Durham Research Online Deposited in DRO

22 Some aspects of metal-catalyzed heterogeneous enantioselective reactions are reviewed with specific 23 reference to four different systems where the phenomena that control enantioselection appear to be very 24 different. In the case of glucose electro-oxidation it is clear that any intrinsic chirality present at the 25 metal surface plays a vital role. With -keto hydrogenation, achiral surfaces modified by the adsorption 26 of chiral agents become effective enantioselective catalysts and formation of extended arrays of chiral 27 species appears not to be of importance: instead a 1:1 docking interaction controlled by hydrogen 28 bonding between the adsorbed chiral modifier and the prochiral reactant determines the outcome. 29 Hydrogen bonding also plays a central role in -ketoester hydrogenation, but here fundamental studies 30 indicate that the formation of ordered arrays involving the reactant and chiral ligand is of importance. 31 Asymmetric C=C hydrogenation, though relatively little studied, has the potential for major impact in 32 synthetic organic chemistry both at the laboratory scale and in the manufacture of fine chemicals and 33 pharmaceuticals. The structural attributes that determine whether or not a given chiral ligand is effective 34 have been identified; the ability to form strong covalent bonds with the metal surface while also 35 resisting hydrogenation and displacement by the strongly-adsorbing reactant under reaction conditions 36 are essential necessary conditions. Beyond these, ligand rigidity in the vicinity of the chirality center 37 coupled with resistance to SAM formation are critically important factors whose absence results in 38 racemic chemistry. 39