A seven-coordinate iron platform and its oxo and nitrene reactivity

We present a new structurally determined seven-coordinate iron platform supported by the tris(2-picolyl)amine ligand 6,6′-(pyridin-2-ylmethylazanediyl)bis(methylene)bis(N-tert-butylpicolinamide) (TPA2C(O)NHtBu, 3) and its reactivity with oxo and nitrene transfer agents. Oxidation of the pentagonal bipyramidal, seven-coordinate iron(II)–triflate complex [TPA2C(O)NHtBuFeII(OTf)][OTf] (4) with PhIO produces the corresponding diiron(III) μ-oxo complex [(TPA2C(O)NHtBuFeIII)2(O)][OTf]4 (5). Mössbauer and magnetic measurements on 5 in the solid-state establish antiferromagnetic coupling between its two Fe(III) centers. Reactions of 4 with the nitrene transfer agents PhINTs (Ts = p-MeC6H4SO2) and PhINNs (Ns = p-NO2C6H4SO2) provide the corresponding iron(III)-amide congeners [TPA2C(O)NHtBuFeIII(NHTs)][OTf]2 (6) and [TPA2C(O)NHtBuFeIII(NHNs)][OTf]2 (7), respectively, affording a rare pair of isolable Fe(III)-amide compounds formed from nitrene transfer. By characterizing well-defined products in the crystalline form, derived from atom and group transfer to seven-coordinate iron, the collective data provide a starting point for the exploration of high-valent and metal–ligand multiply bonded species supported by approximate pentagonal-type ligand fields.

Graphical abstractWe present a new seven-coordinate iron(II) platform and its reactivity with oxo and nitrene transfer agents to give diiron(III) μ-oxo and iron(III) amido complexes characterized by single-crystal X-ray diffraction and Mössbauer spectroscopy. By obtaining well-defined products in crystalline form, derived from group transfer to seven-coordinate iron, the collective data provide a starting point for the exploration of high-valent and metal-ligand multiply bonded species supported by approximate pentagonal-type ligand fields with different donor sets in the equatorial plane.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► A pentagonal-enforcing ligand gives a new seven-coordinate iron(II) platform. ► Reactivity with oxo and nitrene transfer agents gives diiron(III) μ-oxo and iron(III) amido complexes. ► Mössbauer spectroscopy establishes the electronic structures of the iron(III) products.