Synthesis,Characterization,and Thermal Stability of New Mononuclear Hydrogenperoxocopper(II) Complexes with N_3O-Type Tripodal Ligands Bearing Hydrogen-Bonding Interaction Sites

摘要

In order to understand the effect of an oxygen-containing ligand on the physico-chemical properties and reactivities of hydrogenperoxocopper complexes,new copper(II) complexes with the N_3O-type tripodal ligand bearing pivalamido groups,N,N-bis(6-pivalamido-2-pyridylmethyl)glycine (Hbpga),and N,N-bis(6-pivalamido-2-pyridylmethyl)-beta-alanine (Hbpaa),have been designed and synthesized.Copper(II) complexes without any external ligand and those with a mon-odentate ligand,such as azido and chloro,have been prepared and characterized with the aid of electronic absorption and ESR spectroscopic,cyclic voltammetric,and X-ray structure analytical methods.The redox potential values of the Cu(II) complexes,when they were compared with the Cu(II) complex of bis(6-pivalamido-2-pyridylmethyl)(2-pyridylmethyl)-amine (bppa),reported previously,shifted toward the negative side upon the introduction of a carboxylate group in the place of one pyridine of bppa.Reactions of [Cu(bpga)]ClO_4 (la) and [Cu(bpaa)]PF_6 (2a) with hydrogen peroxide in the presence of triethylamine in both MeCN and MeOH solutions gave mononuclear copper(II) complexes with hydro-genperoxide( 1 -),Cu-bpga-OOH (1d) and Cu-bpaa-OOH (2d) systems,respectively.The intense absorption bands,assignable to LMCT (HOO~- -> Cu(II)) and d-d bands,and ESR and resonance Raman spectra have revealed that they form trigonal bipyramidal copper complexes with OOH~- in an end-on fashion.The thermal stabilities of 1d and 2d have also been studied by following the reduction rate of the LMCT bands at 283 K.Those of copper(II) complexes with hydrogenperoxide( 1-) have been reduced in the order 1d > 2d 3 [Cu(bppa)(OOH)]~+ (3d),all of which are rather stable compared with that of Cu(II)-tpa-OOH (tpa = tris(2-pyridylmethyl)amine).These findings indicate that the hydro-genperoxocopper(II) complexes are activated by introducing carboxylate coordination,although they are stabilized by hydrogen-bonding interactions.