Nonheme iron catalysts are attractive for bioinspired aerobic oxidations and oxygenations, as well as for the oxygen reduction reaction (ORR), although their potential in ORR remains largely underexploited. This study presents a rare example of such a system, displaying O2 activation activity and ORR catalytic selectivity toward H2O generation. The triiron (II) complex FeIIL3 (BF4) 3, where L- is a thiolate-containing N3S donor bis (2-pyridylmethyl) amine derivative, was fully characterized in the solid state and in MeCN solution, where it dissociates into the mononuclear solvent adduct FeL (MeCN) +. Upon exposure to O2 in an acetonitrile solution, FeL (MeCN) + generates a μ-oxo diiron (III), that further evolves to an adduct featuring an original Fe4OF53+ core. In the presence of 2, 6-lutidinium tetrafluoroborate (proton source), and octamethylferrocene (reducing agent), FeL (MeCN) + catalyzes the ORR with exclusive production of H2O. This system is finally discussed with respect to a few other reported nonheme Fe-based ORR catalysts operating under chemical conditions.
Sun et al. (Tue,) studied this question.