Interaction between peroxide ion and phenol group which are coordinated tothe same iron(III) ion

We have prepared several new iron(III) complexes with ligands which contain a phenol group; these are tetradentate [(X-phpy)H, X and H(phpy) represent the substituents on the phenol ring and N,N-bis(2-pyridylmethyl)-N-(2-hydr oxybenzyl)amine, respectively] and pentadentate ligands [(R-enph-X)H; R = e thyl(Et) or methyl(Me) derivative and H(Me-enph) denotes N,N-bis(2-pyridylm ethyl)-N "-methyl-N "-(2 "-hydroxyl-benzylamine)ethylenediamine] and have d etermined the crystal structures of Fe(phpy)Cl-2, Fe(5-NO2-phpy)Cl-2,and Fe (Me-enph)ClPF6, which are of a mononuclear six-coordinate iron(III) complex with coordination of one or two chloride ion(s). These compounds are highl y colored (dark violet) due to the coordination of phenol group to an iron( III:) atom. When hydrogen peroxide was added to the solution of the iron(II I) complex, a color change occurs with bleaching of the violet color, indic ating that oxidative degradation of the phenol moiety occurred in the ligan d system. The bleaching of the violet color was also observed by the additi on of t-butylhydroperoxide, The rate of the disappearance of the violet col or is highly dependent on the substituent on the phenol ring; introduction of an electron-withdrawing group in the phenol ring decreases the rate of b leaching, suggesting that disappearance of the violet band should be due to a chemical reaction between the phenol group and a peroxide adduct of the iron(III) species with an eta(1)-coordination mode and that in this reactio n the peroxide adduct acts as an electrophile towards phenol ring, The intr amolecular interaction between the phenol moiety and an iron(III)-peroxide adduct may induce activation of the peroxide ion, and this uas supported by several facts that the solution containing an iron(III) complex and hydrog en peroxide exhibits high activities for degradation of nucleosides and alb umin. (C) 1998 Elsevier Science Ltd. All rights reserved.