Wednesday, June 25, 2008
Congressional Room (Capital Hilton)

Fluorinated Polymeric Binap Ligand for Asymmetric Hydrogenation in Sc CO2

Ozlem Erdem and Bilgehan Guzel. CU Science and Letters, Adana, Turkey

In the past decades, the attachment of homogeneous catalysts to soluble polymer supports has been attracting considerable attention owing to its potential combination of the advantages, and minimization of the disadvantages, of homogeneous and heterogeneous catalysis [1].

Here, we report use of polymeric chiral diphosphine ligands for asymmetric hydrogenation. BINAP was chosen as a model ligand for this study, since it is probably the most versatile and effective ligand among all the chiral phosphine ligands which have been studied for asymmetric catalysis [1,2]. The chiral polymeric BINAP ligands were synthesized in 71% yield by condensation of the 6,6'diaminoethyl-BINAP with terephtaldicarboxaldehyde in N-methyl-2-pyrrolidone (NMP).

The ligands were characterized 1H, 19F and 31P NMR. The molecular weights of polymeric ligands were determined by gel permeation chromatography (GPC). Solubility studies in sc CO2 were performed at the conditions of 343oK, 2300 psi pressure. Complexed with rhodium it gives 85% conversation and enantioselectivies from 62% for the hydrogenation of -ketoester. Hydrogenation was carried out in 0,032 mol-L-1 (0.063 mmol of ligand) solution of sc CO2 under following reaction conditions: Substrate/catalyst= 200 (molar ratio); H2 pressure 6,76 x 106 Pa., CO2 pressure 2300 psi. Conversation and ee were determined by chiral GC analysis.

[1] Q. Fan, Y.Chen, X. Chen, D. Jiang, F. Xi, A. S. Chen, Chem. Commun, 2000, 789-790.

[2] C. Saluzzo, T. Lamouille, F. Guyader, M. Lemaire, Tetrahedron Asymmetry 13, 2002, 1141-1146.