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 with a range of 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 reactions of 1 and Na[BArX4] with [Fe(NCC6H4NO2)(dppe)Cp][BArX4] gave bimetallic [{Fe(dppe)Cp}2{mu N.CC6H4N(O)}][BArF4]2. However, reactions of 1 and Na[BArX4] with 4nitrophenol gave the first example of the bench-stable iron half-sandwich phenolate complex [Fe(OC6H4NO2)(dppe)Cp]+ rather than NO2 activation. The formation of complexes [3]+ likely proceeds via the unusual blue bimetallic species [{Fe(dppe)Cp}2{mu,.2O,O'-O2NAr}]2+. This compound undergoes N-O bond cleavage, resulting in [3]+ and a FeIV.O species, which reacts via an internal C-H activation of the dppe ligand to give [FeIII(.3O,P,P'-P(2-O-C6H4)(Ph)-C2H4PPh2)Cp]+. Complexes [3]+ are stable under ambient conditions, are readily purified by column chromatography and can be isolated in up to 50% yield, considering that 0.5 equiv of 1 is required as the oxygen acceptor.

Automated summary

Activation of [FeCl(dppe)Cp] by chloride abstraction with Na[BArX4] allows reactions with various nitro aromatics to form cationic iron nitroso complexes. Different substrates lead to different products, including bimetallic compounds and stable iron half-sandwich phenolate complexes.