Unlocking Heteroaromatic Ring Systems through Chalcogen Insertion into Boroles.

In this work, we report the reactivity of various annulated borole derivatives toward chalcogen (O, S, and Se) insertion. Among a series of 9-borafluorenes with different boron substituents (Ph, Br, or o-carboranyl) and a mixed thiophene-benzene-fused derivative, only the 9-o-carboranyl-substituted 9-borafluorene yielded the complete set of chalcogen-containing heteroarenes, including the first 1,2-selenaborinine derivative. To evaluate the aromaticity of this heterocyclic analogue of phenanthrene, nucleus-independent chemical shift (NICS) values were computed and compared to those of its lighter group 16 congeners.

Construction of a Diverse Range of Boron Heterocycles via Ring Expansion of a Carboranyl-Substituted 9-Borafluorene.

Direct insertion of unsaturated substrates into a five-membered borole ring is a useful method to obtain valuable heterocycles containing one or more three-coordinate boron atoms. A highly Lewis acidic 9-o-carboranyl-9-borafluorene, in which the o-carboranyl substituent is connected via one of the cluster carbon atoms to the boron atom of the 9-borafluorene unit, was found to react with a vast array of unsaturated molecules, such as alkynes, aldehydes and various organic azides, to form larger boraheterocyclic products. The ring expansion reactions of the central borole ring proceed rapidly at room temperature, cementing the role of the o-carboranyl substituent in enhancing the insertion reactivity of 9-borafluorenes.

Alkene insertion reactivity of a o-carboranyl-substituted 9-borafluorene.

The synthesis of 9-borafluorene with an electron-withdrawing o-carboranyl substituent and its reactions with a series of alkenes are described. The o-carboranyl substituent is bonded via one of the cluster carbon atoms to the boron atom of the 9-borafluorene moiety. In all cases, the reactions afford partly saturated analogs of borepins (i.e. 6,7-dihydroborepins) by unprecedented alkene insertion into the endocyclic B-C bond of the borole ring. Comparative studies with 9-bromo-9-borafluorene illustrate the superior insertion reactivity of the carboranyl-substituted derivative. A suite of experimental and computational techniques disclose the unique properties of the 9-borafluorene and provide insight into how the 9-carboranyl substituent affects its chemical reactivity.

Stable and Storable N(CF3 )2 Transfer Reagents.

Fluorinated groups are essential for drug design, agrochemicals, and materials science. The bis(trifluoromethyl)amino group is an example of a stable group that has a high potential. While the number of molecules containing perfluoroalkyl, perfluoroalkoxy, and other fluorinated groups is steadily increasing, examples with the N(CF3 )2 group are rare. One reason is that transfer reagents are scarce and metal-based storable reagents are unknown. Herein, a set of CuI and AgI bis(trifluoromethyl)amido complexes stabilized by N- and P-donor ligands with unprecedented stability are presented. The complexes are stable solids that can even be manipulated in air for a short time. They are bis(trifluoromethyl)amination reagents as shown by nucleophilic substitution and Sandmeyer reactions. In addition to a series of benzylbis(trifluoromethyl)amines, 2-bis(trifluoromethyl)amino acetate was obtained, which, upon hydrolysis, gives the fluorinated amino acid N,N-bis(trifluoromethyl)glycine.

Reduction and Rearrangement of a Boron(I) Carbonyl Complex.

The one-electron reduction of a cyclic (alkyl)(amino)carbene (CAAC)-stabilized arylborylene carbonyl complex yields a dimeric borylketyl radical anion, resulting from an intramolecular aryl migration to the CO carbon atom. Computational analyses support the existence of a [(CAAC)B(CO)Ar].- radical anion intermediate. Further reduction leads to a highly nucleophilic dianionic (boraneylidene)methanolate.

Pentafluoroethylaluminates: A Combined Synthetic, Spectroscopic, and Structural Study.

Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2 F5 )4 ]- were obtained from AlCl3 and LiC2 F5 . They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2 F5 )4 ]- ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF3 ) under formation of [(C2 F5 )4-n AlFn ]- (n=1-4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2 F5 )AlF3 ]- ion was structurally characterized.

An indenide-tethered N-heterocyclic stannylene.

The structure of (µ-1κN:2(η2),κ2 N,N'-(2-{[2,6-bis(propan-2-yl)phen-yl]aza-nid-yl}eth-yl)[2-(1H-inden-1-yl)eth-yl]aza-nido)(1,4,7,10,13,16-hexa-oxa-cyclo-octa-dec-ane-1κ6 O)lithiumtin, [LiSn(C8H16O4)(C25H31N2)], at 100 K has monoclinic (P21/n) symmetry. Analysis of the coordination of the Sn to the indenyl ring shows that the Sn inter-acts in an η2 fashion. A database survey showed that whilst this coordination mode is unusual for Ge and Pb compounds, Sn displays a wider range of coordination modes to cyclo-penta-dienyl ligands and their derivatives.

[Follow-up care of patients after heart attack]. / Nachsorge von Herzinfarktpatienten in der Hausarztpraxis.

Survivors of a myocardial infarction are at increased risk for future cardiac events, including recurrent infarction, heart failure, arrhythmia, stroke, and sudden cardiac death. The primary care physician needs to be aware of the potential risks and complications facing these patients. Secondary preventive measures after myocardial infarction include an optimal medical therapy (dual antiplatelet therapy, Statin, ACE-inhibitor, and in most cases a beta-blocker) and life style modifications (quit smoking, regular physical activity, Mediterranean-style diet). Patients should be informed about how to recognize and react to cardiac symptoms.

Iron-sulfur cluster N2 of the Escherichia coli NADH:ubiquinone oxidoreductase (complex I) is located on subunit NuoB.

The proton-pumping NADH:ubiquinone oxidoreductase, also called respiratory complex I, couples the transfer of electrons from NADH to ubiquinone with the translocation of protons across the membrane. One FMN and up to 9 iron-sulfur (Fe/S) clusters participate in the redox reaction. There is discussion that the EPR-detectable Fe/S cluster N2 is involved in proton pumping. However, the assignment of this cluster to a distinct subunit of the complex as well as the number of Fe/S clusters giving rise to the EPR signal are still under debate. Complex I from Escherichia coli consists of 13 polypeptides called NuoA to N. Either subunit NuoB or NuoI could harbor Fe/S cluster N2. Whereas NuoB contains a unique motif for the binding of one Fe/S cluster, NuoI contains a typical ferredoxin motif for the binding of two Fe/S clusters. Individual mutation of all four conserved cysteine residues in NuoB resulted in a loss of complex I activity and of the EPR signal of N2 in the cytoplasmic membrane as well as in the isolated complex. Individual mutations of all eight conserved cysteine residues of NuoI revealed a variable phenotype. Whereas cluster N2 was lost in most NuoI mutants, it was still present in the cytoplasmic membranes of the mutants NuoI C63A and NuoI C102A. N2 was also detected in the complex isolated from the mutant NuoI C102A. From this we conclude that the Fe/S cluster N2 is located on subunit NuoB.