59Co NMR, a tool for the study of the structure, reactivity and supramolecular chemistry of Co(III) complexes derived from a series of N-alkyl-N-alkyl(aryl)-N’-acyl(aroyl)thioureas
| dc.contributor.advisor | Koch, Klaus Robert | en_ZA |
| dc.contributor.advisor | Gerber, Wilhelmus Jacobus | en_ZA |
| dc.contributor.author | Barnard, Ilse | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. | en_ZA |
| dc.date.accessioned | 2020-02-13T07:39:00Z | en_ZA |
| dc.date.accessioned | 2020-04-28T15:10:20Z | en_ZA |
| dc.date.available | 2020-02-13T07:39:00Z | en_ZA |
| dc.date.available | 2020-04-28T15:10:20Z | en_ZA |
| dc.date.issued | 2020-03 | en_ZA |
| dc.description | Thesis (PhD)--Stellenbosch University, 2020. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: A large library of Co(III) complexes, derived from selected monopodal and bipodal N,N- dialkyl-N’-acyl(aroyl)thioureas, have been synthesized and characterized. These ligands form tris(chelated) complexes in the thermodynamically more stable fac geometry with the cobalt metal. The monopodal ligands, and their corresponding Co(III) complexes, were separated into two groups based on the two R substituents of the C(S)-NRR’ function. The first group were named the symmetrically substituted acylthiourea derivatives, where R = R’. Due to the increased stability provided by the chelate effect as well as the selective population of the lower-energy d-orbitals, such complexes are generally expected to be kinetically stable in solution. Nonetheless, the ‘symmetrical’ Co(III) complexes were utilized for the study of the unexpected, slow and spontaneous ligand exchange reaction between non-identical homoleptic pairs of low-spin d⁶ octahedral fac-[Co(LA-κS,O)3] and fac-[Co(LB-κS,O)3] complexes in organic solvents. The exchange reaction between these complexes result in mixtures of their corresponding heteroleptic fac-[Co(LA-κS,O)2(LB-κS,O)] and fac-[Co(LA-κS,O)(LB-κS,O)2] complexes in solution. This discovery was followed by a quantitative determination of the ligand exchange equilibria as well as a relative rate study, as a function of temperature, of the reaction using rp-HPLC. It was then established that the high chemical shift sensitivity of ⁵⁹Co NMR is a powerful tool for the easy characterization of the Co(III) complexes derived from symmetrically substituted acylthioureas in solution. The utility of ⁵⁹Co NMR as a spectroscopic tool was exemplified after utilizing this technique for further additional studies of factors shown to dramatically affect the relative rate of ligand exchange in these complexes, specifically light and solvent. The second group of monopodal acylthiourea ligands investigated were named the asymmetrically substituted acylthioureas, where R ≠ R’. The partial double bond character in the C-N bond of the C(S)-NRR’ function results in the E,Z configurational isomerism of these ligands in solution. The isomerism is expressed as duplicate resonances in the ¹H NMR spectra of the uncoordinated ‘asymmetrical’ acylthiourea ligands. The Z to E isomer ratio varies depending on the two R and R’ substituents of the thiourea moiety. Notably, the isomerism in the uncoordinated ligands is passed on to the Co(III) chelates after coordination. As for the symmetrically substituted acylthiourea Co(III) complexes, we find that the ⁵⁹Co NMR chemical shift is very sensitive to the structure of the asymmetrical fac-[Co(Lⁿ-κS,O)3] complexes in solution. Significantly, the presence of the four, theoretically possible, fac- [Co(EEE-Lⁿ-κS,O)3], fac-[Co(EEZ-Lⁿ-κS,O)3], fac-[Co(EZZ-Lⁿ-κS,O)3] and fac-[Co(ZZZ-Lⁿ- κS,O)3] isomers is readily observable by means of ⁵⁹Co NMR, which shows four well-resolved resonances. From the relative peak integrals of the ⁵⁹Co NMR peaks, a semi-quantitative estimate of the relative amounts of the configurational isomers in solution was possible, although assignment of the isomers is not trivial. The assignment of the ⁵⁹Co peaks to each of the EEE, EEZ, EZZ and ZZZ configurational isomers of the asymmetrical fac-[Co(Lⁿ-κS,O)3] complexes were based on the relative E/Z ratio of the uncoordinated ligands, which was established from their ¹H NMR spectra. However, this assignment assumes that the relative E/Z ratio does not vary significantly during coordination to cobalt and remains therefore ambiguous. The distribution of the EEE, EEZ, EZZ and ZZZ configurational isomers was shown to be dependent on the solvent used during the analyses. Moreover, we evaluated the temperature needed to lift the barrier to rotation in the C-N bond of the coordinated ligands. Finally, the ⁵⁹Co NMR trends of several complexes isolated for single crystal X-ray diffraction analysis were complemented by DFT linear transit calculations of their configurational isomers. Finally, we investigate the interesting coordination chemistry of the well-ordered and multinuclear coordination systems of the bipodal acylthiourea analogues, namely aroylbis(N,N-dialkylthioureas). Two ligands were selected for this purpose, including isophthaloylbis(N,N-diethylthiourea) and a bipodal ligand with a modified aromatic spacer derived from catechol. These were utilized as pre-programmed chelating ligands to form metallamacrocyclic octahedral facial Cobalt(III) complexes via self-assembly. The latter catechol-spaced ligand was used for the synthesis of a number of oligometallic Co(III) complexes by one-pot reactions of the ligand, Co³⁺ and a variety of monovalent cations, to form metallacryptates of type {M⁺ ⊂ [Co2(L-κS,O))3]}(PF6), M⁺ = K⁺, Rb⁺, Cs⁺ and NH4+. A significant discovery, owing to the unique sensitivity of the ⁵⁹Co nucleus, was the instrumental role ⁵⁹Co NMR played in our attempt to characterize the metallacryptates and to determine their conditional stabilities in solution. This was achieved by way of several biphasic exchange experiments of cations between an aqueous and non-aqueous phase. This is a novel discovery that has allowed for the study of various factors shown to effect the stability of the metallacryptates in solution. | en_ZA |
| dc.description.abstract | AFRIKAANS OPSOMMING: ʼn Groot reeks van Co(III) komplekse, afgelei van verskeie monopodal en bipodal N,N-dialkiel- N’-asiel(ariel)tioureas, was gesintetiseer en gekaraktiseer. Hierdie ligande vorm tris(chelaat) komplekse in die termodinamiese meer stabiele fac geometrie met die kobalt metaal. Die monopodal ligande, en hul ooreenstemmende Co(III) komplekse, was opgedeel in twee verskillende groepe gebaseer op die twee R substituente van die C(S)-NRR’ eenheid. Die eerste groep, was die simmetriese afgeleide asieltioureas genoem, waar R = R’. Danksy die stabiliteit wat deur die chelaat effek voorsien word sowel as die selektiewe vervulling van die laer-energie d-orbitale, word daar gewoonlik verwag van sulke komplekse om kineties stabiel in oplossing te wees. Nietemin, die ‘simmetriese’ Co(III) komplekse was gebruik tydens die studie van die onverwagse, stadige en spontane ligand uitruilingsreaksie tussen die nie-identiese ‘homoleptic’ pare lae-spin d⁶ oktahedrale fac-[Co(LA-κS,O)3] en fac-[Co(LB-κS,O)3] komplekse in organiese oplosmiddels. Die uitruilings- reaksie tussen hierdie komplekse het gelei na ʼn mengsel van hul ooreenstemmende ‘heteroleptic’ fac-[Co(LA-κS,O)2(LB-κS,O)] en fac-[Co(LA-κS,O)(LB- κS,O)2] komplekse in oplossing. Hierdie ontdekking het gelei na ʼn kwantitatiewe bepaling van die ligand uitruiling ekwilibria sowel as ʼn studie van die relatiewe spoed, as n funksie van die temperatuur, van die reaksie deur middel van rp-HPLC. Dit was later bepaal dat die hoë sensitiwiteit van die chemiese verskuiwing van ⁵⁹Co KMR ʼn sterk hulpbron is vir die maklike karakterisering van alle Co(III) komplekse afgelei van die simmetriese gesubstitueerde asieltioureas in oplossing. Die nut van ⁵⁹Co KMR as ʼn spektroskopiese tegniek was uitgebeeld nadat dit gebruik is vir verdere addisionele studies van faktore wat ʼn dramatiese effek het op die relatiewe spoed van ligand uitruiling in hierdie komplekse, spesifiek lig en oplosmiddel. Die tweede groep van monopodal asieltiourea ligande wat ondersoek is was die asimmetriese asieltioureas genoem, waar R ≠ R’. Die gedeeltelike dubbelbinding karakter in die C-N binding van die C(S)-NRR’ eenheid lei na E,Z konfigurasie isomere van hierdie ligande in oplossing. Die isomere word uitgedruk as duplikaat resonanse in die ¹H KMR spektra van die ongekoördineerde asimmetriese asieltiourea ligande. Die Z tot E isomeer verhouding wissel afhangende van die twee R en R’ substituente van die tiourea eenheid. Noemenswaarlik word die isomere in die ongekoördineerde ligande oorgedra na die Co(III) chelate tydens koördinering. Soos vir die simmetriese gesubstitueerde Co(III) komplekse, vind ons dat die ⁵⁹Co KMR chemiese verskuiwings baie sensitief is vir die struktuur van die asimmetriese fac-[Co(L-κS,O)3] komplekse in oplossing. Dit is indrukwekkend dat die teenwoordigheid van die vier, teoreties moontlike, fac-[Co(EEE-Lⁿ-κS,O)3], fac-[Co(EEZ-Lⁿ-κS,O)3], fac-[Co(EZZ-Lⁿ- κS,O)3] en fac-[Co(ZZZ-Lⁿ-κS,O)3] isomere maklik waarneembaar is deur middel van ⁵⁹Co KMR, wat duidelik vier resonanse toon. Van die relatiewe piek integrale van die ⁵⁹Co KMR pieke was ʼn semi-kwantitatiewe beraming van die relatiewe aantal konfigurasie isomere in oplossing moontlik, alhoewel toekenning van die isomere is nie voor die hand liggend nie. Die toekenning van die ⁵⁹Co pieke tot die EEE, EEZ, ZZE en ZZZ-konfigurasie isomere was gebaseer op die relatiewe E/Z verhouding van die ongekoördineerde ligande, wat bepaal is van hul ¹H KMR spektra. Hierdie manier van toekenning aanvaar alhoewel dat die relatiewe E/Z verhouding nie merkwaardig verander tydens koördinering aan kobalt nie en bly dus onseker. Die verspreiding van die EEE, EEZ, ZZE en ZZZ-konfigurasie isomere was gewys as afhanklik van die oplosmiddel wat tydens die analise gebruik word. Verder het ons die temperatuur beraam wat benodig is om die hindernis tot rotasie in die C-N binding in die gekoördineerde ligande op te hef. Laastens, die ⁵⁹Co KMR tendense van verskeie komplekse wat geïsoleer is vir enkel-kristal X-straal diffraksie analise was ook gekomplementeer deur DFT lineêre deurgangsberekeninge van hul konfigurasie isomere. Laastens het ons die interessante koördinasie chemie van die goed-geordende en multi-nukleêre koördinasie stelsels van die bipodal asieltiourea analoë ondersoek, naamlik arielbis(N,N- dialkieltioureas). Twee ligande was vir hierdie doel geselekteer, insluitend isophtalielbis(N,N- dietieltiourea) en ʼn bipodal ligand met ʼn gewysigde aromatiese ‘spacer’ afgelei van catechol. Hierdie ligande was gebruik as vooraf geprogrammeerde chelaat ligande om metallamakrosikliese oktahedrale facial Cobalt(III) komplekse te vorm deur middel van self- samestelling. Die laasgenoemde ‘catechol-spaced’ ligand was gebruik vir die sintese van ʼn verskeidenheid van oligometalliese Co(III) komplekse deur ʼn een-pot reaksie van die ligand, Co³⁺ en ʼn verskeie aantal monovalent katione, om sodoende metallacryptates te vorm van die tipe {M⁺ ⊂ [Co2(L-κS,O))3]}(PF6), waar M⁺ = K⁺, Rb⁺, Cs⁺ en NH4 . ʼn Betekenisvolle + ontdekking, danksy die unieke sensitiwiteit van die ⁵⁹Co kern, was die instrumentele rol wat ⁵⁹Co KMR gespeel het in die poging om die metallacryptates te karakteriseer en hul kondisionele stabiliteit in oplossing te bepaal. Dit was bereik deur middel van verskeie bifasiese uitruilings eksperimente van katione tussen ʼn waterige en nie-waterige fase. Dit is 'n nuwe ontdekking wat toegelaat het vir die studie van verskeie faktore wat die stabiliteit van die metallacryptates in oplossing affekteer. | af_ZA |
| dc.description.version | Doctorate | en_ZA |
| dc.embargo.terms | 2022-03-01 | en_ZA |
| dc.format.extent | xxi, 193 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/108340 | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University, 2020 | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Supramolecular chemistry | en_ZA |
| dc.subject | Acylthioureas | en_ZA |
| dc.subject | Ligand exchange | en_ZA |
| dc.subject | Configurational isomerism | en_ZA |
| dc.subject | Co(III) metallacryptates | en_ZA |
| dc.subject | Cobalt compounds | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | 59Co NMR, a tool for the study of the structure, reactivity and supramolecular chemistry of Co(III) complexes derived from a series of N-alkyl-N-alkyl(aryl)-N’-acyl(aroyl)thioureas | en_ZA |
| dc.type | Thesis | en_ZA |