Design of Redox-active Ligands: In Pursuit of Stable Radicals, their Complexes, and Assembly of Paramagnetic Coordination Clusters.

Abstract

This thesis describes the design, synthesis, properties, and coordination chemistry of redoxactive ligands. This thesis also explores new ways of expanding our ligand systems, in order to improve their binding capacities. We accomplished this by utilizing familiar redox-active moieties and structures to those published previously in our group, but with enhanced topological capacities and predictable structural outcomes. Chapter 1 begins with a general outline of the fundamental principles that govern organic radicals including; their reactivity, their properties and applications, and how these can be applied to the design of ligands for polynuclear assembly. Chapter 2 starts with a brief overview of arylazo ligands and the synthesis of a new hydrazone substituted phenalenol ligand (2.1). In the following section (2.2) we use this ligand to produce homoleptic ligand mixed-valence complexes featuring trivalent cobalt and iron metals. The chapter is concluded (2.3) with the synthesis of a new ditopic aryl-azo ligand and its cobalt coordination chemistry involving a neutral tetra-radical/tetra-nuclear molecular grid featuring valence tautomerism. Chapter 3 begins with the design and synthesis of a new ditopic diamino phenol ligand, which was found to oxidize to a neutral stable phenoxyl radical (3.1-3.2). The solution properties, which include reversible pi-dimerization of this stable radical are also described (3.3), and later the substitution chemistry of this new ligand is explored (3.4). In chapter 4, we describe the coordination chemistry of this new ditopic aminophenol ligand, which includes assembly into several coordination clusters involving copper (4.2), iron (4.3), nickel (4.4), and zinc (4.5). These coordination clusters feature the ligand in a variety of oxidation states; including rare examples of dianion “aminyl” radical clusters. In chapter 5, we begin with a description of a new synthetic derivative which can be used for the construction of larger tetratopic or asymmetric diamino phenol ligands. In 5.2 we describe the synthesis of a tetratopic aminophenol ligand along with its reactivity and aerial oxidation to a tri-phenoxyl radical. In 5.3, we conclude the thesis with the use of an asymmetric diamino phenol ligand and it’s Cu(II/III) coordination chemistry, which displayed unique reactivity with molecular oxygen.