Scorpionate-supported models of nickel-dependent superoxide dismutase

Ligation of nickel(II) by Trofimenko’s hydrotris(3,5-dimethyl-1-pyrazolyl)borate anion (TpMe,Me) and zwitterionic organoxanthate or dithiocarbamate co-ligands affords neutral high-spin pentacoordinate complexes with formally trianionic N3S2 ligand fields, similar to that of the nickel-dependent superoxide dismutase active site. Given this analogy to NiSOD, the structure, dynamics, and redox properties of the product complexes were examined. X-ray structures revealed rotation of the dithioacid chelates against the scorpionate face, giving coordination geometries between square pyramidal and trigonal bipyramidal limits. The complexes accordingly adopt paramagnetic (S = 1) d8 electron configurations, but magnetic susceptibilities suggest partial isomerization to a diamagnetic state in solution. The complexes also exhibit quasi-reversible one-electron redox couples at potentials suitable for SOD activity.

The scorpionate anion TpMe,Me is incorporated into NiSOD model complexes with N3S2 ligand fields. These exhibit structural and dynamic differences compared to analogues supported by the bulkier TpPh,Me ligand. The ability to manipulate ligand and complex properties through substitution on the pyrazole donor rings is a hallmark of Trofimenko’s legacy.Figure optionsDownload as PowerPoint slide