Mononuclear Copper(II)-Acylperoxo Complexes

Article abstract of DOI:10.1021/ic00115a035

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 (O2) processing. Having been implicated in certain copper monooxygenases, mononuclear Cu(II)-OOR speciesare 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(O2(2-)](2+) (5) with m-chloroperoxybenzoic acid (m-CPBA); hydrogen peroxide isa byproduct in this acid-base reaction. A trigonal-bipyramidal mononuclear coordination in 1 is supported by UV-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 PPh3 at-80°C gives O=PPh3 and the carboxylato complex [Cu(TMPA)(m-ClC6H4C(O)O(-))](+) (6) (νCO = 1620 cm**-1). [Cu(Me2im)3(m-ClC6H4C(O)OO(-))](+) (2; Me2im = 1,2-dimethylimidazole) is formed by reaction of m-CPBAwith the peroxo-dicopper(II) species [Cu2(Me2im)6(O2)](2+) (8) in CH2Cl2 at -90°C. Solution and solid-state spectroscopic data are consistent with a mononuclear formulation while νCO = 1745 cm**-1 also suggests terminal percarboxylato coordination. While 1 and 2 are stable atroom 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)].2H20 (9) with m-CPBAat -75°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 PPh3 (-80°C) causes a rapid change, giving O=PPh3 and the carboxylato complex [Cu(CPY2-O(- ))(m-CIC6H4C(O)O(-))] (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.