The sluggish oxidants, [FeIV(O)(TMC)(CH3CN)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [FeIV(O)(d12-TMCN)(OTf)]+ (3d; d12-TMCN = 1,4,7,11-tetra-d3-methyl-1,4,7,11-tetraazacyclotetradecane), are transformed into a highly reactive oxidant, [FeIV(O)(TMCO)(OTf)]+ (1; TMCO = 4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane), upon replacement of a -NMe donor in the TMC and TMCN ligands by an O-atom. A rate enhancement of 5 – 6 orders of magnitude in both H-atom and O-atom transfer reactions is observed upon oxygen incorporation into the macrocyclic ligand and can be explained based upon 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.

Copper nitrenes are proposed as reactive intermediates in a number of copper mediated aziridination and amination reactions. However, the isolation and characterization of such intermediates have proved challenging because of their transient nature. One successful approach for the stabilization of the copper‐nitrene cores is the employment of a redox innocent Lewis acid (LA) like Sc3+. We herein report the stabilization of two transient copper nitrene species 3 and 4 in the absence of LAs by employing electronegative −CF3 and −NO2 groups in the nitrene substituent. Detailed investigations of the spectroscopic properties of 3 and 4 by theoretical and experimental methods, and a comparison of their reactivities in presence and absence of LAs provide some vital insights into the effect of LAs on the geometric and electronic structures of the copper nitrenes.

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.

Iron Oxo Complexes In their Communication on page 14384 ff., W. Nam, M. Swart, K. Ray, et al. show that the oxoiron(IV) center in [FeIV(O)(TMCO)(OTf)]+ (bottom right) with an N3O environment is significantly more reactive than that in [FeIV(O)(TMC)(CH3CN)]2+ (top left) with an N4 environment.

Eisenoxido‐Komplexe In der Zuschrift auf S. 14576 ff. demonstrieren W. Nam, M. Swart, K. Ray et al., dass das Oxoeisen(IV)‐Zentrum in [FeIV(O)(TMCO)(OTf)]+ in einer N3O‐Umgebung reaktiver ist als der [FeIV(O)(TMC)(CH3CN)]2+‐Komplex in einer N4‐Umgebung.