W Tungsten

The catalytic activity of ruthenium(IV) ([Ru(η³:η³-C₁₀H₁₆)Cl₂L]; C₁₀H₁₆=2,7-dimethylocta-2,6-diene-1,8-diyl, L=pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, 3-methyl-5-phenylpyrazole, 2-(1H-pyrazol-3-yl)phenol or indazole) and ruthenium(II) complexes ([Ru(η⁶-arene)Cl₂(3,5-dimethylpyrazole)]; arene=C₆H₆, p-cymene or C₆Me₆) in the redox isomerisation of allylic alcohols into carbonyl compounds in water is reported. The former show much higher catalytic activity than ruthenium(II) complexes. In particular, a variety of allylic alcohols have been quantitatively isomerised by using [Ru(η³:η³-C₁₀H₁₆)Cl₂(pyrazole)] as a catalyst; the reactions proceeded faster in water than in THF, and in the absence of base. The isomerisations of monosubstituted alcohols take place rapidly (10–60 min, turn-over frequency=750–3000 h⁻¹) and, in some cases, at 35 °C in 60 min. The nature of the aqueous species formed in water by this complex has been analysed by ESI-MS. To analyse how an aqueous medium can influence the mechanism of the bifunctional catalytic process, DFT calculations (B3LYP) including one or two explicit water molecules and using the polarisable continuum model have been carried out and provide a valuable insight into the role of water on the activity of the bifunctional catalyst. Several mechanisms have been considered and imply the formation of aqua complexes and their deprotonated species generated from [Ru(η³:η³-C₁₀H₁₆)Cl₂(pyrazole)]. Different competitive pathways based on outer-sphere mechanisms, which imply hydrogen-transfer processes, have been analysed. The overall isomerisation implies two hydrogen-transfer steps from the substrate to the catalyst and subsequent transfer back to the substrate. In addition to the conventional Noyori outer-sphere mechanism, which involves the pyrazolide ligand, a new mechanism with a hydroxopyrazole complex as the active species can be at work in water. The possibility of formation of an enol, which isomerises easily to the keto form in water, also contributes to the efficiency in water.

Bifunctional catalysis in water: Bis(allyl) ruthenium(IV) complexes that contain pyrazole-type ligands are highly efficient catalysts in the redox isomerisation of allylic alcohols in water (see scheme, TOF=turnover frequency). DFT studies provide a valuable insight into the role of water in the activity of bifunctional catalysts and imply the formation of aqua complexes.

The effects of calcination temperature and feedstock pretreatment on the catalytic performance of Co/γ-Al₂O₃ catalysts were studied for partial oxidation of methane (POM) to synthesis gas, with emphasis on the role of feedstock pretreatment. The physicochemical properties of the catalysts were characterized by N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR), and Raman spectroscopy. The results showed that the pretreatment of the catalyst by reaction gas significantly improved the catalytic activity and stability for the POM reaction. On the other hand, the effect of calcination temperature was less significant. Although the initial activity was increased by an increased calcination temperature, the catalyst without the feedstock pretreatment suffered a rapid deactivation. The reaction-atmosphere pretreatment was revealed as a process that mainly modified the surface structure of the catalyst. In that process, the formation of a CoAl₂O₄-like compound led to high Co metal dispersion after reduction, and the transformation of the carrier into α-Al₂O₃ occurred over the catalyst surface. Both the high dispersion of cobalt and the presence of α-Al₂O₃ surface phase were assumed as the important factors resulting in an excellent catalytic performance in terms of high activity and high stability.

A pretreatment by reaction gas! A simple but efficient approach improves the catalytic performance of Al₂O₃-supported Co catalysts for partial oxidation of methane to syngas. Catalysts pretreated with feedstock showed higher activity and higher stability for the reaction than those without this pretreatment. For the sake of comparison, the effect of calcination temperature was also investigated.

A series of 1,2,4-trioxanes were synthesized in which the key peroxy bonds were installed through a molybdenum-catalyzed perhydrolysis of the epoxy rings. A core structure was identified that may serve as a promising lead structure for further investigations because of its high antimalarial activity (comparable to that of artesunate and chloroquine), apparent potential for scale-up and derivatization, and facile monitoring/tracing by using UV light.

The temple of artemisinin: The key peroxy bonds in a series of 1,2,4-trioxanes were installed by molybdenum-catalyzed perhydrolysis of the epoxy rings. A novel core structure with potent antimalarial activity was identified.

Functionalized 3,4-dihalogenated furan-2(5 H)-ones can be readily prepared in moderate to good yields by treating 4-hydroxy-4-arylbut-2-ynoate derivatives with ICl, IBr, and I₂. Both halogen atoms of the electrophile are incorporated in the product. The resulting halides can further afford polycyclic aromatic compounds using known palladium-catalyzed coupling reactions.

Three amigos: Functionalized 3,4-dihalogenated furan-2(5 H)-ones can be readily prepared in moderate to good yields by treating 4-hydroxy-4-arylbut-2-ynoate derivatives with ICl, IBr, and I₂. Both halogen atoms of the electrophile are incorporated in the product (see scheme).

A carbohydrate-modifiednanodiamond is a valuable new material for the straightforward detection and efficient removal of pathogenic bacteria from polluted water sources. It is nontoxic and can readily be used in difficult environments. Furthermore, sugar specificity of bacterial surface proteins allows for identification and targeted sectioning of particular virulent strains through tailored glycosylation of the nanodiamond surface. For more details see the Full Paper by A. Krueger, T. K. Lindhorst et al. on page 6485 ff.

Pendant amines incorporated in the second coordination sphere of nickel bis(diphosphine) catalysts for H₂ oxidation and H₂ production play a crucial role in the breaking and forming of the HH bond of molecular hydrogen. An accurate and comprehensive theoretical study is reported in the Full Paper by S. Raugei et al. on page 6493 ff., which allows for a deeper atomistic understanding, that will guide the design of more efficient electrocatalysts for the intercorversion between electrical energy and fuels.