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.