Asymmetric Hydrogenation And Functionalization Of Calix [4] Arenes And Their Catalysis

This thesis includes the study of the asymmetric hydrogenation of ketones and alkenes and the hydrosilylation and cyanosilylation of carbonyl compounds by the catalysis of bifunctional crown ethers and calix[4]arene-based catalysts.Concretely, in the first part we have reported a novel"NH/Ï€interaction"in the Ru-catalyzed asymmetric hydrogenation of aryl ketones using Noyori's catalysts. We propose that one of the NH2 in the diamine, due to its increased acidity by coordination with Ru, would interact with the aryl group in the ketone via electrostatic attraction. This observation, validated by the Hammett relationship observed in the asymmetric hydrogenation of substituted aryl ketones and acetophenones. This result will have important implications in the design of more efficient asymmetric hydrogenation catalysts.In the second part we synthesized a series of calix[4]arene-based chiral bisphosphite ligands and examined the catalytic efficiency of their in situ generated rhodium complex in asymmetric hydrogenation of dehydroamino acid esters 1a and 1b. Substituents at both upper and lower rims of the calix[4]arenes have significant influence on the catalytic efficiency and stereoselectivity. The best catalyst 3b/Rh complex afforded the reduced product in up to 98% ee. We have also synthesized a series of novel t-butyl-calix[4]arene 1,3-diesters and evaluated their activity in catalytic esterification of alcohols and phenols.The third part features the catalytic activity of the bifunctional catalysts formed by complexation of alkali metal ions with crown ethers and calix[4]arenes in the hydrosilylation and cyanosilylation of carbonyl compounds using PMHS. Our catlysts have shown to exhibit good catalytic reactivity in these reactions. The cavity in the crown ethers and calix[4]arenes remarkably facilitates the reactivity by binding the substrates together. The stereoselectivity of this reaction is still unsatisfactory, however. In the cyanosilylation of acetophenones, the bifunctional catalysts show good reactivities as well, in which the activation effect of lithium ion is particularly remarkable.