Palladium metal/silk fibroin

Alternatively, the surface of a metal can be modified with an enantiomerically pure additive. For example, in 1956 palladium metal/silk fibroin was used for the hydrogenation of alkenes with moderate enantioselectivity. However, most success with modified metal siufaces has been achieved in the hydrogenation of ketones. The reduction of 3-keto esters with a Raney nickel/tartaric acid/sodium bromide catalyst provides good enantioselectivities. For example, P-keto ester (3.108) affords the P-hydroxy ester (3.109). Platinum metal modified with cinchona alkaloids has been successfully used with a-keto esters. The reaction yields product with up to 90% ee in the reduction of a-keto ester (3.110). ... 

The active site of the catalyst has been considered to be metallic palladium deposited in the -structure of silk fibroin as an a mmetric chelate. However, as a result of the examination of the reproducibility of these atymmetric hydrogenation reactions, the asymmetric modification Cpommii ) of palladium by S-a-amino acid was suspected, the latter being concomitantly formed by the l rdrolysis of silk protein with hydrochloric acid from palladium(II) chloride in the course of the catalyst preparation (4). 

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