Iron Coordination Chemistry of N 2 Py 2 Ligands Substituted by Carboxylic Moieties and Their Impact on Alkene Oxidation Catalysis

A biomimetic approach based on Rieske dioxygenase mimics has been undertaken, which uses the tetradentate N 2 Py 2 ligand platform that contains two pyridine moieties linked to a 1,2‐diaminoethane or a trans ‐1,2‐diaminocyclohexane backbone. Here we report the impact of the incorporation of carboxylic functionalities with the N 2 Py 2 ligand on the catalytic efficiency of its Fe II complexes during epoxidation with H 2 O 2 as the oxidant. Five complexes have been characterized in the solid state and solution. The X‐ray structure of a ferrous complex with a ligand that contains two carboxylic acid moieties shows an unexpected N 4 O 3 ‐type iron coordination sphere. Moreover, the two carboxylic groups of the ligand remain protonated and bound by its sp 2 oxygen atom. Two substitutions of the ligand with carboxylic moieties was found to be deleterious to the reactivity of the complex during alkene oxidation, whereas monosubstitution led to a slight change in the reactivity. Moreover, the catalyst built from the optically active trans ‐1,2‐diaminocyclohexane backbone, L 3 , catalyzes the asymmetric epoxidation of trans ‐2‐heptene with up to 17 % yield. The addition of acetic acid leads to better selectivity, enantioselectivity (38 %), and yield of the epoxidation of nonaromatic alkenes.