Date of Award
Fall 2015
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Ryan, Michael D.
Second Advisor
Dockendorff, Chris
Third Advisor
Huang, Jier
Abstract
Advances in the field of biomimetic inorganic chemistry require the design of sophisticated ligand frameworks that reflect the amazing complexity of metalloenzyme active sites. For instance, most active sites feature extensive hydrogen-bonding interactions between ligands bound to the metal center (the “first” coordination sphere) and nearby units in the outer (or “second”) sphere. Since these interactions modify the structural and electronic properties of the active sites, a number of inorganic chemists have sought to design ligands that permit outer-sphere functional groups to interact with first-sphere donors. This dissertation describes our contribution to these broader efforts to model the second coordination sphere. To date, our efforts have centered on the two classes of ligands based on second-sphere amide groups. The first set consists of 2,6-pyridinedicarboxamides with pendant pyridine or pyrimidine groups. Compared to the pincer ligands, the tripodal ligands posed a significantly greater synthetic challenge. We have succeeded in preparing a series of target ligands consisting of one, two, or three second-sphere heterocycles. My work has suggested that the second coordination sphere hydrogen bond interaction can be performed in our synthetic model. In addition, metalloenzymes with homobinuclear and heterobinuclear active sites play a central role in the chemistry of life. We have generated ligand scaffolds that support homo- and heterobimetallic complexes of relevance to metalloenzyme active sites. Firstly, the synthesis and coordination chemistry of a new asymmetric ligand designed to support nickel based heterobimetallic structures with relevance to bioinorganic chemistry is described. Additionally, we report the synthesis and coordination chemistry of ‘non-innocent’ pentadentate ligands intended to provide multiple sites for ligand-based oxidation and reduction. This ‘non-innocent’ ligand series contains a central diarylamido donor that serves as electron donor, in addition to ‘hard’ donor ligands (oxygen atoms), electron acceptor units, and ‘soft’ donor ligands. The resulting homobimetallic complexes (M = Co, Cu, and Zn) were characterized with X-ray crystallography and electrochemical methods. In addition, our studies found that the dicobalt(II) complex is a stable and efficient electrocatalyst for both H2 generation and H2O oxidation processes (i.e., water splitting).