engleski

Application of new chiral phospine Rh(I) complexes in enantioselective catalytic hydrogenation reactions

Asymmetric catalysis is of crucial importance in science and industry. Traditionally, chiral induction in asymmetric catalysis is achieved by the vicinity of a chiral source and the reaction center. However, we have shown that chiral induction can also be achieved by a distant source of chirality ; a maximal selectivity of 84 % ee was achieved by using aminoacid based phosphine ligands [1]. In our quest to increase the enantioselectivity we have shifted our attention from chiral aminoacids to chiral cyclic aliphatic diamines, since they are know to induce very high selectivity [2]. We have prepared a series of novel monodentate ligands comprised of three building blocks (Figure 1). The metal binding building block is a triphenylphospine with different substitution patterns: para-, meta- and dimeta-. The next building block is a disubstituted chiral diamine, cyclohexanediamine or cyclopentanediamine. Finally, the last building block is designed to study the steric and electronic influence on selectivity in catalysis by incorporating different voluminous substituents or differently para-substituted benzoic acids. Rhodium complexes of the ligands were generated in situ and used as catalysts in asymmetric hydrogenation of model substrates, acetamidoacrylate S1 and acetamido-cinnamate S2. The best result was achieved with the anthracene cyclohexanediamine m-phospine ligand which gave 91 % ee for S1 and 96 % ee for S2. Further plans are to test our ligands on a wider range of model and commercially important substrates.

Asymmetric catalysis ; rhodium complexes

nije evidentirano