Metal‐free Transformations of Nitrogen‐Oxyanions to Ammonia via Oxoammonium Salt

Abstract

Transformations of nitrogen‐oxyanions (NOx−) to ammonia impart pivotal roles in sustainable biogeochemical processes. While metal‐mediated reductions of NOx− are relatively well known, this report illustrates proton‐assisted transformations of NOx− anions in the presence of electron‐rich aromatics such as 1,3,5‐trimethoxybenzene (TMB−H, 1 a) leading to the formation of diaryl oxoammonium salt [(TMB)2N+=O][NO3−] (2 a) via the intermediacy of nitrosonium cation (NO+). Detailed characterizations including UV/Vis, multinuclear NMR, FT‐IR, HRMS, X‐ray analyses on a set of closely related metastable diaryl oxoammonium [Ar2N+=O] species disclose unambiguous structural and spectroscopic signatures. Oxoammonium salt 2 a exhibits 2 e− oxidative reactivity in the presence of oxidizable substrates such as benzylamine, thiol, and ferrocene. Intriguingly, reaction of 2 a with water affords ammonia. Perhaps of broader significance, this work reveals a new metal‐free route germane to the conversion of NOx to NH3.

Modeling Reactivity of Nitrite and Nitrous Acid at a Phenolate Bridged Dizinc(II) Site: Insights into NO Signaling at Zinc

“…Thus, comparison of the 15 N chemical shifts for the reaction mixture of (1 H -O 15 NO + PTSA) relative to (Na 15 NO 2 + PTSA) perhaps suggest that the peak at ~244 ppm correspond to the 15 N-nitrosonium moiety in 2 H -15 N. The 15 N resonances around 370 ppm are tentatively assigned to 15 NO 3 À and 15 N-nitroaromatic (originating due to the ligand nitration), in line with the literature data. [25,26,27] Control reactions of the free ligand (L H H) with t BuONO / NaNO 2 under the present reaction conditions neither show the formation of green species nor results in any change in the proton resonances of the ligand, [21] thereby highlighting the role of the [Zn II ] site. We believe that the [Zn II ] allows the formation of the structurally characterized tetra-Zn II core (3 H ), which bears pi-stacked aromatic rings essential for the stabilization of the NO + -charge transfer species (2 H ).…”

Metal-Free Activation of Molecular Oxygen by Quaternary Ammonium-Based Ionic Liquid: A Detail Mechanistic Study

“…Benzaldehyde ( 6a ) was obtained as the sole product here (control 2) . ( E )- N -benzyl-1-phenylmethanimine ( 7a ) was obtained as a major product when benzylamine was treated with anhydrous TBAB under the above-mentioned condition (control 3) . − The mechanism of oxygen activation was further corroborated by the detection of hydrogen peroxide in the reaction medium (Figures S2 and S3). Here, benzylamine under the hydrated TBAB condition first formed a benzylimine intermediate, which was further converted to benzaldehyde in the presence of water ( control 2 ).…”

NO Generation from Nitrite at Zinc(II): Role of Thiol Persulfidation in the Presence of Sulfane Sulfur

“…Neither [( Bn 3 Tren )Zn II –nitrite] + ( 1 ) nor NaNO 2 react with 2,4-DTBP at room temperature to provide nitro-derivative 6-nitro-2,4-DTBP, while a solution containing a mixture of NaNO 2 and Zn(OTf) 2 reacts with 2,4-DTBP to afford 6-nitro-2,4-DTBP (38%) ( Figures 4 and S14 ). 21 Likewise, 1,2,4-trimethoxybenzene (1,2,4-TMB) reacts with a mixture of NaNO 2 and Zn(OTf) 2 to yield 1,2,4-trimethoxy-5-nitrobenzene (21%), 31 although complex 1 does not react with 1,2,4-TMB ( Figure S15 ). 15 N NMR spectroscopic studies on the sample generated from the reactions of Zn(OTf) 2 + Na 15 NO 2 + 2,4-DTBP (or 1,2,4-TMB) depict the 15 N-chemical shifts δ( 15 N) at 374 (or 368) ppm consistent with the nitrations of 2,4-DTBP and 1,2,4-TMB, respectively ( Figure S16 ).…”

“…15 N NMR of the reaction mixture consisting of 15 S14). 21 Likewise, 1,2,4-trimethoxybenzene (1,2,4-TMB) reacts with a mixture of NaNO 2 and Zn(OTf) 2 to yield 1,2,4-trimethoxy-5nitrobenzene (21%), 31 although complex 1 does not react with 1,2,4-TMB (Figure S15). 15 N NMR spectroscopic studies on the sample generated from the reactions of Zn(OTf) 2 + Na 15 NO 2 + 2,4-DTBP (or 1,2,4-TMB) depict the 15 Nchemical shifts δ( 15 N) at 374 (or 368) ppm consistent with the nitrations of 2,4-DTBP and 1,2,4-TMB, respectively (Figure S16).…”

“…Moreover, trapping of headspace in the presence of acid followed by 1 H NMR spectroscopic analysis in DMSO-d 6 shows a triplet centered at δ = ∼7.18 ppm ( 1 J NH = 50.3 Hz), which is assigned to NH 4 + (Figures S26 and S27). 31 The formation of NH 3 from the above reaction may be attributed to the complex reaction between NO and H 2 S/HS − , as suggested in the previous literature. 41…”