The Modification of Supported Palladium and Nickel Catalysts for Asymmetric Hydrogenation

This thesis describes the study of asymmetric heterogeneous catalysis with the objective of developing new chiral solid surfaces which can be used to establish a more general framework for the generation of chiral centres on heterogeneous catalyst surfaces. To this end the adsorption of a family of binaphthalene derivatives, namely R- and S-2,2'-dihydroxybinaphthalene, (+/-)-dimethoxybinaphthalene and R- and S-2,2'-diaminobinapthalene, have been studied as potential chiral modifiers. The results show that the amount of modifier adsorbed is dependent on the initial concentration of the modifier in the modifying solution and the time of modification. Both the dihydroxybinaphthalene and diaminobinaphthalene modifiers are strongly adsorbed on to Ni/silica, Pd/silica and Pd/carbon catalysts. The extent of adsorption is different for the different modifiers and varies between the metals. The dimethoxybinaphthalene modifier was only adsorbed by the Pd/carbon catalyst. In separate experiments, using the support materials themselves, evidence has been obtained for the direct adsorption of the modifiers on to the carbon, but not on to the silica. From studies of the effects of washing, following the modification, it is apparent that a small proportion of the modifier that is adsorbed on the metal and most of the modifier which is adsorbed on the support is only weakly adsorbed. These results are interpreted as a strong dissociative adsorption via the O-H or the N-H groups on to the metal surfaces resulting in the binaphthyl modifiers being orientated on the surface in a 'near vertical' mode, with the naphthalene ring units directed up and away from the surface. It is proposed that adsorption on the carbon support is through a weak interaction between the naphthyl rings of the modifier and the support surface to orientate the binaphthyl molecule in a 'horizontal' mode. All the catalysts modified with R- and S-forms of the dihydroxy and diaminobinaphthyls have been screened for enantioselectivity in the hydrogenation of methyl tiglate, tiglic acid and 3-coumaranone at atmospheric pressure and temperatures in the range 0 - 2