No description available.

The purpose of this study was to prepare and characterize the coordination compounds produced by the reaction of five cycloalkanecarboxylic acids and a rhodium salt. The five acids that furnished the ligands were: cyclopropanecarboxylic acid, cyclobutanecrboxylic acid, cyclopentanecarboxylit acid, cyclohexanecarboxylic acid, and a cycloheptanecarboxylic acid. The rhodium (Ill) ion was provided by the salt Na3RhCl6•12H20, A survey of the available literature indicated that these rhodium (Ill) cyclo-alkane carboxylates had not previously been prepared.

No description available.

No description available.

A detailed study was made of the rates of hydrolysis of trans-[Co(en)₂ (NO₂)₂] NO₃ as a function of acid concentration in perchloric, hydrochloric, hydrobromic, sulfuric, and nitric acids up to high concentrations of acid. All the data could be fitted 1 to the equations proposed by Bunnett¹. (1) [log k₁ - log (H +)] = w*log a_w + Ratio and (2) [log k₁ - log Hₒ] = wlog a_w + Constant. In these equations, k₁ is the first-order rate constant, (H+) is the hydrogen-ion concentration, a_w is the activity of water in the solution, and Hₒ is the Hammett acidity function. The w and w* are the slopes"Ratio" and"Constant" are the intercepts, of plots of the left side of eq. 1 or eq. 2 versus the log a_w. Bunnett proposed that for the hydrolysis of organic compounds, wand w* values are indicative of mechanism. From the constant values of w* obtained in hydrobromic, hydrochloric, sulfuric, and perchloric acids, a mechanism involving water acting as a nucleophile was indicated. The different value of w* obtained in nitric acid was consistent with the known difference in hydration in nitric acid. Values of w also were consistent with nucleophilic attack by water. Rates of hydrolysis of trans-[Co(en)₂ (NO₂)₂] NO₃ were also measured as a function of temperature. In perchloric acid, good linear Arrhenius plots were obtained from which the energy of activation was 23.6 + 0.8 kcal. and the activation entropy was 2.9 + 2.3 eu. at the 95% confidence level. Arrhenius plots in hydrochloric, hydrobromic, sulfuric, and nitric acids were curved, the amount of curvature increasing with acid concentration and temperature. At lower temperatures, the activation energy was 23-24 kcal. but decreased to as low as 12 kcal. at high acid concentrations and higher temperatures. This behavior is consistent with two consecutive reactions, the second reaction having the lower activation energy; the latter reaction was identified with addition of an anion to the intermediate nitroaquo complex. A series of dinitro complexes with"inert" ligand size varying from ammonia to 1, 10-phenanthroline was made; these complexes were studied in hydrochloric and perchloric acids. The first-order rate constant decreased as the size of the ligand increased, indicating direct participation of water in an SN₂ reaction. The values of w* in both acids were consistent with nucleophilic participation of water; for the bipyridine and orthophenanthroline complexes a lower value of w was observed. This observation could be related to the expectation that these large complexes would not be hydrated as much as the smaller compounds. A mechanism for the hydrolysis reaction consistent with the observed behavior was given. According to this mechanism, the complex is first protonated in an equilibrium step; the protonated species reacts with water to give the nitroaquo complex as the rate determaining step for all compounds· in all acids. Finally, the nitroaquo complex reacts with an anion Z⁻ (except when Z⁻ is ClO₄⁻) to give the final product of reaction. This investigation shows that Bunnett's equations are useful for correlating data, but some caution in accepting Bunnett's mechanistic interpretations from the values of w and w* is necessary. It is satisfying that application of these ideas to a totally different system (inorganic complexes) lead to a mechanism consistent with current ideas about the reactivity of coordination compounds of cobalt(III). / Doctor of Philosophy

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / A comprehensive, comparative structural study of gold(I), gold(II) and gold(III) compounds with the general formula [Aux(C6F5)y(tht)z] (tht = tetrahydrothiophene) was performed. The series of compounds included the unprecedented dinucleur gold(II) compound, tetrakis(pentafluorophenyl)bis(tetrahydrothiophene)digold(II), which could be prepared in a rational manner. This very unique compound represents the first example of an unbridged dinucleur gold(II) compound in which the gold(II) centres are not stabilised by chelating ligands. Formation of this compound was postulated to have taken place by radical pentafluorophenyl (pfp) ligand migration along with AuII–AuII bond formation. It may therefore be regarded as a rare example of labile behaviour by a generally inert pfp ligand. In addition to this compound, the crystal and molecular structures of the wellknown gold(I) and gold(III) precursor compounds, (pentafluorophenyl)(tetrahydrothiophene) gold(I) and tris(pentafluorophenyl)(tetrahydrothiophene)gold(III) were carried out and are described for the first time. The latter underwent a unique mononuclear ligand rearrangement (metathesis or disproportionation) reaction in solution to yield the novel rearrangement product, bis(pentafluorophenyl)bis(tetrahydrothiophene)gold(III)tetrakis- (pentafluorophenyl)gold(III). In all the complexes, the Au–C and Au–S bond lengths displayed a variation which appears to be dependent on the oxidation state of the central gold atom. Both of these bond types were found to descrease in the order Au(II) > Au(III) > Au(I)...

Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008. / In this study the coordination of ligands with several coordination sites, 2-aminoazoles (2- amino-4-methylthiazole), 2-aminobenzothiazole, 2-aminobenzoimidazole and 2- aminothiazoline and a biguanidine (N-(2-methylphenyl)imidodicarbonimidic diamide) to soft metal centres [gold(I) (group 11), chromium(0) (group 6) and tungsten (0) (group 6)] was investigated. The aminoazoles have three coordination sites, an exocyclic amine nitrogen, an endocyclic imine nitrogen and an endocyclic thioether sulphur. The biguanidine ligand has three sites for deprotonation, one central amine and two imine nitrogens, and at least five sites available for nitrogen coordination.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Resorcinarenes are macrocyclic products formed from the condensation of aldehydes (aliphatic or aromatic) and resorcinol and have been used in a wide range of applications since their first synthesis. Applications include: HPLC stationary phases for the separation of pyrimidine bases, racemic drugs and isomers, the selective extractions of lanthanides and actinides, as molecular receptors, catalysis, NMR chiral shift agents, GC separations and as starting materials for the synthesis of macrocyclic compounds (e.g. cavitands and carcerands) to name but a few. The use of resorcinarenes in catalysis is still quite new and unexplored, while catalysis using calix[4]arenes, a related macrocycle, has been widely studied. In this thesis it was attempted to synthesise a C2v symmetric resorcinarene precursor that could be further functionalised to form distal bidentate ligands for coordination to transition metals. These compounds would then ultimately be used in catalytic testing, especially for Pd catalysed C-C bond formation. A dibromo resorcinarene precursor was synthesised starting from resorcinarene, using methodology developed by Shivanyuk. This molecule was functionalised with a small range of different electrophiles using lithium halogen exchange methodology, although low yields were returned for the expected distal resorcinarene compounds. Other methods of functionalisation of the resorcinarene, using an anionic ortho-Fries rearrangement and the reduction of a dinitrile resorcinarene to amine and aldehyde functionalities proved unsuccessful. Using a dithioether resorcinarene a di-nuclear coordination compound was formed with Pd(II). This compound was tested for catalytic activity with a Heck reaction, showing low yields for the coupling of styrene with bromobenzene. / AFRIKAANSE OPSOMMING: Resorsinarene is makrosikliese produkte wat gevorm word deur die kondensasie van aldehiede (alifaties of aromaties) met resorsinol en word in ‘n verskeidenheid van toepassings gebruik sedert hulle eerste sintese. Tipiese voorbeelde sluit in: stationêre fases vir die HPLC-skeiding van pirimidien-basisse, rasemiese farmaseutiese middels en isomere, die selektiwe ekstraksie van lantaniede en aktiniede, molekulêre reseptore, katalise, chirale verskuiwingsreagense vir KMR spektrometrie, GC-skeidings en as uitgangverbindings vir die sintese van ander makrosikliese verbindings (bv. kavitande en karserande). Die gebruik van resorsinarene in katalise is ’n splinternuwe onontginde veld. In teenstelling hiermee is calix[4]areen, ’n verwante makrosikliese verbinding, baie meer bestudeer en vir katalise gebruik. Die doel van hierdie tesis was om ’n C2v simmetriese uitgangstof te sintetiseer wat verder gefunksionaliseer kan word om distale, bidentate ligande vir koordinasie met oorgangsmetale te lewer. Daar is beplan om die katalitiese eienskappe van die komplekse te toets, veral vir Pd-gekataliseerde C–C-koppelings reaksies. Deur gebruik te maak van ’n protokol wat deur Shivanyuk ontwikkel is, is ’n dibromo-resorsinareen gesintetiseer uit resorsinareen. Verskillende elektrofiele is in ’n litium-halogeen uitruilreaksie gebruik om ’n beperkte verskeidenheid nuwe ligande te sintetiseer wat verskillende funksionele groepe besit. Ongelukkig was die opbrengste aan distale ligande baie laag en ander metodes is dus ook ondersoek om die funksionalisering te bewerkstellig. ’n Anioniese orto-Fries herrangskikkingsreaksie en die reduksie van ’n dinitriel-resorsinareen om amien- en aldehiedfunksies te lewer, was ook onsuksesvol. Die reaksie tussen ‘n Pd(II) sout en ‘n ditioeter-gederivatiseerde resorsinareen het ‘n koordinasie verbinding met twee metaalkerne gelewer. Hierdie kompleks is deur middel van ‘n Heck-koppelingsreaksie vir katalitiese aktiwiteit getoets, maar het lae opbrengste gelewer in die koppeling van stireen en bromobenseen.

Thesis (PhD (Chemistry and Polymer Science))—University of Stellenbosch, 2006. / This study describes the exploitation of numerous donor ligand possibilities presented by selected nitrogen-rich heterocyclic ligands towards gold(I). The preparation and structural characterisation of novel gold(I) complexes, apart from conventional gold(I) bonding possibilities, also encompassed a study of bi- and polytopic bonding modes within a range of multifunctional ligands.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Benzoxazoles are an important class of π-electron-excessive, benzene-fused heterocyclic compounds found in natural products and display a wide range of pharmacological applications. It is therefore a widely used starting scaffold for drug and agrochemical discovery programs. Other applications include: chiral auxiliaries in asymmetric reactions, chiral receptors for the resolution of racemic mixtures, fluorescent whitening dyes, various photochromic materials and as ligands for a wide range of catalytic reactions. Due to our interests in resorcinarenes, we came across 4-hydroxybenzoxazoles, a structural motif that has not been explored as potential asymmetric ligands. In this thesis it was attempted to investigate the synthesis, functionalisation and coordination chemistry of these compound class and finally look at a method of synthesising chiral 4-hydroxybenzoxazoles from amino acids. A small library of achiral 4-hydroxybenzoxazoles were synthesised in good yields. These compounds were then reacted with various transition metals, of which only the Pd-salts proved to return any usable compounds. The first structural evidence of the bonding of 4- hydroxybenzoxazoles was recorded from single crystal X-ray diffraction analysis of the coordination compounds that formed. Different coordination modes were recorded, depending on the ligand and the Pd-salt used. The PdCl2 compounds were also tested for catalytic activity with a Heck reaction, showing good conversions for the reaction between iodobenzene and styrene to form stilbene. Further examination pointed to the ligands playing an insignificant role in the reaction and the products possibly due to only the PdCl2’s reactivity. During this period it was also attempted to functionalise the phenol group with P(III) groups and repeat the coordination and catalytic studies. Efforts to synthesise these compounds were not successful, with oxidation of the P(III) to P(V) groups or degradation of these compounds. Efforts to synthesise these via phosphorous protection, utilising BH3 or the in situ trapping of the compounds with transition metals, were also not successful. During the trapping experiments the phosphinite and Pd-salt formed a re-arranged product that is a known and useful catalyst on its own. Finally a small library of chiral benzoxazoles and 4-hydroxybenzoxazoles were synthesised, starting from amino acids and utilising a Mitsunobu reaction to perform the ring closing. Antimicrobial tests with these compounds did not return any appreciable results. / AFRIKAANSE OPSOMMING: Bensoksasool is 'n belangrike klas van π-elektron-ryk, benseen-saamgesmelte heterosikliese verbindings wat in natuurlike produkte voorkom en 'n wye verskeidenheid van farmakologiese funksies vertoon. Dit is dus 'n baie algemene basis struktuur vir dwelm- en landbouchemiese ontdekkings programme. Ander gebruike sluit in: chirale ligande in asimmetriese reaksies, chirale reseptore vir die resolusie van rasemiese mengsels, fluoresserende verwittings kleurstowwe, verskeie fotochromiese materiaal en as ligande vir 'n wye verskeidenheid van katalitiese reaksies. As gevolg van ons belangstelling in resorsinarene, het ons op 'n strukturele motief afgekom wat nog nie ondersoek is as potensiële asimmetriese ligande nie, die 4- hidroksiebensoksasole. In hierdie tesis is gepoog om die sintese, funksionalisering en koördinasie chemie van hierdie klas verbindings te ondersoek en uiteindelik 'n metode te ontwikkel om die sintese van chirale 4-hidroksiebensoksasole vanaf aminosure te bewerkstellig. 'n Klein biblioteek van achirale 4-hidroksiebensoksasole was gesintetiseer in goeie opbrengste. Hierdie verbindings was toe behandel met verskeie oorgangsmetale, waarvan slegs die Pdsoute enige bruikbare verbindings gevorm het. Die eerste strukturele bewyse van die binding van die 4-hidroksiebensoksasole is aangeteken met behulp van enkelkristal X-straaldiffraksie ontleding van die koördinasieverbindings wat gevorm is. Verskillende koördinasie mode is aangeteken, afhangende van die ligand en die Pd-sout wat gebruik was. Die PdCl2 verbindings is ook vir katalitiese aktiwiteit met 'n Heck reaksie getoets. Die reaksie het baie goeie omskakeling gewys vir die reaksie tussen iodobenseen en stireen na stilbeen. Verdere ondersoeke het getoon dat die ligande nie ‘n beduidende rol in die reaksie speel nie en die produkte moontlik slegs as gevolg van die PdCl2 se reaktiwiteit is. Gedurende hierdie tydperk was daar ook probeer om die fenol groep met P(III) groepe te funksionaliseer. Met die uitgangstowwe sou die koördinering en katalitiese studies herhaal word. Pogings om hierdie verbindings te sintetiseer was nie suksesvol nie, met oksidasie van die P(III) na P(V) groepe of afbreking van hierdie verbindings. Pogings om dit te sintetiseer via fosfor beskermingstegnieke, deur gebruik te maak van BH3 of die in situ vasvang van die verbindings met oorgangsmetale, was ook nie suksesvol nie. Gedurende die vasvang eksperimente het die fosfien en PdCl2 ‘n herrangskikkings-produk gevorm wat op sy eie ‘n bekende en nuttige katalisator is. Ten slotte was 'n klein biblioteek van chirale bensoksasole en 4-hidroksiebensoksasole gesintetiseer, vanaf aminosure. Om die ringsluiting te bewerkstellig was ‘n Mitsunobu reaksie gebruik. Antimikrobiese toetse met hierdie verbindings het nie enige noemenswaardige resultate opgelewer nie.