Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Holland, Patrick

Abstract

This thesis describes the synthesis, characterization, and reactivity towards N2 reduction of a number of group 6 and 7 transition metal complexes bearing redox-active ligands. Chapter 1 introduces the field of nitrogen fixation, the role of transition metal catalysts in mediating nitrogen reduction, and some of the challenges that potential catalysts must overcome. Chapter 2 describes a number of molybdenum porphyrin complexes that were viable catalysts for N2 reduction with samarium diiodide and alcohol. The reduction of the ligand facilitates chemical transformations at the metal with strong acids and leads to NH3 formation. Chapter 3 describes the effects of exchanging a halide supporting ligand for a neutral, π-accepting redox-active isocyanide ligand in a rhenium PNP system. The isocyanide accepts electron density, leading to a 1.5 V anodic shift in the initial reduction potential, which corresponded to a 10 kcal/mol increase in the imido N−H bond strength. This change enabled productive electrochemical ammonia formation, and additional reduction (formally localized on the isocyanide) enabled nucleophilic attack on CO to form an isocyanate ligand. Chapter 4 expands upon the work in Chapter 3 and varies the auxiliary supporting ligand in the rhenium PNP system. The effect of each ligand in the series on the reduction potential, imido N−H bond strength, and reactivity towards N2 reduction is examined, providing a guide for researchers interested in incorporating redox-active ligands into their catalyst.

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