Electronic Modification of a Reduced Mononuclear Nonheme Iron Nitrosyl Complex Leads to HNO Release

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Abstract
A new pentadentate-fluorinated N4S(thiolate) ligand was synthesized. Reaction with Fe(BF4)2·6H2O gives a new thioether complex, [FeII(CH3CN)(N3PypFSEtCN)][BF4]2 (1), and on-metal deprotection gives the thiolate complex, [FeII(CH3CN)(N3PypFS)][BF4] (2). Reaction of 2 with NO forms a low-spin ground state (S = 1/2) {FeNO}7 complex (3). Chemical reduction of 3 with cobaltocene gives a metastable intermediate spin S = 1 {FeNO}8 complex (4). Protonation of 4 releases nitroxyl (HNO), as observed by ESI-MS and 31P NMR trapping experiments with PPh3. Complexes 1 and 2 were characterized by single-crystal X-ray crystallography, complexes 2-4 were characterized by EPR and FT-IR spectroscopies, and all iron complexes were characterized by 19F NMR, UV-vis, and 57Fe Mössbauer spectroscopies. These results show that a nonheme iron complex can generate and release HNO, suggesting that nonheme iron centers could be endogenous or exogenous sources of HNO in biological systems. Additionally, the fluorine-substituted N4S(thiolate) ligand provides a unique spectroscopic handle to monitor the reactivity of the iron center several bonds away from the fluorine substituent.
Funding Information
  • Division of Chemistry (CHE-1955527)
  • National Institute of General Medical Sciences (GM147588)

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