An Oxoiron(IV) Complex Supported by an N-Alkylated Cyclam Ligand System Containing a Pendant Alcohol Moiety

Abstract

The effect of a pendant neutral alcohol moiety in the N-alkylated cyclam (1,4,8,11-tetraazacyclotetradecane) ligand backbone is examined for the non-heme mononuclear oxoiron(IV) unit in [FeIV(Osyn)(TMC-HOR)(NCCH3)]2+ (1-syn) (TMC-HOR=2-(4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecan1-yl)ethan-1-ol). Unlike in the related [FeIV(Oanti)(TMC-SR)]+ (3-anti) (TMC-SR=1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) complex, bearing an axial mono-anionic thiolate ligand trans to the oxo unit, the alcohol moiety in 1-syn stays protonated and does not axially coordinate to iron. The protonation of the alcohol moiety is a prerequisite for the stabilization of the oxoiron(IV) core; it presumably serves as a hydrogen bonding donor to the oxoiron(IV) unit, which is positioned syn to the three methyl groups. Comparative reactivity studies reveal 1-syn to be a stronger hydrogen atom abstraction but weaker oxygen atom transfer agent relative to the [FeIV(Osyn)(TMC)(NCCH3)]2+ (2-syn) complex, bearing the N-tetramethylated cyclam (TMC) ligand.