Synthesis and characterization of transitional metal pyridine containing complexes with both catalytic and therapeutic applications

Abstract

Pyridinophanes derived from pyclen are the focus of many studies as biological mimics, chelators, and catalytic precursors. Therefore, the desire to tune the reactivity of metal pyridinophane complexes has inspired modifications that include expansion of ring size and substitutions to the N-atoms. However, substitution on the pyridine moiety is largely unexplored to date. Herein, new synthetic strategies for pyclen-congeners bearing electron donating and electron withdrawing groups are introduced, resulting in doubling the number of pyridine functionalized molecules in literature. Further, the influence of such modifications on properties and reactivity of two metals (Fe(III) and Cu(II)) is described. For the Fe(III) system, 4-substitution of the pyridine ring successfully provides a regulatory handle on the electronic properties and the catalytic C-C coupling activity of the respective Fe complexes. These are the first examples of a structure-activity relationship study with the impact of electronic properties decoupled from structural properties and investigated. The Fe(III) system was also explored in a catalase mimetic study to determine the role of ligand design on the activity of the metal center through changing electronic properties and rigidity of the ligand. Varying the electronic properties of the ligand has a minor effect on catalase activity, but changes to the geometry of the complex have significant impacts on the system. This activity was also successfully observed to cellular models. The Cu(II) system was investigated as a superoxide dismutase mimic. Cu(II) Pyclen complexes, specifically, has been shown to match its coordination environment and to have high binding affinity. My studies highlight that modifications to the pyridine ring of the ligand can tune the redox potential, while exhibiting high binding stabilities and retaining the coordination environment. In fact, one of the complexes studied exhibits one of the highest SOD activities reported to date, which is hypothesized to be the result of not only the electronic properties of the Cu center but also the high binding stability exhibited by this complex. Altogether, this work focused on functionalizing the pyridine ring in pyridinophanes and studying the effect of the modifications on the electronics of metal complexes and their reactivity with both catalytic and potential therapeutic application.