Stabilization of a high-spin three-coordinate Fe(iii) imidyl complex by radical delocalization

Abstract

High-spin, late transition metal imido complexes have attracted significant interest due to their group transfer reactivity and catalytic C−H activation of organic substrates. Reaction of a new two-coordinate iron complex,...

Mechanism of Nitrogen-Carbon Bond Formation From Iron(IV) Disilylhydrazido Intermediates During N2 Reduction

“…Overall, the Fe-N interactions are reminiscent of imido complexes where a formally iron(IV) complex was described as an iron(III) complex with a nitrenyl radical. [38][39][40][41][42][43][44][45][46][47][48] The amount of radical character on the N is similar to that in tris(phosphino)borane-supported FeNNMe2 complexes studied in detail by Peters. 31 However, in 5a we emphasize that the N radical is not the dominant configuration; rather, 5a can still be viewed as a formally iron(IV) complex with substantial covalency and an iron-nitrogen triple bond, as shown by the presence of two unoccupied orbitals with Fe-N p* character.…”

A low-coordinate iron organoazide complex

“…As such we turned to CASSCF calculations on [ A ], using the quintet and the triplet geometry from TPSSh calculations. In the quintet state the imido ligand binds in a linear fashion (176°) with Fe–N of 1.70 Å, in line with the geometric features of related computed 9 or structurally characterized 8,20 imido iron complexes. CASSCF[8,7] gives a quintet ground state (Δ E q/t = +0.35 eV).…”

“…During the 1 H NMR spectroscopic studies, two minor transient signals at −2.6 ppm and 8 ppm became visible (ratio 4 : 1), which we tentatively assigned to the putative trigonal imido iron complex [Fe(N t Bu)(NR 2 ) 2 ], [ A ] (Scheme 1), in resemblance to the aromatic imido complexes of the type [Fe(NMes)L 2 ] (L = –N{Dipp}SiMe 3 , –N{Dipp}-CMe 3 ). 8,20 The transformation of the azide adduct 1 could also be observed by IR spectroscopy: solid 1 (pre-cooled and kept dark until measurement) exhibits a diagnostic single band at 2116 cm −1 for the azide unit. This band vanishes over the course of 10 minutes, which confirms a rapid conversion of 1 at ambient temperatures.…”

“…Nitrene insertion into a C–H bond of an ancillary ligand was already observed for the reaction of [Fe(NR 2 ) 2 ] with an aliphatic azide 9 and of the related linear [Fe(N{Dipp}CMe 3 ) 2 ] with adamantyl azide. 20 To gain possible insights into [ A ] we turned to 57 Fe Mössbauer spectroscopy. Careful warming of crystalline 1 in the sample holder to −20 °C, 0 °C and later to room temperature for up to 24 h within the sample chamber showed however no transformation.…”

Mechanism of Nitrogen-Carbon Bond Formation from Iron(IV) Disilylhydrazido Intermediates during N2Reduction

“…Overall, the Fe–N interactions are reminiscent of imido complexes where a formally iron­(IV) complex was described as an iron­(III) complex with a nitrenyl radical. − The amount of radical character on the N is similar to that in tris­(phosphino)­borane-supported FeNNMe 2 complexes studied in detail by Peters et al However, in 5a , we emphasize that the N radical is not the dominant configuration; rather, 5a can still be viewed as a formally iron­(IV) complex with substantial covalency and an iron–nitrogen triple bond, as shown by the presence of two unoccupied orbitals with Fe–N π* character. However, this description as iron­(IV) is not complete because there are contributions from iron­(III)-hydrazyl radical and iron­(II)-isodiazene resonance structures.…”