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FRANC MEYER
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Cooperating Metal Centers in Action:
Bioinorganic Models – Two-Center Catalysis –
Nanoswitches – Molecular Magnetism
Franc Meyer
Many enzymes take advantage of the synergetic effect of
two proximate metal ions within their active site in order
to mediate transformations of biological substrates. In
“small” synthetic compounds such cooperative reactivity
can be achieved by the use of suitable ligand scaffolds
that preorganize two metal ions at proper distance. Investigation of these bioinspired complexes helps to understand basic functional principles of the metalloproteins and provides great inspiration for the design of new
catalysts – not just for biomimetic reactivity, but for twocenter catalysis in general. Cooperativity between metal
ions is also crucial in, inter alia, electron transfer and
magnetism. Understanding and controlling these phenomena has important implications for the development of
new materials. Work in our group addresses various
aspects of metal ion cooperativity, ranging from metallobiosite modelling to organometallic catalysis and molecule-based magnetism.
Biomimetic Iron-Sulfur Clusters
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 emulate
characteristic spectroscopic features and unusual reactivities of the biological sites, such as radical-based sulfur
transfer from Fe/S cofactors during natural product synthesis. A recent example from our work is the isolation and
full characterization of a first synthetic analogue of Riesketype [2Fe-2S] clusters [1].
Functional Models of Metalloenzyme Active Sites – Bioinspired Catalysis
Metal ion cooperativity in metalloproteins is particularly important for biological oxidase or oxygenase activity, where
the metal ions serve to activate the kinetically inert O2,
and where the combined redox power of the two metal
ions is used to mediate and to control the multi-electron
Fig. 1: Rieske protein and synthetic model of its [2Fe-2S] cofactor with some
characteristic spectroscopic features [1].
redox processes. It is also pivotal for the synergetic activation of biological substrates by two adjacent Lewis acids
for, e.g., hydrolytic bond cleavages. In order to identify the
factors that govern such bimetallic enzyme reactions and
to employ two-center catalysis in a broader sense, we have
developed highly preorganized binuclear complexes based
on a set of multifunctional pyrazolate ligands. In these systems, fundamental parameters such as the metal-metal
separation, coordination numbers and redox potentials
can be controlled by subtle variations of the binucleating
ligand scaffold.
Current projects in our group focus on, inter alice,
(i) the binding and transformation of urea at dinickel sites
(relevant to the urease metalloenzyme), (ii) the hydrolytic
cleavage of phosphate diesters (phosphatase activity) and
␤-lactam antibiotics (metallo-β-lactamase activity) by binuclear zinc complexes [2], (iii) the catalytic oxidation of phenols by highly preorganized dicopper complexes [3], and
(iv) C-H activation and oxygenation with O2 mediated by
biomimetic diiron systems. These investigations provide insight into metalloenzyme mechanisms, and our synthetic
complexes have also become promising candidates for
new bioinspired catalysts.
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FRANC MEYER
Fig. 2: Dicopper complexes for bioinspired oxidation and oxygenation catalysis
(left) and dinickel complexes as models for the urease metalloenzyme (right).
Two-Center Organometallic Catalysis
Just as in bioinorganic chemistry, metal ion cooperativity
offers great perspectives in organometallic catalysis, since
concerted action of two or more proximate metal ions
may open new reaction paths. Ligands that provide two
binding pockets to arrange the metal centers in suitable
distance are crucial for this approach. In our ligand design
we combine a central pyrazolate bridging unit with classical donor groups (Cp, imine, N-heterocyclic carbene) to
provide rigid, yet tuneable, scaffolds for hosting the active
metal sites. As an example, pyrazole ligands with appen-
Molecular Nanoswitches and Molecular Magnetism
Magnetic coupling between paramagnetic metal ions can
be controlled by suitable bridging ligands. The topical
field of molecule-based magnetism indeed provides bright
prospects for novel devices and advanced materials. In
our work we use bi- and trimetallic complexes with welldefined spin ground state for the construction of highnuclearity clusters or extended 1D coordination polymers,
aiming for interesting quantum effects or materials with
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) moleculebased switches with magnetic hysteresis due to a structural phase transition near room temperature [5], and (ii)
robust spin-crossover grid complexes that can reversibly
shuttle between different magnetic or redox states, thus
representing molecular components for quantum cellular
automata (QCA) [6]. In close collaboration with physicists
we deposit these compounds on surfaces to address and
manipulate them on a single-molecule level.
Fig. 4: Rigid and switchable [2x2] grid complexes: STM image of a string of grid
molecules on HOPG surface (left) and molecular grid structure showing the
spin-crossover and redox multistability (right).[6]
Further projects in the group deal with unusual intermolecular interactions (anion-π interactions) [7] and the
development of self-reducing molecular precursors for
thin film or nanoscale metal and metal-oxide deposition.
Fig. 3: Homogeneous olefin polymerization with highly preorganized bimetallic
catalysts [4].
ded bulky imine chelate arms serve as valuable frameworks for bimetallic dinickel and dipalladium complexes
that exhibit high activity and metal ion cooperativity in,
e.g., homogeneous olefin polymerization [4].
Fig. 5: Highly air-sensitive compounds we handle in glove-boxes.
INSTITUTE
While synthesis is the cornerstone of most of our research, we apply a wide range of analytical and spectroscopic tools to answer the specific scientific questions. In
addition to common methods (NMR, IR, UV/vis spectroscopy, mass spectrometry, single crystal X-ray diffraction)
our group is equipped with instruments for low-temperature
stopped flow experiments, SQUID measurements, EPR,
Raman and Mößbauer spectroscopy, as well as for handling highly air-sensitive compounds.
Depending on the project topic, PhD students and
postdocs may be supported by the IRTG 1422 (Metal Sites
in Biomolecules: Structures, Regulation and Mechanisms;
see www.biometals.eu), the PhD program CaSuS (Catalysis for Sustainable Synthesis; see www.casus.uni-goettingen.de), or the SFB 602 (Complex Structures in Condensed Matter from Atomic to Mesoscopic Scale; see
www.sfb602.uni-goettingen.de). For more details about
our group and our research, or for a list of publications,
visit our web-site www.meyer.chemie.uni-goettingen.de.
OF INORGANIC
CHEMISTRY
Fig. 6: For investigating magnetic properties we use a modern SQUID
magnetometer.
Selected publications
[1] J. Ballmann, A. Albers, S. Demeshko, S. Dechert, E. Bill, E. Bothe, U. Ryde, F. Meyer, A Synthetic Analogue of Rieske-Type [2Fe-2S] Clusters.
Angew. Chem. 2008, 120, 9680; Angew. Chem. Int. Ed. 2008, 47, 9537.
[2] F. Meyer, Clues to Dimetallohydrolase Mechanisms from Studies on Pyrazolate-Based Bioinspired Dizinc Complexes - Experimental Evidence for
a Functional Zn-O2H3-Zn Motif. Eur. J. Inorg. Chem. 2006, 3789.
[3] A. Prokofieva, A. I. Prikhod’ko, S. Dechert, F. Meyer, Selective Benzylic C-C Coupling Catalyzed by a Bioinspired Dicopper Complex. Chem. Commun. 2008,
1005.
[4] A. Sachse, M. John, F. Meyer, A Unique Pd4 Platform with CH3 and µ-CH2 Groups and Its C-C Coupling Reaction with Simple Olefins, Angew. Chem. 2010,
122, 2030-2033; Angew. Chem. Int. Ed. 2010, 49, 1986-1989.
[5] G. Leibeling, S. Demeshko, S. Dechert, F. Meyer, Hysteretic Magnetic Bistability Based on a Molecular Azide Switch. Angew. Chem. Int. Ed. 2005, 117, 7273.
[6] B. Schneider, S. Demeshko, S. Dechert, F. Meyer, A Double-Switching Multistable Fe4 Grid Complex with Stepwise Spin Crossover and Redox Transitions,
Angew. Chem. 2010, 122, 9461-0464, Angew. Chem. Int. Ed. 2010, 49, 9274-9277.
[7] S. Demeshko, G. Leibeling, S. Dechert, F. Meyer, Anion-␲ Interactions in a Carousel Copper(II)-Triazine Complex. J. Am. Chem. Soc. 2004, 126, 4508.
Franc Meyer (born 1965) studied Chemistry
at RWTH Aachen where he got his Diploma
(1991) and PhD (1993) working on azaborane clusters (advisor: Peter Paetzold). He
then spent a year as a DFG postdoctoral
fellow studying gas phase ion-molecule reactions with Peter Armentrout in Salt Lake
City/Utah. After moving to Heidelberg he
completed his Habilitation in 2000 (mentor:
Gottfried Huttner), and he became Professor of Inorganic Chemistry at the University
of Göttingen in 2001. As Dean of Studies
(2005 – 2007) he implemented the new
B.Sc./M.Sc. programs. His awards include
the RWTH Borchers medal, Liebig and Heisenberg fellowships, the Freudenberg prize
of the Heidelberg Academy of Sciences,
and a FCI Dozentenstipendium. He is coordinator of the DFG-funded IRTG 1422 and
the international PhD program CaSuS,
elected member of the DFG Chemistry Review Board, and member of the Scientific
Advisory Board of the MPI for Bioinorganic
Chemistry. His research interests are in the
areas of bioinorganic chemistry, organometallic catalysis, and molecular magnetism.
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