorption enthalpy was investigated.