Wichtige Termine im Wintersemester 2021/22


  • Beginn der Vorlesungszeit: 11.10.2021
  • Ende der Vorlesungszeit: 04.02.2022
  • Die Vorlesungen fallen aus:
    24.12.2021 - 06.01.2022
  • Dies acdemicus: 01.12.2021
  • Feiertage: 01.11.2021


Bonn International Graduate School of Chemistry

GDCh Ortsverband Bonn


Vorsitzender: Prof. Dr. A. Lützen
Jungchemikerforum Bonn


KOPO 2019

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Carl-Glaser-Symposium 2019

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KOPO 2017

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Graduiertenkolleg "Template-designed Organic Electronics

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FOR 2685: Fossilization


FG Chemie auf

Die 7. Folge der "Frag
die Bonner Forscher" beschäftigt sich
mit der Frage, warum die Elemente im
Periodensystem genau auf diese Weise
angeordnet sind. Im Videoclip wird u. a.
der Schalenaufbau der Elektronenhülle
und der daraus resultierende Aufbau
des Periodensystems erklärt.


Chemiker berechnen „Abkürzung“ für Katalysator
O. Hollóczki, S. Gehrke, Angew. Chem. 2017, 10.1002/ange.201708305. (link)
In der Zeitschrift Angew. Chem. stellen Dr. Oldamur Hollóczki, Mulliken Center für Theoretische Chemie der Universität Bonn, und Sascha Gehrke, Mulliken Center für Theoretische Chemie der Universität Bonn und Max-Planck-Institut für Chemische Energiekonversion, einen neuartigen Reaktionsweg für die Organokatalyse mit N-heterozyklischen Carbenen (NHCs)  vor. Der Protonentransfer und die Herstellung der Bindung zwischen Katalysator und Substrat geschehen gleichzeitig in einem einzelnen Elementarschritt, ohne dass eine freie Carbenspezies in der Reaktionsmischung auftritt.
Weitere Informationen: (link)
Are There Carbenes in N-Heterocyclic Carbene Organocatalysis?
O. Hollóczki, S. Gehrke, Angew. Chem. Int. Ed. 2017,10.1002/anie.201708305 (link)
A novel reaction pathway for N-heterocyclic carbene organocatalysis has been identified. In this process, proton transfer and the binding of the substrate to the catalyst occur simultaneously in a single elementary reaction step, without the formation of a free carbene molecule in the reaction mixture.


Sie sind hier: Startseite


auf der Homepage des Kekulé-Institut für Organische Chemie und Biochemie der Rheinischen Friedrich-Wilhelms-Universität Bonn

Prof. Dr. S. Höger
Tel.: +49 (0) 228 73-6127
Fax: +49 (0) 228 73-5662
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Nanoscale π-conjugated ladders

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A packet of energy is created on a molecular ladder by the absorption of light. The background shows a real measurement of the ladder structure using a scanning tunnelling microscope. (Credit: Joshua Bahr and Tristan Keller) 


S. A. Meißner, T. Eder, T. J. Keller, D. A. Hofmeister, S. Spicher, S.-S. Jester, J. Vogelsang, S. Grimme, J. M. Lupton, S. Höger
Nanoscale π-conjugated ladders
Nature Communications 2021,12, 6614. (link)
 It is challenging to increase the rigidity of a macromolecule while maintaining solubility. Established strategies rely on templating by dendrons, or by encapsulation in macrocycles, and exploit supramolecular arrangements with limited robustness. Covalently bonded structures have entailed intramolecular coupling of units to resemble the structure of an alternating tread ladder with rungs composed of a covalent bond. We introduce a versatile concept of rigidification in which two rigid-rod polymer chains are repeatedly covalently associated along their contour by stiff molecular connectors. This approach yields almost perfect ladder structures with two well-defined π-conjugated rails and discretely spaced nanoscale rungs, easily visualized by scanning tunnelling microscopy. The enhancement of molecular rigidity is confirmed by the fluorescence depolarization dynamics and complemented by molecular-dynamics simulations. The covalent templating of the rods leads to self-rigidification that gives rise to intramolecular electronic coupling, enhancing excitonic coherence. The molecules are characterized by unprecedented excitonic mobility, giving rise to excitonic interactions on length scales exceeding 100 nm. Such interactions lead to deterministic single-photon emission from these giant rigid macromolecules, with potential implications for energy conversion in optoelectronic devices.

A family of heterobimetallic cubes shows spin-crossover behaviour near room temperature






M. Hardy, J. Tessarolo, J. J. Holstein, N. Struch, N. Wagner, R. Weisbarth,   M. Engeser, J. Beck, S. Horiuchi, G. H. Clever, A. Lützen, Angew. Chem. Int. Ed. 2021, 60, 22562-22569. DOI:10.1002/anie.202108792.
Starting from simple building blocks, six heterobimetallic cubes were obtained, following a straight-forward subcomponent self-assembly strategy. Three iron(II) based cages showed spin-crossover behaviour in solution. The crossover temperature was strongly dependent on interchangeable aldehyde components, giving rise to an efficient toolkit to manipulate magnetic behaviour.

Nanopatterns entering the third dimension







S. Henzel, S. Becker, D. Hennen, T. J. Keller, J. Bahr, S.-S. Jester, S. Höger,
Highly Strained Nanoscale Bicyclophane Monolayers Entering the Third Dimension: A Combined Synthetic and Scanning Tunneling Microscopy Investigation
ChemPlusChem 2021, 86, 803-811. (link)
Rising above the surface: Bicyclophanes of different sizes with different central units have been synthesized, including species with central units pointing out of the ring plane. Scanning tunneling microscopic investigations of self-assembled monolayers of these compounds at the solid/liquid interface on graphite provide submolecularly resolved insights into the nanopatterns formed. After adsorption the central units point along the surface normal and protrude by up to 1.6 nm into the volume phase.


Terpene Biosynthesis 
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A. Hou, J. S. Dickschat, The Biosynthetic Gene Cluster for Sestermobaraenes – Discovery of a Geranylfarnesyl Diphosphate Synthase and a Multiproduct Sesterterpene Synthase from Streptomyces mobaraensis, Angew. Chem. Int. Ed. 2020, 59, 19961-19965.
A biosynthetic gene cluster from Streptomyces mobaraensis encoding the first cases of a bacterial geranylfarnesyl diphosphate synthase and a type I sesterterpene synthase was identified. The structures of seven sesterterpenes produced by these enzymes were elucidated, including their absolute configurations. The enzyme mechanism of the sesterterpene synthase was investigated by extensive isotope labeling experiments.

Terpene Biosynthesis
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L. Lauterbach, B. Goldfuss, J. S. Dickschat, Two Diterpene Synthases from Chryseobacterium: Chryseodiene Synthase and Wanjudiene Synthase, Angew. Chem. Int. Ed. 2020, 59, 11943-11947. (link)
Two bacterial diterpene synthases (DTSs) from Chryseobacterium were characterised. The first enzyme yielded the new compound chryseodiene that closely resembles the known fusicoccane diterpenes from fungi, but its experimentally and computationally studied cyclisation mechanism is fundamentally different to the mechanism of fusicoccadiene synthase. The second enzyme produced wanjudiene, a diterpene hydrocarbon with a new skeleton, besides traces of the enantiomer of bonnadiene that was recently discovered from Allokutzneria albata.

Terpene Biosynthesis

TOC Graphic 4-20.png F. L. Lin, L. Lauterbach, J. Zhou, Y. H. Wang, J. M. Lv, G. D. Chen, D. Hu, H. Gao, X. S. Yao, J. S. Dickschat, Mechanistic Characterization of the Fusicoccane-Type Diterpene Synthase for Myrothec-15(17)-en-7-ol, ACS Catal. 202010, 4306-4312.

Fusicoccane (FC)-type diterpenes, featuring a common 5-8-5 tricyclic skeleton, possess diverse biological functions. Up to date, only FC-type diterpene synthases (DTSs) for three out of the sixteen possible stereochemically distinct sub-types of the FC skeleton have been discovered.
Herein, a (2Si,6Si,10Re,14Si)-FC-type DTS from Myrothecium gramineum is reported, that produces the diterpene alcohol myrothec-15(17)-en-7-ol. Based on homology modellings, the I189F variant was obtained by site-directed mutagenesis that prevents the penultimate carbocation from water attack, resulting in the deprotonation product myrotheca-7,15(17)-diene. VCD calculations in combination with chemical correlations through an enantioselective labeling strategy established the absolute configurations of these diterpenes. DFT calculations revealed a water-mediated proton transfer mechanism, which is supported by isotope labeling experiments, in contrast to the deprotonation/reprotonation mechanism reported in previous studies.


 Dynamic Complex‐to‐Complex Transformations

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M. Hardy, N. Struch, J. J. Holstein, G. Schnakenburg, N. Wagner, M. Engeser, J. Beck, G. H. Clever, A. Lützen, Angew. Chem. Int. Ed. 2020, 59, 3195-3200.
DOI: 10.1002/anie.201914629.

Two new heterobimetallic cages, a trigonal‐bipyramidal and a cubic one, were assembled from the same mononuclear metalloligand by adopting the molecular library approach, using iron(II) and palladium(II) building blocks. The ligand system was designed to readily assemble through subcomponent self‐assembly. It allowed the introduction of steric strain at the iron(II) centres, which stabilizes its paramagnetic high‐spin state. This steric strain was utilized to drive dynamic complex‐to‐complex transformations with both the metalloligand and heterobimetallic cages. Addition of sterically less crowded subcomponents as a chemical stimulus transformed all complexes to their previously reported low‐spin analogues. The metalloligand and bipyramid incorporated the new building block more readily than the cubic cage, probably because the geometric structure of the sterically crowded metalloligand favours the cube formation. Furthermore it was possible to provoke structural transformations upon addition of more favourable chelating ligands, converting the cubic structures into bipyramidal ones.

 Coupling therapy

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T. Eder, J. Vogelsang, S. Bange, K. Remmerssen, D. Schmitz, S.‐S. Jester, T. J. Keller, S. Höger, J. M. Lupton, Interplay Between J‐ and H‐Type Coupling in Aggregates of π‐Conjugated Polymers: A Single‐Molecule Perspective
Angew. Chem. Int. Ed. 2019, 58, 18898-18902. (link)
In organic electronics, J‐type coupling between monomers along the chain and H‐type coupling of chromophores between chains compete, which makes the two types of coupling hard to discern in the ensemble. A single‐molecule H‐type aggregate of fixed spacing and variable length of up to 10 nm is introduced, and HJ‐type aggregate formation is visualized intuitively in the scatter of single‐molecule spectra.

Unprecedented rearrangement


The stereochemistry of the structurally unique myxobacterial polyketides tuscolid/tuscorons was determined by a combination of high‐field NMR studies, molecular modeling, and chemical derivatization and confirmed by a modular total synthesis of tuscorons D and E. Together with the discovery of three novel tuscorons, this study provides detailed insight into the chemically unprecedented tuscolid/tuscoron rearrangement cascade.

B. Göricke, M. F. Bieber, K. E. Mohr, D. Menche*, Stereochemical Determination of Tuscolid/Tuscorons and Total Synthesis of Tuscoron D and E: Insights into the Tuscolid/Tuscoron Rearrangement
Angew. Chem. 2019, 131, 13153–13157; Angew. Chem. Int. Ed. 2019, 58, 13019-13023. (link)

 Merging Regiodivergent Catalysis with Atom-Economical Radical Arylation

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Indolines and tetrahydroquinolines from the same substrates by titanocene catalysis! The absolute configuration of the cyclopentadienyl ligand and the inorganic ligand determine the regioselectivity of ring opening and diastereoselectivity of radical arylation in the regiodivergent radical arylation of epoxides.
Mühlhaus, F.; Weißbarth, H.; Dahmen, T.; Schnakenburg, G.; Gansäuer. A., Angew. Chem. 2019, 131, 14346-14350; Angew. Chem. Int. Ed. 2019, 58, 14208-14212. DOI: 10.1002/anie.201908860 and 10.1002/ange.201908860 (link)

Terpene Biosynthesis

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J. S. Dickschat, Bacterial Diterpene Biosynthesis, Angew. Chem. Int. Ed. 2019, 58, 15964-15976.
This Minireview summarises recent developments in the biosynthesis of diterpenes by diterpene synthases in bacteria. It is structured by the class of enzyme involved in the first committed step towards diterpenes, starting with type I diterpene synthases, followed by type II enzymes and the more recently discovered UbiA‐related diterpene synthases. A special emphasis lies on the reaction mechanisms of diterpene synthases that convert simple linear precursors through cationic cascades into structurally complex, usually polycyclic carbon skeletons with multiple stereogenic centres. A further main focus of this Minireview is a discussion of how these mechanisms can be unravelled. Downstream modifications to bioactive molecules are also covered.


Terpene Biosynthesis

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K. Murai, L. Lauterbach, K. Teramoto, Z. Quan, L. Barra, T. Yamamoto, K. Nonaka, K. Shiomi, M. Nishiyama, T. Kuzuyama, J. S. Dickschat, An Unusual Skeletal Rearrangement in the Biosynthesis of the Sesquiterpene Trichobrasilenol from Trichoderma, Angew. Chem. Int. Ed. 2019, 58, 15046-15050. (Link)
The skeletons of some classes of terpenoids are unusual, because they contain a larger number of Me groups (or their biosynthetic equivalents such as olefinic methylene groups, hydroxymethyl groups, aldehydes or carboxylic acids and their derivatives) than provided by their oligoprenyl diphosphate precursor. This is sometimes the result of an oxidative ring opening reaction at a terpene cyclase derived molecule containing the regular number of Me group equivalents, as observed for picrotoxan sesquiterpenes. In this study a sesquiterpene cyclase from Trichoderma is described that can convert farnesyl diphosphate (FPP) directly via a remarkable skeletal rearrangement into trichobrasilenol, a new brasilane sesquiterpene with one additional Me group equivalent compared to FPP. A mechanistic hypothesis for the formation of the brasilane skeleton is supported by extensive isotopic labelling studies.

Master-Studentin des Kekulé-Instituts erhält Theodor-Laymann-Stipendium 2019

Der Theodor-Laymann-Stiftungsfonds hat im Sommersemester 2019 ein Stipendium an eine förderungswürdige Studentin aus der Organischen Chemie für die letzte Phase des Studiums vergeben. Das sechsmonatige Stipendium wird für die Zeit der Bearbeitung der Masterarbeit im Studiengang Chemie vergeben. Die Förderungswürdigkeit bestimmt sich einmal nach der Qualifikation und zu anderen nach sozialen Gesichtspunkten. Das Stipendium wird monatlich mit 735 Euro finanziert.
Wir gratulieren der Stipendiatin zu ihrem Erfolg.

Anti-Markovnikov Alcohols by Epoxide Hydrogenation the Radical Way

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Anti-Markovnikov Alcohols via Epoxide Hydrogenation through Cooperative Catalysis
Chengbo Y., Dahmen, T.; Gansäuer, A.; Norton, J. Science 2019, 364, 764-767.
DOI: 10.1126/science.aaw3913

Link zum Artikel in der FAZ
Link zur Pressemitteilung der Universität Bonn

We describe an epoxide hydrogenation that delivers the less-substituted anti-Markovnikov alcohols. The key-feature of our reaction is the coupling of titanocene catalyzed epoxide opening with chromium catalyzed hydrogen activation. Titanocene catalysis enforces the formation of the higher substituted radical and, hence, the anti-Markovnikov regioselectivity. Chromium catalysis enables the highly unusual stepwise transfer of H2 as H+, e-, and H●. Our unique dual catalysis approach sidesteps the typical regioselectivity of epoxide ring-opening by an SN2 mechanism that leads to the formation of the common Markovnikov alcohols by preventing the formation of hydric intermediates. The atom-economy of the reaction is excellent. Each step of the catalytic cycles has been observed separately.

Terpene Biosynthesis
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J. Rinkel, S. T. Steiner, J. S. Dickschat, Diterpene Biosynthesis in Actinomycetes: Studies on Cattleyene Synthase and Phomopsene Synthase, Angew. Chem. Int. Ed. 2019, 58, 9230-9233. (link)
Three diterpene synthases from actinomycetes were studied. The first enzyme from Streptomyces cattleya produced the novel compound cattleyene, and the other two enzymes from Nocardia testacea and Nocardia rhamnosiphila were identified as phomopsene synthases. The cyclisation mechanism of cattleyene synthase and the EI-MS fragmentation mechanism of its product were extensively studied by incubation experiments with isotopically labelled precursors. Oxidative transformations expanded the chemical space of these unique diterpenes.

Organic Photovoltaic Sensors for Photocapacitive Stimulation of Voltage‐Gated Ion Channels in Neuroblastoma Cells

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O. S. Abdullaeva, F. Balzer, M. Schulz, J. Parisi, A. Lützen, K. Dedek, M. Schiek, Adv. Funct. Mater. 2019, 29, 1805177. (link)                                                                                 
Organic semiconductors are emerging as promising candidates for novel electrically self‐sufficient photovoltaic prosthetics for neurostimulation, especially for restoration of light sensitivity in degenerate retina. Considering future applications, it is essential to gain fundamental insight into the signaling mechanisms at the organic photosensor–electrolyte–neuron interface. Particularly, targeting voltage‐gated ion channels by a pure photocapacitive stimulation is a preferred therapeutic approach as it avoids redox reactions involved in Faradaic charge injection. The present study investigates whether single neuroblastoma (N2A) cells, grown on a photosensor based on a small molecular squaraine:fullerene photoactive layer blend, optionally covered with silicon dioxide, can be activated by photocapacitive stimulation. Indeed, upon pulsed illumination, a rapid transient photocurrent strongly depolarizes the membrane potential and sub-
sequently activates fast‐responding voltage‐gated sodium channels. The dielectric top coating on the organic layer ensures sufficient capacitive charge injection efficiency while maintaining the rapid response of the device. Due to the high irradiance level required for photocapacitive stimulation, another slower, independent, and unintended, nonelectrical signaling pathway is identified. This activates voltage‐gated potassium channels, presumably by photothermal effects. The present study provides the basis for further improvements on standalone photovoltaic neurostimulating platforms based on organic photoactive layers.

Chiral Excitonic Organic Photodiodes for Direct Detection of Circular Polarized Light

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M. Schulz, F. Balzer, D. Scheunemann, O. Arteaga, A. Lützen, S. C. J. Meskers, M. Schiek, Adv. Funct. Mater. 2019, 29, 1900684.  (link)
A facile route to soft matter self-powered bulk heterojunction photodiode detectors sensitive to the circular polarization state of light is shown based on the intrinsic excitonic circular dichroism of the photoactive layer blend. As light detecting materials, enantiopure semiconducting small molecular squaraine derivates of opposite handedness are employed. Via Mueller matrix ellipsometry, the circular dichroism is proven to be of H-type excitonic nature and not originating from mesoscopic structural ordering. Within the green spectral range, the photodiodes convert circular polarized light into a handedness-dependent photocurrent with a maximum dissymmetry factor of ±0.1 corresponding to 5% overall efficiency for the polarization discrimination under short circuit conditions. On the basis of transfer matrix optical simulations, it is rationalized that the optical dissymmetry fully translates into a photocurrent dissymmetry for ease of device design. Thereby, the photodiode's ability to efficiently distinguish between left and right circularly polarized light without the use of external optical elements and voltage bias is demonstrated. This allows a straightforward and sustainable future design of flexible, lightweight, and compact integrated platforms for chiroptical imaging and sensing.

Supramolecular nanopatterns of H-shaped molecules

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M. Hündgen , K. A. Maier , S. Höger, S.-S. Jester, Supramolecular nanopatterns of H-shaped molecules
Chem. Commun.
, 2018, 54, 10558-10561. (link)
Scanning tunneling microscopy is applied to image self-assembled monolayers on graphite at the solid/liquid interface. H-shaped arylene–alkynylene backbones that are substituted with alkoxy side chains form a nanopattern to which a brick-like tiling scheme is indexed.
Alkoxy-substituted phenylene–ethynylene–butadiynylenes (PEBs) are connected via 1H-benzimidazole units to form H-shaped molecular scaffolds that self-assemble on graphite at the solid/liquid interface. Spacer lengths and end groups determine supramolecular tiling patterns, as shown via scanning tunneling microscopy (STM).

Terpene Biosynthesis
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J. Rinkel, L. Lauterbach, J. S. Dickschat, A Branched Diterpene Cascade: The Mechanism of Spinodiene Synthase from Saccharopolyspora spinosa, Angew. Chem. Int. Ed. 2019, 58, 452-455. (link)
A diterpene synthase from Saccharopolyspora spinosa was found to convert geranylgeranyl diphosphate into the new natural products spinodiene A and B, accompanied by 2,7,18‐dolabellatriene. The structures and the formation mechanism of the enzyme products were investigated by extensive isotopic labelling experiments, which revealed an unusual branched isomerisation mechanism towards the neutral intermediate 2,7,18‐dolabellatriene. A Diels–Alder reaction was used to convert the main diterpene product with its rare conjugated diene moiety into formal sesterterpene alcohols.

Terpene Biosynthesis

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G. Bian, J. Rinkel, Z. Wang, L. Lauterbach, A. Hou, Y. Yuan, Z. Deng, T. Liu, J. S. Dickschat, A Clade II-D Fungal Chimeric Diterpene Synthase from Colletotrichum gloeosporioides Making Dolasta-1(15),8-diene, Angew. Chem. Int. Ed. 2018, 57, 15887-15890. (link)
Based on a terpenoid overproduction platform in yeast for genome mining, a chimeric diterpene synthase from the endophytic fungus Colletotrichum gloeosporioides ES026 was characterized as the (5R,12R,14S)‐dolasta‐1(15),8‐diene synthase. The absolute configuration was independently verified through the use of enantioselectively deuterated terpene precursors, which unequivocally established the predicted C1‐III‐IV cyclization mode for this first characterized clade II‐D enzyme. Extensive isotopic labeling experiments and isolation of the intermediate (1R)‐δ‐araneosene supported the proposed cyclization mechanism.


 OH geht zur Hand

Die diastereoselektive Synthese von N‐tosylierten 1,3‐Aminoalkoholen gelang durch Aziridinierung von acyclischen Allylalkoholen und regioselektive Hydrosilylierung der entstehenden α‐Hydroxyaziridine durch eine SN2‐Reaktion, die sogar an tertiären C‐Atomen abläuft. Computerstudien zeigen, dass π‐Komplexe der Olefine mit Br2 oder BrCl in der Aziridinierung involviert sind, nicht jedoch, wie früher vorgeschlagen, Bromonium‐Ionen.
Y.-Q. Zhang, F. Bohle, R. Bleith, G. Schnakenburg, S. Grimme, A. Gansäuer, Synthesis of 1,3-Amino Alcohols by Hydroxy-Directed Aziridination and Aziridine Hydrosilylation, Angew. Chem. 2018, 130, 13716-13720; Angew. Chem. Int. Ed. 2018, 57, 13528-13532. (link)

 Metallosupramolecular Chemistry
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First the cage, then the ring: A BODIPY‐based bis(3‐pyridyl) ligand undergoes self‐assembly upon coordination to tetravalent palladium(II) cations to form a Pd6L12 metallosupramolecular assembly with an unprecedented structural motif that resembles a rotaxane‐like cage‐in‐ring arrangement. This assembly is not mechanically interlocked in the sense of a catenation but it is stabilized only by attractive noncovalent interactions.
M. Käseborn, J. J. Holstein, G. H. Clever, A. Lützen, A Rotaxane‐like Cage‐in‐Ring Structural Motif for a Metallosupramolecular Pd6L12 Aggregate, Angew. Chem. Int. Ed. 2018, 57, 12171-12175. (link

Giant intrinsic circular dichroism of prolinol-derived squaraine thin films

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Molecular chirality and the inherently connected differential absorption of circular polarized light (CD) combined with semiconducting properties offers great potential for chiral opto-electronics. Here we discuss the temperature-controlled assembly of enantiopure prolinol functionalized squaraines with opposite handedness into intrinsically circular dichroic, molecular J-aggregates in spincasted thin films. By Mueller matrix spectroscopy we accurately probe an extraordinary high excitonic circular dichroism, which is not amplified by mesoscopic ordering effects. At maximum, CD values of 1000 mdeg/nm are reached and, after accounting for reflection losses related to the thin film nature, we obtain a film thickness independent dissymmetry factor g = 0.75. The large oscillator strength of the corresponding absorption within the deep-red spectral range translates into a negative real part of the dielectric function in the spectral vicinity of the exciton resonance. Thereby, we provide a new small molecular benchmark material for the development of organic thin film based chiroptics.
M. Schulz, J. Zablocki, O. S. Abdullaeva, F. Balzer, A. Lützen, O. Arteaga, M. Schiek, Nat. Commun. 2018, 9, 2413. DOI: 10.1038/s41467-018-04811-7

Terpene Biosynthesis

This work is dedicated to the Rheinische Friedrich-Wilhelms University of Bonn on the occasion
of its 200th anniversary.
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L. Lauterbach, J. Rinkel, J. S. Dickschat, Two Bacterial Diterpene Synthases from Allokutzneria albata for Bonnadiene and for Phomopsene and Allokutznerene, Angew. Chem. Int. Ed. 2018, 57, 8280-8283. (link)
Two diterpene synthases from Allokutzneria albata were studied for their products, resulting in the identification of the new compound bonnadiene from the first enzyme. Although phylogenetically unrelated to fungal phomopsene synthase, the second enzyme produced a mixture of phomopsene and a biosynthetically linked new compound, allokutznerene, besides spiroviolene. Both enzymes were deeply studied for their mechanisms by isotopic labelling experiments, metal cofactor variation and site-directed mutagenesis. Oxidation products of phomopsene and allokutznerene are also discussed.

Mechanism-Based Condition-Screening for Sustainable Catalysis in Single Electron Steps by Cyclic Voltammetry

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A cyclic voltammetry based screening method for Cp2TiX-catalyzed reactions is introduced. Our mechanism-based approach enables the study of the influence of various additives on the electrochemically generated active catalyst Cp2TiX which is in an equilibrium with catalytically inactive [Cp2TiX2]-. Thioureas and ureas are most efficient in the generation of Cp2TiX in THF. The precise knowledge of the position of the equilibrium between Cp2TiX and [Cp2TiX2]- allows the identification of conditions for bulk electrolysis of Cp2TiX2 complexes and for Cp2TiX-catayzed radical arylations without having to carry out the reactions. Our time and resource efficient approach is of general interest for the reaction design in catalysis in single electron steps.

Liedtke, T.; Spannring, P.; Riccardi, L.; Gansäuer, A. Angew. Chem. 2018, 130, 5100-5104; Angew. Chem. Int. Ed. 2018, 57, 5006-5010. (link)

Cp2TiX Complexes for Sustainable Catalysis in Single Electron Steps 
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Richrath, R. B.; Olyschläger, T.; Hildebrandt, S.; Enny, D. G.; Fianu, G. D.; Flowers, R. A. II; Gansäuer, A. Chem. Eur. J. 2018, 24, 6371-6379. (link)
We present a combined electrochemical, kinetic, and synthetic study with a novel and easily accessible class of titanocene catalysts for catalysis in single electron steps. The tailoring of the electronic properties of our Cp2TiX-catalysts that are prepared in situ from readily available Cp2TiX2 is achieved by varying the anionic ligand X. Of the complexes investigated, Cp2TiOMs proved to be either equal or substantially superior to the best catalysts developed earlier. The kinetic and thermodynamic properties pertinent to catalysis have been determined. They allow a mechanistic understanding of the subtle interplay of properties required for an efficient oxidative addition and reduction. Therefore, our study highlights that efficient catalysts do not require the elaborate covalent modification of the cyclopentadienyl ligands.

Kekulé Postdoc Workshop "Women in Science 2018"
Monday, Mai 14th 2018
09:15 - 17:00, Chemische Institute Endenich, Hörsaal 2
In this workshop young female scientists will present their individual scientific results in the field of molecular or synthetic chemistry.
Click  here for more information

Molecular excitonic seesaws
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P. Wilhelm, J. Schedlbauer, F. Hinderer, D. Hennen, S. Höger, J. Vogelsang, J. M. Lupton
Molecular excitonic seesaws
PNAS 2018, 115, E3626-E3634.
Transformation of light into electronic excitation energy and the spatial redistribution of this energy within a complex of molecular units constitute the processes central to photochemical energy conversion in photosynthesis. Excitations migrate downward in energy between molecules, ultimately localizing at a global energetic minimum. But, how does energy flow in a system with built-in bistability, a local and a global energetic minimum? A molecular excitonic seesaw structure probes such fundamental intramolecular bistability. Much like watching a pen balanced on its tip fall randomly, in single molecules, energy flows nondeterministically to one or the other energetic minimum. Such a labile excitonic seesaw makes energy transfer highly susceptible to external stimuli and can be controlled, for example, by the incident light polarization.
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Terpene Biosynthesis
TOC Graphic Dickschat 3-18.jpg                           
J. Rinkel, L. Lauterbach, P. Rabe, J. S.
Dickschat, Two Diterpene Synthases for Spiroalbatene and Cembrene A from Allokutzneria albata, Angew. Chem. Int.
2018, 57, 3238-3241. (link)
Two bacterial diterpene synthases from the actinomycete Allokutzneria albata were investigated, resulting in the identification of the structurally unprecedented compound spiroalbatene from the first and cembrene A from the second enzyme. Both enzymes were thoroughly investigated in terms of their mechanisms by isotope labeling experiments, site-directed mutagenesis, and variation of the metal cofactors and pH value. For spiroalbatene synthase, the pH- and Mn2+-dependent formation of the side product thunbergol was observed, which is biosynthetically linked to spiroalbatene.

Terpene Biosynthesis
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J. Rinkel, L. Lauterbach, J. S. Dickschat, Spata-13,17-diene Synthase, an Enzyme with Sesqui-, Di- and Sesterterpene Synthase Activity from Streptomyces xinghaiensis, Angew. Chem. Int. Ed. 2017, 56, 16385-16389. (link)
A terpene synthase from the marine bacterium Streptomyces xinghaiensis has been characterised, including a full structure elucidation of its products from various substrates and an in-depth investigation of the enzyme mechanism by isotope labelling experiments, metal cofactor variations, and mutation experiments. The results revealed an interesting dependency of Mn2+ catalysis on the presence of Asp-217, a residue that is occupied by a highly conserved Glu in most other bacterial terpene synthases.

Aziridine radical opening
Gansäuer Aziridines.png
Y.-Q. Zhang, E. Vogelsang, Z.-W, Qu, S. Grimme, A. Gansäuer, Angew. Chem. Int. Ed. 2017, 56, 12654-12657. (link)
The first catalytic generation of β-amido substituted radicals from N-acyl aziridines is described. The radicals that are generated with excellent regioselectivity are useful intermediates for intermolecular additions, reductions, and cyclizations to yield functionalized amides. Through calculations we have shown that the ring opening is concerted and not step-wise as previously postulated.

 Inside or outside?
Lützen Inside or outside.png       
Simultaneous endo and exo Complex Formation of Pyridine[4]arene Dimers with Neutral and Anionic Guests
A. Kiesilä, L. Kivijärvi, N. Kodiah Beyeh, J. O. Moilanen, M. Groessl, T. Rothe, S. Götz, F. Topić, K. Rissanen, A. Lützen,  E. Kalenius, Angew. Chem. Int. Ed. 2017, 56, 10942-10946. (link)
The formation of noncovalent complexes between hexafluorophosphate (PF6) and tetraisobutyloctahydroxypyridine[4]arene has been studied in the gas phase, in the solid state, and in solution. In all states of matter, simultaneous endo complexation of solvent molecules and exo complexation of PF6 anions with the pyridine[4]arene dimers was observed.

 Tetrahedral cages
Two supramolecular cages based on a trifluoromethyl-substituted pyridylimine ligand have been synthesised where the iron(II) complex shows host–guest chemistry and complex-to-complex transformations.
Lützen Tetra cages.gif                   
           Lützen tetra cages Titelblatt.gif
Electron-deficient trifluoromethyl-substituted sub-components affect the properties of M4L4 tetrahedral cages 
N. Struch, F. Topić, K. Rissanen,  A. Lützen, Dalton Trans. 2017, 46, 10809-10813. (link)

SN2 at Tertiary Carbons by Epoxide Hydrosilylation
TOC for SN2 at tertiary-2.jpg
Y.-Q. Zhang, C. Poppel, A. Panfilova, F. Bohle, S. Grimme, A. Gansäuer, Angew. Chem. Int. Ed. 2017, 56, 9719-9722.
SN2 reactions at tertiary carbon centers in epoxides are possible when the angle of ‘backside attack’ is controlled! This is achieved by binding of the reagent and its activation to hydride transfer by fluoride. The reaction proceeds with excellent regioselectivity and allows the synthesis of many acetate and propionate derived 1,3-diol units pertinent to natural product synthesis.

Metallosupramolecular Chemistry
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N. Struch, C. Bannwarth, T. Ronson, Y. Lorenz, B. Mienert, N. Wagner, M. Engeser, E. Bill, R. Puttreddy, K. Rissanen, J. Beck, S. Grimme, J. R. Nitschke, A. Lützen
An Octanuclear Metallosupramolecular Cage Designed to Exhibit Spin-Crossover Behavior
Angew. Chem. Int. Ed. 2017, 56, 4930-4935. DOI: 10.1002/anie.201700832. (link)
By employing the subcomponent self-assembly approach utilizing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or its zinc(II) complex, 1H-4-imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O-symmetric cages having a confined volume of ca. 1300 Å3. The use of iron(II) salts yielded coordination cages in the high-spin state at room temperature, manifesting spin-crossover in solution at low temperatures, whereas corresponding zinc(II) salts led to the corresponding diamagnetic analogues. The new cages were characterized by synchrotron X-ray crystallography, high-resolution mass spectrometry, and NMR, Mössbauer, IR, and UV/Vis spectroscopy. The cage structures and UV/Vis spectra were independently confirmed by state-of-the-art DFT calculations. A remarkably high-spin-stabilizing effect through encapsulation of C70 was observed. The spin-transition temperature T1/2 is lowered by 20 K in the host–guest complex.

A Liquid-Crystalline Phenylene-Based Shape-Persistent Molecular Spoked Wheel
A. Idelson, C. Sterzenbach, S.-S. Jester, C. Tschierske, U. Baumeister, S. Höger
A Liquid-Crystalline Phenylene-Based Shape-Persistent Molecular Spoked Wheel
J. Am. Chem. Soc. 2017, 139, 4429–4434. (link)
Molecular spoked wheels with an all-phenylene backbone and different alkoxy side chain substitution patterns were synthesized using a cobalt-catalyzed [2+2+2] cycloaddition and subsequent template-directed cyclization via Yamamoto coupling. The two-dimensional organization of the molecules at the solid/liquid interface was investigated by means of scanning tunneling microscopy allowing imaging the molecular structure with submolecular resolution. With the right proportion of the flexible alkyl corona to the rigid core, mesomorphic behavior of one compound could be observed over a wide temperature range.

 Terpene Biosynthesis
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P. Rabe, J. Rinkel, E. Dolja, T. Schmitz, B. Nubbemeyer, T. H. Luu, J. S. Dickschat, Mechanistic investigantions on two bacterial diterpene cyclases:
Spiroviolene Synthase and Tsukubadiene Synthase, Angew.
Chem. Int. Ed.
2017, 56, 2776-2779. (link)
The mechanisms of two diterpene cyclases from streptomycetes - one with an unknown product that was identified as the spirocyclic hydrocarbon spiroviolene and one with the known product tsukubadiene - were investigated in detail by isotope labeling experiments. Although the structures of the products were very different, the cyclization mechanisms of both enzymes proceed through the same initial cyclization reactions, before they diverge towards the individual products, which is reflected in the close phylogenetic relationship of the enzymes.


Nachruf Prof. Dr. Fritz Vögtle
Fritz Vögtle.JPG
Am 3. Januar 2017 ist unser lieber Freund und Kollege Prof. Dr. rer. nat. Dr. phil. h.c. Fritz Vögtle im Alter von 77 Jahren verstorben. Er war uns menschlich und wissenschaftlich immer ein Vorbild, und er hat die Bonner Chemie in den vergangenen vier Jahrzehnten entscheidend mitgeprägt. Wir werden ihn stets in ehrender Erinnerung halten.

 Bent π-systems: 
Angewandte_Chemie_International_Edition cover klein.jpg

P. Wilhelm, J. Vogelsang, G. Poluektov, N. Schönfelder, T. J. Keller, S.-S. Jester, S. Höger, J. M. Lupton
Molecular polygons probe the role of intramolecular strain in the photophysics of π-conjugated chromophores
Angew. Chem. Int. Ed. 2017, 56, 1234–1238. (link)
Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.
The π-system of conjugated macromolecules can be bent in a controlled fashion by incorporating chromophores in molecular polygon templates. Bending leads to isotropic polarization in absorption and fluorescence but also influences excited-state properties. On the single-molecule level, a correlation emerges between luminescence spectrum and lifetime, which arises from subtle variations in the bending radius of the molecules.

Dickschat komp 2

P. Rabe, J. Rinkel, B. Nubbemeyer, T. G.
Köllner, F. Chen, J. S. Dickschat, Terpene Cyclases from Social Amoebae, Angew. Chem. Int. Ed. 2016, 55, 15420-15423. (link)

Genome sequences of social amoebae reveal the presence of terpene cyclases (TCs) in these organisms. Two TCs from Dictyostelium discoideum converted farnesyl diphosphate into (2S,3R,6S,9S)-(−)-protoillud-7-ene and (3S)-(+)-asterisca-2(9),6-diene. The enzyme mechanisms and EI-MS fragmentations of the products were studied by labeling experiments.

Natural products in synthesis and biosynthesis II
Dickschat komp


Jeroen S. Dickschat, Beilstein J. Org. Chem. 2016, 12, 413–414. (link)
Natural products continue to be an inspiring field of research and an important source of potent biologically active compounds. Currently, also in the pharmaceutical industry, natural products are experiencing a revival as viable drug candidates, which is a pleasing development since many infectious diseases continue to threaten human health. From the numerous articles in daily newspapers, it is obvious that politicians have also realised the urgent need for new drugs and the potential associated with natural products and their derivatives. Certainly, the recent technological advances in many fields related to natural products, analytical chemistry, gene synthesis, and genome sequencing and editing offer an efficient toolbox to natural products chemists. In addition, classical methods such as isotopic labelling experiments continue to be important.

Metal-Free Room-Temperature Dual Singlet–Triplet Emitters
Höger TOC 2016
Reprinted with permission from J. Phys. Chem. Lett. 2016, 7, 4802–4808. Copyright 2016 American Chemical Society.

W. Ratzke, L. Schmitt, H. Matsuoka, C. Bannwarth, M. Retegan, S. Bange, P. Klemm, F. Neese, S. Grimme, O. Schiemann, J. M. Lupton, S. Höger
Effect of Conjugation Pathway in Metal-Free Room-Temperature Dual Singlet–Triplet Emitters for Organic Light-Emitting Diodes
J. Phys. Chem. Lett. 2016, 7, 4802–4808.
DOI: 10.1021/acs.jpclett.6b01907  (link)

Management of spin statistics is crucial to the operation of OLEDs. Electrons and holes recombine as bright singlet and dark triplet excitations. To maximize efficiency, one has to make triplets bright. This can be achieved by either increasing spin-orbit coupling, which increases singlet-triplet mixing, raising the transition rate; or by decreasing non-radiative triplet relaxation by blocking internal conversion.
Perplexingly, only the former approach is used in OLED technology. This is all the more surprising, since the most efficient OLEDs are not strictly “organic” at all – they only work because of the incorporation of organometallic emitters.
The alternative approach has, in principle, been known for a long time, but has never been applied systematically to OLEDs. Orthogonalization of molecular orbitals effectively inhibits internal conversion and provides modest spin-orbit coupling to enable phosphorescence. A simple way to achieve this is to design molecules with transitions involving npi* orbitals. As we demonstrate here, such purely organic molecules show strong electrophosphorescence, at room temperature – with no metal ion in sight! The present letter discusses design rules to jumpstart this research direction. In particular, we explore the effect of extended conjugation and non-trivial isomerization on electrophosphorescence.

Dickschat TOC Graphic 8-11.jpg    

J. Rinkel, P. Rabe, P. Garbeva, J. S. Dickschat, Lessons from 1,3-Hydride Shifts in Sesquiterpene Cyclisations, Angew. Chem. Int. Ed. 2016, 55, 13593-13596. (link)
Stereospecifically labelled precursors were subjected to conversion by seven bacterial sesquiterpene cyclases to investigate the stereochemistry of their initial 1,10-cyclisation-1,3-hydride shift cascades. Enzymes with products of known absolute configuration showed a coherent stereochemical course, except for (-)-α-amorphene synthase, for which the obtained results are better explained by an initial 1,6-cyclisation. The link between the absolute configuration of the product and the stereochemical course of the 1,3-hydride shifts enabled assignment of the absolute configurations of three enzyme products, which were confirmed independently through the absolute configuration of the common byproduct germacrene D-4-ol.

 Die regiodivergente Epoxidöffnung: Kann links wie rechts
Abb Gansäuer AC  
N. Funken, F. Mühlhaus, A. Gansäuer
General, Highly Selective Synthesis of 1,3- and 1,4-Difunctionalized Building Blocks by Regiodivergent Epoxide Opening, Angew. Chem. Int. Ed. 2016, 55, 12030-12034. (link)
 Die Synthese enantiomerenreiner, linearer und unverzweigter 1,3- und 1,4-difunktionalisierter Verbindungen stellt einen wichtigen, aber noch recht unerforschten Teil der Organischen Synthese dar. Hier präsentieren wir eine zuverlässige und hoch selektive Synthese von sowohl 1,3- als auch 1,4-difunktionalisierten Verbindungen ausgehend von β-epoxy-funktionalisierten Substraten. Die hervorragenden Selektivitäten resultieren aus der Titan(III) katalysierten regiodivergenten Epoxidöffnung (REO) mit Kagan-Komplex. Durch den Einsatz verschiedener Pyridiniumsalze kann über Anioneneffekte Einfluss auf Selektivität und Dauer der Reaktion genommen und letztere um bis zu 97% gesenkt werden. Damit handelt es sich bei der REO um eine hervorragende Reaktion sowohl für die TOS (target oriented synthesis) als auch für die DOS (diversity oriented synthesis).  

 Naturstoffe als Spinsonden
Menche cover
EPR and DEER studies of V-ATPase complexes with spin labeled inhibitors DCC and archazolid enable insights into non-covalent binding dynamics and analysis of the key functional subunit c and demonstrate the general usefulness of natural product derived spin labels as innovative tools for chemical biology.

 J. P. Gölz, S. Bockelmann, K. Mayer, H.-J. Steinhoff, H. Wieczorek, M. Huss, J. P. Klare, D. Menche, EPR Studies of V-ATPase with Spin-Labeled Inhibitors DCC and Archazolid: Interaction Dynamics with Proton Translocating Subunit c, ChemMedChem 2016, 11, 420-428. (link)


Dickschat TOC Graphic.jpg

  T. A. Klapschinski, P. Rabe, J. S. Dickschat,
  Pristinol, a Sesquiterpene Alcohol with
  Unprecedented Skeleton from Streptomyces
, Angew. Chem. Int. Ed. 2016,
  55, 10141-10144. (link)
A terpene cyclase from Streptomyces pristinaespiralis was characterised as
(+)-(2S,3S,9R)-pristinol synthase. The structure of this sesquiterpene alcohol with a new carbon skeleton was established by NMR spectroscopy and single-wavelength anomalous dispersion X-ray crystallography. Extensive isotopic labelling experiments were performed to distinguish between various possible cyclisation mechanisms of the terpene cyclase and to decipher the EI-MS fragmentation mechanism of pristinol.


 Katalytisch, effizient, atom-ökonomisch: Ein neuer Zugang zu Alkaloidgerüsten
Gansäuer AC-2
S. Hildebrandt, A. Gansäuer, Angew. Chem. Int. Ed. 2016, 55, 9719–9722. (link)
Die katalytische C-H-Funktionalisierung aromatischer Verbindungen ist eines der aktivsten Gebiete der Organischen Synthese. Eine katalytische radikalische Funktionalisierung von Pyrrolen wurde nun durch Titanocen(III)-Katalyse ermöglicht. Da die Reaktion atom- ökonomisch, unter milden Bedingungen, mit einem ungiftigen und gut verfügbaren Metall unter niedriger Katalysatorbeladung verläuft, genügt sie den modernen Anforderungen an nachhaltige Chemie. Die entstehenden Alkaloidstrukturen sind wertvolle Intermediate in der Synthese komplexer Naturstoffe.

Dickschat Literatur

I. Burkhardt, T. Siemon, M. Henrot, L. Studt, S. Rösler, B. Tudzynski, M. Christmann, J. S. Dickschat, Mechanistic Characterisation of two Sesquiterpene Cyclases from the Plant Pathogenic Fungus Fusarium fujikuroi, Angew. Chem. Int. Ed. 2016, 55, 8748-8751. (link)
Two sesquiterpene cyclases from Fusarium fujikuroi were expressed in Escherichia coli and purified. The first enzyme was inactive because of a critical mutation, but activity was restored by sequence correction through site-directed mutagenesis. The mutated enzyme and two naturally functional homologues from other fusaria converted farnesyl diphosphate into guaia-6,10(14)-diene. The second enzyme produced eremophilene. The absolute configuration of guaia-6,10(14)-diene was elucidated by enantioselective synthesis, while that of eremophilene was evident from the sign of its optical rotation and is opposite to that in plants but the same as in Sorangium cellulosum. The mechanisms of both terpene cyclases were studied with various 13C- and 2H-labelled FPP isotopomers.

Epoxid-Hydrosilylierung: Hydroborierung vor dem wohlverdienten Ruhestand? 
 Gansäuer Klare weiss 2

D. Schwarz G. Henriques, K. Zimmer, S. Klare, A. Meyer, E. Rojo-Wiechel, M. Bauer, R. Sure, S. Grimme, O. Schiemann, R. A. Flowers II, A. Gansäuer
Highly Active Titanocene Catalysts for Epoxide Hydrosilylation: Synthesis, Theory, Kinetics, EPR Spectroscopy
Angew.Chem. Int. Ed
. 2016, 55, 7671 –7675. (link)
Epoxid-Hydrosilylierungen ermöglichen die lang begehrte anti-Markownikow-Addition von Wasser an Alkene in zwei Stufen. DFT- Rechnungen zusammen mit kinetischen, EPR-spektroskopischen und synthetischen Untersuchungen führten zu einer neuartigen, einfach durchführbaren Katalysatorgenerierung. Sie erlaubten ferner einen tiefen Einblick in den Reaktionsmechanismus mit einem ungewöhnlichen Resting State.
Dank der hohen Ausbeuten kombiniert mit hohen Regio- und Diastereoselektivitäten mit Silanen als umweltfreundliches Reduktionsmittel wird sich die Epoxid-Hydro-silylierung als nachhaltige Konkurrenz zur klassischen Hydroborierung etablieren.

Wie formstabil ist „formstabil”?

TOC AC Schweez groß
Bei neuartigen Phenylen-Ethinylen-Butadiinyl-Rotaxanen, die über einen kovalenten Templatansatz synthetisiert wurden, wird ein Abfädeln der Rad- von der Achskomponente beobachtet (siehe Bild). Der Abfädelungsmechanismus wurde durch DFT-basierte Molekülmechanikrechnungen und eine String-Methode zur Simulation seltener Ereignisse untersucht.
C. Schweez, P. Shushkov, S. Grimme, S. Höger
Synthesis and Dynamics of Nanosize Phenylene-Ethynylene-Butadiynylene Rotaxanes and the Role of Shape Persistence
Angew. Chem. 2016, 128, 3389-3394 (pdf); Angew. Chem. Int. Ed. 2016, 53, 3328-3333 (pdf).  DOI: 10.1002/anie.201509702R2 and 10.1002/ange.201509702R2

Gansäuer cover d
Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.
Katalytischer Tango: Die Katalysezyklen
greifen ineinander wie der Tanz eines
Tangopaars. Durch kooperative Katalyse können Radikale generiert und dann reduziert werden. Der milde Prozess eignet sich auch für gezielte Modifikation von Naturstoffen.
Y.-Q. Zhang, V. Jakoby, K. Stainer, A. Schmer, S. Klare, M. Bauer, S. Grimme, J. M. Cuerva, A. Gansäuer
Amid-substituierte Titanocene für die H-Atom-Transfer-Katalyse
Angew. Chem. 2016,128, 1546-1550. (link)
DOI: 10.1002/ange.201509548
(Pressemitteilung der UBonn)


Ein π-konjugiertes molekulares Wagenrad mit 6nm Durchmesser liefert neue Einsichten in die Photophysik konjugierter Polymere.
V. Aggarwal, A. Thiessen, A. Idelson, D. Kalle, D. Würsch, T. Stangl, F. Steiner, S.-S. Jester, J. Vogelsang, S. Höger, J. M. Lupton
Fluctuating exciton localization in giant π-conjugated spoked-wheel macrocycles
Nat. Chem. 2013, 5, 964-970. (link)