Five-coordinate MII-semiquinonate (M = Fe, Mn, Co) complexes: reactivity models of the catechol dioxygenases

A series of five-coordinate M-II-semiquinonate (M = Fe, Mn, Co) complexes were synthesized and characterized, including the first example of a mononuclear Fe-II-semiquinonate. Intermediates were observed in the reactions of M-II-phenSQ (M = Fe, Co) with O-2. Evidence for the relevance of these intermediates to the intradiol catechol dioxygenases was obtained by characterization of the oxidized semiquinone-derived product, muconic anhydride, resulting from the reaction of [PhTt(tBu)] Co-II(3,5-DBSQ) with O-2.