Andreas Dumrath

A General Palladium‐Catalyzed Amination of Aryl Halides with Ammonia

A new robust palladium/phosphine catalyst system for the selective monoarylation of ammonia with different aryl bromides and chlorides has been developed. The active catalyst is formed in situ from [Pd(OAc)(2)] and air- and moisture-stable phosphines as easy-to-handle pre-catalysts. The productivity of the catalyst system is comparable to that of competitive Pd/phosphine systems; full conversion is achieved with most substrates with 1-2 mol % of Pd source and a fourfold excess of ligand (L).

Palladium‐Catalyzed Carbonylations of Aryl Bromides using Paraformaldehyde: Synthesis of Aldehydes and Esters

Carbonylation reactions represent useful tools for organic synthesis. However, the necessity to use gaseous carbon monoxide is a disadvantage for most organic chemists. To solve this problem, novel protocols have been developed for conducting palladium-catalyzed reductive carbonylations of aryl bromides and alkoxycarbonylations using paraformaldehyde as an external CO source (CO gas free). Hence, aromatic aldehydes and esters were synthesized in moderate to good yields.

Recyclable Catalysts for Palladium‐Catalyzed CO Coupling Reactions, Buchwald–Hartwig Aminations, and Sonogashira Reactions

Palladium-catalyzed coupling reactions have become an effective tool for advanced organic synthesis in both academic and industrial laboratories. 2] In particular, homogeneous palladium complexes allow for the reliable construction of all kinds of C C and C X bonds (X = O, N, S) from aryl and heteroaryl halides. Among the multitude of palladium complexes available for modern coupling reactions, bulky electron-rich phosphanes have become a privileged class of ligands, 4] which in addition to established coupling processes also enable more challenging reactions with water, alcohols, ammonia, fluoride, and synthesis gas. The drawbacks of these sophisticated ligands are their multistep preparation and costs, which are often price determining for the respective catalyst system. Hence, recycling these ligands still constitutes a major challenge. Common concepts for the recycling of palladium catalysts involved in coupling reactions include heterogenization of ligands on polymeric supports and palladium-supported heterogeneous catalysts. Recently, Jin and Lee also fixed homogeneous palladium catalysts onto nanoparticles to combine the advantages of homogeneous and heterogeneous catalysis. 13] On the basis of the development of liquid– liquid biphasic catalysis and the immobilization of molecular catalysts on solid surfaces, elegant concepts for catalyst recycling have been realized in the last decade. For example, Wasserscheid and co-workers demonstrated the feasibility of supported ionic liquid phases as a catalyst support (SILP) in Fischer–Tropsch and hydrogenation reactions. Despite all these developments, to date there exist no examples of the recycling of ligands and palladium catalysts in difficult coupling reactions. In this respect, we describe a general and facile generation of novel sterically hindered, nucleophilic phosphane ligands, which allow for easy recycling and direct reuse in palladium-catalyzed C O, C N, and C C bond-forming reactions.

Ruthenium Catalysts for Hydrogenation of Aromatic and Aliphatic Esters: Make Use of Bidentate Carbene Ligands

Committed carbenes: The convenient application of bidentate carbene ligands is described for the hydrogenation of carboxylic acid esters. The ligand precursors are easily synthesized through the dimerization of N-substituted imidazoles with diiodomethane. The catalyst is generated in situ and exhibits good activity and functional group tolerance for the hydrogenation of aromatic and aliphatic carboxylic acid esters.

How Important are Impurities in Catalysis? An Example from Ring‐Closing Metathesis

The dramatic effect of substrate impurities on the performance of a specific ruthenium catalyst system is demonstrated in the benchmark metathesis reaction of diethyl diallylmalonate. Based on detailed two‐dimensional GC–time‐of‐flight MS measurements, the significant influence of small amounts of different contaminations, especially various organic halides, is shown. This work serves as an incisive example of the importance of impurities to catalyst performance, also in homogeneous catalysis, which is often ignored in academic research.

Lewis Acid Assisted Ruthenium‐Catalyzed Metathesis Reactions

The combination of a ruthenium–arene complex, a noncoordinating salt, and a Lewis acid facilitates access to a highly active and selective in situ metathesis catalyst. The catalyst is formed from an inexpensive ruthenium precursor and olefins are used as the substrates. RCM=Ring‐closing metathesis, acac=acetylacetonate.

Practical Ruthenium Catalysts for the Synthesis of Cyclic Olefin Oligomers, Polymers, and their Hydrogenated Derivatives

Herein, we demonstrate the efficient ring‐opening metathesis polymerization (ROMP) of cyclic dienes and olefins catalyzed by several ruthenium–arene complexes as well as commercially available Grubbs‐type catalysts. The molecular mass and polydispersity of the oligomers was effectively controlled with the aid of different chain‐transfer agents. Furthermore, a highly practical and scalable sequential one‐pot synthesis method was successfully established to obtain hydrogenated ROMP oligomers with a homogenous hydrogenation catalyst.

The German Catalyst for Success: Weimar

The 44 Jahrestreffen Deutscher Katalytiker was organized by DECHEMA at the conference center in Weimar in March 2011 together with the 4 Jahrestreffen Reaktionstechnik. The intention of this joint conference was to intensify the communication between the scientific communities of homogeneous/heterogeneous catalysis and reaction engineering, which are mutually connected in many areas. The conference attracted 680 participants from academia and industry with a broad range of interest in the fields of homogeneous and heterogeneous catalysis, as well as reaction engineering. Moreover two presentations were held by the awardees of the “Jochen Block Preis 2010” and “Hanns Hofmann Preis 2011”, Drs. Regina Palkovits and Raimund Horn, respectively (Figure 1), who presented their recent research activities in the fields of chemical usage of biomass and in situ methods for high temperature catalytic reactions. Further highlights of the conference were the two poster workshops on “Transformation of Renewable Feedstocks” and “Electroand Photocatalysis”. In the field of heterogeneous catalysis the broad interest in renewable feedstocks was evident. In the first plenary lecture Ib Chockendorf discussed the potential and limitations of the photocatalytic production of hydrogen from water splitting. The current applicability and the future lines of development in the field of electromobility were presented in a very illustrative contribution by Prof. Hubert Gasteiger, who discussed not only the wide expectations, but also the limitations related to the future (CO2 neutral) mobility. A presentation from industry was led by Martin Votsmeier who discussed that neither the control of automotive convertors under dynamic operation nor the deactivation mechanisms of the applied catalytic materials are completely understood. Additionally, the requirements in the catalysts in terms of air pollution control increase in the future. An interesting presentation by Kristian Voelskow applied modeling tools to describe the production of carbon nanotubes in a technical fluidized bed reactor. Large scale industrial processes discussed included the oxidation of o-xylene to phthalic anhydride and industrial carbohydrate chemistry, for which the improvement in selectivity for bulk chemicals plays an important role in industrial research and development. This is underlined by the efforts in understanding the reaction network and the search for novel classes of catalysts for the partial oxidation of oxylene presented by Robert Marx and Stephan Schunk, respectively. Further emerging topics are in situ methods for investigation flow and concentration fields in chemical reactors and electricity storage for use in individual transportation. It would be desirable to address these topics at the next conference. This year the homogenous catalysis was embossed by sustainability and renewable resources. From new techniques for process optimization and the exchange of the catalyst metal to water splitting the range was quite broad. In this respect, Thomas M ller presented his recent results in the usage of CO2 as a renewable C1 building block. His group was able to conFigure 1. Prof. Dr. Regina Palkovits and Dr. Raimund Horn receiving their awards.