Metal–metal vs. metal–ligand cooperation in iron-mediated activation and catalytic reduction of nitrous oxide and nitrobenzene

Abstract

There is an increasing interest in developing catalysts for transforming nitrous oxide (N₂O), though systems based on Earth-abundant metals are limited. We report the synthesis of [Fe^II(depe)(Cp*)N₂][BAr^F] (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 hydrazinyl oxide (⁻O–N(R)–N(H)₂) moiety competing with a metal–metal cooperation route to form a transient Fe^IV-oxo species. The latter leads to [Fe^III(depe)(Cp*)(OH)][BAr^F] (3) and a product with a dehydrogenated phosphine arm (5). Precursor 2 also reacts with nitrobenzene, allowing the identification of a unique nitrosobenzene complex, [Fe^II(depe)(Cp*)(κ¹N–C₆H₅NO)][BAr^F] (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 exhibits superior performance to current homogeneous catalysts.