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

Abstract

Oxidation of the nucleophilic nitride, (salen)Mn≡N (1) with stoichiometric [Ar N][X] initiated a nitride coupling reaction to N , a major step toward catalytic ammonia oxidation (salen=N,N'-bis(salicylidene)-ethylenediamine dianion; Ar=p-bromophenyl; X=[SbCl ] or [B(C F ) ] ). N production was confirmed by mass spectral analysis of the isotopomer, 1- N, and the gas quantified. The metal products of oxidation were the reduced Mn dimers, [(salen)MnCl] (2) or [(salen)Mn(OEt )] [B(C F ) ] (3) for X=[SbCl ] or [B(C F ) ] , respectively. The mechanism of nitride coupling was probed to distinguish a nitridyl from a nucleophilic/electrophilic coupling sequence. During these studies, a rare mixed-valent Mn /Mn bridging nitride, [(salen)Mn (μ-N)Mn (salen)][B(C F ) ] (4), was isolated, and its oxidation-state assignment was confirmed by X-ray diffraction (XRD) studies, perpendicular and parallel-mode EPR and UV/Vis/NIR spectroscopies, as well as superconducting quantum interference device (SQUID) magnetometry. We found that 4 could subsequently be oxidized to 3. Furthermore, in view of generating a catalytic system, 2 can be re-oxidized to 1 in the presence of NH and NaOCl closing a pseudo-catalytic "synthetic" cycle. Together, the reduction of 1→2 followed by oxidation of 2→1 yield a genuine synthetic cycle for NH oxidation, paving the way to the development of a fully catalytic system by using abundant metal catalysis.

Cationic Charges Leading to an Inverse Free‐Energy Relationship for N−N Bond Formation by MnVI Nitrides

“…Their reactivity is dictated by their nucleophilic or electrophilic character, which is in turn dependent on the identity of the metal, oxidation state, and ligand environment –. Although nucleophilic Mn V N(salen) complexes have been studied for several decades, Storr and Menard recently uncovered a new reactivity pattern. One‐electron oxidation of the Mn V N(salen) derivatives A , B , C , and D (Scheme ) was pursued to generate a metal nitride with radical character.…”

“…The reactivity of A [5] and B, C,and D [4] as previously described. The reactivity of A [5] and B, C,and D [4] as previously described.…”

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Scheme 1. The reactivity of A [5] and B, C,and D [4] as previously described. The reactivity of 1K, 1Ba, 1Na,a nd 1Sr compared to A are discussed herein.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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Homogeneous electrocatalytic oxidation of ammonia to N 2 under mild conditions

“…More recent work has focused on oxidations of coordinated NH 3 (25), where three-electron oxidations can yield nitrides (26)(27)(28)(29). Some of these undergo N-N coupling (26,29), as illustrated in the stoichiometric nitride pathway in Fig. 1.…”

Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

“…[14] Forexample,homolytic activation of M-NH 3 and M-NH 2 groups upon hydrogen atom abstraction (HAA), [15,16] oxidative addition, [17] metal-ligand cooperative addition, [18,19] bimetallic NÀHb ond activation, [20] coordination-induced bond weakening of NH 3 to generate H 2 , [21] as well as the electrochemical formation of N 2 from NH 3 [22] have been demonstrated. [23] Notably, Hamann, Smith and co-workers showed [(trpy)-(dmabpy)Ru II (NH 3 )][PF 6 ] 2 (trpy = 2,2':6',2''-terpyridine; dmabpy = 4,4'-bis(dimethylamino)-2,2'-bipyridine) is amolecular electrocatalyst for NH 3 oxidation to N 2 . [23] Notably, Hamann, Smith and co-workers showed [(trpy)-(dmabpy)Ru II (NH 3 )][PF 6 ] 2 (trpy = 2,2':6',2''-terpyridine; dmabpy = 4,4'-bis(dimethylamino)-2,2'-bipyridine) is amolecular electrocatalyst for NH 3 oxidation to N 2 .…”