A Reactive, Photogenerated High-Spin (S=2) FeIV(O) Complex via O2 Activation

Addition of dioxygen at low temperature to the nonheme ferrous complex Fe-II(Me(3)TACN)((OSiPh2)(2)O) (1) in 2-MeTHF produces a peroxo-bridged diferric complex Fe-2(III)(mu O-2)(Me(3)TACN)(2)((OSiPh2)(2)O)(2) (2), which was characterized by UV-vis, resonance Raman, and variable field Mossbauer spectroscopies. Illumination of a frozen solution of 2 in THF with white light leads to homolytic O-O bond cleavage and generation of a Fe-IV(O) complex 4 (nu(Fe=O) = 818 cm(-1); delta = 0.22 mm s(-1), Delta E-Q = 0.23 mm s(-1)). Variable field Mossbauer spectroscopy measurements show that 4 is a rare example of a high-spin S = 2 Fe-IV(O) complex and the first synthetic example to be generated directly from O-2. Complex 4 is highly reactive, as expected for a high-spin ferryl, and decays rapidly in fluid solution at cryogenic temperatures. This decay process in 2-MeTHF involves C-H cleavage of the solvent. However, the controlled photolysis of 2 in situ with visible light and excess phenol substrate leads to competitive phenol oxidation, via the proposed transient generation of 4 as the active oxidant.