Thermally Induced Stoichiometric and Catalytic O-Atom Transfer by a Non-Heme Iron (III)-Nitro Complex: First Example of Reversible {Fe-NO}~7 <-> Fe~(III)-NO_2 Transformation in the Presence of Dioxygen

摘要

In recent years, a few Fe and Co porphyrin complexes with a bound nitro group have been employed to transfer an oxygen atom to substrates such as PPh_3, Me_2S, and styrene. Other transition-metal nitro complexes have also been successfully used in stoichiometric and catalytic O-atom transfer to CS_2, CO, alcohols, and alkenes. However, no non-heme iron complex with a bound nitrite group has been shown to perform O-atom transfer to any such substrate. In this paper we report the first non-heme Fe~(II) complex [(PaPy_3)Fe(NO_2)] (ClO_4) (1) derived from the N, N-bis-(2-pyridylmethyl) amine-N-ethyl-2-pyridine-2-carboxamide ligand (PaPy_3H = N-[N, N-bis (2-pyridylmetyl) aminoethyl]-2-pyridinecarboxamide; H is the dissociable amide proton), which promotes stoichiometric and catalytic O-atom transfer to PPh_3 under mild conditions. We also report that the {Fe-NO}~7-type species [(PaPy_3)Fe(NO)] (ClO_4) (2) is the intermediate in the nitrite-to-nitrosyl conversion following O transfer to PPh_3. Since 2 is rapidly converted into 1 via electrophilic attack of dioxygen to the coordinated NO in 2, the O-atom transfer reaction can be made catalytic in an atmosphere of dioxygen. We also report that in absence of dioxygen, the {Fe-NO}~7 intermediate 2 is converted into the μ-oxo diiron (III) species [(PaPy_3)FeOFe(PaPy_3)] (ClO_4)_2 (3) via a disproportionation, as reported by Lippard and co-workers. Complex 3 is the final product obtained from the O-atom transfer reaction.