Mononuclear, Nonheme, High-Spin {FeNO}7/8 Complexes Supported by a Sterically Encumbered N4S-Thioether Ligand.

The synthesis of a new nonheme iron NO binding complex, [FeII(CH3CN)(N3Py2PhSEtCN)](BF4)2 (1), is reported. Complex 1, which contains two sterically encumbering phenyl substituents, exhibits a high-spin (hs) FeII (S = 2) ground state in contrast to the S = 0 ground state for unsubstituted [FeII(CH3CN)(N3PySEtCN)(BF4)2. Reaction of 1 with NO(g) in CH3CN yields an {FeNO}7 (S = 3/2) complex 2, which slowly decays at 25 °C with loss of NO• to regenerate 1. One-electron reduction of 2 with Cr(C6H6)2 at -40 °C yields the metastable, S = 1 {FeNO}8 complex 3. The nitrosyl moieties in thioether-ligated 2 and 3 are significantly less activated than in thiolate-ligated [Fe(NO)(N3PyS)]+/0, a structurally analogous pair of hs {FeNO}7/8 complexes. Calculations reveal that reduction of 2 is iron-centered, which may be a general property of hs {FeNO}7/8 complexes.