Session: ACS Award for Encouraging Women into Careers in the Chemical Sciences: Symposium Honoring Katherine Franz :

M–OH complexes have been implicated in the catalytic cycles of certain metalloproteins, such as non-heme lipoxygenases. While the identities of some M–OH complexes in biology have been confirmed, the preparation of synthetic analogues has proved difficult due to the reactive nature of these compounds and the challenges associated with controlling their coordination environments. We have been investigating the formation of 3d transition metal–hydroxido complexes by using structural principles found within the active sites of metalloproteins: namely, the use of non-covalent interactions within the secondary coordination sphere. These interactions are now known to influence a variety of properties that include tuning the reactivity of various metal center(s). To simulate these effects, we synthesize metal complexes with ligand frameworks that incorporate moieties to support non-covalent interactions, such as intramolecular hydrogen bonds (H–bonds) and electrostatic interactions. Past work from the group has used these design principles to successfully prepare mononuclear Co–OH complexes. These studies produced several examples of Co^II–OH complexes, however isolation and characterization of Co^III–OH complexes proved more difficult. This poster describes the synthesis and characterization of a number of Co–OH complexes supported by two different ligand frameworks. The first ligand framework is a “hybrid” tripodal ligand which incorporates two ureayl moieties and one phosphinic amide to provide three intramolecular H-bonds to stabilize mononuclear M–OH complexes. Co^II/III–OH complexes have been successfully isolated and characterized structurally and spectroscopically. The reactivity of the Co^III–OH species towards external substrates has been investigated. The second framework features a C₃–symmetric tripodal ligand bearing appended phosphinic-amide groups, which have been shown to act both as H–bond acceptors and bind to a second metal ion, affording bimetallic complexes, including bridging hydroxido species.

Andrew Borovik

Univ of California

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