Ligand-Constraint-Induced Peroxide Activation for Electrophilic Reactivity.

μ-1,2-peroxo-bridged diiron(III) intermediates P are proposed as reactive intermediates in various biological oxidation reactions. In sMMO, P acts as an electrophile, and performs hydrogen atom and oxygen atom transfers to electron-rich substrates. In cyanobacterial ADO, however, P is postulated to react by nucleophilic attack on electrophilic carbon atoms.

Temperature Dependence of the Catalytic Two- versus Four-Electron Reduction of Dioxygen by a Hexanuclear Cobalt Complex.

The synthesis and characterization of a hexanuclear cobalt complex 1 involving a nonheme ligand system, L1, supported on a SnO stannoxane core are reported. Complex 1 acts as a unique catalyst for dioxygen reduction, whose selectivity can be changed from a preferential 4e/4H dioxygen-reduction (to water) to a 2e/2H process (to hydrogen peroxide) only by increasing the temperature from -50 to 25 °C. A variety of spectroscopic methods (Sn-NMR, magnetic circular dichroism (MCD), electron paramagnetic resonance (EPR), SQUID, UV-vis absorption, and X-ray absorption spectroscopy (XAS)) coupled with advanced theoretical calculations has been applied for the unambiguous assignment of the geometric and electronic structure of 1.

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N O Macrocyclic Ligand.

The sluggish oxidants [Fe (O)(TMC)(CH CN)] (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [Fe (O)(TMCN-d )(OTf)] (TMCN-d =1,4,7,11-tetra(methyl-d )-1,4,7,11-tetraazacyclotetradecane) are transformed into the highly reactive oxidant [Fe (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.

Oxidation Reactions with Bioinspired Mononuclear Non-Heme Metal-Oxo Complexes.

The selective functionalization of strong C-H bonds and the oxidation of water by cheap and nontoxic metals are some of the key targets of chemical research today. It has been proposed that high-valent iron-, manganese-, and copper-oxo cores are involved as reactive intermediates in important oxidation reactions performed by biological systems, thus making them attractive targets for biomimetic synthetic studies. The generation and characterization of metal-oxo model complexes of iron, manganese, and copper together with detailed reactivity studies can help in understanding how the steric and electronic properties of the metal centers modulate the reactivity of the metalloenzymes.

Evidence of two-state reactivity in alkane hydroxylation by Lewis-acid bound copper-nitrene complexes.

The behavior of the Lewis-acid adducts of two copper-nitrene [Cu(NR)](+) complexes in nitrene-transfer and H-atom abstraction reactions have been demonstrated to depend on the nature of the nitrene substituents. Two-state reactivity, in which a singlet ground state and a nearby triplet excited-state both contribute, provides a useful model for interpreting reactivity trends of the two compounds.