Catechol Thioesters: Ligands for Hierarchically Formed Lithium-Bridged Titanium(IV) Helicates and Helicate-Based Switches

The thioester moiety is introduced as a lithium binding unit for the hierarchical formation of titanium(IV) catecholate-based lithium-bridged helicates. In solution, the coordination compounds show a monomer–dimer equilibrium which —in comparison to the oxo esters— is significantly shifted towards the monomers. In addition, the influence of the thioester side chain on the dimerization behavior is investigated and an expansible/compressible molecular switch is synthesized. In the latter case expansion and compression are performed reversibly in methanol, whereas in DMSO spontaneous expansion occurs.     

Coverages on inverse semigroups

Semigroup Forum - First we give a definition of a coverage on an inverse semigroup that is weaker than the one given by Lawson and Lenz and that generalizes the definition of a coverage on a...     

Hetero-Substituted αβ-Fused BODIPY

Here, we report the synthesis and properties of heterosubtituted αβ-fused BODIPY fluorophores. The compounds were obtained in good yields by sequential and selective Stille cross-coupling reactions from 2,3,5,6-tetrahalo-BODIPY, allowing the introduction of different substituents at the 3,5 and 2,6 positions of the BODIPY ring. The final fused compounds were synthesized using oxidative cyclisation with ferrous chloride. The fully fused compounds show a strong bathochromically shifted emission along with a hyperchromic shift of the absorption maxima. The fluorescence quantum yields remain relatively large for compounds emitting in this wavelength range. Computational studies have been carried out to fully understand the photophysical behaviour of these dyes.     

An anhydrous precursor approach to BaYF5-based upconverting nanocrystals

With an objective to have easy access to high quality BaYF₅ matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF₅ NCs co-doped with Yb³⁺/Tm³⁺ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed.     

New two-step sequence involving a hetero-Diels-Alder and a nonphenolic oxidative coupling reaction: a convergent access to analogs of steganacin

A new family of analogs of steganacin, an important antimitotic compound, was accessed. It takes advantage of a completely stereoselective sequence of two key steps. The central dihydropyrane core is built by a highly diastereoselective and facially controlled hetero-Diels-Alder reaction. It is followed by a nonphenolic biaryl oxidative coupling with a complete atropo-stereoselectivity. It leads to a quick way to form cyclic biaryl lignans.