The dimeric dioximatomanganese(II) complex [Mn-2(HL)(2)](BPh4)(2) (1) (where H2L is [HON=C(CH3)C(CH3)=NCH2CH2](2)NH) dissociates to the monomer [Mn(HL)](+) (2) upon dissolution in MeOH. Complex 2 is a functional phenoxazinone synthase model catalyzing the base-assisted oxidative dimerization of 2-aminophenol (H(3)ap) to 2-amino-3H-phenoxazine-3-one (apx) by dioxygen under ambient conditions via an o-benzoquinone monoimine (bqmi) intermediate, which, however, cannot be directly detected due to its high reactivity. If H3ap is replaced by 2-anilino-4,6-di-tert-butylphenol (3), a structural analog where the required positions are blocked, oxidation occurs without dimerization, affording the corresponding N-substituted o-quinone monoimine. Free radical intermediates were detected by ESR spectroscopy in both reactions. The kinetics of the catalytic oxidation of H3ap was studied spectrophotometrically and the corresponding rate equation established. It is consistent with a mechanism involving the formation of a catalyst-H(2)apO(2) ternary complex, which decomposes in the rate-determining step, generating a semiquinone monoimine undergoing noncatalytic oxidative dimerization to apx. (c) 2006 Elsevier B.V. All rights reserved.