Organo-Polyoxometalate-Based Hydrogen-Bond Catalysis.

Several urea-inserted organo-polyoxometalates (POMs) derived from polyoxotungstovanadate [P2 V3 W15 O61 ]9- were prepared. The insertion of the carbonyl into the polyoxometallic framework activates the urea toward Hydrogen-bond catalysis. This was shown on the Friedel-Crafts arylation of trans-ß-nitrostyrene. Modelling shows that the most stable form of the organo-POMs features a cis-trans arrangement of the two N-H bonds, but that the likely catalytically active trans-trans form is accessible at room temperature. Finally, it is possible that the oxo substituents next to the vanadium atoms may help the approach of the nucleophile via H-bonding.

Synthesis and Properties of Higher Nuclearity Polyazanes.

Polyazanes (i.e., higher nuclearity homologues of hydrazines) with increasing numbers of bound nitrogen atoms (from 3 to 5), including the first pentazane ever described, were prepared by the addition of lower-order polyazanes to diazo reagents. A structure was obtained. It was shown that the polynitrogen chains adopt a helical conformation. DFT modeling shows that the arrangement persists in solution. Although the polyazanes are all reducing agents, they become less so as the number of nitrogens increases.

Elucidation of the Conformation of Polyglycine Organo-Polyoxotungstates: Evidence for Zipper Folding.

The conformation of a family of α1 and α2 polyglycine-containing organo-polyoxometalates was determined through a mixed experimental/molecular dynamics approach. The flexible peptide arm folds around the metal oxide surface in a rigid arrangement in low to average polarity solvents. The topology of the hybrid is the main factor that determines which oxos from the metal-oxide surface accept a H-bond from the closest amino acid. The rest of the peptide follows in a zipper mechanism that establishes a H-bond network that locks the system. The covalent constraint leads to a new type of H-bond where two consecutive amino acids clamp down terminal oxo ligands.

Grafting of Secondary Diolamides onto [P2 W15 V3 O62 ](9-) Generates Hybrid Heteropoly Acids.

The Dawson tungstovanadate [P2 W15 V3 O62 ](9-) can be grafted to secondary diolamides. The electron-withdrawing character of the polyanion increases the acidity of the amide proton, leading to an organo-polyoxometalate, which can be used as a Brønsted organocatalyst. High-field NMR and DFT modeling indicate that the amide proton stays on the nitrogen and that the exalted acidity derives from the interaction between the organic and inorganic parts of the organo-polyoxometalate. The amide-inserted vanadotungstates thus form a new family of (hybrid) heteropolyacids, offering new perspectives for the application of POM-based catalysis in organic synthesis.

Catalytic self-propulsion of supramolecular capsules powered by polyoxometalate cargos.

Multicompartment, spherical microcontainers were engineered through a layer-by-layer polyelectrolyte deposition around a fluorescent core while integrating a ruthenium polyoxometalate (Ru4POM), as molecular motor, vis-à-vis its oxygenic, propeller effect, fuelled upon H2O2 decomposition. The resulting chemomechanical system, with average speeds of up to 25 µm s(-1), is amenable for integration into a microfluidic set-up for mixing and displacement of liquids, whereby the propulsion force and the resulting velocity regime can be modulated upon H2O2-controlled addition.