Decay of Iron(V) Nitride Complexes By a NN Bond‐Coupling Reaction in Solution: A Combined Spectroscopic and Theoretical Analysis

Abstract

Cryogenically trapped Fe(V) nitride complexes with cyclam-based ligands were found to decay by bimolecular reactions, forming exclusively Fe(II) compounds. Characterization of educts and products by Mössbauer spectroscopy, mass spectrometry, and spectroscopy-oriented DFT calculations showed that the reaction mechanism is reductive nitride coupling and release of dinitrogen (2 Fe(V)≡N→Fe(II)-N=N-Fe(II)→2 Fe(II)+N2). The reaction pathways, representing an "inverse" of the Haber-Bosch reaction, were computationally explored in detail, also to judge the feasibility of yielding catalytically competent Fe(V)(N). Implications for the photolytic cleavage of Fe(III) azides used to generate high-valent Fe nitrides are discussed.

Towards Catalytic Ammonia Oxidation to Dinitrogen: A Synthetic Cycle by Using a Simple Manganese Complex

“…The oxidation‐initiated reduction of 1 → 2 or 1 → 3 resulted in loss of nitride and subsequent 3e − metal reduction via an intermediate 1 + to Mn III ( 2 or 3 ). As was observed in other systems, such metal‐nitride reduction is typically accompanied by N 2 generation ,. To unambiguously confirm this herein, we isotopically enriched the nitride in 1 to 1 ‐ 15 N by using 15 NH 3 in the initial synthesis .…”

“…For the latter N−N bond‐formation pathways, intermediate metal‐nitride coupling ( B → C )—either through proposed bimolecular nitridyl (M≡N⋅) or nucleophilic (M≡N δ − )+electrophilic (M≡N δ + ) coupling (Scheme , bottom)—is proposed as the main pathway to μ‐N 2 or N 2 formation. Other nitrides, generated by N‐atom transfer chemistry (e.g., N 3 − photolysis), have also shown similar coupling behavior ,. Although significant progress has been made towards NH 3 oxidation to various products ( B , C , D ), closing the cycle in a fully catalytic or pseudo‐catalytic “synthetic” cycle, is rare.…”

“…The known nucleophilic Mn V nitride, (salen)Mn≡N ( 1 ), generated through NH 3 oxidation with NaOCl, represents the first step of a potential synthetic cycle ( A→B , Scheme , top and Figure ). We were interested in determining if chemical oxidation of 1 to 1 + would induce nitride radical character (nitridyl) or render it electrophilic and susceptible to nucleophilic attack by an equivalent of 1 (Scheme , bottom) . Electrochemical analysis of 1 using cyclic voltammetry in dichloromethane (DCM) revealed a quasi‐reversible oxidation event at 0.53 V relative to the Fc/Fc + (Fc=ferrocene) couple (Figure (right)), accessible using the known commercially available oxidant, [Ar 3 N][SbCl 6 ] (Ar= p ‐bromophenyl; E 0 =0.70 V vs. Fc/Fc + ) .…”

High‐Valent Iron‐Oxo and ‐Nitrido Complexes: Bonding and Reactivity

“…In contrast, the iron(V)‐nitrido complexes with four‐fold symmetry are rather reactive. Upon melting a frozen solution of [Fe V (N)(Cyclam‐ac)] + , facile N−N bond coupling takes place, leading to a ferrous compound and release of N 2 , which hampers full manifestation of its intrinsic reactivity toward organic substrates. Therefore, the reactivity of iron‐nitrido complexes with four‐fold symmetry has to be investigated in the gas phase.…”

Spin‐State‐Controlled Photodissociation of Iron(III) Azide to an Iron(V) Nitride Complex

“…[17] Initially,m ost iron nitrides were successfully prepared in frozen solutions, [17][18][19] which indicated that as olid matrix and low temperatures were required for their generation. [19,20] However,u ltrafast experiments have recently shown the formation of iron nitrides at room temperature. [21][22][23] Herein, we report the photodissociation of iron(III) azides studied at the molecular level by ion spectroscopy using different temperatures (3-310 K).…”