Effects of proton acceptors on formation of a non-heme iron(IV)-oxo complex via proton-coupled electron transfer

Abstract

Rates of formation of a non-heme iron(IV)-oxo complex, [Fe IV(O)(N4Py)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2- pyridyl)methylamine), via electron-transfer oxidation of [FeIII(OH) (N4Py)]2+ in acetonitrile (MeCN) containing H2O (0.56 M) were accelerated as much as 390-fold by addition of proton acceptors such as CF3COO-, TsO- (p-MeC6H 4SO3 -), NsO- (o-NO2C 6H4SO3 -), DNsO- (2,4-(NO2)2C6H3SO3 -), and TfO- (CF3SO3 -). The acceleration effect of proton acceptors increases with increasing basicity of the proton acceptors. The one-electron oxidation potential of [Fe III(OH)(N4Py)]2+ was shifted from 1.24 to 0.96 V vs SCE in the presence of TsO- (10 mM). The electron-transfer oxidation of FeIII-OH complex was coupled with the deprotonation process by proton acceptors in which deuterium kinetic isotope effects were observed when H 2O was replaced by D2O. © 2013 American Chemical Society.