Download Application of new chiral phospine Rh(I)

25. Hrvatski sastanak kemičara i kemijskih inženjera, Poreč, 2017.
Application of new chiral phospine Rh(I) complexes
in enantioselective catalytic hydrogenation reactions
Primjena novih kiralnih fosfinskih kompleksa Rh(I)
u reakcijama katalitičkog enantioselektivnog hidrogeniranja
Saša Opačak, Zoran Kokan, Zoran Štefanić, Berislav Perić, Srećko I. Kirin*
Institut Ruđer Bošković, Bijenička cesta 54, 10000 Zagreb
E-pošta: [email protected]
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 acetamidocinnamate S2. The best result was achieved with the anthracene cyclohexanediamine mphospine 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.
Figure 1: General ligand structure.
References
[1] Z. Kokan, Z. Glasovac, M. Majerić Elenkov, M. Gredičak, I. Jerić, S. I. Kirin, Organometallics, 33
(2014) 4005-4015.
[2] B. M. Trost, M. L. Crawley, Chem. Rev., 103 (2003) 2921-2943.