Deciphering the mechanism of O2 reduction with electronically tunable non-heme iron enzyme model complexesElectronic supplementary information (ESI) available. CCDC 1833291-1833295 and 1833299. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8sc01621f

A homologous series of electronically tuned 2,2 ′ ,2 ′′ -nitrilotris( N -arylacetamide) pre-ligands ( H 3 L R ) were prepared (R = NO 2 , CN, CF 3 , F, Cl, Br, Et, Me, H, OMe, NMe 2 ) and some of their corresponding Fe and Zn species synthesized. The iron complexes react rapidly with O 2 , the final products of which are diferric mu-oxo bridged species. The crystal structure of the oxidized product obtained from DMA solutions contain a structural motif found in some diiron proteins. The mechanism of iron mediated O 2 reduction was explored to the extent that allowed us to construct an empirically consistent rate law. A Hammett plot was constructed that enabled insightful information into the rate-determining step and hence allows for a differentiation between two kinetically equivalent O 2 reduction mechanisms. A homologous series of electronically tuned ligands were prepared and some of their corresponding Fe complexes were prepared and a Hammett plot of the rates of O 2 reduction allowed us to infer important details of the mechanism.