No description available.

The fundamental knowledge of Cr(III) chemistry has been enhanced via detailed structural and spectroscopic studies of largely novel compounds that may potentially be active tri- and tetramerisation precursors. The compounds are based on various monodentate and bidentate nitrogen and phosphorus ligands which have been coordinated to [CrCl3 (thf) 3]. The few compounds that have been synthesised previously have in this study been made via novel synthetic routes and incorporate a combination of new and more detailed analysis than was carried out previously. The eight structures determined, in addition to offering novel crystallographic data, also provided insights into the synthetic pathways leading to compound formation. The isolation of monomeric structures suggests direct ligand substitution, while the cationic-anionic structures suggest the presence of dimeric intermediates which have been cleaved asymmetrically. Infrared and Raman spectra of these structures were able to add weight to these pathway proposals and, by means of vibrational comparisons, assisted in the general band assignments of the compounds' spectra where structures were not available. Vibrational shifts relative to the free ligands, as well as metal–ligand vibrations in the far infrared region, were also of significant value in terms of ligand coordination and geometry. Closely associated with the infrared and Raman spectra analysis was the generation of theoretical spectra using Density Functional Theory calculations. The excellent agreement between the calculated and experimental spectra confirmed the vibrational assignments. Also generated by computational means were the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of the compounds which indicated the sites of potential nucleophilic and electrophilic attack. 1H NMR spectroscopy is a technique normally avoided when studying paramagnetic materials. However, by employing a largely novel approach, information pertaining to both ligand coordination and reaction times was obtained. FAB-MS assisted in the confirmation that the single crystal determinations did indeed reflect the composition of the bulk precipitated samples. It also provided additional structural information through the identification of fragmentation patterns which could not be gained by techniques such as elemental analysis. / Thesis (PhD)--University of Pretoria, 2010. / Chemistry / unrestricted

No description available.

No description available.

No description available.

The reactions of 1, 2–bis(difluorophosphino)cyclohexane, PF2C6H10PF2, with hexacarbonyls of Cr(O), Mo(O), and W(O) have been extensively investigated. The hexacarbonyls react, either under photolytic or thermolytic conditions, to produce carbon monoxide and oily mixtures of products of the general formulations, [M(CO)4(PF2C6H10PF2C)]x, where x varies apparently from 1 – 4. The higher values of x, corresponding to species involving bridging ligands, are more common to the photolysis rather than the thermolysis reactions. Photolysis reactions of Mo(Co)6 with increasing amounts of the ligand does not result in the higher substitution products, Mo(Co)2(PF2C6H10PF2)2 and Mo(PF2C6H10PF2)3. The reactions of PF2C6H10PF2 with the norbornadiene tetracarbonyl complexes of Cr(O), Mo(O), and W(O) produce relatively air-stable chelates of the general formulation, M(Co)4(PF2C6H10PF2). Mo(CO)4(PF2C6H10PF2) will react with more PF2C6H10PF2 to give [Mo(CO)2(PF2C6H10PF2)2]2. A slight excess of PF2C6H10PF2 also reacts readily with ditoluenemolybdenum (O) displacing toluene to give Mo(PF2C6H10PF2)3, and air-stable monomer. Analysis of the infrared spectra of these chelates indicates that the ligand fits into a sequence of π–acceptor strength as: PF3>PCI3~ PF2C6H10PF2>RN(PF2)2>>Ph2PC2H4PPh2. NMR spectral parameters for the chelates verify the very strong coordination of the bidentate ligand to the metals. 1, 2-bis(difluorophosphino)cyclohexane has also been found to react with pentacarbonyliron(O), Fe(Co)5 and with pentacarbonylmanganese(I) bromide, Mn(CO)5Br, in hexane, displacing two moles of carbon monoxide per mole of ligand. The products resulting, (PF2C6H10PF2)Fe(Co)3, (PF2C6H10PF2)2Fe(CO), (PF2C6H10PF2)Mn(CO)3Br, and (PF2C6H10PF2)2Mn(CO)Br, are all air-stable solid monomers indicating that the ligand is an effective chelating agent. Analysis of their and nmr spectral data supports the conclusion that PF2C6H10PF2 functions as a strong π–acceptor and assists in assigning structures. The reactions of PF2C6H10PF2 in solution with Co2(CO)8 and the chlorides of Ni(II), Pd(II), and Pt(II) have been investigated. The resultant complexes are not well defined. The characterization of the complexes has given ambiguous results, although the nickel group metal complexes appear to be dimeric. The ligand, 1,2-bis(difluorophosphino)ethane, PF2C2H4PF2, reacts with tetracarbonylnickel(O), Ni(Co)4, in the gas phase and in solution, to produce carbon monoxide and the polymer, [Ni(PF2C2H4PF2)2]x. PF2C2H4PF2 displaces norbornadiene from (C7H8)Mo(Co)4 to yield the relatively air-stable complex, Mo(CO)4(PF2C2H4PF2). Analysis of the infrared spectrum of the monomeric complex indicates that the ligand exhibits π–acceptor strength equal to PF2C6H10PF2.

This thesis is a report on the design, synthesis and molecular structure of a set of chiral Co(III) metal complexes, in the solution and solid state. The complexes that have been synthesised will potentially intercalate between the base pairs of DNA. The structure of the bound tetradentate ligand, S,S-picchxnMe2 in the solid state was investigated to determine the flexibility of this seemingly rigid ligand. The bidentate ligands, R- and S-glu, were also bound to the Co complex and the differences in the tetradentate ligand were observed. The differences observed in the bonded tetradentate ligands were due to the chirality of the bonded amino acid. The aromatic amino acids, R- and S-phe, were used as bidentate ligands because of their ability to intercalate with DNA. Several scientific experiments were conducted and the results analysed in great depth / Doctor of Philosophy (PhD)

Les complexes carbéniques ont connu un essor considérable ces dernières années. L'introduction générale présente les différentes facettes de ces complexes aux propriétés aussi diverses qu'uniques. D'abord utilisés comme réactifs stoechiométriques, les complexes carbéniques sont devenus des catalyseurs de choix dans de nombreuses réactions. Dans ce contexte, nous présenterons différentes approches pour la synthèse de complexes carbéniques hétérosubstitués.<br /><br />Le premier chapitre présente la synthèse et la chimie de coordination d'aminoarylcarbènes possédant un squelette biphényl ou binaphtyl. Dans les complexes obtenus, la topologie du squelette biaryl est différente de celle rencontrée dans les complexes de phosphines biarylées. En fait, les différences observées proviennent de l'hybridation sp2 ou sp3 du site donneur (phosphine ou carbène). Cette topologie particulière entraîne des modes de coordination originaux et différents de ceux mis en jeu dans les complexes de phosphines analogues. Des essais préliminaires en catalyse d'α-arylation de cétones ont donné des résultats encourageants pour le couplage de chlorure d'aryl à température ambiante.<br /><br />Le deuxième chapitre présente la synthèse de complexes mixtes aminocarbène/phosphine par insertion d'un fragment métallique dans la liaison P-C d'un C-aminoylure. Appliquée à des C-(amino)ylures cycliques basés sur le squelette biphényl, cette méthodologie permet d'accéder à des complexes hétéroditopiques carbène/phosphine, analogues des complexes de BIPHEP et BINAP.<br /><br />La synthèse et la coordination d'α-diazophosphines est décrite dans le troisième chapitre. Les complexes d'α-diazodiphosphines ne sont pas stables et se réarrangent en complexes de C-chlorodiphosphinométhanides. L'étude expérimentale et théorique de la dissociation de C-pyridinodiphosphinométhanides révèlent la formation transitoire de métalladiphosphinocarbènes. Les calculs DFT réalisés sur ce composé, montrent une structure électronique inversée tout à fait originale. Celle-ci est favorisée par des interactions transannulaires PdC dont la symétrie est opposée à celle rencontrée dans les complexes de Fischer (donation σPd→C et rétrodonation πC→Pd).

The well-defined ruthenium-carbene complexes reported by Grubbs and co-workers were the first ruthenium catalysts to show good activity and selectivity in metathesis of acyclic and cyclic olefins. Unfortunately the use of the Grubbs type catalysts is limited to the small scale synthesis of polymers and essential organic reactions, due to cost and instability of the catalyst at elevated temperatures. Some of the most successful Grubbs-type catalysts included hemilabile ligands. By releasing a free coordination site (the so-called "on-demand-open-site") for an incoming nucleophile, hemilabile ligands have the ability to increase the thermal stability and activity of a catalytic system, by stabilization of the transition metal centre. Previous studies indicated that the incorporation of a sterically hindered N and 0 chelating ligand increased the stability, activity and selectivity of Grubbs type complexes and increasing the electron density of the complex can influence the stability of a complex and therefore the catalytic performance. In this study alicyclic, bidentate N and 0 chelating ligands (16-19) were modelled in order to evaluate the hemilability of these ligands. The modelling was used as a comer stone from which the synthesis was conducted. Molecular modelling showed that of the four ligands identified only two (16 and 18) could potentially be hemilabile. 17 would rather form a transaunular ether compound. The modelling results were incondusive for ligand 19 and further investigation is necessary for this compound… / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2010.

The well-defined ruthenium-carbene complexes reported by Grubbs and co-workers were the first ruthenium catalysts to show good activity and selectivity in metathesis of acyclic and cyclic olefins. Unfortunately the use of the Grubbs type catalysts is limited to the small scale synthesis of polymers and essential organic reactions, due to cost and instability of the catalyst at elevated temperatures. Some of the most successful Grubbs-type catalysts included hemilabile ligands. By releasing a free coordination site (the so-called "on-demand-open-site") for an incoming nucleophile, hemilabile ligands have the ability to increase the thermal stability and activity of a catalytic system, by stabilization of the transition metal centre. Previous studies indicated that the incorporation of a sterically hindered N and 0 chelating ligand increased the stability, activity and selectivity of Grubbs type complexes and increasing the electron density of the complex can influence the stability of a complex and therefore the catalytic performance. In this study alicyclic, bidentate N and 0 chelating ligands (16-19) were modelled in order to evaluate the hemilability of these ligands. The modelling was used as a comer stone from which the synthesis was conducted. Molecular modelling showed that of the four ligands identified only two (16 and 18) could potentially be hemilabile. 17 would rather form a transaunular ether compound. The modelling results were incondusive for ligand 19 and further investigation is necessary for this compound… / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2010.