Angewandte Chemie - International Edition
Angewandte Chemie - International Edition
4 years ago

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N3O Macrocyclic Ligand

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N3O Macrocyclic Ligand
Erik R. Farquhar, Elumalai Kumaran, Yong-Min Lee, Inés Monte Pérez, Mi Yoo, Jason England, Eckhard Bill, Marcel Swart, Wonwoo Nam, Kallol Ray, Xenia Engelmann
The sluggish oxidants [FeIV(O)(TMC)(CH3CN)]2+ (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [FeIV(O)(TMCN-d12)(OTf)]+ (TMCN-d12=1,4,7,11-tetra(methyl-d3)-1,4,7,11-tetraazacyclotetradecane) are transformed into the highly reactive oxidant [FeIV(O)(TMCO)(OTf)]+ (1; TMCO=4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane) upon replacement of an NMe donor in the TMC and TMCN ligands by an O atom. A rate enhancement of five to six orders of magnitude in both H atom and O atom transfer reactions was observed upon oxygen incorporation into the macrocyclic ligand. This finding was explained in terms of the higher electrophilicity of the iron center and the higher availability of the more reactive S=2 state in 1. This rationalizes nature's preference for using O-rich ligand environments for the hydroxylation of strong C−H bonds in enzymatic reactions. The oxoiron(IV) center in [FeIV(O)(TMCO)(OTf)]+ (TMCO=4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane; see picture) in an N3O environment exhibits drastically enhanced reactivity relative to the [FeIV(O)(TMC)(CH3CN)]2+ (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) complex in an N4 environment. This explains nature's preference for using oxygen-rich ligand environments for the hydroxylation of strong C−H bonds.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201707872

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