Pincer Ligands for the Control of Metal Coordination Spheres

Metalloenzymes are efficient catalysts, operating both stereo- and regioselectively with high reaction rates at ambient temperatures in aqueous conditions. In order to generate synthetic catalysts which operate in similarly efficient pathways, it is useful to study biomimeticcomplexes which incorporate the techniques used by biological systems. In this report, several pincer ligand frameworks are used to incorporate the interplay between primary coordination sphere effects and secondary coordination sphere effects observed in metalloenzyme active sites. H4dippy, which combines appendant dipeptides to create a chiral environment as well as distal hydrogen-bonding groups was prepared and used to generate CuIIH2dippy. Further experiments probed the oxidation of CuIIH2dippy with aqueous H2O2. A new phosphonamide bis(aminophenyl)amine ligand, H3tap, was used to prepare a cobalt(II) complex with opticalfeatures consistent with a [Co2N2] diamond core structure. Reaction with oxidants generated species with spectroscopic characteristics consistent with ligand oxidation and retention of a dinuclear complex. Finally, the redox-active sulfonamide bis(aminophenyl)amine, H3ibaps, as well as H3tap, were used to generate putative iron(III) thiolate complexes. These complexes were studied by reaction with the oxo-transfer reagent isopropyl iodoxybenzoate and subsequent reaction with substrate