Synthesis and characterization of Ni^IIIN3S2 complexes as active site models for the oxidized form of nickel superoxide dismutase

Nickel complexes, [Ni(H₂BA^RTPP)](ClO ₄)₂ (R=Ph for 1 or iPr for 2), supported by a pentadentate ligand H₂BA^RTPP were synthesized and oxidized to form Ni^III species having a N3S2 coordination environment to mimic the active site of the oxidized form of nickel superoxide dismutase (NiSODox). The Ni^III species 2⁺ exhibited a rhombic signal with gvalues at 2.15, 2.12 and 2.02 similar to that of NiSODox. DFT calculations revealed that 2⁺ has an unpaired electron primarily located in the d z 2 orbital of the Ni^III center, which strongly overlaps with the p _z orbital of the axial pyridine nitrogen of H₂BA ^PrTPP. SOD's law: Complexes [Ni(H₂BA^RTPP)] (ClO₄)₂ (R=Ph or iPr; see structure), supported by a pentadentate ligand H₂BA^RTPP, were synthesized and oxidized to form Ni^III species having a N3S2 coordination environment to mimic the active site of the oxidized form of NiSOD (NiSOD_ox). DFT calculations reveal that the oxidized compound has an unpaired electron primarily located in the d z 2 orbital of the Ni^III center.