Transition metal complex catalyzed reactions in two immiscible liquid phases can be industrially important alternatives to homogeneously catalyzed one-phase-reactions. The synthesis of butyric aldehyde by the Ruhrchemie/Rhône-Poulenc-process [1] serves as one example as well as the production of α-olefins in the SHOP-Process . After the catalytic reaction one phase solves the products and the other phase contains the catalyst. After simply separating the two phases, the catalyst phase can be recycled without any further treatment. Another innovative effect of two-phase catalysis is the possibility to extract primary products during the catalytic reaction into the organic phase. This often results in novel possibilities of controlling the product selectivity [3]. A very suitable solvent for the catalyst phase is water, since it is very cheap and immiscible with many organic solvents, which may serve as solvents for the products [4]. However, ionic liquids (room temperature molten salts) have also proved to be particularly useful for two-phase catalytic reactions [5]. In most cases the transition metal complexes are soluble in ionic liquids whereas organic compounds are often immiscible.
We are interested in selective transformations of multifunctional substrates using two-phase-catalysis. The hydrogenation of the industrially available sorbic acid 1 can lead to many different products, some of them being shown in scheme 1.
Generally, hexenoic acids like 2 -5, bearing one C=Cbond, are interesting starting materials for the production of fine chemicals. We could show that it is possible to hydrogenate 1 stereoselectively by means of homogeneous ruthenium catalysis . Esters of sorbic acid and sorbic alcohol were hydrogenated using catalytic