A silver-based catalyst system has been discovered that effectively promotes the protodecarboxylation of various carboxylic acids at temperatures of 80-120 degrees C--more than 50 degrees C below those of the best known copper catalysts.

The protodecarboxylation of aromatic carboxylic acids by various copper and silver catalysts is investigated with the help of density functional calculations and experimental studies. The computational results reveal that the catalytic activity of copper(I)–1,10‐phenanthroline catalysts increases with the introduction of electron‐rich substituents at the phenanthroline ligand. They also predicted that for some substrates, silver complexes should possess a substantially higher decarboxylating activity than copper, which is confirmed by experimental studies, leading to the discovery of a silver(I) catalyst that effectively promotes the protodecarboxylation of various carboxylic acids at temperatures in the range of 80–120 °C—more than 50 °C below those of the best known copper(I) catalyst. The scope of the new system complements that of the copper(I)‐based method as it includes benzoates for example, with halogen or ether groups in the ortho positions.

The dimeric Pd(I)-complex [Pd(μ-Br)(P(t)Bu3)]2 was found to be highly active for catalyzing double-bond migration in various substrates such as unsaturated ethers, alcohols, amides, and arenes, under mild conditions. It efficiently mediates the conversion of allylic esters into enol esters, rather than inserting into the allylic C-O bond. The broad applicability of this reaction was demonstrated with the synthesis of 22 functionalized enol esters.

The ruthenium-catalyzed hydroamidation of terminal alkynes has evolved to become a broadly applicable tool for the synthesis of enamides and enimides. Depending on the catalyst system employed, the reaction leads chemo-, regio-, and stereoselectively to a single diastereoisomer. Herein, we present a comprehensive mechanistic study of the ruthenium-catalyzed hydroamidation of terminal alkynes, which includes deuterium-labeling, in situ IR, in situ NMR, and in situ ESI-MS experiments complemented by computational studies. The results support the involvement of ruthenium-hydride and ruthenium-vinylidene species as the key intermediates. They are best explained by a reaction pathway that consists of an oxidative addition of the amide, followed by insertion of a π-coordinated alkyne into a ruthenium-hydride bond, rearrangement to a vinylidene species, nucleophilic attack of the amide, and finally reductive elimination of the product.

The reaction mechanism of decarboxylative cross-couplings of benzoates with aryl halides to give biaryls, which is cooperatively catalyzed by copper/palladium systems, was investigated with DFT methods. The geometries and energies of all starting materials, products, intermediates, and transition states of the catalytic cycle were calculated for the two model reactions of potassium 2- and 4-fluorobenzoate with bromobenzene in the presence of a catalyst system consisting of copper(I)/1,10-phenanthroline and the anionic monophosphine palladium complex [Pd(PMe3)Br](-). Several neutral and anionic pathways were compared, and a reasonable catalytic cycle was identified. The key finding is that the transmetalation has a comparably high barrier as the decarboxylation, which was previously believed to be solely rate-determining. The electronic activation energy of the transmetalation is rather reasonable, but the free energy loss in the initial Cu/Pd adduct formation is high. These results suggested that research aimed at further improving the catalyst should target potentially bridging bidentate ligands likely to assist in the formation of bimetallic intermediates. Experimental studies confirm this somewhat counterintuitive prediction. With a bidentate, potentially bridging ligand, designed to support the formation of bimetallic adducts, the reaction temperature for decarboxylative couplings was reduced by 70 °C to only 100 °C.