No description available.

D.Phil. (Physics) / Please refer to full text to view abstract

Graduation date: 1998

No description available.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

This thesis is concerned with a systematic study of phosphine-containing transition metal complexes and cluster compounds by high resolution solid state nmr spectroscopy, using the techniques of magic angle spinning and cross polarisation. Previous work has indicated the potential of the solid state nmr technique to investigate a variety of materials: this is considered in the introduction to this thesis, and the reasons for choosing to study transition metal phosphine compounds are discussed. The analysis of spinning sidebands to obtain the principle values of the shielding tensor is examined to determine how well the calculated values represent the true values. Simulations of slow MAS spectra are proposed as a means of testing and refining the calculated tensor components before attempting to correlate the shielding with structural parameters. The results of a study of a series of crystalline phosphine-containing complexes and clusters are presented. The spectra are interpreted on the basis of the known crystal structures: in some cases separate resonances can be resolved in the solid state spectra from the distinct phosphine environments of a cluster framework, and from inequivalent sites in the unit cell. Information is obtained from the isotropic shifts, scalar couplings and the chemical shift anisotropy. Many of the compounds are fluxional in solution, some even at low temperature: whereas a number of these are found to be rigid in the solid state at room temperature, some of the crystalline compounds retain their fluxionality. Investigations of the species formed when transition metal carbonyl clusters are anchored to oxide supports were carried out. These show the presence of several distinct phosphorus-containing species, some of which are not consistent with the simple attachment of the cluster to the surface. The unique importance of the solid state technique is demonstrated in the study of these supported species.

Thermolysis of CoRu(CO)7(m -PPh2) (1) in refluxing 1,2-dichloroethane in the presence of the diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) furnishes the new mixed-metal complexes CoRu(CO)4(μ -P-P)(μ -PPh2) [where P-P = bma (3); bpcd (6)], along with trace amounts of the known complex CoRu(CO)6(PPh3)(μ -PPh2) (4). The requisite pentacarbonyl intermediates CoRu(CO)5(μ -P-P)(μ -PPh2) [where P-P = bma (2); bpcd (5)] have been prepared by separate routes and studied for their conversion to CoRu(CO)4(μ -P-P)(μ -PPh2). The complexes 2/3 and 5/6 have been isolated and fully characterized in solution by IR and NMR spectroscopy. The kinetics for the conversion of 2→3 and of 5→6 were measured by IR spectroscopy in chlorobenzene solvent. On the basis of the first-order rate constants, CO inhibition, and the activation parameters, a mechanism involving dissociative CO loss as the rate-limiting step is proposed. The solid-state structure of CoRu(CO)4(μ -bma)(μ -PPh2) (3) reveals that the two PPh2 groups are bound to the ruthenium center while the maleic anhydride π bond is coordinated to the cobalt atom. Thermolysis of the cluster Ru3(CO)12 with the bis(phosphine)hydrazine ligand (MeO)2PN(Me)N(Me)P(OMe)2 (dmpdmh) in toluene at 75°C furnishes the known clusters Ru4(CO)12[μ -N(Me)N(Me)] (9) and Ru3(CO)11[P(OMe)3] (10), in addition to the new cluster Ru3(CO)10(dmpdmh) (8) and the phosphite-tethered cluster Ru3(CO)9[μ -P(OMe)3] (11). The simple substitution product Ru3(CO)10(dmpdmh), a logical intermediate to clusters 9-11, was synthesized by treating Ru3(CO)12 and dmpdmh with Me3NO in CH2Cl2 at room temperature, and independent thermolysis reactions using cluster 8 were shown to yield clusters 9-11. The tetrahedrane cluster FeCo2(CO)9(μ3-S) reacts with the redox-active ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) to give the disubstituted cluster FeCo2(CO)7(bpcd)(μ3-S) as the sole product. This diphosphine-substituted cluster contains a cobalt-bound, chelating bpcd ligand. The solid-state structure has been unequivocally established by X-ray diffraction analysis. Cyclic voltammetric studies on FeCo2(CO)7(bpcd)(μ3-S) reveal the presence of two quasireversible redox responses assigned to the 0/1- and 1-/2- redox couples. The orbital composition of these redox couples has been examined by carrying out extended Hückel MO calculations on the model complex FeCo2(CO)7(H4-bpcd)(μ3-S), with the results being compared to related cluster compounds.

Ph.D. (Physics) / Please refer to full text to view abstract

Ku, Ka Wai. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.