A Mononuclear, Nonheme FeII–Piloty’s Acid (PhSO2NHOH) Adduct: An Intermediate in the Production of {FeNO}7/8 Complexes from Piloty’s Acid

• Published in: Journal of the American Chemical Society Vol. 141; no. 17; pp. 7046 - 7055
• Main Authors: Confer, Alex M, Vilbert, Avery C, Dey, Aniruddha, Lancaster, Kyle M, Goldberg, David P
• Format: Journal Article
• Language: English
• Published: American Chemical Society 01.05.2019
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b01700

Reaction of the mononuclear nonheme complex [FeII(CH3CN)­(N3PyS)]­BF4 (1) with an HNO donor, Piloty’s acid (PhSO2NHOH, P.A.), at low temperature affords a high-spin (S = 2) FeII–P.A. intermediate (2), characterized by 57Fe 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 (PhSO2NOH–) to [FeII(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)]­BF4 (4), as evidenced by 1H NMR, ATR-IR, and Mössbauer spectroscopies. Isotope labeling experiments with 15N-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 FeII complexes in the assisted degradation of HNO donor molecules.