Peroxocopper complexes are of interest in metal ion mediated oxidative processes and as potential models for the active-site chemistry of copper metalloproteins involved in dioxygen (O-2) processing. Having been implicated in certain copper monooxygenases, mononuclear Cu(II)-OOR species are of particular interest. Here, the generation, spectroscopic characterization, and reactivity with triphenylphosphine of three mononuclear acylperoxo-copper(II) complexes are described. [Cu(TMPA)(m-ClC6H4C(O)OO-)](+) (1; TMPA = tris(2-pyridylmethyl)-amine) was formed by low-temperature reaction of the peroxo-dicopper(II) species [{Cu-II(TMPA)}(2)(O-2(2-))](2+) (5) with m-chloroperoxybenzoic acid (m-CPBA); hydrogen peroxide is a byproduct in this acid-base reaction. A trigonal-bipyramidal mononuclear coordination in 1 is supported by W-vis and EPR evidence, while a 1740 cm(-1) carbonyl infrared absorption suggests the percarboxylato ligand binds as a unidentate oxygen donor ligand. Reaction of 1 with PPh(3) at -80 degrees C gives O=PPh(3) and the carboxylato complex [Cu(TMPA)(m-ClC6H4C(O)-O-)](+) (6) (nu(c=0) = 1620 cm(-1)). [Cu(Me(2)im)(3)(m-ClC6H4C(O)OO-)](+) (2; Me(2)im = 1,2-dimethylimidazole) is formed by reaction of m-CPBA with the peroxo-dicopper(II) species [Cu-2(Me(2)im)(6)(O-2)](2+) (8) in CH2Cl2 at -90 degrees C. Solution and solid-state spectroscopic data are consistent with a mononuclear formulation while nu(c=0) = 1745 cm(-1) also suggests terminal percarboxylato coordination. While 1 and 2 are stable at room temperature as solids, [Cu-II(CPY2-O-)(m-ClC6H4C(O)OO-)] (3; CPY2-OH = bis[2-(2-pyridyl)ethyl][(2-hydroxyphenyl)methyl]-amine) is not. Is was generated by reaction of [Cu(CPY2-O-)(Cl)] . 2H(2)O (9) with m-CPBA at -75 degrees C. At this temperature, a 1750 cm(-1) IR absorption is ascribable to a coordinated perbenzoato ligand. Species 3 is the most reactive of the three Cu((II)-percarboxylato complexes. Addition of PPh(3) (-80 degrees C) causes a rapid change, giving O=PPh(3) and the carboxylato complex [Cu(CPY2-O-)(m-ClC6H4C(OO-)] (10), which was independently synthesized. Percarboxylato complexes 1 and 2 possess enhanced reactivity relative to peroxo-copper(II) complexes with the same ligands, a further example illustrating how electrophilic activation (e.g. by protonation or, here, by acylation) of peroxo groups leads to oxygen atom transfer functionality.