Transition metal complexes of expanded porphyrins
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Over the last three decades, the rapid development of efficient synthetic routes for the preparation of expanded porphyrin macrocycles has allowed the exploration of a new frontier involving “porphyrin-like” coordination chemistry. This doctoral dissertation describes the author’s exploratory journey into the area of transition metal cation complexation using oligopyrrolic macrocycles. The reported synthetic findings were used to gain new insights into the factors affecting the observed coordination modes and to probe the emerging roles of counter-anion effects, tautomeric equilibria and hydrogen-bonding interactions in regulating the metalation chemistry of expanded porphyrins. The first chapter provides an updated overview of this relatively young coordination chemistry subfield and introduces the idea of expanded porphyrins as a diverse family of ligands for metalation studies. Chapter 2 details the synthesis of a series of binuclear complexes and illustrates the importance of metal oxidation state, macrocycle protonation and counter-anion effects in terms of defining the final structure of the observed metal complexes. The binding study reported in Chapter 3 demonstrates a strong positive allosteric effect for the coordination of silver(I) cations in a Schiff base expanded porphyrin. Chapter 4 introduces the use of oligopyrrolic macrocycles for the stabilization of early transition metal cations. Specifically, the preparation of a series of vanadium complexes illustrates the bimodal (i.e., covalent and noncovalent) recognition of the non-spherical dioxovanadium(V) species within the macrocyclic cavities. Experimental procedures and characterization data are reported in Chapter 5.