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Ligand Frameworks for Transition-Metal Complexes That Model Metalloenzyme Active Denan Wang Marquette University

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Ligand Frameworks for Transition-Metal Complexes That Model Metalloenzyme Active Denan Wang Marquette University Marquette University e-Publications@Marquette Dissertations (2009 -) Dissertations, Theses, and Professional Projects Ligand Frameworks for Transition-Metal Complexes That Model Metalloenzyme Active Denan Wang Marquette University Recommended Citation Wang, Denan, "Ligand Frameworks for Transition-Metal Complexes That Model Metalloenzyme Active" (2015). Dissertations (2009 - ). Paper 599. http://epublications.marquette.edu/dissertations_mu/599 LIGAND FRAMEWORKS FOR TRANSITION-METAL COMPLEXES THAT MODEL METALLOENZYME ACTIVE SITES by Denan Wang, B. S. A Dissertation submitted to the Faculty of the Graduate School, Marquette University, in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Milwaukee, Wisconsin December 2015 ABSTRACT LIGAND FRAMEWORKS FOR TRANSITION-METAL COMPLEXES THAT MODEL METALLOENZYME ACTIVE SITES Denan Wang, B. S. Marquette University, 2015 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). i ACKNOWLEDGMENTS Denan Wang, B. S. First of all I would like to thank my advisor, Professor Adam Fiedler for all his guidance and support. I feel so lucky to join to this clean, organized and wonderful working environment. Professor Fiedler was very patient, supportive and encouraging in guiding me towards the right direction, which gave me a tremendous amount of confidence to pursue lab work with much more efficiency. Moreover, he is not only an excellent scientist but also a great friend. He is a very understanding advisor and helps his students in their difficult times. I would like to thank my committee members, Dr. Ryan, Dr. Dockendorff and Dr. Huang, for their time, patience and suggestions. I would like to thank Dr. Sergey Lindeman for solving the crystal structures of my metal complexes. I would like to thank Dr. Sheng Cai, who was always willing to share his expertise in NMR with me. Moreover, I would thank to Chemistry Department of Marquette University for financial support. I would like to thank the Graduate School and all of the Marquette University administration. I would like to thank my lab mates Dr. Heaweon Park, Jake Baus, Mike Bittner, Xixi Hong, Amanda Baum, Ann Fisher and Tim Schluechtermann for their thoughtful discussions and assistance during my time at Marquette. I would like to thank my parents, Jianxing Wang and Bishuang Wu, for always supporting my endeavors. Without their support and patience none of this would have been possible. My sister and brother in law, Lifeng Wang and Chaoqun Lai, have also been very supportive of all my decisions. I would like to specially thank to Yilin for her support and understanding. I would like to thank my relatives who were always there to cheer me up throughout my academic career. I would also like to thank all my friends who accompanied me during my time at Marquette. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS..................................................................................................i LIST OF TABLES..............................................................................................................vi LIST OF FIGURES..........................................................................................................viii LIST OF SCHEMES.........................................................................................................xii CHAPTER 1. Introduction: Bioinspired Ligand Design for the Development of New Models of Metalloenzyme Active Sites ...............................................................................................1 1.1 Bioinorganic Chemistry.....................................................................................2 1.2 Second Coordination Sphere Interaction in Metalloenzymes and Biomimetic Complexes................................................................................................................3 1.2.1 Roles of First and Second Coordination Spheres..................................3 1.2.2 Incorporation of Second Coordination Sphere Effects in Synthetic Complexes ...................................................................................................10 1.3 Bimetallic Active Site in Metalloenzymes and Biomimetic Complexes.........21 1.3.1 Bimetallic Active Sites Involved in Water-Splitting Chemistry.........21 1.3.2 Synthetic Binuclear Complexes as Model of Metalloenzyme Active Site................................................................................................................25 1.4 Specific Aims of Our Research Efforts...........................................................29 2. Synthesis and Characterization of M(II) Complexes with 2,6-Pyridinedicarboxamide Ligands Capable of Forming Intramolecular Hydrogen Bonds........................................ 33 2.1 Introduction .....................................................................................................34 2.2 Experimental Section ......................................................................................38 iii 2.3 Result and Discussion......................................................................................47 2.3.1 Synthesis and Structures of Mononuclear Cu(II) Complexes.............47 2.3.2 Synthesis, Structures, and Magnetism of Dinuclear Cu(II) Complexes....................................................................................................56 2.3.3 Electronic Absorption Spectroscopy...................................................61 2.3.4 Electrochemistry..................................................................................64 2.3.5 Synthesis and Structural Characterization of Fe(II) and Ni(II) Complexes....................................................................................................71 2.4 Conclusions .....................................................................................................74 3. A New Class of Tripodal Ligands Based on the 2,2',2''-Nitrilotris(N-(pyridin-2- yl)acetamide Motif: Synthesis and Coordination Chemistry ............................................80 3.1 Introduction......................................................................................................81 3.2 Experimental Section.......................................................................................83 3.3 Result and Discussion......................................................................................90 3.3.1 Synthesis of Tripodal Ligands.............................................................90 3.3.2 Synthesis and X-ray Characterization of Metal Complexes...............92 3.3.3 DFT Calculations of Possible Ligand Coordination Modes...............95 3.4 Conclusion.......................................................................................................97 4. Synthesis of Homo- and Heterobimetallic NiII−MII (M = Fe, Co, Ni, Zn) Complexes Based on an Unsymmetric Ligand Framework: Structures, Spectroscopic Features, and Redox Properties .............................................................................................................100 4.1 Introduction....................................................................................................101 4.2 Experimental..................................................................................................105
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