Phosphetes via Transition Metal Free Ring Closure – Taking the Proper Turn at a Thermodynamic Crossing

A transition metal free route to phosphetes featuring an exocyclic alkene unit is presented. In this approach phosphanides are added to a variety of diynes generating phosphaallylic intermediates which depending on the reaction conditions transform either to phosphetes or the corresponding phospholes. Investigation of the reaction mechanism by combined quantum chemical and experimental means identifies phosphole formation as thermodynamically controlled reaction path, whereas kinetic control furnishes the corresponding phosphetes. Structural and luminescence properties of the rare class of phosphetes are explored, as well as for selected key intermediates.     

Roll-to-Roll Production of Spider Silk Nanofiber Nonwoven Meshes Using Centrifugal Electrospinning for Filtration Applications

Filtration systems used in technical and medical applications require components for fine particle deep filtration to be highly efficient and at the same time air permeable. In high efficiency filters, nonwoven meshes, which show increased performance based on small fiber diameters (e.g., using nanofibers), can be used as fine particle filter layers. Nanofiber nonwoven meshes made by electrospinning of spider silk proteins have been recently shown to exhibit required filter properties. Needle-based electrospinning, however, is limited regarding its productivity and scalability. Centrifugal electrospinning, in contrast, has been shown to allow manufacturing of ultrathin polymer nonwoven meshes in an efficient and scalable manner. Here, continuous roll-to-roll production of nonwoven meshes made of recombinant spider silk proteins is established using centrifugal electrospinning. The produced spider silk nanofiber meshes show high filter efficiency in the case of fine particulate matter below 2.5 µm (PM2.5) and a low pressure drop, resulting in excellent filter quality.     

Manganese-Catalyzed β-Methylation of Alcohols by Methanol

We report an earth-abundant-metal-catalyzed double and single methylation of alcohols. A manganese catalyst, which operates at low catalyst loadings and short reaction times, mediates these reactions efficiently. A broad scope of primary and secondary alcohols, including purely aliphatic examples, and 1,2-aminoalcohols can be methylated. Furthermore, alcohol methylation for the synthesis of pharmaceuticals has been demonstrated. The catalyst system tolerates many functional groups among them hydrogenation-sensitive examples and upscaling is easily achieved. Mechanistic investigations are indicative of a borrowing hydrogen or hydrogen autotransfer mechanism involving a bimetallic K-Mn catalyst. The catalyst accepts hydrogen as a proton and a hydride from alcohols efficiently and reacts with a chalcone via hydride transfer.     

Nickel(II) Phosphane- and N-heterocyclic Carbene Complexes with Tridentate,Dianionic [S,N,O]2– Ligands

Square-planar dinuclear nickel(II) complexes containing [S,N,O]^2– ligands formed by condensation of acetyl acetone or benzoyl acetone with cysteamine were prepared. These dimeric nickel(II) compounds undergo bridge-cleavage reactions with the cage phosphine PTA (PTA = 1,3,5-triaza-7-phosphaadamantane) or in situ generated N-heterocyclic carbenes. The resulting diamagnetic, square planar Ni^II complexes were characterized by spectroscopic methods and X-ray diffraction.     

Ferrocenes with a Persulfurated Cyclopentadienyl Ring: Synthesis,Structural Studies,and Optoelectronic Properties

Persulfurated arenes are a fascinating class of functional molecules with a wide range of potential applications. Ferrocenes are also a multifaceted class of aromatic compounds that can easily be finetuned for an enormous variety of desired properties. A combination of both substance classes might yield an even wider field of applications. Herein, we describe the synthesis of two ferrocenes with one persulfurated cyclopentadienyl ring [C₅(SR)₅], with R=Me or Ph, together with their crystal structures, optical, and electrochemical properties. Both crystal structures show significant intramolecular sulfur-iron interactions as well as weak intermolecular sulfur– contacts. Cyclovoltammetry of the [C₅(SPh)₅] compound shows a high oxidation potential of 651 mV vs. FcH/FcH⁺.     

Visible-Light-Mediated Liberation and In Situ Conversion of Fluorophosgene

The first example for the photocatalytic generation of a highly electrophilic intermediate that is not based on radical reactivity is reported. The single-electron reduction of bench-stable and commercially available 4-(trifluoromethoxy)benzonitrile by an organic photosensitizer leads to its fragmentation into fluorophosgene and benzonitrile. The in situ generated fluorophosgene was used for the preparation of carbonates, carbamates, and urea derivatives in moderate to excellent yields via an intramolecular cyclization reaction. Transient spectroscopic investigations suggest the formation of a catalyst charge-transfer complex-dimer as the catalytic active species. Fluorophosgene as a highly reactive intermediate, was indirectly detected via its next downstream carbonyl fluoride intermediate by NMR. Furthermore, detailed NMR analyses provided a comprehensive reaction mechanism including a water dependent off-cycle equilibrium.     

Cobalt-Catalyzed Dehydrogenative C−H Silylation of Alkynylsilanes

Herein, we report that a cobalt catalyst permits the general synthesis of substituted alkynylsilanes through dehydrogenative coupling of alkynylsilanes and hydrosilanes. Several silylated alkynes, including di- and trisubstituted ones, were prepared in a one-step procedure. Thirty-seven compounds were synthesized for the first time by applying our catalyst system. The alkynylsilanes bearing hydrosilyl moieties provide an opportunity for further functionalization (e. g., hydrosilylation). The use of primary silanes as substrates and precatalyst activators permits the use of inexpensive and easily accessible 3d metal precatalysts, and avoids the presence of additional activators.