Abstract

Abstract

Abstract

Abstract

Abstract

Caught making a change: Stable sub-nanoordered Pd clusters within the interlayer spaces of montmorillonite efficiently catalyze heterogeneous allylic substitution reactions in which the coordinatively unsaturated Pd atoms enable facile formation of π-allylpalladium intermediates (see scheme). The catalyst is reusable without any loss of activity or selectivity.

Gefangen aktiv: Stabile Pd-Cluster zwischen den Schichten von Montmorillonit katalysieren allylische Substitutionen effizient, wobei die koordinativ ungesättigten Pd-Atome die Bildung von π-Allylpalladium-Zwischenstufen ermöglichen (siehe Schema). Der Heterogenkatalysator lässt sich ohne Verlust an Aktivität oder Selektivität wiederverwenden.

Eines allein: Die Kombination von Palladiumdichlorid mit N,N-Dimethylacetamid (DMA) liefert ein hoch effizientes und wiederverwendbares Katalysatorsystem, das nur mit molekularem Sauerstoff als Reoxidationsmittel die Flüssigphasen-Wacker-Oxidation und die Acetoxylierung terminaler Olefine zu den entsprechenden Methylketonen bzw. linearen Allylacetaten ermöglicht (siehe Schema).

A ruthenium-grafted hydrotalcite (Ru/HT) and hydrotalcite-supported palladium nanoparticles (Pd_nano/HT) are easily prepared by treating basic layered double hydroxide, hydrotalcite (HT, Mg₆Al₂(OH)₁₆CO₃) with aqueous RuCl₃⋅n H₂O and K₂[PdCl₄] solutions, respectively, using surface impregnation methods. Analysis by means of X-ray diffraction, and energy-dispersive X-ray, electron paramagnetic resonance, and X-ray absorption fine structure spectroscopies proves that a monomeric Ru^IV species is grafted onto the surface of the HT. Meanwhile, after reduction of a surface-isolated Pd^II species, highly dispersed Pd nanoclusters with a mean diameter of about 70 Å is observed on the Pd_nano/HT surface by transmission electron microscopy analysis. These hydrotalcite-supported metal catalysts can effectively promote α-alkylation reactions of various nitriles with primary alcohols or carbonyl compounds through tandem reactions consisting of metal-catalyzed oxidation and reduction, and an aldol reaction promoted by the base sites of the HT. In these catalytic α-alkylations, homogeneous bases are unnecessary and the only by-product is water. Additionally, these catalyst systems are applicable to one-pot syntheses of glutaronitrile derivatives.

Die hohe Säurestärke eines durch Protonenaustausch aktivierten Montmorillonit-Katalysators (H-Mont) wurde für die nucleophile Addition von 1,3-Dicarbonylverbindungen an einfache Alkene genutzt (siehe Schema). Auch Benzylierungen und Allylierungen von 1,3-Dicarbonylverbindungen mit Alkoholen sowie nucleophile Additionen von Carbonsäuren an Alkene verlaufen mit H-Mont glatt. Der Katalysator konnte ohne Aktivitätsverlust siebenmal wiederverwendet werden.

Robust und strukturell definiert auf der Ebene einzelner Atome: Eine Ru^IVMn^IVMn^IV-Heterotrimetallspezies auf einer Hydrotalcit-Oberfläche erwies sich als hoch effizienter Heterogenkatalysator für die Flüssigphasenoxidation verschiedener Alkohole mit 1 atm O₂ als Oxidans (siehe Schema).

Montmorillonite-enwrapped copper and scandium catalysts (Cu²⁺- and Sc³⁺-monts) were easily prepared by treating Na⁺-mont with the aqueous solution of the copper nitrate and scandium triflate, respectively. The resulting Cu²⁺- and Sc³⁺-monts showed outstanding catalytic activities for a variety of carbon–carbon bond-forming reactions, such as the Michael reaction, the Sakurai–Hosomi allylation, and the Diels–Alder reaction, under solvent-free or aqueous conditions. The remarkable activity of the mont catalysts is attributable to the negatively charged silicate layers that are capable of stabilizing metal cations. Furthermore, these catalysts were reusable without any appreciable loss in activity and selectivity. The Cu²⁺-mont-catalyzed Michael reaction proceeds via a ternary complex in which both the 1,3-dicarbonyl compound and the enone are coordinated to a Lewis acid Cu²⁺ center.

Robust and structurally defined on the atomic scale: A heterotrimetallic Ru^IVMn^IVMn^IV species coordinated to a hydrotalcite surface is a highly efficient heterogeneous catalyst for the liquid-phase oxidation of various alcohols with 1 atm O₂ as the sole oxidant (see scheme).