Synthesis and Reactivity of Cobalt(III) Complexes Bearing Primary- and Secondary-Side Cyclodextrin Binding Sites

摘要

In recent years, efforts to focus the catalytic power of metals by connection to a binding moiety have received considerable attention. Although the cyclen-Co(III) complex (I) has exhibited amongst the greatest rate accelerations in acyl- and phosphoryl transfer reactions, this catalytic unit has not been used previously in the design of a pre-associating artificial metallo-enzyme. Cyclodextrin (CD) has been used previously for the synthesis of metallo-protein models, but incorporation of a Co(III) metal center onto CD has not been achieved to date. Accordingly, we have synthesized two cyclen-Co(III) complexes positioned alternately on the primary- and secondary-sides of Beta-CD. We now report that artificial metallo-enzyme 7 demonstrates a 900-fold enhancement of metal-promoted ester hydrolysis attributable entirely to the presence of the CD binding unit. Furthermore, we find that the properties of primary- and secondary-side CD's are unexpectedly quite different, in part because the primary-side derivative is able to involve an adjacent hydroxymethyl group in chelation of the metal ion. Reprints. (aw)