Biomimetic Iron-Sulfur Clusters

Biomimetic Fe-S

         Iron-sulfur cofactors are ubiquitous in biological systems and have been of prime importance since the beginning of terrestrial life. Their main role is electron transfer, but other exciting functions (where iron-sulfur clusters act as catalytic sites or sensors) are increasingly recognized – iron-sulfur clusters have thus been termed “nature’s modular multipurpose structures”. Insight into the properties and electronic structures of iron-sulfur cofactors is provided by the investigation of synthetic Fe/S model complexes. Our efforts focus on the development of advanced synthetic analogues – in particular [2Fe–2S] clusters – that unravel the role of so-called alternative (non-cysteine) cluster ligands and that emulate unusual reactivities of the biological sites, such as radical-based sulfur transfer from Fe/S cofactors during natural product synthesis [1–3].

​[1]. "Ligand Rearrangements at Fe/S Cofactors: Slow Isomerization of a Biomimetic [2Fe-2S] Cluster" M. Bergner, L. Roy, S. Dechert, F. Neese, S. Ye, F. Meyer Angew. Chem. Int. Ed., 2017, 56, 4882–48867
[2]. "Model of the MitoNEET [2Fe−2S] Cluster Shows Proton Coupled Electron Transfer" M. Bergner, S. Dechert, S. Demeshko, C. Kupper, J. M. Mayer, F. Meyer J. Am. Chem. Soc., 2017, 139, 701–707.
[3]. "Fast Proton-Coupled Electron Transfer Observed for a High-Fidelity Structural and Functional [2Fe-2S] Rieske Model" A. Albers, S. Demeshko, S. Dechert, C.T. Saouma, J.M. Mayer, F. Meyer J. Am. Chem. Soc. 2014, 136, 3946–3954.

Bimetallic Activation of Small Molecules

Biomimetic activation of small molecule

        Most scenarios for storing energy in, and retrieving energy from, chemical bonds involve the activation and transformation of small ubiquitous molecules (O2, H2O, H2, N2, CO2, CH4); water splitting, generation of dihydrogen, and hydrogenation of dinitrogen and carbon dioxide are some of the key reactions relevant to the global energy challenge. All these transformations usually require the orchestration of multiple proton and electron transfers. For mediating these challenging reactions, nature has evolved sophisticated enzymes that often take advantage of the synergetic effect of two proximate earth-abundant metal ions within their active site. In synthetic bioinspired complexes such cooperative reactivity can be achieved by the use of elaborate ligand scaffolds that preorganize two metal ions at suitable distance. To identify the factors that govern bimetallic enzymatic reactions and to exploit two-center catalysis in a broader sense, our group has developed highly preorganized binuclear complexes based on a set of multifunctional pyrazolate ligands. Current projects in the group focus on, inter alia, (i) the Cu-mediated activation of O2 for oxidation and oxygenation catalysis inspired by biological type III dicopper sites[1]; (ii) the reductive binding of small molecules (including N2) via H2 elimination from oligometallic dihydride complexes[2–4] akin to the key N2 binding step in nitrogenase’s FeMoco; and the diiron-mediated transformation of NO mimicking flavodiiron NO reductases (FNORs) that are relevant in the global nitrogen cycle.[5]

[1]. "Hydrogen Atom Abstraction Thermodynamics of a μ-1,2-Superoxo Dicopper(II) Complex"
N. Kindermann, C.-J. Günes, S. Dechert, F. Meyer J. Am. Chem. Soc., 2017, 139, 9831–9834.
[2]. "Reductive Reductive nitric oxide coupling at a dinickel core: Isolation of a key cis-hyponitrite intermediate en route to N2O formation"
E. Ferretti, S. Dechert, S. Demeshko, M. C. Holthausen, F. Meyer Angew. Chem. Int. Ed. 2019,58, 1705–1709.
[3]. "Reductive O2 Binding at a Dihydride Complex Leading to Redox Interconvertible μ-1,2-Peroxo and μ-1,2-Superoxo Dinickel(II) Intermediates"
P.-C. Duan, D.-H. Manz, S. Dechert, S. Demeshko, F. Meyer J. Am. Chem. Soc., 2018, 140, 4929–4939.
[4]. "Pairwise H2/D2 Exchange and H2 Substitution at a Bimetallic Dinickel(II) Complex Featuring Two Terminal Hydrides"
D.-H. Manz, P.-C. Duan, S. Dechert, S. Demeshko, R. Oswald, M. John, R. A. Mata, F. Meyer J. Am. Chem. Soc., 2017, 139, 16720–16731.
[5]. "Reductive Transformations of a Pyrazolate-Based Bioinspired Diiron−Dinitrosyl Complex"
N. Kindermann, A. Schober, S. Demeshko, N. Lehnert, F. Meyer Inorg. Chem., 2016, 55, 11538–11550.
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Hybrid Systems for Electro- and Photocatalytic Water Oxidation

Hybrid Systems for Electro- and Photocatalytic Water Oxidation

        Efficient catalysts for water oxidation are key to all scenarios for artificial solar water splitting, and in case of molecular catalysts their immobilization on conductive solid supports is considered essential for the construction of photoelectrochemical cells. We develop new families of rugged pyrazolate-based bimetallic water oxidation catalyst and study mechanistic details of their sequential proton coupled electron transfer and O-O bond forming steps, and we synthesize hybrid systems that feature these complexes anchored on mesoporous oxides and other surfaces for driving the water oxidation reaction electro- and photochemically[1–3]. Our work also addresses fundamental aspects of charge transfer across the hybrid systems’ interfaces.

[1]. "Backbone Immobilization of the Bis(bipyridyl)pyrazolato Diruthenium Catalyst for Electrochemical Water Oxidation"
J. Odrobina, J. Scholz, A. Pannwitz, L. Francàs, S. Dechert, A. Llobet, C. Jooss, F. Meyer ACS Catal. 2017, 7, 2116–2125.
[2]. "Efficient Light-Driven Water Oxidation Catalysis by Dinuclear Ruthenium Complexes"
S. Berardi, L. Francàs, S. Neudeck, S. Maji, J. Benet-Buchholz, F. Meyer, A. Llobet ChemSusChem, 2015, 8, 3688–3696.
[3]. "New Powerful and Oxidatively Rugged Dinuclear Ru Water Oxidation Catalyst: Control of Mechanistic Pathways by Tailored Ligand Design"
S. Neudeck, S. Maji, I. López, S. Meyer, F. Meyer, A. Llobet J. Am. Chem. Soc. 2014, 136, 24–27.

Merging of Bioinorganic and Organometallic Concepts for Catalysis

Merging of Bioinorganic and Organometallic Concepts for Catalysis

        Using N-heterocyclic carbenes (NHCs) for stabilizing synthetic analogues of reactive biorelevant intermediates, we aim to develop new substrate transformations by favorably combining biomimetic approaches and classical organometallic concepts. Among the systems currently studied in the group are (i) iron complexes of macrocyclic tetracarbenes that are topologically related to, but electronically distinct from, iron porphyrins, including highly reactive high-valent oxoiron(IV) species capable of C-H activation; and (ii) organometallic variants of functional NiFe hydrogenase models for efficient H2 generation.

[1]. "Disproportionation Equilibrium of a μ‐Oxodiiron(III) Complex Giving Rise to C−H Activation Reactivity: Structural Snapshot of a Unique Oxoiron(IV) Adduct"
C. Kupper, M. Morganti, I. Klawitter, C.Schremmer, S. Dechert, F. Meyer Angew. Chem. Int. Ed., 2019, 58, 10855−10858.
[2]. "Nonclassical Single-State Reactivity of an Oxo-Iron(IV) Complex Confined to Triplet Pathways"
C. Kupper, B. Mondal, J. Serrano-Plana, I. Klawitter, F. Neese, M. Costas, S. Ye, F. Meyer J. Am. Chem. Soc., 2017, 139, 8939–8949.
[3]. "Magnetic Circular Dichroism Evidence for an Unusual Electronic Structure of a Tetracarbene−Oxoiron(IV) Complex"
S. Ye, C. Kupper, S, Meyer, E. Andris, R. Navrátil, O. Krahe, B. Mondal, M. Atanasov, E. Bill, J. Roithová, F. Meyer, F. Neese J. Am. Chem. Soc., 2016, 138, 14312–14325.

Molecular Nanoswitches and Magnetism

Molecular Nanoswitches and Magnetism

        The topical field of molecule-based magnetism offers great prospects for novel devices and advanced materials. In our work we develop 3d transition metal complexes with unusual coordination geometries that induce large magnetic anisotropy, and we use bi- and trimetallic complexes with well-defined spin ground state for the construction of high-nuclearity clusters with interesting quantum effects and valuable macroscopic magnetic properties. Compounds that feature hysteretic magnetic (or electronic) bistability are of particular interest, since they are expected to have great potential for future data storage or sensing applications. Examples from our recent work include (i) robust spin-crossover grid complexes that can reversibly shuttle between different magnetic or redox states, thus representing molecular components for quantum cellular automata (QCA); and (ii) low-valent, low-coordinate and high-symmetry 3d metal complexes that behave as mononuclear single molecule magnets (SMMs). In close collaboration with physicists we deposit these compounds on surfaces to address and manipulate them on a single-molecule level, and we study their excited state electronic structure and dynamics using time-resolved methods.

[1]. "Spin-State Versatility in a Series of Fe4 [2 × 2] Grid Complexes: Effects of Counteranions, Lattice Solvent, and Intramolecular Cooperativity"
M. Steinert, B. Schneider, S. Dechert, S. Demeshko, F.Meyer Inorg. Chem., 2016, 55, 2363–2373.
[2]. "Mixed-Spin [2 × 2] Fe4 Grid Complexes Optimized for Quantum Cellular Automata"
B. Schneider, S. Demeshko, S. Neudeck,S. Dechert, F. Meyer Inorg. Chem., 2013, 52, 13230–13237.

Prof. Dr. Inke Siewert | Institute of Inorganic Chemistry
Prof. Dr. Ricardo Mata | Institute of Physical Chemistry
Prof. Dr. Christian Jooß | Institute of Material Physics
Dr. Dirk Schwarzer | Max Planck Institute for Biophysical Chemistry
Prof. Dr. Frank Neese | Max Planck Institut für Kohlenforschung
Prof. Dr. Serena DeBeer | Max Planck Institut of Chemical Energy Conversion
Prof. Dr. Antoni Llobet | Institute of Chemical Research of Catalonia (ICIQ)
Prof. Dr. Max C. Holthausen | Institute of Inorganic and Analytic Chemistry, Goethe Universität Frankfurt
Prof. Dr. Oliver Wenger | Department of Chemistry, University of Basel
Dr. Carole Duboc | Département de Chimie Moléculaire, Université Grenoble Alpes, UMR CNRS 5250