A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent‐Induced Increase of the Enantiomerization Barrier in 1‐Aza‐[5]helicene

Helicenes and heterohelicenes are attractive compounds with great potential in materials sciences to be used in optoelectronics as ligand backbones in enantioselective catalysis and as chiral sensors. The properties of these materials are related to the stereodynamics of these helical chiral compounds. However, little is known about features controlling stereodynamics in helicenes; in particular, for heterohelicenes the position of the heteroatom could be relevant in this respect. Herein the complete stereodynamic characterization of monoaza[5]helicenes is shown by enantioselective dynamic HPLC and DFT calculations. At variance with previous theoretical calculations, 1‐aza[5]helicene shows a surprisingly high enantiomerization barrier, which is triggered by specific solvent interactions.     

Water-soluble organo-silica hybrid nanotubes templated by cylindrical polymer brushes

We report the preparation of water-soluble organo-silica hybrid nanotubes templated by core-shell-corona structured triblock terpolymer cylindrical polymer brushes (CPBs). The CPBs consist of a polymethacrylate backbone, a poly(tert-butyl acrylate) (PtBA) core, a poly(3-(trimethoxysilyl)propyl acrylate) (PAPTS) shell, and a poly(oligo(ethylene glycol) methacrylate) (POEGMA) corona. They were prepared via the "grafting from" strategy by the combination of two living/controlled polymerization techniques: anionic polymerization for the backbone and atom transfer radical polymerization (ATRP) for the triblock terpolymer side chains. The monomers tBA, APTS, and OEGMA were consecutively grown from the pendant ATRP initiating groups along the backbone to spatially organize the silica precursor, the trimethoxysilyl groups, into a tubular manner. The synthesized core-shell-corona structured CPBs then served as a unimolecular cylindrical template for the in situ fabrication of water-soluble organo-silica hybrid nanotubes via base-catalyzed condensation of the PAPTS shell block. The formed tubular nanostructures were characterized by transmission electron microscopy (TEM), cryogenic TEM, and atomic force microscopy.     

1-Lithio-2,2-diphenyl-1-(phenylsulfonyl)ethen: Synthese und Kristallstruktur

Syntheses and Crystal Structure of 1-Lithio-2,2-diphenyl-1-(phenylsulfonyl)ethene Crystals of [1-lithio-2,2-diphenyl-1-(phenylsulfonyl)ethene]– N,N,N′,N′ -tetramethylethylenediamine (2/2) ( 2 ) were prepared by addition of BuLi to 1,1-diphenyl-2-(phenylsulfonyl)ethene ( 1 ) in the presence of N,N,N′,N′ -tetramethylethylenediamine (TMEDA) at low temperature. The X-ray structure analysis shows a centrosymmetric dimer bridged over an eight-membered (Li? O? S? O)₂ ring. There are no Li–C contacts to the C(α) atoms. Both Li cations are tetracoordinated via the sulfonyl O-atoms and the N-atoms of the TMEDA ligand. The X-ray structure analysis of 1,1-diphenyl-2-(phenylsulfonyl)ethene ( 1 ) also was determined to compare interatomic distances and angles.     

Metal Complexes with Macrocyclic Ligands. Part XXXIX. Mono- and binuclear copper(II) complexes of a bridging bis[1, 4, 7-triazacyclononane]

The new bis-macrocycle 1, 1′-[(1H-pyrazol-3], 5-diyl)bis(methylene)bis[1, 4, 7-triazacyclononane] ( 1 ) was synthesized and its complexation with Cu²⁺ studied. Potentiometric and spectrophotometric titrations indicate that, in addition to the mononuclear species [Cu(LH₂)]⁴⁺, [Cu(LH)]³⁺, [CuL]²⁺, and [Cu(LH_?1)]⁺, binuclear complexes such as [Cu₂L]⁴⁺, [Cu₂(LH_?1)]³⁺, and [Cu₂(LH_-2)]²⁺ are also formed in solution. The stability constants and spectral properties of these are reported. The binuclear species [Cu₂(LH_?1)]³⁺ specifically reacts with an azide ion to give a ternary complex [Cu₂(LH_?1)(N₃)]²⁺, the stability and structure of which were determined spectrophotometrically and by X-ray diffraction, respectively. The two Cu²⁺ ions are in a square-pyramidal coordination geometry. The axial ligand is one of the N-atoms of the 1, 4, 7-triazacyclononane ring, whereas at the base of the square pyramid, one finds the other two N-atoms of the macrocycle, one N-atom of the pyrazolide and one of the azide, both of which are bridging the two metal centres. In [Cu₂(LH_?1)(N₃)]²⁺, a strong antiferromagnetic coupling is present, thus resulting in a species with a low magnetic moment of 1.36 B.M. at room temperature.     

Elektronentransfer und Ionenpaar-Bildung. 40. Mitteilung. Einkristall-Struktur von Bis(Natrium-1,1′-Biphenyl-2-thiolat-Diglyme): Ein Zwischenprodukt der reduktiven Ringöffnung von Dibenzothiophen

Electron Transfer and Ion Pair Formation Single Crystal Structure of Bis(sodium 1,1′-biphenyl-2-thiolate-diglyme): An Intermediate in the Reductive Ring Opening of Dibenzothiophene On Na-metal reduction of dibenzothiophene, the five-membered sulfur ring opens to form a colorless 1,1′-biphenyl-2-thiolate sodium salt, which, according to its single-crystal structure determination, is a dimer containing a four-membered, twice diglyme-solvated ring (diglyme···Na^⊕?SR)₂. Additional measurements provide the following information: cyclic voltammetry in aprotic MeCN solution shows one quasi-reversible electron transfer at E = ?2.58 V. The dibenzothiophene radical anion can be generated in aprotic THF solution at a K mirror and characterized by an 81-line ESR spectrum and its simulation. This blue species is also the first UV/VIS detectable one before the solution changes via green (due to blue + yellow color mixing) to yellow, yielding across an isosbestic point a second and diamagnetic compound. All of the above results suggest a consecutive two-electron reduction followed by an intersystem protonation, M + (e^?) → M^.? (blue) + (e^?) → (M^??, yellow?) + (H^⊕) → MH^? (colorless), to yield the crystallized and structurally characterized reaction intermediate. The diglyme-solvated sodium-salt dimer provides a basis for a quantum-chemical discussion of some facets of the most likely microscopic reduction pathway.     

Synthetic Attempts towards Polymers with Pentafulvene Structural Units

Synthetic attempts towards fully conjugated polymers 9 with pentafulvene-diyl structural units are described. Cationic polymerization of pentafulvenes 1a (R = X = Me) and 1b (R = X = MeS) nearly quantitatively gives polymers 8a and 8b with typical M_n and M_w values of 38800 and 53750, respectively, for 8a , and 12000 and 35900, respectively, for 8b . Key step of the conversion 8a → 9a (Scheme 6) is a quantitative bromination 8a → 32a , the structure of 32a being confirmed by analytical data as well as by spectroscopic comparison with model compound 23 . Best results in view of two-fold the HBr elimination 32a → 9a are obtained with Et₃N, but so far elimination has not been complete. Synthetic sequences are optimized with model compound 21 (Scheme 4). Here again, bromination 21 → 23 is quantitative, while two-fold HBr elimination 23 → 22 with Et₃N proceeds in 51% yield. Dibromide 23 easily undergoes HBr elimination followed by a Br shift to give bromide 29 . Contrary to cationic polymerization, anionic polymerization of simple pentafulvenes 1 to 2 (which would be attractive in view of the conjugated polymers 3 ) is not successful: For pentafulvene 1b (R = X = MeS), the main reaction is Diels-Alder-type dimerization 1b → 15b (Scheme 2), even under anionic conditions.