Rip It off: Nitro to Nitroso Reduction by Iron Half-Sandwich Complexes

Activation of [FeCl(dppe)Cp] (1) by chloride abstraction with Na[BArX4] (X = F, [B(3,5-(CF3)2-C6H3)4]; X Cl, [B(3,5-Cl2-C6H3)4]) permits reactions a range nitro aromatics, RC6H4NO2 (R halogen, Me, OMe, NO2 or NMe2), to give the cationic iron nitroso complexes [Fe{N(O)-C6H4R}(dppe)Cp][BArX4]) ([3][BArX4]). Similar 1 and [Fe(NCC6H4NO2)(dppe)Cp][BArX4] gave bimetallic [{Fe(dppe)Cp}2{?-N?CC6H4N(O)}][BArF4]2. However, 4-nitrophenol first example bench-stable half-sandwich phenolate complex [Fe(OC6H4NO2)(dppe)Cp]+ rather than activation. The formation [3]+ likely proceeds via unusual blue species [{Fe(dppe)Cp}2{?,?2O,O?-O2NAr}]2+. This compound undergoes N–O bond cleavage, resulting in FeIV?O species, which reacts an internal C–H activation dppe ligand [FeIII(?3O,P,P?-P(2-O-C6H4)(Ph)-C2H4-PPh2)Cp]+. Complexes are stable under ambient conditions, readily purified column chromatography can be isolated up 50% yield, considering that 0.5 equiv is required as oxygen acceptor.