Reduction potentials sulfoxide complexes

Having demonstrated the potential of artificial metalloenzymes for the reduction of V-protected dehydroaminoacids, we turned our attention towards organometallic-catalyzed reactions where the enantiodiscrimination step occurs without coordination of one of the reactants to the metal centre. We anticipated that incorporation of the metal complex within a protein enviromnent may steer the enantioselection without requiring transient coordination to the metal. In this context, we selected the palladium-catalyzed asymmetric allylic alkylation, the ruthenium-catalyzed transfer hydrogenation as well as the vanadyl-catalyzed sulfoxidation reaction. Indeed, these reactions are believed to proceed without prior coordination of the soft nucleophile, the prochiral ketone or the prochiral sulfide respectively. Figure 13.5. 

The high affinity of this monomer in chloroform and acetonitrile (Ka > 10 and circa 10" M respectively) implies >99% complexation with the template species in these media, making imprinting with this monomer truly stoichiometric. A potential limitation of the monomer is that the use of more polar solvents, such as dimethyl sulfoxide (DMSO), leads to a reduction in affinity (Ka < 10 M ) due to unfavorable conformational effects. However, this monomer has been used to prepare a series of catalytically active MIPs, possessing high activity and efficiency. The latest in this series also contains a metal ion coordination site, together with the benzami-dine moiety and mimics the action of carboxypeptidase A (Figure 13). ... 

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