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Browsing Chemistry by Advisor "Conradie, J."
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Item Open Access Computational and characterization studies of homogeneous and heterogeneous tris(beta-diketonato) complexes with catalytic applications(University of the Free State, 2017-06) Gostynski, Roxanne; Conradie, J.; Erasmus, E.English: Nine [Mn(β-diketonato)3] [β-diketonato = dipivaloymethanato (dpm), 1; acetylacetonato (acac), 2; benzoylacetonato (ba), 3; dibenzoylmethanato (dbm), 4; trifluoroacetylacetonato (tfaa), 5; thenoyltrifluoroacetonato (tfth), 6; trifluorofuroylacetonato (tffu), 7; trifluorobenzoylacetonato (tfba), 8 and hexaflouroacetylacetonato, 9] complexes were synthesized by adapted methods from literature. An attempt was made to graft [Mn(β-diketonato)3] complexes 2-9 onto two dimensional (2-D) Si-wafer supports (S5-S12) via a silane linker. The X-ray photoelectron spectroscopy (XPS) Mn:F atomic ratio results of fluorine containing [Mn(β-diketonato)3] complexes grafted onto amino-functionalized Si-wafer (S9-S12) gave an indicaton that the [Mn(β-diketonato)3] complexes decomposed during the grafting process. Studying Mn2O3 on the hydroxylated Si-wafer surface by the use of XPS, it was confirmed that the Mn 2p photoelectron lines observed for S5-S12 consist mostly of Mn2O3 that has no interaction with the silane linker. Eight [Mn(β-diketonato)3] complexes 1-8 was wet impregnated onto various three dimensional (3-D) solid supports (S12- S28) to form [Mn(β-diketonato)3] model catalysts. Additionally a selection of [M(acac)3] complexes ([Co(acac)3], 12; [Rh(acac)3], 13, and [Ir(acac)3], 14) were grafted onto two dimensional (2-D) Si-wafer supports (S29-S31). While [M(acac)3] complexes ([Cr(acac)3], 10; [Fe(acac)3], 11; [Co(acac)3], 12; [Rh(acac)3], 13, and [Ir(acac)3], 14) were wet impregnated onto various three dimensional (3-D) solid supports (forming S32-S36). The model 2-D and 3-D catalysts were studied and characterized by the means of XPS, TGA and computational chemistry calculations. Selected model 2-D (S5, S7, S8, S12 and S29-S31) and Mn(acac)3 immobilized onto SiO2 (3-D catalysts, S14 as is and heat treated at 100, 130, 250 and 350 °C) were tested for the catalytic self-solvating reaction between ethanol and hexamethylenediisocyanate (HDI) to form hexamethylenediurethane (HDU) to mimic the industrial production of polyurethane. The model 2-D [Mn(β-diketonato)3] (S5, S7, S8 and S12) catalysts showed that as the total group electronegativity, 3(R + R'), increase a general decrease in turnover frequency (TOF) was observed. The model 2-D [M(acac)3] catalysts (S29-S31) showed that with an increase in the metal centre’s Pauling electronegativity a general increase in TOF was observed. The catalytic test on the Mn(acac)3 immobilized onto SiO2 showed that the sample heat treated at 100°C before hand has the highest TOF, which is most probably due to the loss of only one -diketonato ligand making it more active. The chromium(0) Fischer carbene complexes (Cr-FCCs) ([Cr(CO)4(PPh3)=C(OEt)(Fu)], C1; [Cr(CO)5=C(NHCy)(Fu)], C2; [Cr(CO)5=C(NHCy)(Th)], C3 and [Cr(CO)5=C(OEt)(ThTh)], C4) study was in collaboration with the research group of Dr. M Landman at the University of Pretoria. The four Cr(0) FCCs, were obtained and characterized by electrochemistry, XPS and computational chemistry calculations in this study. Penta-carbonyl Cr-FCCs [Cr(CO)5=C(OEt)(Fu)], C5, and [Cr(CO)5=C(OEt)(Th)], C6, were also supplied and anchored onto an amino-functionalized Si-wafer to create an immobilized Cr-FCCs C7 and C8. XPS results showed that the Cr(CO)5=C(OEt)(Fu)], C5, and [Cr(CO)5=C(OEt)(Th)], C6, was successfully anchored onto an amino-functionalized Si-wafer (C7 and C8). The electrochemical study of C1-4 showed that the oxidation potential (Epa) is influenced by the varied substituents on different sites of the Cr-FCCs. The oxidation order of the Cr-FCCs is: [Cr(CO)5=C(OEt)(ThTh)], C4 > [Cr(CO)5=C(NHCy)(Th)], C3 > [Cr(CO)5=C(NHCy)(Fu)], C2 > [Cr(CO)4(PPh3)=C(OEt)(Fu)], C1. The reduction followed the same trend except for the [Cr(CO)4(PPh3)=C(OEt)(Fu)], C1, complex that is reduced at a higher potential than the aminocarbene complexes, [Cr(CO)5=C(OEt)(ThTh)], C4 > [Cr(CO)4(PPh3)=C(OEt)(Fu)], C1 > [Cr(CO)5=C(NHCy)(Th)], C3 > [Cr(CO)5=C(NHCy)(Fu)], C2. The electronic energies of the different conformations obtained by the computational study showed that certain conformations are preferred over others. The computational results were in good agreement with experimental characterization method results. Computational study of HOMO and LUMO orbitals of the Cr- FCCs confirmed that the oxidation process is metal based and the reduction is based across the carbene ligand. The correlation of the oxidation potential (Epa) of the Cr0/Cr+1 redox couple and reduction potential (Epc) of the ligand based reduction with the HOMO energy (EHOMO) and LUMO energy (ELUMO) respectively, showed that with decreasing molecular orbital energy (HOMO and LUMO) an increase to more positive Epa and Epc potentials are obtained.Item Open Access O,O'-chelated titanium(IV) complexes: a synthetic, kinetic, electrochemical and structural study(University of the Free State, 2008-11) Kuhn, Annemarie; Conradie, J.Synthetic routes to prepare fluorinated tetrahedral mono-β-diketonato titanium(IV) complexes, [Cp2Ti(β)+], octahedral bis-β-diketonato titanium(IV) complexes, Ti(β)2Cl2 and Ti(β)2biphen, as well as dimeric and tetrameric titanium(IV) complexes, were developed and optimised. All complexes were fully characterised, inter alia with UV/vis, IR, 1H and 19F NMR and X-ray crystallography. Further characterisation of the complexes was done by means of electrochemical and kinetic techniques. Solution phase studies using variable temperature 1H and 19F NMR show that all octahedral Ti(β)2Cl2 and Ti(β)2biphen complexes exist in solution as an equilibrium mixture of three cis isomers which rearrange via fast (on NMR timescale) intramolecular exchange processes. The CF3-containing Ti(β)2Cl2 complexes further participate in facile monomer dimer equilibrium, involving the interconversion of chemically distinct compounds. Substitution and exchange reactions involving the ligand(s) in the octrahedrally coordinated bis(β-diketonato)Ti(IV) complexes were investigated by means of UV/Vis and NMR kinetics. Experimental and computational data were mutually consistent indicating that the substitution processes proceeded via a seven-coordinate transition state according to an associative mechanism. The ligand exchange equilibria studies of Ti(β)2biphen complexes showed that the formation of mixed-ligand complexes is a random statistical process when the exchanging β-diketonato ligands contain the same number of CF3 groups, while the equilibrium favours the mixed ligand complex when they differ by one CF3 group, Electrochemical (cyclic voltammetric) studies on the Ti(IV) complexes and the β-diketones were performed in the weakly coordinating CH3CN or DCE/[NBu4][PF6] medium. The reduction of the Ti(IV) complexes Cp2Ti(biphen), Ti(β)2biphen and Ti(β)2Cl2 which form negatively charged reduced species, are to varying degrees chemically unstable. However, the [Cp2Ti(β)]+ complexes, forming a neutral reduced species, are chemically stable. The redox process is electrochemically reversible for Cp2Ti(biphen), Ti(β)2biphen and [Cp2Ti(β)]+ and irreversible for Ti(β)2Cl2 The reduction of the uncoordinated β-diketone, forming an unstable radical anion, is not coupled with a reverse oxidation process. However, when the β-diketone contains two aromatic side groups, the radical anion is stabilised long enough that the redox process, becomes electrochemically reversible (ΔEp < 90 mV) with an increasing peak aniodic current at higher scan rates. The electron density on the titanium(IV) metal centre was manipulated by changing the R groups on the coordinated β-diketonato ligand (RCOCHCOR¢) from electron donating (R = CH3, Ph) to strongly electron withdrawing (R = CF3). The formal reduction potential, E0', of the Ti(IV) complexes (or the reduction potential, Epc, of the ligands), correlated to parameters related to electron density on the Ti centre, i.e., χR + χR' (sum of the group electronegativities of R and R' groups on the β-diketonato ligand R'COCHCOR-) and pKa of the β-diketones. Calculated (DFT) ionisation potentials of [Cp2Ti(β)]+ complexes showed a linear correlation to χR + χR', allowing one to predict electronegativities of the R and R¢ groups if the calculated ionization potential is known.Item Open Access Rhodium and iron complexes and transition states: a computational, spectroscopic and electrochemical study(University of the Free State, 2010-03) Conradie, Marrigje Marianne; Conradie, J.Abstract not availableItem Open Access Synthesis, characterization and electrochemistry of phthalocyanine derivatives with biomedical applications(University of the Free State, 2016) Oosthuizen, Dina Naudé; Fourie, E.; Swarts, J. C.; Conradie, J.English: A series of metal-free phthalocyanines, with ethylene glycol and alkyl peripheral and nonperipheral substituents, were synthesized and characterized with the aid of 1H NMR, IR and UV/vis spectroscopy. The electrochemical study (cyclic voltammetry) showed smaller peak potentials for phthalocyanines with shorter ethylene glycol substituents, thus the shorter the ethylene glycol chain, the higher the electron density of the macrocycle. Electrochemical (cyclic, square wave and linear sweep voltammetry) and computational (including the determination of relevant geometries and molecular orbitals) studies were done on a series of ruthenium phthalocyaninato complexes. A comparison of the peak oxidation potential of the first experimental oxidation process and computed energy of the highest occupied molecular orbitals (HOMO) for the series of (CO)RuPc, showed a linear correlation.. An RC1 reactor was used to study the hydrogenation reaction of 4-nitrophthalonitrile as weak as the oxidation reaction of 2,5-dihexylthiophene and 2,5didodecylthiophene utilizing dimethyldioxirane of oxidizing agent. By making use of the RC1 reactor, the reactions were followed kinetically and thermodynamically, yielding rate constants as well as reaction enthalpies. These results were compared to theoretical reaction enthalpies determined by DFT calculations. Good correlation was found between the experimentally obtained reaction enthalpies and theoretical reaction enthalpies.Item Open Access Synthesis, electrochemical, kinetic and thermodynamic properties of new ferrocene-containing betadiketonato rhodium(I) complexes with biomedical applications(University of the Free State, 2002-11) Klaas, Palesa; Swarts, J. C.; Conradie, J.English: Synthetic routes to prepare new ferrocene-containing β-diketones, FcCOCH2COR, with Fc = ferrocenyl, R = H, CH3, CH2CH3, CH(CH3)2 and C(CH3)3, have been developed. Rhodium complexes of the type [Rh(FcCOCHCOR)(cod)] were obtained in yields approaching 80% by treating these β-diketones with [Rh2Cl2-(cod)2]. Group electronegativities XR of R substituents were determined from a linear relationship between ethyl ester IR carbonyl stretching frequencies of the type RCOOCH2CH3 and group electronegativities of known R groups. pKa values of new β -diketones were determined. 1H NMR studies on FcCOCH2COR indicated that enolisation in the direction furthest from the ferrocenyl group always dominate. This finding is considered to be the result of resonance driving force rather than inductive electronic effects of substituents on the pseudo-aromatic β-diketone core. Formal reduction potentials (Eol values vs. Ag/Ag+) of the iron core in the free β-diketones, FcCOCH2COR, and in [Rh(FcCOCHCOR)(cod)] complexes as well as the peak anodic oxidation potentials, Epa, of the rhodium(I) nucleus were determined. The roles of pKa and group electronegativities on redox potentials are also discussed. Second-order rate constants, k2, for the substitution of the β-diketonato ligand, (FcCOCHCOR), from the complexes [Rh(FcCOCHCOR)(cod)] with 1,10-phenanthroline at 25°C in methanol were determined. Large negative values obtained for entropy of activation suggested an associative substitution mechanism. All substitution reactions were independent of a solvent step. Cytotoxic properties in terms of potential anticancer applications of these newly synthesised β- diketones and their rhodium complexes on cancer cells are described. Cytotoxicity was tested on HeLa, A2780 and A2780 platinum resistant cancer cells lines. Rhodium complexes were observed to be more effective in killing cancer cells than the free β-diketones.Item Open Access Synthesis, electrochemical, kinetic and thermodynamic studies of new ruthenocene-containing betadiketonato rhodium(I) complexes with biomedical applications(University of the Free State, 2004-05) Kemp, Kingsley Christian; Swarts, J. C.; Conradie, J.English: New ruthenocene-containing β -diketones 1-Ruthenocenyl-4,4,4,-trifluorobutan-1,3-dione [Hrctfa, pKa / = 7.31(3)], 1-ruthenocenylbutan-1,3-dione [Hrca, pKa / = 10.22(4)] 1-ruthenocenyl-3- phenylpropan-1,3-dione [(Hbrcm, pKa / = 11.31(4)], 1-ruthenocenyl-3-ferrocenylpropan-1,3-dione [(Hrcfcm; pKa / >13)], and 1,3-diruthenocenylpropane-1,3-dione [(Hdrcm, pKa / >13)], were prepared by the Claisen Condensation of acetylruthenocene and the appropriate ester under the influence of lithium diisopropylamide. The group electronegativity of the ruthenocenyl group (Rc) was determined from the linear relationship between the methyl ester (RCOOMe) infrared carbonyl stretching frequencies and the group electronegativities of known R groups, R = CF3, CH3, C5H5, H, Fc. The [Rh(β -diketonato)(cod)] complexes [Rh(rctfa)(cod)], [Rh(rca)(cod)], [Rh(brcm)(cod)], [Rh(rcfcm)(cod)] and [Rh(drcm)(cod)] were obtained by treating the appropriate β -diketones (Hrctfa, Hrca, Hbrcm, Hrcfcm and Hdrcm) with [Rh2(cod)2Cl2]. Kinetics results for the conversion of the β -diketones (Hrctfa, Hrca, Hbrcm, Hrcfcm and Hdrcm) from the enol to the keto form and vice versa are reported. Kinetics results for the substitution of β -diketonato ligand from the [Rh(β -diketonato)(cod)] complexes ( [Rh(rctfa)(cod)], [Rh(rca)(cod)], [Rh(brcm)(cod)], [Rh(rcfcm)(cod)] and [Rh(drcm)(cod)]) with 1,10-phenantroline in methanol are also presented. Large negative activation entropy values obtained, suggested an associative substitution mechanism. All substitution reactions had no observable mechanistic solvent pathway contribution. Oxidation potentials (Epa vs Ag/Ag + ) for the ruthenium core in the free β -diketones (Hrctfa, Hrca, Hbrcm, Hrcfcm and Hdrcm), as well as in the [Rh(β -diketonato)(cod)] complexes ([Rh(rctfa)(cod)], [Rh(rca)(cod)], [Rh(brcm)(cod)], [Rh(rcfcm)(cod)] and [Rh(drcm)(cod)]) are reported. The peak anodic potentials (Epa vs Ag/Ag + ) for oxidation of the rhodium(I) center were determined.Item Open Access Synthesis, electrochemistry and density functional theory calculations on chrome and cobalt carbene and betadiketonato complexes(University of the Free State, 2014) Liu, Renyuan; Conradie, J.English: Two series of metal(β-diketonato)3 complexes were synthesized: tris(β-diketonato)chromium(III) complexes (where β-diketonato = [R1COCHCOR2]- = acac, ba, dbm, tfba, tfth, tffu, tfaa, hfaa) and tris(β-diketonato)cobalt(III) complexes (where β-diketonato = acac, ba, dbm, tfba, tfaa). These paramagnetic complexes were characterized by mass spectroscopy, X-ray crystallography and melting point measurements. The electrochemical behaviour of tris(β- diketonato)chromium(III) complexes was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and square wave voltammetry (SWV). The reduction potentials of the CrIII(β-diketonato)3 → CrII(β-diketonato)3 process correlate linearly with the following electronic parameters: 1) the acid dissociation constant (pKa) of the uncoordinated β-diketonato ligands, 2) the total electronegativities (Σx) of the side groups (R1 and R2) on the β-diketonato ligands, and 3) the total Hammett sigma constant (Σσ) of the side groups (R1 and R2) on the β-diketonato ligands. DFT-calculations were done on both series of these metal(β-diketonato)3 complexes. Molecular geometry, spin state and respective population of possible isomers were calculated in this study. The understanding of crystal structures was complemented by using DFT-results. For CrIII(β-diketonato)3 complexes, linear dependence was found between their reduction potentials and electron affinity (EA), as well as between reduction potentials and the energies of the lowest unoccupied molecular orbitals (ELUMO). Electrochemical behaviour of chromium(0) carbene complexes was investigated by cyclic voltammetry. The difference in oxidation potential of fac/mer isomers was observed for the first time for chromium(0) carbene complexes and discussed in this study. DFT-calculations revealed the following linear relationships with the redox process of Cr(0) carbene complexes: 1) the linear dependence between the cathodic potential (Epc) and energies of the lowest unoccupied orbitals (ELUMO), and 2) the linear dependence between the anodic potential (Epa) and energies of the highest occupied orbitals (EHOMO).