A crystallographic, computational and mechanistic study of rhodium enaminoketonato complexes
| dc.contributor.advisor | Roodt, Andreas | |
| dc.contributor.advisor | Steyl, Gideon | |
| dc.contributor.author | Venter, Gertruida Jacoba Susanna | |
| dc.date.accessioned | 2017-04-07T07:00:17Z | |
| dc.date.available | 2017-04-07T07:00:17Z | |
| dc.date.issued | 2013-01 | |
| dc.description.abstract | English: This study includes the investigation of enaminoketones as ligand systems in rhodium complexes with possible future application in catalysis. In order to evaluate the influence of substituents on the phenyl ring on activity of the complex, a range of 4-(phenylamino) pent-3-en-2-onate (PhonyH) derivatives with chloride substituents on different positions on the phenyl ring were synthesized and characterized through X-ray crystallography as well as infrared and NMR spectroscopy. The compounds crystallize in a range of space groups and varying crystal systems, are stable in air over a period of several years and soluble in most solvents. The optimized structures of these compounds were calculated using DFT methods. The relative energies of the optimized structures adopt a cumulative nature - the relative energy of 2,4-C-PhonyH with regard to unsubstituted PhonyH is roughly equal to the sum of the relative energies of 2-CIPhonyH and 4-CI-PhonyH, while the relative energy of 2,6-Cb-PhonyH is twice the relative energy of 2-CI-PhonyH. The distortion of the phenyl ring from the ideal planar position presented in the calculated structures corresponds to the distortion observed in the solid state. The synthesis of the uncoordinated compounds was followed by the synthesis and characterization of a range of substituted dicarbonyl-[ 4-(phenylamino )pent-3-en-2-onato]- rhodium(I) complexes. The complexes crystallized in varying crystal systems and space groups. The trans influence of nitrogen was confirmed through the difference in the Rh-CO bonds: the Rh-C bond trans to the nitrogen atom is longer than the Rh-C bond trans to oxygen. The impact of the chloride substituents was observed from differences in geometrical parameters and is supported by information from the calculated structures and literature. The optimized structures of these complexes were calculated using OFT methods, and their optimized energies follow the same cumulative trend as observed in the uncoordinated compounds. A range of carbonyl-[4-(phenylamino) pent-3-en-2-onato ]-triphenylphosphine-rhodium(l) {[Rh(N,O-Bid)(CO)(PPh3)]} complexes were synthesized and characterized, containing both electron-withdrawing chloride atoms and electron-donating methyl groups. These complexes displayed poor solubility, but once dissolved, were stable over a period of several months. Isomorphism was observed between [Rh(2,6-Ch-Phony)(CO)(PPh3)] and [Rh(2,6-Me2- Phony)(CO)(PPh3)] . [Rh(2,6-Ch-Phony)(CO)(PPh3)] and [Rh(2,6-Me2-Phony)(CO)(PPh3)] were chosen to investigate the exchange of triphenylphosphine coordinated in [Rh(N,O-Bid)(CO)(PPh3)] complexes with the uncoordinated phosphine, allowing for the comparison of the electronic effect of the substituents on the phenyl rings. The method chosen for the investigation was magnetization spin transfer, an NMR technique which utilizes the magnetic properties of nuclei and determines the kinetic properties of the exchange reaction by following the rate at which magnetic equilibrium is restored. The rate of the phosphine exchange reaction in [Rh(2,6-Ch-Phony)(CO)(PPh3)] was determined as approximately three times faster than the rate of reaction for phosphine exchange in [Rh(2,6-Me2-Phony)(CO)(PPh3)]. The decreased electron density surrounding the rhodium atom in [Rh(2,6-C12-Phony)(CO)(PPh3)] allows for the reversal of the reaction as indicated by the k-, values of approximately 11 s-1 calculated from the [Rh(2,6-Cl2Phony)(CO)(PPh3)] exchange reaction. This value is absent in the reaction of the [Rh(2,6-Me2Phony)(CO)(PPh3)] complex. The activation parameters of the exchange reaction in [Rh(2,6-C12-Phony)(CO)(PPh3)] (∆H‡ = 25(3) kJ.mol-l and ∆S‡ = -117(9) J.K-l.mol-l) correlate well with the parameters of the exchange reaction in [Rh(2,6-Me2-Phony)(CO)(PPh3)] (∆H‡ = 24(4) kJ.mol-l and ∆S‡ = -124(12) J.K-I.mol-1I). In both cases the value for entropy, ∆S‡, is negative, indicating an associative mechanism. The relative contribution of T∆S‡ to ∆G‡ is approximately 60% for both complexes, whereas the enthalpy (∆H‡) terms are correspondingly small. This indicates that the activation process is primarily controlled by entropy and involves the formation of a stable, well-ordered transition state while bond weakening is less important. The relatively constant values for ∆G‡ imply that the exchange reaction is not very sensitive to changes in temperature. | en_ZA |
| dc.description.abstract | Afrikaans: Hierdie studie sluit die ondersoek van enaminoketone as ligandstelsel in rodium komplekse in, met toepassingsmoontlikhede in katalise. Ten einde die invloed van substituente op die fenielring op die aktiwiteit van die kompleks te evalueer is 'n reeks van 4-(fenielamino) pent-3- en-2-onaat (PhonyH) derivate met chloried substituente op verskillende posisies op die feniel ring vervaardig en gekarakteriseer deur X-straal kristallografie sowel as KMR spektroskopie. Die verbindings kristalliseer in 'n reeks ruimtegroepe en verskeie kristalstelsels, is stabiel in lug oor 'n tydperk van 'n aantal jare en oplosbaar in die meeste oplosmiddels. Die geoptimiseerde strukture van hierdie verbindings is bereken deur OFT metodes. Die relatiewe energieë van die geoptimiseerde strukture neem 'n kumulatiewe natuur aan - die relatiewe energie van 2,4-Cl2- PhonyH ten opsigte van ongewysigde PhonyH is ongeveer gelyk aan die som van die relatiewe energieë van 2-CI-PhonyH en 4-CI-PhonyH, terwyl die relatiewe energie van 2,6-Cl-PhonyH twee maal die energie van 2-CI-PhonyH is. Die vervorming van die feniel ring uit die ideale planêre posisie soos voorgelê in die berekende strukture stem ooreen met die vervorming waargeneem in die vaste toestand. Die sintese van die ongekoërdineerde verbindings is opgevolg deur die sintese en karakterisering van 'n reeks gesubstitueerde dikarboniel-[ 4-(fenielamino )pent-3-en-2-onato ]-rodium(l) komplekse. Die komplekse kristalliseer in verskillende kristalstelsels en ruimtegroepe. Die trans invloed van stikstof is bevestig deur die verskil in die Rh-CO bindings: die Rh-C binding trans ten opsigte van die stikstof atoom is langer as die Rh-C binding trans ten opsigte van die suurstof atoom. Die impak van die chloried substituent is waargeneem vanaf die verskille in geometriese parameters en word ondersteun deur inligting vanaf die berekende strukture en literatuur. Die geoptimiseerde strukture van hierdie komplekse is bereken deur middel van DFT metodes en volg dieselfde kumulatiewe neiging as wat waargeneem is in die ongekoërdineerde verbindings. 'n Reeks karboniel-[ 4-(fenielamino )pent-3-en-2-onato ]-trifenielfosfien-rodium(l) {[Rh(N,OBid)( CO)(PPh3)]} komplekse is vervaardig en gekarakteriseer, en bevat beide elektrononttrekkende chloried atome en elektronskenkende metiel groepe. Hierdie komplekse vertoon swak oplosbaarheid, maar is stabiel oor 'n tydperk van verskeie maande sodra dit opgelos is. Isomorfisme is waargeneem tussen [Rh(2,6-Cl2-Phony)(CO)(PPh3)] en [Rh(2,6-Me2- Phony)(CO)(PPh3)] . [Rh(2,6-Cb-Phony)(CO)(PPh3)] en [Rh(2,6-Me2-Phony)(CO)(PPh3)] is gekies om die uitruiling tussen trifenielfosfien gekoordineer in [Rh(N,O-Bid)(CO)(PPh3)] komplekse met die ongekoërdineerde fosfien te ondersoek, wat die vergelyking van die elektroniese effek van die substituente op die feniel ringe toelaat. Die gekose metode vir die ondersoek is magnetisasie spin oordrag, OnKMR tegniek wat die magnetiese eienskappe van nuklei benut en die kinetiese eienskappe van die uitruilingsreaksie bepaal deur die tempo van die herstel van die magnetiese ewewig te volg. Die tempo van die fosfienuitruilingsreaksie in [Rh(2,6-Cl2-Phony)(CO)(PPh3)] is vasgestel as ongeveer drie maal vinniger as die reaksietempo van fosfienuitruiling in [Rh(2,6-Me2- Phony)(CO)(PPh3)]. Die verminderde elektrondigtheid rondom die rodium atoom in [Rh(2,6- Cl2-Phony)(CO)(PPh3)] laat die ommekeer van die reaksie toe, soos aangedui deur die k-1, waardes van ongeveer 11 S-I, bereken vanaf die [Rh(2,6-C12-Phony)(CO)(PPh3)] uitruilingsreaksie. Hierdie waarde is afwesig in die reaksie van die [Rh(2,6-Me2- Phony)(CO)(PPh3)] kompleks. Die aktiveringsparameters van die uitruilingsreaksie in [Rh(2,6- Cl2-Phony)(CO)(PPh3)] (∆H‡ = 25(3) kJ.mol-1 en ∆S‡ = -117(9) J.K-1.mol-1`) stem goed ooreen met die parameters van die uitruilingsreaksie in [Rh(2,6-Me2-Phony)(CO)(PPh3)] (∆H‡ = 24(4) kJ.mo1-1 en ∆S‡ = -124(12) J.K-1.mo1-l). In beide gevalle is die waarde vir entropie, ∆S‡, negatief, n aanduiding van On assosiatiewe meganisme. Die relatiewe bydraes van T∆S‡ tot ∆G‡ is ongeveer 60% vir beide komplekse, terwyl die entalpie (∆H‡) terme ooreenkomstig klein is. Dit dui aan dat die aktiveringsproses primêr deur entropie beheer word en behels die vorming van On stabiele, goed georganiseerde oorgangstoestand terwyl bindingsverswakking minder belangrik is. Die relatiewe konstante waardes vir ∆G‡ impliseer dat die uitruilingsreaksie nie baie sensitief is ten opsigte van veranderinge in temperatuur nie. | af |
| dc.description.sponsorship | University of the Free State Strategic Academic Cluster Initiative | en_ZA |
| dc.description.sponsorship | SASOL | en_ZA |
| dc.description.sponsorship | South African National Research Foundation (SA-NRF ITHRIP) | en_ZA |
| dc.description.sponsorship | Inkaba ye Afrika Research Initiative | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/6059 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Rhodium | en_ZA |
| dc.subject | Enaminoketone | en_ZA |
| dc.subject | Dicarbonyl | en_ZA |
| dc.subject | X-Ray crystallography | en_ZA |
| dc.subject | Density functional theory | en_ZA |
| dc.subject | Phosphine exchange | en_ZA |
| dc.subject | NMR | en_ZA |
| dc.subject | Magnetization spin transfer | en_ZA |
| dc.subject | Activation parameters | en_ZA |
| dc.subject | Electrochemical analysis | en_ZA |
| dc.subject | Reaction kinetics | en_ZA |
| dc.subject | Thesis (Ph.D. (Chemistry))--University of the Free State, 2013 | en_ZA |
| dc.title | A crystallographic, computational and mechanistic study of rhodium enaminoketonato complexes | en_ZA |
| dc.type | Thesis | en_ZA |