A dimeric form of Jacobsen's catalyst for improved retention in a polydimethylsiloxane membrane

A dimeric form 1 of Jacobsen's catalyst was synthesized for better steric occlusion in a polydimethylsiloxane membrane. In homogeneous conditions, the dimer is about as active and enantioselective as Jacobsen's catalyst itself. The relationship between leaching of the complex out of the membrane on one hand and the solubility of the complex and the swelling of the membrane in the solvent used on the other, showed that leaching could be avoided only if low solubility was combined with low swelling or in the case of complete insolubility. As the dimer is less soluble and larger than the monomeric form, this form leaches less. The yields and enantioselectivities of the heterogenised system are comparable to those of the homogeneous monomer. (C) 1997 Published by Elsevier Science Ltd.