Design and Synthesis of a Series of Redox Active Tetrazine and Triazine Based Transition Metal Complexes by Yixin Zhang A thesis submitted in conformity with the requirements for the degree of Master of Science in Chemistry Department of Chemistry and Biomolecular Sciences University of Ottawa © Yixin Zhang, Ottawa, Canada, 2018 Design and Synthesis of a Series of Redox Active Tetrazine and Triazine Based Transition Metal Complexes Yixin Zhang Master of Science in Chemistry Department of Chemistry and Biomolecular Sciences University of Ottawa 2018 Abstract The use of two different chelating redox active ligands, 2,6-bis(6-methyl-1,2,4,5-3-yl) pyridine (BTZP) and 2,6-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridine (BTP) in heterometallic first row and second row transition metal chemistry has yielded two new families of redox active metal complexes. These complexes were found to exhibit interesting electrochemical and magnetic properties. In this thesis, Chapter 1 lays the foundation for the research presented within. This section covers the fundamentals of the ligand design, ligand synthesis and related coordination chemistry literature review. Chapters 2 and 3 report the results of the current thesis. In Chapter 2, the synthesis and characterization of a family of discrete molecules and supramolecular arrangements, employing the ligand BTZP, is presented. All of the complexes presented in Chapter 2 are successfully synthesized and characterized with electrochemical and magnetic studies. According 2+ to the electrochemical data, it is found that the classic “terpy-like” complexes with [Co(BTZP) 2] formula fosters more stability in the redox process. In Chapter 3, a family of transition metal 2+ complexes with [M(BTP) 2] (M=Fe or Co) inorganic cores were obtained through the employment of the ligand BTP with various anions. In addition, dimeric molecules with [CoX4(BTP)2] formula were also obtained by solvothermal synthesis. The complexes were also electrochemically characterized, with all the complexes capable of being reduced, while only II [Co (BTP)2] (ClO4)2 showed reversible redox process. Similar with BTZP, the series of BTP based complexes are also characterized through magnetic measurement. Only cobalt-based BTP ii II 2+ - - complexes are paramagnetic, with [Co (BTP)2] being spin crossover active when BF4 and ClO4 are present. However, the presence of NCS- and halides lead to either antiferromagnetic interactions and ferromagnetic interactions dominating at different temperature regimes. iii Acknowledgments First and foremost, I would like to express my most sincere gratitude to my supervisor, Prof. Muralee Murugesu, for taking me on as a student and giving me this opportunity to further my skills as a synthetic chemist, offering me the chance to contribute to the molecular magnetism field. Thank you for pushing me to newer and greater heights. I have thoroughly enjoyed the numerous clever analogies you have shared with me over the past 2 years, with your patience, motivation and immense knowledge. I’m looking forward to keeping working with you! I also would like to recognize the contributions of Dr. Bulat Gabidullin, our X-ray crystallographer. There are so many work depending on the X-ray results, and I am very grateful for having someone with your skills participate so actively in my research. I also would like to thank Ms. Rola Mansa for her assistance with TGA measurements. Finally, I would like to thank all previous and current lab group members for their input on this work, including Dr. Amélie Pialat who taught me the basics of organic synthesis. Dr. Jamie Frost helped me a lot in the early stages of research, and thanks for his kindly teaching for the basic research principles. A special mention to Miss. Katie Harriman for helping me out measuring the samples in the SQUID magnetometry and teaching me a lot in the early stages of the research in terms of magnetism part as well as providing invaluable insight. Many thanks to Mr. Paul Richardson for his kindly help for explaining inorganic basic concepts and English correcting. I also would like to thank to Mr. Maykon Lemes, who has been a fantastic colleague and friend to work with throughout my graduate studies. I also would like to thank Mr Gabriel Brunet for his assistance with PXRD measurements, solving magnetic problems as well as grammar checking. Finally, I would like to recognize Mr. Thomas Lacelle, who gives me a numerous help during the past two years. It was a really unforgettable time for taking class with you. Thank you so much for helping me to pass all exams. Last but not least, I would like to give thanks to all my friends who live in Ottawa, as well as living in all around the world now. Thank you so much about contributions that you given to me, and I really enjoy the moment with you. Special mention to my best friend back in China now Prof. Sha Feng, who has been an amazing organic synthetic chemist, and taught me a lot of tricks in the organic synthesis as well as numerous general chemistry contents. I also sincerely appreciate iv Mr Bowen Wang for being a fantastic supporter in every single moment together. Thank you so much for teaching me how to be a researcher in the very early stage and how to solve problem by myself. With your support and help, I could be always positive and get over any challenges I have had during the study. Finally, I would like also to give my sincere gratitude to my parents, even though they cannot understand any single English word, but support me all the time and encourage me to try what I would like to do. I really thank them to give me this great opportunity to study chemistry in the University of Ottawa and accomplish my dream. v Table of Contents Acknowledgments .................................................................................................................... iv Table of Contents ..................................................................................................................... vi 1 General introduction .............................................................................................................1 1.1 Tetrazines and triazines ..................................................................................................1 1.2 Ligand design .................................................................................................................3 1.2.1 The choice of redox activity ..............................................................................3 1.2.2 Chelating ligand .................................................................................................4 1.3 Literature method for synthesis of BTZP and BTP .......................................................6 1.4 Previous literature review ..............................................................................................8 1.4.1 Coordination chemistry of BTZP .......................................................................8 1.4.2 Coordination chemistry of BTP .........................................................................9 1.5 Project goal ..................................................................................................................11 2 Synthesis and characterizations in the molecular and supramolecular arrangements of transition metal complexes with a 2,6-bis(6-methyl-1,2,4,5-3-yl) pyridine ligand. ...........13 2.1 Introduction ..................................................................................................................14 2.2 Experimental ................................................................................................................15 2.2.1 Materials and methods .....................................................................................15 2.2.2 Synthesis of 2,6-dicyanopyridine .....................................................................15 2.2.3 Synthesis of the bis-tetrazine ligand (BTZP) ...................................................16 II 2.2.4 Synthesis of the [Co (BTZP)2](ClO4)2·2MeCN (1) ........................................17 II 2.2.5 Synthesis of the [Ni (BTZP)(MeCN)3](ClO4)2 (2) .........................................17 II 2.2.6 Synthesis of the [Ni Cl2(BTZP)(MeCN)]·2MeCN · H2O (3a) .......................17 II 2.2.7 Synthesis of the [Ni Cl2(BTZP)(MeCN)]·MeCN (3b) ...................................18 vi II 2.2.8 Synthesis of the {[Cd (NO3)2(BTZP)]}n (4) ...................................................18 2.2.9 Physical measurements ....................................................................................19 2.2.10 X-ray crystallography ......................................................................................19 2.2.11 Magnetic measurements ...................................................................................20 2.2.12 X-ray powder diffraction (XRPD) ...................................................................20 2.3 Results and discussion .................................................................................................22 2.3.1 Synthesis of BTZP ligand ................................................................................22 2.3.2 Synthesis and structure analysis for complex 1-4 ............................................23 2.3.3 UV-vis spectroscopy ........................................................................................30 2.3.4 Electrochemical studies of complexes 1-4 .......................................................31 2.3.5 Magnetic studies ..............................................................................................35