The current focal points of research of the group of Prof. Fritz E. Kühn are mainly based on organometallic complexes as catalysts for both bond formation reactions and bond cleavage reactions (1); novel, carbene type ligands are synthesized an applied as steering ligands in organometallic catalysts (2); both inorganic and organometallic compounds are used for the synthesis of organometallic frameworks (3); newly developed ionic liquids are both applied as reaction media and reaction promoters (4);
Organometallic and Inorganic complexes are tailor made for medical applications (5).
This work is done in cooperation with research groups with complementary research experience, and with industry.
(1) A significant part of the research group are charged with the synthesis of highly efficient organometallic epoxidation catalysts, based on the metals rhenium and molybdenum. The goal of this research is to reach both high turnover frequencies and stability (in order to recycle the catalysts) with an eye on real industrial applicability for selected substrates. Accordingly, the group has on this topic several industry co-operations (e. g. Clariant/Süd-Chemie, DSM). Chirality transfer and catalyst immobilization on both surfaces and in organometallic frameworks as well as in membranes are currently the highest ranking research goals. Co-operation with groups with long experience in chirality transfer are intended in this area. Mechanistic details and mechanistic examinations are also of significant importance to understand reaction pathways and catalytic cycles and beside own calculations, we have worked with external theoreticians (e. g. Prof. N. Rösch, formerly Munich, now Singapore; Prof. M. J. Calhorda, Lisbon) in cooperation and intend to continue with that. Additional to synthesis the group relies in this (and all other areas) heavily on a multitude of characterization methods, among them quite prominently heteroatom NMR (e. g. 17O-, 95Mo-NMR). Recently the Kühn group discovered a novel iron catalyst that reaches turnovers of almost a million per hour. A number of both original papers and reviews has been published by the Kühn group during the last 15 years. See for example: F. E. Kühn et al. Chem. Eur. J. 1999, 33, 192-198; Chem. Eur. J. 2002, 8, 2370-2383; Inorg. Chem., 2002, 41, 4468-4477; Organometallics, 2003, 22, 2112-2118; Adv. Synth. Catal. 2005, 347, 473-483; Chem. Rev. 2006, 106, 2455-2475; Adv. Synth. Catal., 2006, 348, 1752-1759; Chem. Eur. J., 2007, 3, 158-166; Angew. Chem. Ind. Ed., 2007, 46, 7901-7903; Green Chem., 2007, 12, 1296-1298; Green Chem., 2008, 10, 442-446; Organometallics, 2009, 28, 639-645; Adv. Synth. Catal., 2009, 351, 230-234; Inorg. Chem., 2009, 48; 6812-6822; Adv. Synth. Catal., 2010, 352, 547-556; J. Catal., 2011, 283, 55-67; Adv. Synth. Catal., 2011, 353, 3014-3022; Cat. Sci. Tech., 2012, 2, 722-724; Cat. Sci. Tech. 2013, 3, 388-393.
Beside oxidation catalysis, the Kühn group is also interested in catalysts for aldehyde and ketone olefination and has developed several systems for that. The goal here is to find catalysts based on cheaper metals with similar or even higher activity than the currently used rare metal compounds or noble metal complexes. Publications of in this are for example: J. Am. Chem. Soc., 2003, 125, 2414-2415; J. Catal., 2004, 227, 253-256; Chem. Eur. J., 2004, 10, 6313-6321; Organometallics, 2007, 26, 302-309; Adv. Synth. Catal., 2012, 354, 1827-1831.
Also in the context of bond formation reactions is the interest in catalytic polymerization reactions. This work was originally based on a co-operation with BASF SE on cationic polymerization reactions, where several patents emerged. In the mean time the research group’s interest in catalyzed polymerization reaction has broadened and we are co-operation also with other companies (e. g. Wacker) und University based groups (e. g. Prof. O. Nuyken, Munich, Prof. B. Voit, Dresden) on the development of more efficient (currently largely inorganic) catalysts. Selected publications in this area: Angew. Chem. Int. Ed., 2003, 42, 1307-1310; Chem. Eur. J. 2004, 10, 6323-6332; Angew. Chem. Int. Ed., 2007, 46, 7290-7292; Chem. Eur. J., 2008, 14, 7997-8003; Chem. Rev., 2009, 109, 2061-2080; Progress in Polym. Sci., 2010, 35, 687-713; Cat. Sci. Tech., 2012, 2, 725-729.
(2) Overlapping with the topic described above is the synthesis and application of organometallic compounds with carbine ligands. Research in this area started in the Kühn started group about 5 years ago. (Subtopics: Carbene chemistry and bio-renewables; activation of small molecules). N-heterocyclic carbenes (NHCs) are applied as steering ligands for both catalytic bond formation and bond cleavage reactions. Recent interest has been focused on CO2-activation and C-H activation (with CH4-activation as target) to contribute to a sustainable chemistry. Co-operations with other research institutions, e. g. KAUST (Prof. J. M. Basset), University of Udine (Prof. W. Baratta), University of Edinburg (Prof. P. L. Arnold, Dr. J. Love) and companies, e. g. Wacker AG exist. Additionally, work is dedicated to the activation and degradation of compounds derived from renewable resources and are developing catalysts for that, in many cases using NHCs as ligands. NHCs are also combined to (so far) bis- to tetradentate ligands and for the attachments of the catalysts to carrier materials. Catalytic hydrogenations, transfer hydrogenation and related reactions reactions play an important role in this area. In order to be able to get access to cheap hydrogen resources sun energy certainly has to play a major role. In order to close this cycle in a truly energy saving way, a co-operation with groups that are specialized in collecting / harvesting solar energy and using it for hydrogen production is intended. Selected publications in this area are: Green Chem., 2009, 11, 13-26; Green Chem., 2009, 11, 1610-1617; Organometallics, 2010, 29, 5681-5692; J. Am. Chem. Soc., 2011, 133, 1589-1596; Angew. Chem. Int. Ed., 2011, 123, 8662-8690; ChemSusChem, 2011, 4, 1275-1279; Cat. Sci. Tech., 2012, 2, 725-729; ACS Catalysis, 2012 2, 613-621; Organometallics, 2012, 32, 2792-2800; J. Catal., 2012, 296, 1-14; ChemCatChem, 2012, 4, 1703-1712; Angew. Chem. Int. Ed., 2013, 52, 270-289; Organometallics, 2013, 32, 741-744; ChemCatChem, 2013, 5, 1321-1324; Organometallics, 2013, 32, 3376-3384; Organometallics, 2013, 32, 4042-4045; Organometallics, 2013, 32, 4082-4091. Additional to this work, which has, beside synthesis, characterization and mechanistic considerations also a rather applied orientation, some basic research on carbene chemistry to exploit new, potentially interesting ligand classes and compare their behavior to known ones in order to make predictions about their applicability as ligands for catalysts is executed. This subgroup is co-supervised by the junior scientist Dr. Alexander Pöthig. Selected papers of the group in this area are: Chem. Commun., 2012, 48, 3857-3859; Organometallics, 2012, 31, 8249-8256; Inorg. Chem., 2013, 52, 6142-6152; Inorg. Chem., 2013, 52, 7031-7044.
(3) The synthesis of organometallic wires and networks dates back to Prof. Kühn’s postdoctoral research in the group of F. A. Cotton (Texas A & M University), where he synthesized metal-metal multiply bonded units. Based on them first organometallic wires and, much more recently, organometallic frameworks were synthesized. It could be shown that in solution, under mild conditions organometallic frameworks and their constituting units (e. g. squares and triangles) can be formed. Potential applications of the wires for electron transport or the MOFs to include catalyst molecules in either the framework or the cavities are currently under examination. A cooperation with Nanyang Technological University (NTU) and some companies in Singapore is currently being established. Further co-operation is intended with Nanjing University (Prof. J. L. Zuo). Selected publications in this area are: Dalton Trans., 1999, 4103-4110; Dalton Trans., 2002, 1100-1107; Dalton Trans., 2011, 40, 5746-5754; Dalton Trans., 2011, 40, 11490-11496; Organometallics, 2013, accepted (ID om-2013-00518f).
(4) The ionic liquid topic was originally limited to applications as solvent for two- and multiphase catalysis in Prof. Kühn’s group, however, a few years ago we noted the applicability of metal containing ionic liquids first as reaction promoters (when applied in bulk phase) and then as catalysts (when applied in catalytic amounts). This work is done largely in co-operation with the groups of Prof. S. L. Zang and Prof. M. D. Zhou (Shenyang / Fushun). The ionic liquid subgroup, concentrating on CO2-activation (e. g. with epoxides) is co-supervised by the junior scientist Dr. Mirza Cokoja. The research group is also starting to examine ionic liquids as electrolytes for advanced batteries in co-operation with TUM CREATE and NTU in Singapore. Selected publications on that topic are for example: ChemSusChem, 2010, 3, 559-562; Coord. Chem. Rev., 2011, 255, 1518-1540; RSC Advances, 2012, 2, 8416-8420; Chem. Eur. J., 2013, 19, 5972-5979.
(5) The application of organometallic compounds in medicine emerged only this year, initiated by an exploratory workshop in early May 2013 at the Institute for Advanced Study at TUM, following an idea of the year before. As a student Prof. Kühn had worked in the group of Prof. Roger Alberto (now University of Zurich) and during his stay as principal researcher at the Instituto Tecnologico Nuclear in Sacavem he came again in close contact with nuclear medicine. In cooperation with bio-inorganic chemists (Prof. A. Casini (Groningen), Prof. J. D. G. Correia (Sacavem), Prof. O. Iranzo (Marseille)) the group intends to make some contributions to this area, particularly in the field of cancer diagnosis and therapy with rhenium and technetium based transition metal compounds. A first review, prepared by this subgroup is accepted and will appear soon (J. Organomet. Chem., 2013, in press – http://dx.doi.org/10.1016/j.jorganchem.2013.07.042).