N-Heterocyclic Carbene Modified Palladium Catalysts for the Direct Synthesis of Hydrogen Peroxide.

Heterogeneous palladium catalysts modified by N-heterocyclic carbenes (NHCs) are shown to be highly effective toward the direct synthesis of hydrogen peroxide (H2O2), in the absence of the promoters which are typically required to enhance both activity and selectivity. Catalytic evaluation in a batch regime demonstrated that through careful selection of the N-substituent of the NHC it is possible to greatly enhance catalytic performance when compared to the unmodified analogue and reach concentrations of H2O2 rivaling that obtained by state-of-the-art catalysts. The enhanced performance of the modified catalyst, which is retained upon reuse, is attributed to the ability of the NHC to electronically modify Pd speciation.

Non-Directed Cross-Dehydrogenative (Hetero)arylation of Allylic C(sp3 )-H bonds enabled by C-H Activation.

Herein, we report the selective, non-directed and cross-dehydrogenative coupling of allylic C(sp3 )-H bonds with C(sp2 )-H bonds of (hetero)arenes. The methodology employs olefins and (hetero)arenes which are abundantly available chemical feedstocks, and could be applied in late-stage functionalization reactions of pharmaceuticals. Furthermore, the system exclusively delivers the allylic C-C coupling products highlighting the preservation of the olefin substitution pattern for further derivatization.

Molecular Adsorbates Switch on Heterogeneous Catalysis: Induction of Reactivity by N-Heterocyclic Carbenes.

We report the N-heterocyclic carbene (NHC)-induced activation of an otherwise unreactive Pd/Al2O3 catalyst. Surface analysis techniques demonstrate the NHC being coordinated to the palladium particles and affecting their electronic properties. Ab initio calculations provide further insight into the electronic effect of the coordination with the NHC injecting electron density into the metal nanocluster thus lowering the barrier for bromobenzene activation. By this NHC modification, the catalyst could be successfully applied in the Buchwald-Hartwig amination of aryl chlorides, bromides, and iodides. Various heterogeneity tests could additionally show that the reaction proceeds via a heterogeneous active species.

Influence of the Headgroup of Azolium-Based Lipids on Their Biophysical Properties and Cytotoxicity.

A series of (un-)charged NHC derivatives bearing two pentadecyl chains in the backbone was studied in detail to find cooperative effects between the membrane and the NHC derivative. The tendency to show lipid-like behavior is dependent on the properties of the NHC derivative headgroup, which can be modified on demand. The surface activity was investigated by film balance measurements, epifluorescence microscopy, and differential scanning calorimetry. Additionally the cytotoxicity was evaluated against different cell lines such as eukaryotic tumor cell lines. These novel lipid-like NHC derivatives offer a broad spectrum for biological applications.

Tunable Heterogeneous Catalysis: N-Heterocyclic Carbenes as Ligands for Supported Heterogeneous Ru/K-Al2O3 Catalysts To Tune Reactivity and Selectivity.

Here we report, for the first time, an extensive characterization of an N-heterocyclic carbene (NHC)-modified supported heterogeneous catalyst. The existence of the metal-carbene bond could be proven by (13)C-SS-NMR experiments. Furthermore, it could be shown that the modification with NHCs does not structurally change the catalyst itself. The effect of the nature and the loading of the NHC on the activity and selectivity of the heterogeneous catalyst is presented by a hydrogenation study, finally leading to an NHC-enabled tunable heterogeneous catalyst for chemoselective hydrogenation.

Trichloromethylthiolation of N-Heterocycles: Practical and Completely Regioselective.

The first trichloromethylthiolation of a broad range of indoles and pyrroles is reported employing bench-stable N-trichloromethylthiosaccharin as reagent. This methodology is highly regioselective, exhibits high functional group tolerance, and provides access to two previously unknown classes of potentially bioactive compounds.

Transition-metal-free trifluoromethylthiolation of N-heteroarenes.

A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N-heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups.

Pd/C as a catalyst for completely regioselective C-H functionalization of thiophenes under mild conditions.

The completely C3-selective arylation of thiophenes and benzo[b]thiophenes was achieved by using Pd/C as a heterogeneous catalyst without ligands or additives under mild reaction conditions. The practicability of this transformation is demonstrated by notable functional group tolerance and the insensitivity of the reaction to H2 O and air. This method is also applicable to nitrogen- and oxygen-containing heterocycles, yielding the corresponding C2-arylated products. Three-phase tests along with Hg-poisoning and hot-filtration tests suggest that the catalytically active species is heterogeneous in nature.

Regioselective synthesis of benzimidazolones via cascade C-N coupling of monosubstituted ureas.

A direct method for the regioselective construction of benzimidazolones is reported wherein a single palladium catalyst is employed to couple monosubstituted urea substrates with differentially substituted 1,2-dihaloaromatic systems. In this method, the catalyst is able to promote a cascade of two discrete chemoselective C-N bond-forming processes that allows the highly selective and predictable formation of complex heterocycles from simple, readily available starting materials.