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Boroles – Five-‐Membered Heterocycles with a Boron Atom – Are

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Boroles – Five-‐Membered Heterocycles with a Boron Atom – Are Boroles – five-membered heterocycles with a fundamental concepts of aromaticity and boron atom – are one of the more curious antiaromaticity.” families of molecule. They have four π-electrons, Using Electron Paramagnetic Resonance making them “antiaromatic” and, at least on spectroscopy, they showed that the unpaired paper, unlikely to be stable. Yet, synthetic electron is located on the boron, confirmed by chemists prepared them by bulking up the its reactivity as a boron-centred radical. groups around the ring, creating a shield of According to Mr. Wahler, there is still a lot of aromatic groups that stops them from work to be done: “Future work will include decomposing. If you add two electrons to a borole you increase the π-electron count to six – making them “aromatic”, and chemists have isolated this form as synthesis of related borole radical anions and well. The group of Prof. Holger Braunschweig other fancy borole derivatives - a job that is wondered: what about the missing borole with challenging but rewarding.” The results were five -electrons? π published recently in Angewandte Chemie, By pushing the protection of the boron atom International Edition. to the extreme and adding just one electron to the molecule, doctoral student Johannes Wahler Link to article: isolated the 5-electron borole, a radical anion. In http://onlinelibrary.wiley.com/doi/10.1002/anie his words: “Boroles are real multi-talents in .201108632/abstract terms of reactivity, which is governed by the Braunschweig Research Group: antiaromatic nature of this class of molecules. By http://www-anorganik.chemie.uni- the synthesis of a borole radical anion we wuerzburg.de/Braunschweig/ intended to create a junction between the two Supramolecular interactions – the way a squaraines that form in non-polar solvents. They molecule interacts with other molecules – can found that this organisation begins with the have a huge effect on the properties of coupling of two squaraines to form a dimer, functional materials. Squaraines, promising followed by stacking of the dimers to form long molecules for applications as fluorescent dyes, chains about three nanometres in width, which have both large flat pi-systems ideally suited to eventually clump together in bundles about nine intermolecular pi-pi stacking and the possibility nanometres wide. for hydrogen bonding. These structural traits result in the well- Link to article: known, property-altering aggregation of http://pubs.rsc.org/en/content/articlelanding/2 Squaraines. Despite their potential as molecular 012/sc/c2sc00996j materials, no studies of the aggregation of Würthner Research Group: squaraines have been performed in the absence http://www-organik.chemie.uni- of water, which can interfere with non-covalent wuerzburg.de/lehrstuehlearbeitskreise/wuerthn interactions. Recognising this, the group of Prof. er/ Dr. Frank Würthner set out to study the aggregation of squaraines in exclusively non- polar solvents – conditions where the weak intermolecular interactions can truly shine. In a publication in the new journal Chemical Science, Dipl. Chem. Ulrich Mayerhöffer and Prof. Würthner use UV-visible spectroscopy and atomic force microscopy (AFM) to study and visualise the long fibres of pi-pi-stacked Defects in polymeric materials like graphene are The first hurdle to overcome was the unavoidable, and often annoying. But in synthesis of a tribenzotriquinacene with six graphene, defects can change the way the substituents at para-positions (i.e. the portion material responds to external stimulus – shown in black in the figure). After much sometimes in desirable ways. tribulation, two variations of the desired These defects occur in graphene when the structure were isolated, and their progress has usual honeycomb-like pattern of hexagons is recently been published in the journal Chemical interrupted by pentagons or heptagons. As we Communications. The next step in the process, all learn as children, there’s no way to make flat connecting the three arene rings to create three networks of pentagons or heptagons, so these more rings, beckons. defects create blisters in an otherwise dead-flat sheet of carbon atoms. Link to article: To study how such a defect disturbs the http://pubs.rsc.org/en/content/articlelanding/2 electronic and magnetic properties of graphene, 012/cc/c1cc14703j the group of Prof. Dr. Anke Krueger has Krueger Research Group: targetted an isolated, molecular version of the http://www-organik.chemie.uni- irregularity, a “defective graphite flake” with a wuerzburg.de/lehrstuehlearbeitskreise/krueger/ tribenzotriquinacene core. But while the defects startseite/ occur naturally in graphene, synthesising a molecular version is very tricky indeed. Even high-school students will tell you that four- what is next on the list? “I really would love to coordinate carbon is tetrahedral, and this see someone trying to add a fifth metal to the concept holds too for carbon’s neighbours boron boron”, said Mr. Östreicher. and nitrogen. However, a new report in Angewandte Chemie, International Edition from Link to article: the research group of Prof. Dr. Holger http://onlinelibrary.wiley.com/doi/ Braunschweig suggests otherwise. By attaching 10.1002/anie.201107248/abstract four transition metals to a boron atom, they Braunschweig Research Group: have prepared two complexes in which the http://www-anorganik.chemie.uni- boron is essentially flat. wuerzburg.de/Braunschweig/ The students who performed the syntheses, Dr. Katharina Kraft and Dipl. Chem. Sebastian Östreicher, spent over a year trying to add the crucial fourth metal fragment to the boron atom, but did not expect that both complexes would turn out to be planar. As Mr. Östreicher explains, “The sheer fact that coordination of four metal atoms to boron was even possible came as a big surprise to us.” Since forcing boron to contort and form unsual geometries is a founding principle of the Braunschweig research group, .
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