A hydrophilic metal–ligand complex formed from the precursor [dicarbonyl(acetylacetonato)rhodium(I)] {[Rh(acac)(CO)₂]} and the bidentate ligand [2,7-bis(SO₃Na)-4,5-bis(diphenylphosphino)-9,9-dimethylxanthene] (SulfoXantPhos), was found to be a suitable candidate as a catalyst complex for the hydroformylation of 1-dodecene in multiphase systems formulated from water, 1-dodecene, and a nonionic surfactant. To improve the solubilization of the olefin in the aqueous phase, surfactants were added. The multiphase system acted as a tunable solvent, through which not only the interfacial area was increased during the reaction but also the phase separation behavior could be manipulated through temperature changes, thus allowing an easy separation of the expensive rhodium complex from the organic phase after the reaction. The influence of different process parameters such as the type of surfactant, type of ligand, and the metal/ligand ratio was investigated and discussed. Also the influence of the phase state on the reaction was determined. Under optimized reaction conditions, turnover frequencies of >300 h⁻¹ and selectivities of 98:2 towards the linear product could be achieved.

Heterogenization is a powerful approach for the generation of easily recyclable catalysts. In this study, a modified tethered rhodium(III)- p-toluenesulfonyl-1,2-diphenylethylenediamine (Rh-TsDPEN) complex immobilized on polymeric supports was applied to kinetic and up-scaling experiments on the asymmetric transfer hydrogenation of acetophenone in water. Study of the catalyst has helped in understanding some aspects of its operating mode. The results indicate that, in the investigated range, a simple second-order model describes the enantioselective conversion of acetophenone to phenylethanol. Optimal reaction conditions were determined, and particularly the solution pH was found to play a decisive role for the activity and reusability of the catalyst. The good performance under optimized conditions emphasizes the practical usefulness of this recyclable catalytic system for environmentally benign asymmetric transfer hydrogenation processes.

In dieser Übersicht wird ein Konzept für die reaktionstechnische Nutzung von wässrigen Tensidlösungen und Wasser/Tensid/Lösungsmittel-Gemischen als Reaktionsmedien für katalytische Reaktionen vorgestellt. Dabei werden drei Beispiele beschrieben, für die ein Reaktionsmedium formuliert werden konnte, das sowohl optimale Bedingungen für den Ablauf der Reaktionen bietet als auch eine effiziente Rückgewinnung des Katalysators ermöglicht.

In this review a concept is introduced for the application of micellar solutions and microemulsions in chemical reaction engineering. For three examples it is shown how to formulate a reaction medium which offers optimal conditions for the reaction as well as for the catalyst recycling.

A facile and rapid preparation method for a wide variety of medium surface area perovskite-type catalysts on the laboratory scale is presented. The cellulose templating method allows for catalysts with high phase purity, even at the relatively low calcination temperatures. Among the versatile compositions of perovskites based on the SrCoO_x system, straightforward modifications could be performed to optimize the catalytic performance in the oxidation of CH₄. Substitutions in both the A and B positions in the ABO₃ lattice can remarkably affect the catalytic activity. Compared to other preparation methods, the cellulose templating method is a rapid process and the catalytic performances obtained with SrCoO_x and LaCoO_x are at least as good as with materials prepared by conventional methods.

Catalyst immobilization through covalent attachment onto a support is one strategy to provide recyclable systems. Here, soluble and surface-functionalized solid polymers were used as supports for a modified tethered rhodium(III)-p-toluenesulfonyl-1,2-diphenylethylenediamine [Rh(III)-TsDPEN] complex. The supported catalysts were applied to the asymmetric transfer hydrogenation of phenyl ketones in aqueous solution of sodium formate. High ee values (up to 99%) and good activities were achieved. It was discovered that the solid polymer-supported catalyst could be recycled at least four times without a significant decrease of the activity when a mixture of sodium formate and formic acid was used as the hydrogen source. This catalytic system provides a promising approach towards an ecologically and economically rational production of enantioenriched building blocks.