A Reactive, Photogenerated High-Spin ( S = 2) Fe IV (O) Complex via O 2 Activation.

Addition of dioxygen at low temperature to the non-heme ferrous complex Fe II (Me 3 TACN)((OSi Ph2 ) 2 O) ( 1 ) in 2-MeTHF produces a peroxo-bridged diferric complex Fe 2 III (μ-O 2 )(Me 3 TACN) 2 ((OSi Ph2 ) 2 O) 2 ( 2 ), which was characterized by UV-vis, resonance Raman, and variable field Mössbauer 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 (ν(Fe=O) = 818 cm -1 ; δ = 0.22 mm s -1 , Δ E Q = 0.23 mm s -1 ). Variable field Mössbauer 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.