Titania enantioselective

The reduction of the catalyst precursor with sodium formate resulted in a lower Pd dispersion than the catalyst prepared by hydrogen reduction, the particle size is much larger in the former catalyst. The mesoporous carbon supported Pd catalysts are near to those of Pd on titania with respect to their enantiodifferentiating ability. Besides the metal dispersion, the availability of the Pd surface in the pores for the large modifier molecules seems to be the determining factor of the enantioselectivity. 

Sipos et al. " considered the characteristics of Pd-titania catalysts modified with (-)-DHVin in the enantioselective hydrogenation of isophorone. They used supports that were different in crystalline forms and in surface areas. 

In the system Cnd-2-phenylcinnamic acid the alkaloid interacts with the acid via two hydrogen bonds Interaction of the C9-OH group is the crucial influence in the chiral induction. Substitution of OH for OMe will weaken the interaction between modifier and the substrate. A second hydrogen bond between the N-atom in the quiniclidine group and the carboxylic group was revealed by experiments of modification of Pd-titania catalyst with a mixture of (Cnd + 9-MeO-DHCnd). Therefore esterification of the carbox-yhc group resulted in complete loss of enantioselectivity. 

Sipos, E., Farkas, G., Tungjer, A., Figueiredo, J.l. (2002) Enantioselective hydrogenation of isophorone with titania supported Pd catalysts modified with (-)-dihydroapovincaminic acid ethyl ester effect of the support and the reduction method, J. Mol. Catal. A. Chem. 179,107-112. 

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