Synthesis, Characterization, and Reactivity Studies of Pyridine Bis(anilide) Iron Complexes

Citation

Weintrob, Edward Charles (2012) Synthesis, Characterization, and Reactivity Studies of Pyridine Bis(anilide) Iron Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/M1Y4-RM69. https://resolver.caltech.edu/CaltechTHESIS:08112011-151147364

Abstract

The unifying concept within this thesis is the investigation of pyridine bis(anilide) (NNN) iron complexes. Within this topic, chapter 1 speaks to the motivation behind studying these complexes, and how they relate to problems within iron catalysis in general. Chapter 2 introduces the general ligand design and the features which are thought to give unique and desirable properties to the complexes derived from it. The mesityl susbstituted ligand [MesNNN]H2 and subsequently ferrous ([MesNNN]Fe(THF)) and ferric ([MesNNN]FeI and ([MesNNN]Fe)2O) complexes are synthesized. The properties of the complexes are investigated using a variety of characterization techniques. Such techniques include paramagnetic 1H NMR spectroscopy, X-ray crystallography, Evans method, cyclic voltammetry, DFT calculations, and UV-vis spectrscopy. A detailed explanation of the challenges and solutions involved in using paramagnetic NMR are discussed. Crystallographic data indicate that the ligand framework confers a quite unusual geometry about the iron center, especially for the ferrous derivative [MesNNN]Fe(THF). The factors involved in this geometry are discussed, and DFT calculations supplement this discussion. Chapter 3 focuses on the reactivity of the iron complexes. Various oxidants and reductants were employed which interconvert the iron derivatives in chapter 2. Organometallic derivatives [MesNNN]FeR (R = hydride, alkyl, aryl) were not accessible, likely due to homolytic processes. L ligand exchange for [MesNNN]Fe(THF) was investigated. Ethylene reversibly binds, while cyclohexene does not. Trimethylphosphonium methylidene displaces THF to generate [MesNNN]FeCH2PMe3. Although the I oxidation state was accessible for [MesNNN]Fe(THF) electrochemically, attempts to chemically produce Fe I complexes based on the NNN ligand led to multiple products. Chapter 4 focuses on the intramolecular C-H activation of [MesNNN]Fe(THF) with RN3 to afford [MesNNN-NHR]Fe (R = SiMe3, adamantyl). The kinetics of the reaction with Me3SiN3 was investigated in detail, and a mechanism was proposed. Iron complexes based on the pincer ligands [tBuNNN] and [ONO] were investigated.

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