Masters Degrees (Chemistry)

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Browsing Masters Degrees (Chemistry) by Author "Brink, Alice"

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    A crystallographic and mechanistic study of Mn triad complexes as model radiopharmaceuticals
    (University of the Free State, 2015-02) Mokolokolo, Petrus Pennie; Visser, Hendrik; Brink, Alice
    A series of fac-manganese(I) tricarbonyl complexes were synthesized and analysed to better understand the chemical properties of the group 7 radiopharmaceutical model complex. Five new complexes containing N,O’, N,N’,O and O,O’ donating functionalities were successfully synthesized. The Schiff base ligands, SalH-mTol = 2-(m-tolyliminomethyl)phenol, SalH-cyHex = 2-(Cyclohexyliminomethyl)phenol and 5Me-SalH-Hist = 2-(2-imidazol-4-yl)ethyliminomethyl-5-methylphenol are derived from a salicylidene backbone. The O,O’ are the β-diketone ligands (acetylacetone= AcacH and trifluoroacetylacetone = TfacacH). The ligands were strategically selected to ensure systematic variation in electronic and steric effects. The synthesis of complexes fac-[Mn(Sal-mTol)(CO)3]2, fac-[Mn(Sal-CyHex)(CO)3]2, fac-[Mn(4-Me-Sal-Hist)(CO)2], fac-[Mn(Acac)(CO)3(OHCH3)] and fac-[Mn(Tfacac)(CO)3(OHCH3)] is reported and all the complexes were characterised by IR, NMR, UV-Vis and single crystal X-Ray diffraction to better understand the solid and solution state. All complexes afford an octahedral environment around the metal centre with the chelating ligands and three carbonyl ligands in facial arrangement. The octahedron is satisfied by a bridging oxygen atom in the dimeric complexes fac-[Mn(Sal-mTol)(CO)3]2 and fac-[Mn(Sal-CyHex)(CO)3]2, and a methanol molecule in complexes fac-[Mn(Acac)(CO)3(OHCH3)] and fac-[Mn(Tfacac)(CO)3(OHCH3)] Substitution kinetics of the coordinated methanol molecule in complexes fac-[Mn(Acac)(CO)3(OHCH3)] and fac-[Mn(Tfacac)(CO)3(OHCH3)] by a neutral imidazole ligand was evaluated. The negative values obtained for the activation entropy parameter, Δ𝑆��≠ [-88(1) J K-1 mol-1 and -18(6) J K-1 mol-1], in both complexes is suggestive of an associative type mechanism. As anticipated, the overall rate of methanol substitution in complex fac-[Mn(Acac)(CO)3](OHCH3)] is faster than in fac-[Mn(Tfacac)(CO)3(OHCH3)] as indicated by the overall larger k1 and K1, due to the presence of electron withdrawing fluorine atoms on the ligand backbone.
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    ItemOpen Access
    A mechanistic study of sulphur, nitrogen and oxygen donor bidentate ligand interactions on the rhenium (I) tricarbonyl core
    (University of the Free State, 2015-12) Nkoe, Pheello Isaac; Schutte-Smith, Marietjie; Brink, Alice
    English: The nuclear properties of rhenium (186/188Re) and technetium (99mTc) are used for their application as diagnostic and therapeutic radiopharmaceuticals. Researchers have shown a significant interest in rhenium and technetium tricarbonyl complexes of the form fac-[M(CO)3X(L,L’-Bid)]n where M = Tc(I) or Re(I), X = entering monodentate ligand and L-L’-Bid = different donor atom bidentate ligands, as potential diagnostic and therapeutic radiopharmaceuticals. These fac-[M(CO)3X(L,L’-Bid)]n type complexes are prepared from the starting synthons fac-[M(CO)3(Br3)]2- and fac-[M(CO)3(H2O)3]+ that was initially prepared by Alberto et al. in 1999. This starting synthon is a favourite all around for the synthesis of potential radiopharmaceuticals due to the easy preparation and the stability of fac-[M(CO)3(H2O)3]+ in aqueous solution in the pH range of 2 - 12 for several hours. The carbonyl ligands are tightly coordinated to the metal and form the stable fac-[M(CO)3]+ core. The three bromido or water ligands can be easily substituted by different functional groups such as thioethers, thiols, phosphines and amines. The aim of this study was to investigate the ability of the chosen donor atom N,O; S,S’; S,O bidentate and S,S’S” tridentate ligands to coordinate to the fac-[Re(CO)3]+ core. The results were compared to previous studies reported on N,O and O,O’ bidentate ligand systems to observe the variation in coordination behaviours. The chosen ligands include: 5-phenylazo-8-hydroxyquinoline, 5-(m-Tol)azo-8-hydroxyquinoline, 5-(2,3- diMephenyl)azo-8-hydroxyquinoline, 5-(2,6-diMe phenyl)azo-8-hydroxyquinoline, 5- (3,4-diMe phenyl)azo-8-hydroxyquinoline, methyl benzo[b]thiophene-2-carboxylate, benzothiophene-2-methanol, 2-mercaptophenol, 2-methoxythiophenol, 5-bromo-2,2`- bithiophene, 2,2′-bithiophene-5-carboxylic acid, benzene-1,2-dithiol, toluene-3,4- dithiol, and 2,2`-thiodiethanethiol. The synthesis of the complexes are described in Chapter 4 and characterized by IR, UV/Vis, NMR (1H and 13C) and elemental analysis. The following crystal structures were obtained fac-[Re2(CO)6(TS)(Py)] (1), fac-[Re2(CO)6PPh3(BSOPhC)2(Py)] (2), fac- [NEt4][Re2(CO)6(BSOPhC)3] (3) and fac-[Re2(CO)6(m-TolBSPh)2] (4). All four of the structures has four molecules per unit cell (Z = 4). (1) and (4) crystallized in the P1̅ space group while (2) and (3) crystallized in a monoclinic space group. In all four these structures the ligands form sulphur bridges between two rhenium (I) centres. The Re-CO bond distances of all the crystal structures range from 1.88(3) Å to 1.95(10) Å and the Re-S bond distances vary from 2.44(2) Å to 2.56(7) Å. (2) has a Re-P bond distance of 2.51(12) Å and a Re-N bond distance of 2.24(4) Å. The S-Re-S bond angles range from 76.26(3) ° to 94.99(8) ° and the Re-S-Re bond angles from 87.28(9) ° to 100.60(4) ° with the non-bonding rhenium to rhenium distances of 3.796(8) Å for (1), 3.845(10) Å for (2), 3.488(10) Å for (3) and 3.654(16) Å for (4). The non-bonding Re…Re distances are directly proportional to the Re-S-Re angles and follow the following trend: (3) < (4) < (1) < (2). A fairly good comparison could be made between previously reported structures with S,S’; S,O; N,O and O,O’-bidentate ligands coordinated to the fac-[Re(CO)3]+ core. The structure of (4) has been reported before and a very good correlation is found between this structure and the reported structure. After an in depth study it was confirmed that the structures of all the compounds with S,O; S,S’ and S,S’,S’’ ligands have to be analysed by single crystal XRD or at least a quantitative NMR study. For one ligand system (BSOPhC), two different structures were obtained with only a slight change in the synthetic procedure. It is not that easy to determine and speculate the bonding modes of these type of ligands. Therefore a complete crystallographic study will form part of the future work for this project. Excellent results were obtained for anti-mitochondrial activity screening for five compounds. The next step will be to improve the solubility of these complexes, especially in water as solvent; this illustrates the possible use of these compounds as potential radiopharmaceuticals.
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    ItemOpen Access
    Phosphorus bidentate ligand interaction at platinum group metals: A catalytic and solid state study
    (University of the Free State, 2015-02) Kama, Dumisani Vincent; Visser, Hendrik G.; Brink, Alice
    English: Hydroformylation of alkenes (olefins) is one of the world’s leading aldehyde producing process. The resulting aldehydes can easily be converted to secondary products such as alcohols for production of plasticizers and detergents. Recent studies are directed towards the production of highly selective catalysts as linear aldehydes are the most desired products. A number of phosphine ligands have been investigated regarding this process, showing that fine tuning of the ligands electronic and steric properties significantly affects the activity and selectivity of a catalyst. A range of diphosphinoamine (PNP) ligands with various substituents on the nitrogen atom were synthesized and characterized, namely (1) N,N-Bis(diphenylphosphino)-p-toluidine [CH3-Ph-PNP],(2) N,N-Bis(diphenylphosphino)-4-chloroaniline [Cl-Ph-PNP], (3) N,N-Bis(diphenylphosphino)-4-fluoroaniline [F-Ph-PNP], (4) N,N-Bis(di-p-tolylphosphino)-p-toluidine [5-p-tolyl-PNP], (5) N,N-Bis(di-p-tolylphosphino)-o-toluidine [4-p-tolyl-o-tol], (6) N,N-Bis(di-p-tolylphosphino)cyclohexylamine [Chzyl-4-p-tolyl] and (7) N,N-Bis(di-p-tolylphosphino)cyclobutylamine [Cbutyl-4-p-tolyl] (see Figure 1). These ligands were systematically synthesized to induce different steric and electronic properties on the nitrogen atom. All the ligands were coordinated to Pt(II) and Pd(II) metals to serve as models for Rh(I) pre-catalysts systems to be used in hydroformylation of 1-octene. Metal complexes which produced crystals suitable for X-ray data analysis were (A) Dichloro-[N,N-Bis(di-p-tolylphosphino)-p-toluidine-k2P,P’]platinum(II) [Pt(5-p-tolyl-PNP)Cl2], (B) Dichloro-[N,N-Bis(di-p-tolylphosphino)-o-toluidine-k2P,P’]platinum(II) [Pt(4-p-tolyl-o-tol)Cl2], (C) Dichloro-[N,N-Bis(diphenylphosphino)-4-chloroaniline-k2P,P’]palladium(II) [Pd(Cl-Ph-PNP)Cl2], (D) Dichloro-[N,N-Bis(diphenylphosphino)-p-toluidine-k2P,P’]palladium(II) [Pd(5-p-tolyl-PNP)Cl2], (E) Dichloro-[N,N-Bis(di-p-tolylphosphino)cyclobutylamine-k2P,P’]platinum(II) [Pt(Cbutyl-4-p-tolyl)Cl2] and (F) Dichloro-[N,N-Bis(di-p-tolylphosphino)cyclohexylamine-k2P,P’]palladium(II) [Pd(Chzyl-4-p-tolyl)Cl2] (see Figure 2). This data provided information regarding the coordination modes of the ligands. To evaluate the electronic properties of ligand 1, 2 and 3, the first order coupling constants J(Pt-P) were determined and correlated. Hydroformylation of 1-octene was performed using a Rh(I)-PNP catalyst. An increase in linear product yield was observed when the ligand electron withdrawing ability and the steric bulk on the nitrogen were systematically increased. The highest recorded linear product yield was 35.1 % with Ligand 3 and the lowest was 20.3 % with ligand 4 in the first three hours of the sampling period. The highest calculated θN-sub was 80.6 ° for ligand 6 and gave a linear product of 28.5%. The lowest recorded θN-sub was 33.7 ° for ligand 4. These results showed that both the electronic and the steric properties have a significant influence on the catalysts selectivity.
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    Rhenium (1) tricarbonyl schiff base complexes: a mechanistic study
    (University of the Free State, 2016-06) Tsosane, Mampotso. Selina.; Brink, Alice; Visser, Hendrik. G.; Roodt, Andreas.
    English: Both technetium and rhenium have been studied extensively over the years, due to their ability to coordinate with mono- and bidentate ligands to form metal(I) tricarbonyl complexes, fac-[M(CO)3(X)(L,L’-Bid)] (M = Tc(I) and Re(I), L,L’-bid = bidentate ligand and X = MeOH, H2O or Br). The interest in these complexes is based on the diagnostic properties of technetium and therapeutic properties of rhenium in the study of radiopharmaceuticals. These complexes possess characteristics that can be utilized for the application in nuclear medicine. The aim of this study was based on the study of the chemistry of technetium and rhenium to gain more information about their ability to coordinate with potential ligands such as Schiff base ligands. From this, a Schiff base ligand such as 5-methyl-(2- cyclohexyliminomethyl)phenol – 5Me-Sal-Cyhex was synthesized and characterized. This was successfully coordinated to fac-[M(CO)3]+ core to form metal(I) tricarbonyl complexes. The synthesis and characterization of the N,O-bidentate ligand or Schiff base ligand and all metal complexes are reported in Chapter 3. All rhenium products obtained were characterized by UV/Vis, NMR (1H and 13C) and IR. The rhenium complexes, fac-[Re(CO)3(X)(N,O-Bid)], were synthesized with variety of monodentate ligands (X = MeOH, imidazole, pyridine and pyrazole) coordinated on the sixth position. Three crystal structures of 5-methyl-(2-cyclohexyliminomethyl)phenol – 5Me-Sal- Cyhex, fac-[Re(CO)3(MeOH)(5Me-Sal-Cyhex)] and fac-[Re(CO)3(Imid)(5Me-Sal-Cyhex)] were obtained from the characterization performed by X-ray diffraction. These complexes crystallised in the orthorhombic and monoclinic crystal systems in the respective space groups of P212121, C2/c and P21/n. Technetium(I)-99 tricarbonyl complexes, fac-[99Tc(CO)3(MeOH)(5Me-Sal-Cyhex)] and fac- [99Tc(CO)3(MeCN)(5Me-Sal-Cyhex)] were synthesized and characterized by HPLC to determine the reaction completion and chemical similarity between rhenium and radioactive technetium-99. A kinetic investigation was performed on the formation reaction between 5Me-Sal-Cyhex and [NEt4]2[Re(CO)3(Br)3]. It was observed that the formation reaction would unsuccessfully be determined due to the small absorbance changes over time. A model N,N’-bidentate ligand system (ethylenediamine) was therefore selected to study the formation reaction. The UV/Vis analysis showed two reactions that occur during the formation reaction between ethylenediamine and ReAA. Since the first fast reaction has the half-life, t1/2 = <5 seconds, the stopped flow kinetic investigation is required. The second slow formation reaction between ethylenediamine and ReAA was monitored at 14.8oC, 25.2oC, 35.0oC and 45.0oC. Rate constants and activation parameters (ΔH≠ = 28 ± 0.05 kJ mol-1 and ΔS≠ = -188 ± 0.17 J K-1 mol-1) of the formation reaction between ethylenediamine and [NEt4]2[Re(CO)3(Br)3] were obtained. The negative ΔS≠ value is indicative of an associative-type mechanism. In addition to the above UV/Vis study, 1H NMR analysis was performed which confirmed the mechanistic and kinetic observations of the reaction between ethylenediamine and ReAA that forms in over 13 hour period. From the 1H NMR investigation, it was observed that the formation reaction between ethylenediamine and ReAA occurs via two reactions, defined as a first fast and second slow reaction.
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    ItemOpen Access
    Rhodium(I) betadiketone complexes as model catalysts in methanol carbonylation
    (University of the Free State, 2009-06-09) Brink, Alice; Roodt, Andreas; Visser, Hendrik G.
    Abstract not available