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Coordination chemistry of tetraneopentoxyphthalocyaninatocobalt(II) Wu, Haiying


The thesis work reports developments in the coordination chemistry of tetra-neopentoxyphthalocyaninatocobalt(II) (CoTNPc) complexes. The preparation, characterization, and ligand binding measurements in solution of seven new compounds are described in this thesis. Some additional complexes are studied in situ. Measurement of the equilibrium constants by UV-visible spectroscopy for the 1:1 binding reactions of the axial ligands (L = imidazole, N-methylimidazole, pyridine, 4-picoline, 4-tert-butylpyridine, piperidine, tetrahydrofuran) to CoTNPc in toluene solution allow for an estimation of the enthalpies for the binding of the N-donor ligands (7 - 12 kcal/mol) and the O-donor ligand (~ 4 kcal/mol). The order of equilibrium constants for ligand binding at room temperature is found to be: N-MeIm > pip > 4-[formula omitted]Bupy > Im > py > THF. Seven five-coordinate CoTNPc species have been isolated (L = N-MeIm, py, 4-pic, 4-[formula omitted]Bupy, pip, THF, DMSO) and characterized by elemental analyses, and UV-visible, MS (FAB), and NMR spectroscopy. The magnetic moment of CoTNPc in the solid state is found to be 2.23 ± 0.10 B.M. at ambient temperature, while the magnetic moment is 2.47 ± 0.10 B.M. in toluene solution. The magnetic moment of the five-coordinate species (py)CoTNPc is 2.61 ± 0.10 B.M. in toluene solution. It is concluded that CoTNPc and the five-coordinate complex (py)CoTNPc at room temperature are low spin with one unpaired electron. The ¹H NMR spectra of the paramagnetic species (CoTNPc, LCoTNPc, L = Im, N-MeIm, py, 4-pic, 4-[formula omitted]Bupy, pip, THF, PPh₃) are studied. The ¹H NMR spectra of CoTNPc are found to be solvent dependent; the α- and β-proton signals of the phthalocyanine ring are very broad in DMSO-d₆ and benzene-d₆, and in chloroform-d₁ these signals are so broad that they could not be observed. Some irregular multiplicities in these proton NMR spectra result from the cobalt(II) complexes being mixtures of isomers. The isotropic shift vs.l/T Curie plot for (py)CoTNPc shows that the extrapolated isotropic shifts of the benzo-, methylene, and methyl protons on the phthalocyanine ring at infinite temperature are not zero, indicating there is a contribution from a dipolar interaction. For the axial ligands, the proton signals of the methyl groups of some ligands (L = N-MeIm, 4-pic, 4-[formula omitted]Bupy) are observed, and these signals are averaged by rapid chemical exchange between the free and coordinated ligands; the ligand aromatic proton signals of these ligands are not observed. However, the ²H NMR spectra, when L = pyridine-d₆, show that the ϒ-²H signal shifts in a direction different to signals from the α- and β-²H deuterons, suggesting a contact shift mechanism is dominant in this case. The ³¹P NMR spectra of in situ PPh₃/CoTNPc samples do not give any peaks, indicating that signals for the phosphine are extremely broad. The elemental analyses, UV-visible spectra, IR, NMR, and ESR results suggest that CoTNPc and its five-coordinate species do not bind oxygen at the temperatures examined (77 K to ambient temperature).

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