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

Abstract

Activation of [FeCl(dppe)Cp] (1) by chloride abstraction with Na[BAr X 4] (X = F: [B(3,5-(CF3)2-C6H3)4]; X = Cl: [B(3,5-Cl2-C6H3)4]) permits reaction with a range of nitro aromatics, RC6H4NO2 (R = halogen, Me, OMe, NO2 or NMe2) to give cationic iron nitroso complexes [Fe{N(O)-C6H4R}(dppe)Cp] + ([3] + ). Similar reactions of 1 and NaHowever, reactions of 1 and Na [BAr X 4] with 4-nitrophenol gave the first example of a 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, bluecoloured bimetallic species [{Fe(dppe)Cp}2{,κ 2 O,O'-O2NAr}] 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-C6H4)(Ph)-C2H4-PPh2)Cp] + . Complexes [3] + are stable under ambient conditions, readily purified by column chromatography and isolated in up to 50 % yield, considering 0.5 equiv of 1 to be required as the oxygen acceptor.

Migration of Condensed Aromatic Hydrocarbons During Alkyne‐Vinylidene Rearrangements

“…À in non-coordinating solvents, such as toluene or 1,2-dichloroethane. [23] In addition to their demonstrated capacity to promote the smooth rearrangement of internal alkynes, the {M(dppe)Cp} + fragments were chosen to evaluate the impact of the size of the reaction pocket at the metal generated after halide abstraction, which differs signifi-cantly between 3d and 4d transition metals (VdW atomic radii: Fe = 0.69 Å; Ru = 0.82 Å, see also Table S4). [24]…”

“…This particular combination of (di)phosphine and η 5 ‐motif avoids the complications of side‐reactions, which are known to occur for η 5 ‐indenyl [21] and dppm [22] auxiliary ligands. From 1 a and 1 b , generation of the reactive 16‐valence electron (VE) coordinatively unsaturated {M(dppe)Cp} + species is achieved by halide abstraction with sodium salts of weakly coordinating tetraarylborates Na[BAr F 4 ] ([BAr F 4 ] − =[B(3,5‐(CF 3 ) 2 ‐C 6 H 3 ) 4 ] − ) or Na[BAr Cl 4 ] ([BAr Cl 4 ] − =[B(3,5‐Cl 2 ‐C 6 H 3 ) 4 ] − in non‐coordinating solvents, such as toluene or 1,2‐dichloroethane [23] . In addition to their demonstrated capacity to promote the smooth rearrangement of internal alkynes, the {M(dppe)Cp} + fragments were chosen to evaluate the impact of the size of the reaction pocket at the metal generated after halide abstraction, which differs significantly between 3d and 4d transition metals (VdW atomic radii: Fe=0.69 Å; Ru=0.82 Å, see also Table S4) [24]…”