No abstract

An added bonus in the optimization of a catalyst for the hydrostannation with tin hydrides was the discovery that molybdenum isonitrile complexes are also suitable for distannations. Further developments in this respect led to a new tungsten isonitrile complex, which catalyzed this reaction highly efficiently and selectively (see scheme, THP=tetrahydropyranyl).

Ein Nebeneffekt bei der Optimierung eines Katalysators für die Hydrostannylierung mit Zinnhydriden war die Entdeckung, dass Molybdän‐Isonitril‐Komplexe auch für Distannylierungen geeignet sind. Weitere Katalysatorentwicklung unter diesem Aspekt brachte einen neuartigen Wolfram‐Isonitril‐Komplex hervor, der diese Reaktion hoch effizient und selektiv katalysiert (siehe Schema, THP=Tetrahydropyranyl).

THF/carbonyl complexes of molybdenum and tungsten are suitable precursors for the synthesis of the corresponding monoisonitrile carbonyl complexes. Whereas complexes with electron-rich isonitriles are suitable for regioselective hydrostannations, complexes with electron-poor isonitriles are efficient catalysts for distannations, without reduction of aromatic halides. This allows for the synthesis of halogenated distannylated allyl ethers, which can be subjected to intramoleculare Stille couplings giving rise to heterocycles, which can be further modified at the remaining stannyl group.

The amino acid l-methionine is an essential amino acid and is commonly used as a feed supplement in terrestrial animals. It is less suitable for marine organisms because it is readily excreted. It is also highly water soluble and this results in loss of the feed and eutrophication of the water. To address these problems, the dipeptide dl-methionyl-dl-methionine (trade name: AQUAVI Met-Met) has been developed as a dedicated methionine source for aquaculture. The commercial product is a mixture of a racemic crystal form of d-methionyl-d-methionine/l-methionyl-l-methionine and a racemic crystal form of d-methionyl-l-methionine/l-methionyl-d-methionine. In this work, we have computationally, structurally, spectroscopically and by electron microscopy characterised these materials. The microscopy and spectroscopy demonstrate that there is no interaction between the dd–ll and dl–ld racemates on any length scale from the macroscopic to the nanoscale.