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Stereoelectronic control and modulation of metal electronic properties in beta-octafluorometalloporphyrins
Abstract
The rationale for preparing β-octafluorinated porphyrins (Chapter 1) was based on the hypothesis that fluorine atoms at β-positions should have strong effects on the porphyrin π- and σ-electronic systems, while introducing minimal structural perturbations. This combination of steric and electronic properties should distinguish β-octafluoroporphyrins from their β-octachlorinated and β-octabrominated analogs, which have highly nonplanar structures arising from halogen-aryl steric interactions at porphyrin periphery. For the zinc and cobalt complexes of 2,3,7, 8,12,13,17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, the porphyrin ring is essentially planar, as it is in the corresponding structures of 5,10,15,20-tetraphenylporphynn derivatives. In contrast, incorporation of relatively electron-rich aryl substituents results in nonplanar porphyrin rings. A zinc complex of 2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetra-phenylporphyrin adopts highly saddled conformation. We attributed the differences in the structures of β-octafluorinated metalloporphyrins containing electron-deficient and electron-rich aryl groups to electrostatic interactions between the β-fluorine atoms and aryl rings. We crystallized several free base porphynns (Chapter 2) and found that core conformations of β-octafluoroporphyrins depend on the amount of electron density on the meso-aryl substituents. Electron-deficient aryl rings favor planar macrocycle geometry while electron-rich substituents induce saddle distortion. Regardless of planarity, β-octafluoroporphyrins show blue shifts in UV-vis spectra when compared to other tetraarylporphyrins. Experiments with cobalt complexes (Chapters 3) showed that metal ion bound by F28TPP remains highly electrophilic. Thus, CoF28 TPP binds axial ligands with the highest formation constants reported for Co(II) porphyrins. An unprecedented spin state modulation of the Co(II) ion in a porphyrin upon coordination of two axial ligands was demonstrated crystallographic ally and by NMR. The high-spin Co(II) was obtained without displacement of the metal ion from the porphyrin plane consistent with a strongly reduced ligand field. In addition, fundamental studies of electron transfer rates for the cobalt derivatives show large inner sphere reorganization energies for the Co(II) oxidation process in fluorinated porphyrins (Chapter 4). Strongly Lewis-acidic acetates, chlorides, iodides, and triflates of electron-deficient zirconium(IV) porphyrins are described in Chapter 5. The iodides are precursors for organometallic (Me, Bu) zirconium(IV) complexes.
Subject Area
Chemistry|Organic chemistry
Recommended Citation
Smirnov, Valeriy V, "Stereoelectronic control and modulation of metal electronic properties in beta-octafluorometalloporphyrins" (2004). ETD collection for University of Nebraska-Lincoln. AAI3117807.
https://digitalcommons.unl.edu/dissertations/AAI3117807