O₂ Activation by Bis(imino)pyridine Iron(II)−Thiolate Complexes

The new iron(II)−thiolate complexes [(iPrBIP)FeII(SPh)(Cl)] (1) and [(iPrBIP)FeII(SPh)(OTf)] (2) [BIP = bis(imino)pyridine] were prepared as models for cysteine dioxygenase (CDO), which converts Cys to Cys-SO2H at a (His)3FeII center. Reaction of 1 and 2 with O2 leads to Fe-oxygenation and S-oxygenation, respectively. For 1 + O2, the spectroscopic and reactivity data, including 18O isotope studies, are consistent with an assignment of an iron(IV)−oxo complex, [(iPrBIP)FeIV(O)(Cl)]+ (3), as the product of oxygenation. In contrast, 2 + O2 results in direct S-oxygenation to give a sulfonato product, PhSO3−. The positioning of the thiolate ligand in 1 versus 2 appears to play a critical role in determining the outcome of O2 activation. The thiolate ligands in 1 and 2 are essential for O2 reactivity and exhibit an important influence over the FeIII/FeII redox potential.