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

Activation of [FeCl(dppe)Cp] ( 1 ) by chloride abstraction with Na[BAr X 4 ] (X = F, [B(3,5-(CF 3 ) 2 -C 6 H 3 ) 4 ]; X = Cl, [B(3,5-Cl 2 -C 6 H 3 ) 4 ]) permits reactions with a range of nitro aromatics, RC 6 H 4 NO 2 (R = halogen, Me, OMe, NO 2 or NMe 2 ), to give the cationic iron nitroso complexes [Fe{N(O)-C 6 H 4 R}(dppe)Cp][BAr X 4 ]) ([ 3 ][BAr X 4 ]). Similar reactions of 1 and Na[BAr X 4 ] with [Fe(NCC 6 H 4 NO 2 )(dppe)Cp][BAr X 4 ] gave bimetallic [{Fe(dppe)Cp} 2 {μ-N≡CC 6 H 4 N(O)}][BAr F 4 ] 2 . However, reactions of 1 and Na[BAr X 4 ] with 4-nitrophenol gave the first example of the bench-stable iron half-sandwich phenolate complex [Fe(OC 6 H 4 NO 2 )(dppe)Cp] + rather than NO 2 activation. The formation of complexes [ 3 ] + likely proceeds via the unusual blue bimetallic species [{Fe(dppe)Cp} 2 {μ,κ 2 O , O '-O 2 NAr}] 2+ . This compound undergoes N-O bond cleavage, resulting in [ 3 ] + and a Fe IV ═O species, which reacts via an internal C-H activation of the dppe ligand to give [Fe III (κ 3 O , P , P '-P(2-O-C 6 H 4 )(Ph)-C 2 H 4 -PPh 2 )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.