Abstract
Reaction of the mononuclear nonheme complex [Fe(II)(CH(3)CN)(N3PyS)]BF(4) (1) with an HNO donor, Piloty's acid (PhSO(2)NHOH, P.A.), at low temperature affords a high-spin ( S = 2) Fe(II)-P.A. intermediate (2), characterized by (57)Fe Mössbauer and Fe K-edge X-ray absorption (XAS) spectroscopies, with interpretation of both supported by DFT calculations. The combined methods indicate that P.A. anion binds as the N-deprotonated tautomer (PhSO(2)NOH(-)) to [Fe(II)(N3PyS)](+), leading to 2. Complex 2 is the first spectroscopically characterized example, to our knowledge, of P.A. anion bound to a redox-active metal center. Warming of 2 above -60 °C yields the stable {FeNO}(7) complex [Fe(NO)(N3PyS)]BF(4) (4), as evidenced by (1)H NMR, ATR-IR, and Mössbauer spectroscopies. Isotope labeling experiments with (15)N-labeled P.A. confirm that the nitrosyl ligand in 4 derives from P.A. In contrast, addition of a second equivalent of a strong base leads to S-N cleavage and production of an {FeNO}(8) species, the deprotonated analog of an Fe-HNO complex. This work has implications for the targeted delivery of HNO/NO(-)/NO· to nonheme Fe centers in biological and synthetic applications, and suggests a new role for nonheme Fe(II) complexes in the assisted degradation of HNO donor molecules.