Mononuclear Cu-II--OOH entities or derived species have been seriously considered as important in chemical or biochemical oxidations. Yet, synthetic chemistry investigations have thus far revealed they have very limited substrate reactivity. Here, a significant aryl hydroxylation reaction occurs from a hydroperoxocopper(II) complex possessing a tripodal tetradentate ligand with appended aryl substituent. A phenolate-Cu(II) complex is detected following a proposed O-O cleavage event, that is suggested on the basis of precedent from non-heme iron chemistry. A bis-mu-oxo-dicopper(III) complex as active oxygenating agent is ruled out.