Mn complexes of N,N',N"-trimethyl-1,4,7-triazacyclononane (Mn-tmtacn) exhibit good catalytic activity, at ambient temperatures, for the benzylic oxidation of aromatics selectively to the corresponding alcohol and carbonyl compounds with H2O2 as oxidant in the presence of carboxylate buffers. The active Mn species in the reaction medium was investigated by UV-visible (UV-Vis), FT-IR-attenuated total reflectance (FT-IR-ATR) and electron spin resonance (ESR) spectroscopic techniques. The studies revealed the formation of terminal oxo- and mu-oxo-Mn(IV)-tmtacn complexes during the reaction. The oxo-manganese complexes and the nature of the carboxylic acid play an important role in the activation of the benzylic C-H bond. (C) 2002 Elsevier Science B.V. All rights reserved.