Metal–Metal vs Metal–Ligand Cooperation in Iron-Mediated Activation and Catalytic Reduction of Nitrous Oxide and Nitrobenzene

Abstract

There is increasing interest in developing catalysts for transforming nitrous oxide (N2O), though systems based on Earth-abundant metals are limited. We report the synthesis of [FeII(depe)(Cp*)N2][BArF] (2; depe = 1,2-bis(diethylphosphino)-ethane; Cp* = η5-C5Me5) and its intriguing reactivity with N2O, which involves a complex manifold of competing routes. This includes an exotic metal-ligand cooperation pathway towards a Cp*-tethered hydrazenyl oxide (-O‒N(R)‒N(H)2) moiety competing with a metal-metal cooperation route to form a transient FeIV-oxo species. The latter leads to [FeIII(depe)(Cp*)(OH)][BArF] (3) and a product with a dehydrogenated phosphine arm (5). Precursor 2 also reacts with nitrobenzene, allowing the identification of a unique nitrosobenzene complex, [FeII(depe)(Cp*)(κ1N-C6H5NO)][BArF] (6-N), via bimetallic cooperation. The proposed mechanisms are supported by experimental methods and DFT calculations. Furthermore, 2 is an efficient catalyst for the O-transfer reaction from N2O to HBpin (pinacolborane), as well as for the reduction of nitrobenzene, where it surpasses the performance of current catalysts.