The research of my group focuses primarily on the relationship between electronic structure and chemical or physical properties of transition-metal coordination compounds. As the main research objective, we address the mechanistic details how multiple electrons or holes transfer effectively to, within, and from a metal complex in the context of a chemical reaction. One goal is to identify structures that mediate the interconversion of electrical and chemical bond energies in an efficient manner. Another goal is to devise atom economic redox chemical methodologies for the generation of reactive main group radical species that merge with state-of-the-art protocols for catalytic bond formation and functionalization. At present, we make use of the distinct physical and chemical properties of metal-sulphur bonds of late transition metal thiolate complexes for the named purposes. We aim for devising metal-thiolate structures based on a bottom-up approach rather than mimicking structure-property relationships of systems found in nature. Starting from a structurally and electronically flexible dithiophenolate ligand scaffold, we have studied the mechanistic aspects of two-electron storage and reactivity of binuclear structures of nickel for hydrogen evolution and oxidation. Studies of radical-ligand complexes of group 10 metals establish a complementary research topic that focusses on the properties of metal complex near-infrared chromophores in addition to redox mechanisms for bond activation. Single-crystal X-ray diffraction, variable temperature magnetic spin resonance, vibrational and electronic absorption spectroscopy and electrochemistry are routine experimental techniques applied in studying electronic structure-property relationships. Expertise of collaborators on computational studies of electronic structure-property relationships of open-shell coordination compounds has complemented and expanded the scope of our experimental efforts.
A.B. is indepted to the Stipendien-Fonds der Chemischen Industrie, the Eliteprogram for Postdocs of the Baden-Württemberg Stiftung, and the Deutsche Forschungsgemeinschaft (DFG) for the financial support of research projects.
We currently pursue research on three primary topics. First, we investigate the phenomenon of cooperative reactivity between late transition-metal atoms in binuclear structures, with special emphasis on multiple electron reactivity. In this context, we carry out mechanistic work on energy efficient evolution and oxidation of dihydrogen. Second, we explore the electronic structure-property relationship of radical-ligand metal complexes. Because of their unique electronic structures, complexes featuring open-shell ligands possess intriguing chemical and physical properties. Examples include tuneable and electrochemically switchable absorptivity in the NIR and IR spectral region and H-atom abstraction reactivity that is of interest for catalytic bond formation protocols. Third, we devise strategies for the controlled switching of structural and electronic properties of mono- and bimetallic coordination compounds by electro- and photochemical stimuli. Notably, at present, all areas of research rely on the use of the same chemical entity: the transition metal-sulphur bond. This is possible because of the distinct properties of novel 1,4-terphenyldithiophenols that we have developed as a ligand platform. More precisely, the alignment of two thiophenols across a 1,4-disubstituted p-system creates a structurally and electronically unique donor environment that suits to support a single as well as multiple metal sites in various oxidation states. In addition, combining thiolates and π-systems enables the ligand framework to store and shuttle electrons and protons. The following three examples briefly highlight the strategy that we pursue to devise defined electronic structures for detailed studies of reactivity and physical properties.