Synthesis of a hafnocene disilene complex

Reaction of the magnesium transmetalation product of a 1,2-dipotassiodisilane with hafnocene dichloride gives a disilene hafnocene complex. X-ray crystallography of the respective trimethylphosphane adduct provides structural proof for this assignment.     

Eine Apparatur für differentiate und integrale katalytische Hydrierung

Zusammenfassung Es wird eine Hydrierapparatur beschrieben, bei der das in der Zeiteinheit verschwindende H₂-Volumen durch ein gleichgroßes Volumen elektrolytisch ersetzt wird, so daß der Gasdruck in dem Reaktionsgefäß konstant bleibt.Die in jedem Augenblick der Reaktion herrschende Stromstärke in Ampere ist dann ein Maß für die vorliegende Hydriergeschwindigkeit, und das im H₂-Coulombmeter abgelesene H₂-Volumen ist zahlenmäßig identisch mit dem bis zu diesem Zeitpunkt aufgenommenen H₂-Volumen.Trägt man die jeweils herrschende Hydriergeschwindigkeit oder die Hydrierstärke eines Katalysators in Abhängigkeit von dem jeweils aufgenommenen H₂-Volumen auf, so resultieren bei der Hydrierung des Benzalazetons Treppenkurven, deren Stufen im allgemeinen stöchiometrisch den verschiedenen Doppelbindungen des Benzalazetons entsprechen.Für verschiedene Katalysatoren des Handels und der Literatur wurde ihre Hydrierstärke und Selektivität bei der Hydrierung des Benzalazetons experimentell ermittelt. Hinsichtlich der Selektivität einiger Trägerkatalysatoren ergab sich Übereinstimmung mit den Messungen anderer Autoren.Der Deutschen Forschungsgemeinschaft sprechen wir für die Unterstützung dieser Arbeit unseren Dank aus.     

Twisting of Porphyrin by Assembly in a Metal-Organic Framework yielding Chiral Photoconducting Films for Circularly-Polarized-Light Detection

While materials based on organic molecules usually have either superior optoelectronic or superior chiral properties, the combination of both is scarce. Here, a crystalline chiroptical film based on porphyrin with homochiral side groups is presented. While the dissolved molecule has a planar, thus, achiral porphyrin core, upon assembly in a metal–organic framework (MOF) film, the porphyrin core is twisted and chiral. The close packing and the crystalline order of the porphyrin cores in the MOF film also results in excellent optoelectronic properties. By exciting the Soret band of porphyrin, efficient photoconduction with a high On-Off-ratio is realized. More important, handedness-dependent circularly-polarized-light photoconduction with a dissymmetry factor g of 4.3×10⁻⁴ is obtained. We foresee the combination of such assembly-induced chirality with the rich porphyrin chemistry will enable a plethora of organic materials with exceptional chiral and optoelectronic properties.     

Wavelength‐Gated Dynamic Covalent Chemistry

Chemical reactions are classically controlled by the judicious choice of functional groups as well as external factors such as temperature and catalysts. However, the use of light‐induced reactions not only offers precise temporal and spatial control, but critically allows highly specific reaction channels to be selectively addressed through wavelength and intensity, thereby enabling targeted covalent bonds to be made and broken. Photoreversible cycloadditions are the most promising candidates to seize the outlined potential upon selective cyclization and cycloreversion, but are today still far from fulfilling these expectations. The current Minireview critically explores the current challenges in the application of photoreversible cycloadditions and discusses the steps necessary to realize their potential in molecular biology, biomimetic systems, 3D laser lithographic processes, and advanced soft matter materials with reprogrammable and self‐healing properties.     

Concerning the Conformation of Isolated Benzylideneaniline

From PE.-spectroscopical studies the torsional angle φ of the N-phenyl ring in isolated benzylideneaniline 1 has been found to be definitely smaller than φ= 90°. An approximate valueφ= 36°has been estimated which is even smaller than the one observed in the crystal (φ= 55°) and suggested to prevail also in solutions of 1 . A reevaluation of the gas phase optical spectrum of isolated 1 supports a torsional angle similar to that found in the other phases. Calculations of the most stable conformation of 1 as well as of stilbene and azobenzene by the MINDO/3-technique lead to torsional angles φ= 90° for both phenyl rings in all cases. These results are at variance with the experimental results and suggest that MINDO/3-like its less advanced precursor MINDO/2 or like CNDO/2–is unreliable for low energy processes involving rotation of π-systems connected by essential single bonds. It is concluded that the π-energy of benzylideneaniline, like that of stilbene or azobenzene, would favor a planar conformation. The increased torsional angle in 1 as compared to the other two iso-conjugate systems arises from a larger steric interaction between phenyl- and bridgeprotons.     

Synthesis, spectroscopic, and structural aspects of two trinuclear cyano-bridged heterometallic complexes

Two new cyano-bridged trinuclear heterometallic complexes [Sr₂(Phen)₄(CF₃CO₂)(H₂O)₃Fe(CN)₆]·2H₂O (1) [Ca₂(Phen)₄(CF₃CO₂)(H₂O)Co(CN)₆]·2H₂O (2) (where Phen=1,10-phenanthroline) have been synthesized and their crystal structures have been determined. The structure of complex (1) features a central [Fe(CN)₆]³⁻ unit that links a monocation, [Sr(Phen)₂(OH₂)(OOCCF₃)]⁺ and a dication, [Sr(Phen)₂(OH₂)₂]²⁺ via two trans cyanide bridges. The complex (2) features a central [Co(CN)₆]³⁻ unit that links two monocations of [Ca(Phen)₂(OH₂)(OOCCF₃)]⁺ (the positions of the trifluoro acetate and water molecules are disordered over two positions) via two trans cyanide bridges. Each metal atom is seven coordinated and achieves pentagonal bipyramidal geometry. Two cocrystallized water molecules are present in both the complexes. The presence of an extensive network of hydrogen bonding imparts the overall stability to both the systems.     

The ring opening of cyclopentene oxides by pyrimidines and purines as a pathway to carbocyclic nucleoside analogues

Summary Various carbocyclic nucleosides withxylo-configuration have been synthesized using ring opening of 5-O-acetyl-1,2-anhydro-3-O-benzylcarba--DL-xylo-pentofuranose (6) by thymine, uracil, 4-N-benzoylcytosine, adenine, 6-N-benzoyladenine, and 2-amino-6-chloropurine in alkaline medium. For this purpose, the use of triethylaluminum is introduced into carbanucleoside chemistry. The new method proved to be superior over the application of sodium hydride and potassium or caesium carbonate.

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Ringöffnung von Cyclopentenoxiden mit Pyrimidinen und Purinen als Syntheseweg zu carbocyclischen Nucleosidanalogen

Zusammenfassung Ringöffnung von 5-O-Acetyl-1,2-anhydro-3-O-benzylcarba--DL-xylo-pentofuranose (6) mit Thymin, Uracil, 4-N-Benzoylcytosin, Adenin, 6-N-Benzoyladenin und 2-Amino-6-chlorpurin in alkalischem Medium ergab die entsprechendenxylo-konfigurierten carbocyclischen Nucleoside. Als Hilfsbase wurde Triethylaluminium verwendet, was deutliche Vorteile gegenüber der Verwendung von Natriumhydrid und Kalium- oder Cäsiumcarbonat bezüglich Produktreinheit und Ausbeute bietet.

     

Korrelation zwischen photoelektronen- und elektronen-spektren—II : Untersuchung aromatischer π-systeme mit modifizierten PPP-SCF-CI-parametern

By modified PPP-SCF-CI-parameters the PE- and UV-spectra of naphthalene, anthracene and naphthacene can be interpreted within the error-limit of experimental values. It is shown that ionisation- and excitation-induced bond-length changes on the basis of a structural model of benzene are significant.     

Korrelation zwischen photoelektronen- und elektronen-spektren—III : Eine methode zur deutung der pe- und uv-spektren vom toluol

Within the PPP-SCF-CI-model a method is developed, with which the PE- and UV- spectroscopical measurements of toluene can be interpreted within the error-limit of experimental values. By this way the controversial ionisation potential of 12·06 [eV] can be assigned to the π-b₁-orbital of toluene.