Mononuclear copper(II)-superoxo complexes 2(X)-OO(*) having triplet (S = 1) ground states were obtained via reaction of O(2) with the copper(I) starting materials 1(X) supported by tridentate ligands L(X) [1-(2-p-X-phenethyl)-5-(2-pyridin-2-ylethyl)-1,5-diazacyclooctane; X = CH(3), H, NO(2)] in various solvents. The superoxo complexes 2(X)-OO(*) mimic the structure [tetrahedral geometry with an end-on (eta(1))-bound O(2)(*-)] and the aliphatic C-H bond activation chemistry of peptidylglycine alpha-hydroxylating monooxygenase and dopamine beta-monooxygenase.

Selective hydroxylation of benzene to phenol has been achieved using H2O2 in the presence of a catalytic amount of the nickel complex [Ni(II)(tepa)](2+) (2) (tepa = tris[2-(pyridin-2-yl)ethyl]amine) at 60 °C. The maximum yield of phenol was 21% based on benzene without the formation of quinone or diphenol. In an endurance test of the catalyst, complex 2 showed a turnover number (TON) of 749, which is the highest value reported to date for molecular catalysts in benzene hydroxylation with H2O2. When toluene was employed as a substrate instead of benzene, cresol was obtained as the major product with 90% selectivity. When H2(18)O2 was utilized as the oxidant, (18)O-labeled phenol was predominantly obtained. The reaction rate for fully deuterated benzene was nearly identical to that of benzene (kinetic isotope effect = 1.0). On the basis of these results, the reaction mechanism is discussed.