Diastereoselective formation of seven-membered oxacycles by ring-expansion of cyclopropanated galactal

The cyclopropanation and ring-expansion of 4,6-O-di-(tert-butyl)silanediyl-d-galactal using catalytic amounts of TMSOTf and silated nucleophiles gave a range of substituted oxepanes. Good to excellent yields were obtained in addition to very high selectivities.     

Nickel(0)-induzierte C---C-verknüpfung von heterokumulenen: Bildung von oxanilid aus phenylisocyanat

In the presence of small amounts of aromatic N-heterocycles, nickel(0) couples two phenylisocyanate molecules with C---C bond formation. After hydrolysis oxanilide is obtained.     

Durch nickel(II)-salze induzierte carbamoylierung von alkinen

Mono- and di-substituted alkynes react with CO and secondary amines such as Et₂NH in the presence of Ni^II salts to form carbamoyl products of the types Et₂NCOC(R)C(R′)CONEt₂ and RCCCONEt₂. Depending on the NiX₂ salt (X = Cl, Br, I) employed and the temperature (20–100°C), a product selectivity is observed. The mechanism of the reaction is discussed.     

Diphosphan-tetraphenylnickelacyclopentadien

Reaction of 1,2-bis(diorganophosphino)ethanenickel dibromide (I) with 1,2,3,4-tetraphenyl-1,4-dilithiumbutadiene (II) at ?30°C yields diphosphannickelacyclopentadiene (III) which at elevated temperatures isomerizes to diphosphanecyclobutadienenickel(0) (IV). The thermodynamic and kinetic parameters of the rearrangement were determined. The structural and conformational analyses of III were carried out by means of ¹³C NMR, ³¹P NMR and Raman spectroscopy. The reactions of III and IV with CH₃COOH, CO, RCCR and RNCNR have been axamined and the observed reactivities III ? IV are discussed.     

Bis(tetraphenylcyclobutadien)palladium(0)

Tetraphenylcyclobutadienepalladium dichloride reacts with 1,2,3,4-tetraphenyl-1,4-dilithiumbutadiene or with sodium with abstraction of halide to give the sandwich compound bis(tetraphenylcyclobutadiene)palladium(0). The structure of the latter is elucidated by spectroscopic methods and its reactions with Br₂, H₂, K and HNO₃ are described.     

Antibacterial Activity of Biosynthesized Selenium Nanoparticles Using Extracts of Calendula officinalis against Potentially Clinical Bacterial Strains

The use of selenium nanoparticles (SeNPs) in the biomedical area has been increasing as an alternative to the growing bacterial resistance to antibiotics. In this research, SeNPs were synthesized by green synthesis using ascorbic acid (AsAc) as a reducing agent and methanolic extract of Calendula officinalis L. flowers as a stabilizer. Characterization of SeNPs was performed by UV-vis spectrophotometry, infrared spectrophotometry (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques. SeNPs of 40–60 nm and spherical morphologies were obtained. The antibacterial activity of marigold extracts and fractions was evaluated by disk diffusion methodology. The evaluation of SeNPs at different incubation times was performed through the colony-forming unit (CFU) count, in both cases against Serratia marcescens, Enterobacter cloacae, and Alcaligenes faecalis bacteria. Partial antibacterial activity was observed with methanolic extracts of marigold leaves and flowers and total inhibition with SeNPs from 2 h for S. marcescens, 1 h for E. cloacae, and 30 min for A. faecalis. In addition, SeNPs were found to exhibit antioxidant activity. The results indicate that SeNPs present a potentiated effect of both antimicrobial and antioxidant activity compared to the individual use of marigold extracts or sodium selenite (Na₂SeO₃). Their application emerges as an alternative for the control of clinical pathogens.     

Neue methoden zur herstellung von trialkylphosphan-alkadien-eisen(0)-komplexen

Mono(1,3-diene)tris(PR₃)iron(0) complexes and bis(1,3-diene)mono(PR₃)iron(0) complexes can be synthesized by reduction of FeCl₂ with magnesacyclopent-3-ene or activated Mg in the presence of 1,3-dienes and the appropriate PR₃ (R = Me, Et, Prⁿ, Cy) ligand. How the various substituted bis(1,3-diene)PR₃Fe⁰ complexes can be obtained from the thermally unstable 1,3-butadiene-tris(PR₃)Fe⁰ complexes by addition of 1,3- or 1,5-dienes is shown. The NMR spectra of these complexes indicate that they are square-pyramidal. This geometry was confirmed by a crystal structure analysis of 1,5-COD-1,3-butadiene-iron(0)-PEt₃. The probable mechanism of formation of these novel iron(0) complexes is discussed and their characteristic properties are described.     

Eine einfache methode zur herstellung von bis(tetraphenylcyclobutadien)nickel

Bis(tetraphenylcyclobutadien)nickel (III). Eine Suspension aus 4.3 g (7.5 mmol) Tetraphenylcyclobutadien-nickeldibromid (I) und 2.8 g (7.5 mmol) 1,2,3,4-Tetraphenyl-1,4-dilithiumbutadien (II) in 250 ml Toluol wurde bei 20°C 4 Tage kräftig gerührt, wobei allmählich eine Verfärbung nach braun-violett eintrat. Nach Abziehen des Lösungsmittels wurde der Rückstand in einem Soxhlet-Extraktor 3 Tage mit 250 ml Benzol extrahiert; die Extraktionslösung wurde bis zur Trockne eingedampft, der Rückstand (3.5 g) in 500 ml Toluol gelöst und bei -20°C umkristallisiert. Erhalten: 2.7 g (47.0%) III. Das Produkt ist laut Elementaranalyse und NMR-Spektrum mit dem bereits beschriebenen [3] identisch.