published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

This thesis describes the development of nickel(I) complexes incorporating ring expanded N-heterocyclic carbene (RE NHC) ligands and examines their electronic characterisation, activation of O2, reactivity and catalytic applications. A series of three coordinate, paramagnetic Ni(I) complexes of the form Ni(RE NHC)(PPh3)Br (1 – 10) were prepared by comproportionation of Ni(COD)2 and Ni(PPh3)2Br2 in the presence of RE NHCs. The RE NHCs employed varied in the degree of ring expansion (6-, 7- and 8-membered), extent of N-substituent steric bulk (Mes, oTol, oAnis) and the donor/acceptor properties of the carbene (diamino vs. diamido). EPR and DFT electronic characterisation of 1 – 10 confirmed that the unpaired electron was located on the nickel ion in a mixed orbital of predominantly 3dz2 character. Yellow solutions of 1 or 6 (RE NHC = 6Mes and 7Mes respectively) immediately became purple in the presence of O2 due to O2 activation and incorporation of the oxygen atoms as bridging ligands resulting from C-H activation/oxygenation of an RE NHC N-substituent. This generated the dimeric Ni(II) complexes Ni(6/7Mes)Br(µ-OH)(µ-O-6/7Mes)’NiBr (6Mes = 13; 7Mes = 14). Mass spectrometry demonstrated that the doubly activated complexes [NiBr(µ-O-6/7Mes)’]2 (15 and 16 respectively) were also formed in the reactions. UV-vis spectroscopy revealed the reactions took place rapidly, even at 190 K. Contrasting reactivity was observed when 2 or 7, bearing the less sterically encumbered N-oTol substituents 6oTol and 7oTol respectively, were exposed to O2, which led to the ligand redistribution products NiII(6/7oTol)(PPh3)Br2 (17 and 18 respectively). The less electron rich diamido analogue containing 6MesDAC (5), underwent dissociation and oxidation of the RE NHC and PPh3 ligands. Attempts to abstract the bromide from 1 generated novel two and three coordinate Ni(I) products. Reaction with additional 6Mes produced the two coordinate cation [Ni(6Mes)2]+ (19), which could be reduced with KC8 to Ni(6Mes)2 (20). SQUID analysis of 19 revealed it to be the first example of a nickel containing mononuclear single molecular magnet (SMM). Addition of [Et3Si]+ to 1 followed by work up in toluene led to the isolation of the Ni(I)-(η2-toluene) complex [Ni(6Mes)(η2-C6H5CH3)]+ (21). Mesitylene generated the analogous [Ni(6Mes)(η2-C6H3(CH3)3)]+ (23), but neither 1,4-xylene nor naphthalene gave isolable products. In all cases, cocrystallisation of [6MesH]+…arene was observed in variable amounts, which compromised reaction studies of the Ni-arene complexes. Removal of bromide from 1 with TlPF6 in THF generated the solvent coordinated cationic species [Ni(6Mes)(PPh3)(THF)]+ (24). Attempts to remove the ligated THF molecule were unsuccessful, however, it could be directly substituted by CO to form [Ni(6Mes)(PPh3)(CO)]+ (26). Similarly to 1, complex 24 activated O2, generating a dimer analogous to the singly activated complex 13 (Ni(6Mes)(PPh3)(µ-OH)(µ-O-6Mes)’NiBr (25)). Reactivity of 1 with NaBH4 produced [Ni(6Mes)(κ2-BH4)]2 (28), a Ni(I) dimer bridged by two BH4 ligands. The catalytic efficiency of neutral 1 in Kumada cross-coupling of aryl halides and PhMgCl or MesMgBr was probed. Of note was the high activity towards both aryl chlorides and aryl fluorides. Comparisons with cationic 24, larger 7- (7) and 8-membered ring (8 and 9) variants and the Ni(II) complexes Ni(6Mes/6oTol/7oTol)(PPh3)Br2 (29, 17 and 18 respectively) revealed that 1 exhibited the highest reactivity of all the precursors.

This thesis presents an investigation into the synthesis of metal complexes of (Nheterocyclic carbene)-based cyclophanes. There were three main areas of focus: synthesis and complexation of bis(4,5-dihydroimidazolium) salts; the synthesis and complexation of phenol-functionalised imidazolium cyclophanes; and the synthesis and complexation of (N-heterocyclic carbene)-based cyclophanes by C-C bond activation of biimidazolium salts with electron-rich metals. The synthesis of xylyl-linked bis(4,5-dihydroimidazolium) salts was investigated. Attempts to prepare these compounds by the cyclisation of a tetraamine (linear or macrocyclic) were unsuccessful due difficulties in preparing the tetraamines. The target compounds could be prepared by adapting the methods developed for the synthesis of bis(imidazolium) salts however problems associated with purification and stability of the products prevented complexation studies. A series of phenol-, phenoxide- and anisole-functionalised imidazolium cyclophanes were prepared. Their structural properties were investigated using dynamic nmr studies and X-ray crystallography. Complexation of the functionalised cyclophanes was investigated. The phenol cyclophane I formed a dinuclear complex with mercury(II). This complex is the first example of a complex derived from a phenol-functionalised imidazolium cyclophane. However the anisole cyclophane II and the unsymmetrical phenol/ortho cyclophane III were unable to form complexes possibly due to steric hindrance and instability of the cyclophane respectively. Preliminary complexation studies of the bis(imidazolium)phenol V suggested that complexation with palladium(II) and mercury(II) were possible but more work is required to determine the optimum reaction conditions. A series of biimidazolium salts VI (both new and known) were prepared. Previously reported biimidazolium salts have very low solubility in common solvents therefore the incorporation of long alkyl chains to the bridging group was investigated as a means to improve the solubility. The structure of the salts was explored using a range of techniques including dynamic nmr spectroscopy, cyclic voltammetry, UV/Visible spectroscopy, X-ray crystallography and mass spectrometry. Some of the biimidazolium salts were able to rotate about the C2-C2' bond and the free energy of activation for this process was estimated using dynamic nmr studies. C-C bond activation of the biimidazolium salts with palladium(0) was used to form a series of palladium(II) complexes (VII) of (NHC)-based cyclophanes. These reactions are the first examples of the synthesis of bis(NHC) complexes by C-C bond activation. The reactivity of the biimidazolium salts with palladium(0) was compared to their solution structure and it was found that only the biimidazolium that were able to rotate about the C2-C2' bond could react with palladium(0).

For the purpose of incorporating indoles into organometallic complexes for catalysis, as well as in the generation of new heterocyclic systems, various reactions have been carried out at C2, C6 and C7 of the indole system. In order to achieve this, 3-substituted 4,6-dimethoxyindoles and 6-hydroxy- 4-methoxyindoles were necessary as starting materials. Consequently, a lithium-bromide-templated one-pot procedure for the synthesis of some 3-substituted 4,6-dimethoxyindoles and a selective demethylation procedure for 3-substituted 6-hydroxy-4-methoxyindoles were developed. Various kinds of novel methylene-bridged bi-, tri-, and tetradentate pyridyl-indole ligands were synthesised via Vilsmeier-Haack, Friedel-Crafts or electrophilic addition reactions on the indole heterocycle. However, their metal complexing properties were generally weak and variable. Nevertheless, some of the tridentate pyridylindole ligands showed strong anion binding to halides, whereas a remarkable ligand transformation occurred with a bidentate 2-pyridylindole ligand and zinc(II), giving a substituted indolo[2,3-c]pyrrolo-[3,2,1-ij]quinoline system. Two new types of tetradentate Schiff base ligands were prepared from 2-formyl-indoles and 7-formyl-6-hydroxyindoles, and diamines. These preformed ligands were reacted with first- and second-row transition metals to give neutral metal complexes. Novel heterocyclic systems such as 4H-pyrrolo[3,2,1-ij]quinolines, 3H-pyrrolo-[1,2-a]indoles, and 1H-furo[2,3-g]indoles were synthesised from 2-formyl-, 7-formyl-, and 6-hydroxyindoles, utilising mainly intra-molecular Wittig reactions, Claisen-Schmidt condensations or acid- and base-catalysed cyclisations. A common feature of the prepared 4H-pyrrolo[3,2,1-ij]quinolines and 3H-pyrrolo-[1,2-a]indoles was their intense fluorescent character, which was examined as well.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Thesis (Ph. D.), Memorial University of Newfoundland, 1998. / Bibliography: leaves 142-156.

A full IH, l3C and 31P NMR assignments of phosphoric triamides 1-oxo-2,8-diphenyl-2,5,8-triaza-l-phosphabicyclo [3.3.0]octane (1), l-oxo-lO-phenyl-4,7,lO-triaza-2.3-benzo-l-phoshabicyclo [5.3.0]decane (2) and 1-oxo-4,7,lO-triaza-2,3,11,12-dibenzo-l-phosphabicyclo[5.5.0]dodecane (3) which have been recently synthesised was accomplished. The solution state NMR analysis of these compounds showed a number of interesting spin systems upon moving from 1→2→3, spanning from ABC to ABCDX spin systems where X is phosphorus nucleus. The three systems showed a high degree of rigidity in solution state, which made it possible to compare dihedral/torsion angles determined from solution state NMR with those of X-ray diffraction data. Both X-ray diffraction and NMR analysis supported the molecular conformations. A significant solvent effect was observed for solutions of compounds 1, 2 and 3 in benzene-d6 compared to solutions in chloroform-d1 and acetone. Benzene-d6 showed a generally upfield chemical shift of methylene protons in particular, and this is assumed to be due to different solvent-substrate interactions and to the magnetic anisotropic effect of the solvent. / Dissertation (MSc (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

A computational chemistry analysis combined with a crystallographic database study of the bonding in late transition metal N-heterocyclic carbene (NHC) complexes is reported. The results illustrate a metal-carbon bond for these complexes, approximately 4% shorter than that of a M-C single bond found in metal alkyl complexes. As a consequence of this result, two hypotheses are investigated. The first hypothesis explores the possibility of multiple-bond character in the metal-carbon linkage of the NHC complex, and the second, considers the change in the hybridization of the carbenoid carbon to incorporate more p character. The latter hypothesis is supported by the results. Analysis of these complexes using the natural bond orbital method evinces NHC ligands possessing trans influence.

MSc (Chemistry) / Department of Chemistry / Quinolines are well known naturally occurring heterocyclic compounds with nitrogen as a heteroatom. Quinolines are also one of the major classes of naturally occurring compounds and the interest in their chemistry is due to the wide range of their biological activities. The objective of the project was the synthesis of novel tetra-substituted quinoline-3carboxamides and subsequent transformation to other novel derivatives and evaluation of their biological activities against malaria and cytotoxicity. In achieving the objective, 2-chloroquinoline-3-carbaldehyde analogues 54A-G were synthesised from the reaction of acetanilides 53A-G and acetic acid. Knoevenagal reaction of 2chloroquinoline-3-carbaldehydes 54A-G with thiazolidinedi-2,4-one 62 provided 2chloroquinoline-3-methylene thiazolidinedi-2,4-one 55A-G which then underwent nucleophilic substitution reaction with sodium azide and afforded (Z)-5-((tetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56A-F. (Z)-ethyl-2-(2-5-((7bromotetrazolo [1,5a] quinolin-4-yl) methylene-2,4-dioxothiazolidin-3-yl) acetamido) acetate 57 was synthesised from the reaction of (Z)-5-((7-bromotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56D and ethyl-2-(2-chloroacetamido) acetate 65. The structures of the compounds were characterised by 1D NMR (1H, 13C, and DEPT 135), IR spectroscopy, elemental analysis and high-resolution mass spectroscopy. Novel selected synthesised quinoline compounds were evaluated of in vitro for two biological assays; namely anti-malarial activity and cytotoxicity. The anti-malaria activities of the novel quinoline compounds against 3D7 strain of the malaria parasite Plasmodium falciparum displayed that 2,6-dichloroquinoline-3-methylene thiazolidinedi-2,4-one 55C, (Z)-5-((7-fluorotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56B and (Z)-5((7-ethoxytetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56F are potential malaria drugs since they reduced the percentage parasite viability to 25.80, 12.40 and 20.40 respectively. These results were further substantiated by their IC50 values 0.40, 0.04 and 0.50 µg/mL. Compound 56B displayed the highest cytotoxicity activity against human cervix adenocarcinoma cells displaying percentage viability of 14.22 %. Compounds 56F and 56C displayed moderate cytotoxicity activity at 56.60 and 59.81 % viability. / NRF

Methodologies for expanding the architectural diversity of -N-heterocyclic carbene (NHC) pincer ligand precursors and transition metal complexes have been developed for the production of more efficient catalyst, which will be employed in the synthesis of pharmaceuticals. An efficient route for the synthesis and isolation of bis-1,3-(3'-aryl-N-heterocycl-1'-yl)arenes has been established, and preliminary data for metalation and transmetalation of a N, N'-diaryl imidazolium salt has been acquired. Additionally, a proficient methodology for the synthesis of mixed, unsymmetrical -NHC pincer ligand precursors has been discovered, and preliminary data for mixed, unsymmetrical transition metal complexes is also included. These methodological expansions will lead to more efficient catalyst that decrease the expenditure of energy required for the synthesis of pharmaceuticals, thus making their synthesis more favorable for the environment and their price more affordable for consumers.