5,10,15,20-tetrakis(perfluoroalkyl)porphyrins. New highly electron-deficient ligands for transition metal chemistry

This thesis focuses on the synthesis, optical spectroscopy, photophysical properties, electrochemistry, X-ray photoelectron spectroscopy, and NMR spectroscopy of a series of highly electron deficient 5,10,15,20-tetrakis(perfluoroalkyl)porphyrin free base, zinc, and iron complexes. The structures of the monopyridyl adduct of (5,10,15,20-tetrakis(heptafluoropropyl)porphinato) zinc(II) and 5,10,15,20-tetrakis(heptafluoropropyl)porphinato) iron(II)$\cdot$(pyridine)$\sb2$ feature an $\rm S\sb4$-distorted porphyrin core, the most notable aspect of this ferrous porphyrin structure is the fact that it exhibits metrical features commonly manifest in crystallographically characterized ferric porphyrin complexes. Electrochemical studies carried out on the porphyrin free base, (porphinato)zinc(II), and (porphinato)iron(II) and iron(III) complexes indicate that meso-perfluoroalkylporphyrins are among the most electron-deficient porphyrinic species known. The unusual structural, potentiometric, and spectroscopic properties of the (porphinato)iron species arise from substantially reduced metal-centered electron density effected by the macrocycle\u27s non-$\pi$-conjugating, $\sigma$-electron-withdrawing meso-perfluoroalkyl substituents. The photophysical properties of the free base and the (porphinato)zinc(II) compounds differ from all other previously reported highly electron deficient porphyrin macrocycles in that they possess long-lived, fluorescent excited states; hence their optoelectronic features are consistent with a variety of excited-state electron-transfer quenching schemes in which both $\rm\sp1ZnP\sp\*$ and $\rm\sp1H\sb2P\sp\*$ can be utilized as potent photooxidants. The mechanistic study of (porphinato)iron (PFe) -catalyzed isobutane oxidation in which molecular oxygen is utilized as the sole oxidant is presented; these catalytic reactions were carried out and monitored in both autoclave reactors and sapphire NMR tubes. This study represents the first in situ NMR analysis of any catalytic hydrocarbon oxidation, and coupled with separate GC analyses and optical spectra obtained from autoclave reactions has enabled the identification of the predominant porphyrinic species present during (PFe) -catalyzed oxidation of isobutane. The nature and distribution of hydrocarbon oxidation products show that an autoxidation reaction pathway dominates the reaction kinetics, consistent with a radical chain process. Secondly, even highly electron poor $\rm PFe\sp{II}$ species were shown not to be stable under moderate $\rm O\sb2$ pressure; in every case the $\rm PFe\sp{II}$ catalyst precursor was converted quantitatively to high spin $\rm PFe\sp{III}$ complexes prior to the observation of any hydrocarbon oxidation products. Thirdly, once catalytic isobutane oxidation is initiated, all reactions are marked by concomitant decomposition of the porphyrin-based catalyst. Finally, in situ $\rm\sp{17}O$ NMR spectroscopic studies confirm the incorporation of $\rm\sp{17}O$ from labeled water into the oxidation products, implicating the involvement of $\rm PFe\sp{III}{\cdot}OH$ in the catalytic cycle