Bioinspired Oxidation of Methane in the Confined Spaces of Molecular Cages

Abstract

Non-heme iron, vanadium, and copper complexes bearing hemicryptophane cavities were evaluated in the oxidation of methane in water by hydrogen peroxide. According to 1 H nuclear magnetic resonance studies, a hydrophobic hemicryptophane cage accommodates a methane molecule in the proximity of the oxidizing site, leading to an improvement in the efficiency and selectivity for CH 3 OH and CH 3 OOH compared to those of the analogous complexes devoid of a hemicryptophane cage. While copper complexes showed low catalytic efficiency, their vanadium and iron counterparts exhibited higher turnover numbers, ≤13.2 and ≤9.2, respectively, providing target primary oxidation products (CH 3 OH and CH 3 OOH) as well as over-oxidation products (HCHO and HCOOH). In the case of caged vanadium complexes, the confinement effect was found to improve either the selectivity for CH 3 OH and CH 3 OOH (≤15%) or the catalytic efficiency. The confined space of the hydrophobic pocket of iron-based supramolecular complexes plays a significant role in the improvement of both the selectivity (≤27% for CH 3 OH and CH 3 OOH) and the turnover number of methane oxidation. These results indicate that the supramolecular approach is a promising strategy for the development of efficient and selective bioinspired catalysts for the mild oxidation of methane to methanol.

Chirality transfer in a cage controls the clockwise/anticlockwise propeller arrangement of the tris(2-pyridylmethyl)amine ligand

“…The assignment of these resonances was achieved through 2D-NMR experiments (see the ESI †). Contrary to Hm-Ph-TPA, 9,10 and other reported TPA-based cages, 4 1 displays clearly distinct signals for the methylene protons (-CH 2 -N) at the alpha position of the tertiary amine (H a/a 0 , Dd = 0.66 ppm) revealing their diastereotopic character. It should be noted that the highly symmetrical 1 H NMR spectrum observed for 1 in solution, at 298 K, contrasts with the C 1 symmetrical structure observed in the solid-state.…”

Pseudopotential‐fragment spectroscopy for organic molecules and carbon allotropes

“…The interest in cryptophanes and hemicryptophanes lies in their propensity to form Van der Waals complexes as hosts. Some of these complexes have interesting catalytic properties . Our own interest in such molecules is that they combine a range of different carbon environments with a complex electronic structure.…”

“…The molecule we have adopted as a test subject is a Cu(II)hemicryptophane complex, shown in Figure . In order to try to make the investigation as systematic as possible, we decided to group parts of the molecule together as shown in Figure , before building up the number of pseudopotentials used.…”

Conversion of Methane into Liquid Fuels—Bridging Thermal Catalysis with Electrocatalysis

“…This has been exemplified by the supramolecular catalyst with confined hemicryptophane cages for methane oxidation showing enhanced selectivity than nonconfined catalysts. [92] Furthermore, the active site environment within the confined cavity can be judiciously designed for independent tuning of the binding energy of methane and methanol in order to break the conversion-selectivity limit of conventional catalysts. In addition, analyses of reaction networks for methane oxidation www.advancedsciencenews.com ( Figure S1, Supporting Information) can provide fundamental insights into the reaction mechanisms and guide the catalyst design efforts.…”