Template Syntheses, Coordination Chemistry, and Reactivity of Tetraphosphorus Macrocycles: Toward Macrocyclic Iron(II) Complexes for Applications in Nitrogen Coordination
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The preparation of tetraphosphorus macrocycles is a relatively undeveloped field of chemistry. Despite their great potential as ligands for transition metal complexes, no synthesis has been established that is both general and high yielding. One potential use for these macrocycles is with iron(II) metal complexes that can be used as robust catalysts for applications in the coordination and activation of dinitrogen, where the stability of the complex is derived from the "macrocycle effect". This dissertation describes synthetic routes based on template syntheses using copper(I), which can be removed to yield the free macrocyclic phosphine, and attempts at directly using Fe(II) as a template. Chapter I reviews the literature on the synthesis and coordination chemistry of secondary phosphines on transition metals. Chapter II describes methods for preparing tetraphosphorus macrocycles on copper(I) using two bidentate secondary phosphines bridged with two ɑ-ω dihalides. Previous work with copper(I) investigated using the phosphorus Mannich reaction with 1,2-bis[(dihydroxymethyl)phosphino]ethane to form macrocycles and found that the copper complex Cu(DHMPE)2Cl forms a dimer in the solid state. Chapter III investigates this complex using 1H-DOSY NMR spectroscopy to find that the complex is monomeric in solution but dimeric as a solid. Chapter IV describes a synthetic method toward tetraphosphorus macrocycles using a linear open-chain mixed tertiary/secondary phosphine on copper(I). The copper can be removed and the free ligand can be coordinated to iron(II). The complex binds dinitrogen readily at atmospheric pressures. Chapter V investigates using iron(II) directly as a template, cutting out the need for a "surrogate" metal. The synthesis of hydrophilic tetradentate phosphines is also discussed. To conclude, an outlook for the future of this project is discussed. This dissertation includes previously published and unpublished co-authored material.