Kinetics and DFT studies on the reaction of copper(II) complexes and H2O2

Copper(II) complexes supported by bulky tridentate ligands L1(H) (N,N-bis(2-quinolylmethyl)-2-phenylethylamine) and L1(Ph) (NN-bis(2-quinolylmethyl)-2,2-diphenylethylamine) have been prepared and their crystal structures as well as some physicochemical properties have been explored. Each complex exhibits a square pyramidal structure containing a coordinated solvent molecule at an equatorial position and a weakly coordinated counter anion (or water) at an axial position. The copper(II) complexes reacted readily with H2O2 at a low temperature to give mononuclear hydroperoxo copper(II) complexes. Kinetics and DFT studies have suggested that, in the initial stage of the reaction, deprotonated hydrogen peroxide attacks the cupric ion, presumably at the axial position, to give a hydroperoxo copper(II) complex retaining the coordinated solvent molecule (H-R center dot S). H-R center dot S then loses the solvent to give a tetragonal copper(II)-hydroperoxo complex (H-R), in which the -OOH group may occupy an equatorial position. The copper(II)-hydroperoxo complex H-R exhibits a relatively high O-O bond stretching vibration at 900 cm(-1) compared to other previously reported examples.