Search

By combining tandem asymmetric gold catalysis and subsequent stereoconvergent hydrolysis of enol ester in a one-pot process, hydroxylated propargylic esters are converted into chiral β-oxygenated ketones with mostly good enantiomeric ratios and in largely good to excellent yields. The product chiral center is formed via stereoselective cyclization of a hydroxylated allenyl ester intermediate, which is enabled by asymmetric gold-ligand cooperation.

Polyvinyl chloride (PVC) is a problematic waste plastic with limited options for recycling or upcycling. Herein, we demonstrate preliminary results in breaking down the long carbon chains of PVC into oligomers and small organic molecules. First, treatment with a substoichiometric amount of alkali base effects elimination of HCl to form a salt and creates regions of conjugated carbon-carbon double bonds, as determined by 1 H NMR and UV-Vis spectroscopy. Olefin cross metathesis with an added partner alkene then cleaves carbon-carbon double bonds of the polymer backbone. Addition of allyl alcohol to the dehydrochlorination step introduces allyloxy groups by substitution of allylic chlorides. Subsequent metathesis of the pendant allyloxy groups provides a reactive terminal alkene to promote insertion of the metathesis catalyst onto the olefins in the all-carbon backbone. The products obtained are a mixture of PVC oligomers with greatly reduced molecular weights and a small-molecule diene corresponding to the substituents of the added alkene, as evidenced by 1 H and DOSY NMR and GPC. This mild procedure provides a proof of concept towards harvesting carbon resources from PVC waste.

Herein we introduce fully modular synthesis leading to three representative examples of rigid molecular rods that are intended to form sturdy monolayers on various surfaces. These molecules contain two triptycene units that are designed to interlock into a compact "double-decker" structure. Two of the three final products provided suitable crystals for X-ray diffraction (analyzed on synchrotron), allowing deeper insight into packing in the 3-D crystal lattice. The acidity of all three compounds were determined by capillary electrophoresis, and the pKa values ranged between 2.06-2.53. All three rigid rods easily formed Langmuir-Blodgett monolayers (LBMs) on the water-air interfaces, with the area per molecule equal to 55-59 Å2 /molecule, suggesting tight intermolecular packing. The thickness of all three films reached ∼19 Å after transfer to a gold (111) surface, meaning that individual molecules are tilted maximally 38° from the axis perpendicular to the surface. The structure of one of these films on a gold (111) surface was visualized by AFM. These geometrically unique molecules represent promising platforms with a wide scope of applicability in the supramolecular architecture.

The kinetics of ligand exchange between the free oxalate ion, C2 O4 2- , and the bis-oxalato NpV complex, [NpO2 (C2 O4 )2 ]3- , in aqueous solution are reported by using 13 C and 17 O NMR spectroscopy methods. Rates of exchange were measured in the pH regime of 6.5-9.0, at which speciation is shown to be suitably simple. Because the neptunium(V) complex is paramagnetic, the rates of ligand exchange were estimated by following the width of the 13 C and 17 O signals assigned to the free oxalate ion in solution and by applying the Swift-Connick method for measuring rates of exchange. A set of experiments were conducted in which pH and total oxalate concentration were varied, and the linear dependence of the rate on these parameters was demonstrated. Variable-temperature NMR spectroscopy was also performed to measure activation parameters of complexation. At pH8.0 there is almost no dependence on temperature, which is interpreted to indicate that hydrolysis is coupled to ligand exchange under these conditions.

The kinetics of ligand exchange between the free oxalate ion, C2 O4 2- , and the bis-oxalato NpV complex, [NpO2 (C2 O4 )2 ]3- , in aqueous solution are reported by using 13 C and 17 O NMR spectroscopy methods. Rates of exchange were measured in the pH regime of 6.5-9.0, at which speciation is shown to be suitably simple. Because the neptunium(V) complex is paramagnetic, the rates of ligand exchange were estimated by following the width of the 13 C and 17 O signals assigned to the free oxalate ion in solution and by applying the Swift-Connick method for measuring rates of exchange. A set of experiments were conducted in which pH and total oxalate concentration were varied, and the linear dependence of the rate on these parameters was demonstrated. Variable-temperature NMR spectroscopy was also performed to measure activation parameters of complexation. At pH8.0 there is almost no dependence on temperature, which is interpreted to indicate that hydrolysis is coupled to ligand exchange under these conditions.