News AG Wegner
A bidentate Lewis acid catalyzed domino inverse-electron-demand Diels–Alder reaction combined with a photoinduced ring opening formally inserts o-xylene moieties into enamine double bonds. After reduction, phenethylamines were obtained in good yields. The scope of the reaction was determined by variation of all three starting compounds: phthalazines, aldehydes, and amines.
The results were published as open access article in Organic Letters and were selected as ACS Editors' Choice.
He has just started his studies of meta-trisazobenzenes as a molecular triple photoswitch with selectively and independently switchable subunits. We hope, that you will enjoy your time in the Wegner group.
In the context of the scientific exchange between the Justus Liebig University Giessen and the Kazan Federal University, Assoc. Prof. Yakimova has been a guest of the Wegner group from February, 1st until April 30th, 2019. She stayed at the Justus-Liebig University Giessen under the DAAD program Stimuli-responsive macrocyclic assembly induced by complexation of molecular switches.
The absorption of a positively charge-tagged azobenzene molecule is studied in the gas-phase by measuring photoinduced fragmentation of ions as a function of time. This technique provides information on prompt as well as delayed fragmentation, and a single dissociation channel after one-photon absorption is identified. The spectra in solution, as well as in the gas-phase, show a weak S0 → S1, a strong S0 → S2, and a broad absorption band in the UV regime. The bands are assigned through time-dependent density functional theory calculations. The ratio of the various absorption bands depends on the trans to cis isomerization fraction and may be tuned by light irradiation. Gas-phase absorption spectra are presented and discussed in terms of trans and cis isomers.
Their "Enantioselective Synthesis of Azamerone" published in JACS demonstrated the applicability of the air-stable bisboron complex as a powerful tool to catalyse Inverse Electron Demand Diels-Alder(IEDDA) reactions even at a late stage in total synthesis. Especially the possibility to establish IEDDA reactions between tetrazines and electron deficient 1,4-naphthoquinones can be very auspicious to introduce a 2,3-diaza-anthraquinone motif into complex molecular structures.
Link to the Press Release: http://www.uni-giessen.de/ueber-uns/pressestelle/pm/pm10-19
Details to the original publication:
"An Amine Group Transfer Reaction Driven by Aromaticity", S. Ahles, S. Götz, L. Schweighauser, M. Brodsky, S. N. Kessler, A. H. Heindl, H. A. Wegner, Org. Lett., 2018, 20, 7034-7038; DOI: 10.1021/acs.orglett.8b02967
We wish you a successful year and that you keep enjoying your time in the Wegner group!
The deiodination and debromination reactions are triggered either by heating or by locally applying voltage pulses with the tip. We observed a strong hierarchical behavior of the dehalogenation with respect to temperature and voltage. In connection with first-principles simulations we can determine the orientation and position of the pristine molecules as well as adsorbed mono/diradicals and the halogens. We find that the isolated radicals are chemisorbed to Cu(111) top sites, which are lifted by 16 pm (meta-position) and 32 pm (para-position) from the Cu surface plane. This leads to a strongly twisted and bent 3D adsorption structure. After heating, different types of dimers are observed whose molecules are either bound to surface atoms or connected via Cu adatoms. Such knowledge about the intermediate geometry and its interaction with the surface will open the way to rationally design syntheses on surfaces. DOI: 10.1021/acsnano.8b06283
The interdisciplinary research project was designed by Prof. Dr. Ansgar Schnurr (Institute for Art Education), Prof. Dr. Hermann Wegner (Institute for Organic Chemistry), and Jannis Neumann (student of art education and biology), Justus Liebig University (JLU) Giessen.
Sketches from the artists Patrick Borchers, Jette Flügge, and Christoph Kern are presented. Visting the exhibition will be possible until october, 14th from 8.30 am until 11.00 pm at the central library of the university Giessen.
In a ceremony held at the university's main building, JLU-president Prof. Dr. Joybrato Mukherjee handed over the award, which is also supported by the Unfallkasse Hessen, to Prof. Hermann A. Wegner and the members of his group. The prize shall reward the commitment of all members of the group for maintaining a high safety level in everydays laboratory research.
Foto: JLU-Pressestelle / Katrina Friese
For the first publication, a complex of cycloparaphenylene (CPP) with bisazafullerene (C59N)2 was investigated experimentally and computationally. Two CPP rings are bound to the dimeric azafullerene giving CPP⊃(C59N)2⊂CPP. Photophysical and redox properties support an electronic interaction between the components especially with the second CPP bound. Unlike CPP⊃C60, where there is negligible electronic communication between the two species, upon photoexcitation a partial charge transfer phenomenon was revealed between CPP and (C59N)2 reminiscent of CPP encapsulated metallofullerenes. Such an alternative electron‐rich fullerene species demonstrates C60‐like ground‐state properties and metallofullerene‐like excited‐state properties opening new avenues for construction of functional supramolecular architectures with organic materials.
In second publication the adsorption of corannulene (C20H10) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS) was investigated. Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close compact phase with an average intermolecular spacing of ∼10.5±0.5Å. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a three-fold, ∼8.6Å unit mesh) and an on-pentagon (with a four-fold,∼11.5Å unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the three-fold and four-fold phases.
Its stability towards air and moisture was demonstrated by NMR studies enabling its application in organic transformations without glovebox. A one-pot procedure for its synthesis was developed starting from 1,2-bis(trimethylsilyl)benzene greatly enhancing its practicality. Comparative reactions were carried out to evaluate its catalytic activity in IEDDA reactions of diazine including phthalazine as well as 1,2,4,5-tetrazine.
To be competitive with other electrically rechargeable large scale energy storages, the range of active materials for redox flow batteries is currently expanded by organic compounds – this holds especially for the redox active material class of quinones that can be derived from naturally abundant resources at low cost. Here we propose the modified quinone 2,3-diaza-anthracenedione, and two of its derivatives, as promising active material for aqueous redox flow batteries. We systematically study the electrochemical performance (redox potentials, rate constants, diffusion coefficients) for these three compounds at different pH value experimentally and complement the results with density functional calculations: A positive redox potential shift of about 300 mV is achieved by the incorporation of a diaza moiety into the anthraquinone base structure. Our experiments at low pH show that the addition of a methoxy group to the base structure of the 2,3-diaza-anthracenedione strongly increases the electrochemical stability in aqueous acidic media – although the impact of the conjugate base is not clear yet. Furthermore, a functionalization with two hydroxyl groups evokes a negative redox potential shift of 54 mV in acidic and 264 mV in alkaline solution. This demonstrates that this novel class of compounds is very versatile and can be tailor-made for the use as active material in redox flow batteries – either in alkaline or acidic media. The 2,3-diaza-anthracenediones presented in this study were used as anolyte active materials in a full redox flow cell as a proof of concept; best cycling stability was achieved with 2,3-diaza-anthracenediones functionalized with a methoxy group as active material. Transferring our findings to other quinone base structures, such as naphtoquinones, could lead to even better performing catholyte and anolyte active materials for future redox flow batteries with organic active material.