Modeling Non-Heme Iron Halogenases: High-Spin Oxoiron(Ⅳ)-Halide Complexes That Halogenate C-H Bonds

摘要

The non-heme iron halogenases CytC3 and SyrB2 catalyze C-H bond halogenation in the biosynthesis of some natural products via S = 2 oxoiron(Ⅳ)-halide intermediates. These oxidants abstract a hydrogen atom from a substrate C-H bond to generate an alkyl radical that reacts with the bound halide to form a C-X bond chemoselectively. The origin of this selectivity has been explored in biological systems but has not yet been investigated with synthetic models. Here we report the characterization of S = 2 [Fe~Ⅳ(O)(TQA)(Cl/Br)]~+ (TQA = tris(quinory1-2-methyl)amine) complexes that can preferentially halogenate cyclohexane. These are the first synthetic oxoiron(Ⅳ)-halide complexes that serve as spectroscopic and functional models for the halogenase intermediates. Interestingly, the nascent substrate radicals generated by these synthetic complexes are not as shortlived as those obtained from heme-based oxidants and can be intercepted by O_2 to prevent halogenation, supporting an emerging notion that rapid rebound may not necessarily occur in non-heme oxoiron(Ⅳ) oxidations.