Nickel-Catalyzed NO Group Transfer Coupled with NO_x Conversion

Abstract

Nitrogen oxide (NO x ) conversion is an important process for balancing the global nitrogen cycle. Distinct from the biological NO x transformation, we have devised a synthetic approach to this issue by utilizing a bifunctional metal catalyst for producing value-added products from NO x . Here, we present a novel catalysis based on a Ni pincer system, effectively converting Ni−NO x to Ni−NO via deoxygenation with CO(g). This is followed by transfer of the in situ generated nitroso group to organic substrates, which favorably occurs at the flattened Ni(I)−NO site via its nucleophilic reaction. Successful catalytic production of oximes from benzyl halides using NaNO 2 is presented with a turnover number of >200 under mild conditions. In a key step of the catalysis, a nickel(I)− • NO species effectively activates alkyl halides, which is carefully evaluated by both experimental and theoretical methods. Our nickel catalyst effectively fulfills a dual purpose, namely, deoxygenating NO x anions and catalyzing C−N coupling. Article pubs.acs.org/JACS

Nitrate and Nitrite Reductions at Copper(II) Sites: Role of Noncovalent Interactions from Second-Coordination-Sphere

“…In contrast, the inefficiency of [( mC )­Zn II ] 2+ and [( Bz 3 Tren )­Cu II ] 2+ sites in N 2 H 4 ·H 2 O-mediated NO 3 – reductions suggest the importance of the second-coordination-sphere interaction driven coordination of NO 3 – at a copper­(II) site. While the previous reports on NO 3 – reduction primarily utilize oxygen-atom-transfer reactivity of oxophilic metal or reagents for the reduction of NO 3 – , − ,− this report sheds light on an alternative route in the presence of N 2 H 4 ·H 2 O, a facile H + /e – donor reagent. Moreover, this report illustrates the N 2 H 4 ·H 2 O-mediated transformation of copper­(II)-nitrite to NO and N 2 O.…”

“…First, hydrazine-mediated two-electron reduction of nitrite at the copper(II) site may generate NO − /HNO, which subsequently dimerizes to provide N 2 O via hyponitrous acid (H 2 N 2 O 2 ). However, the observation of mixed-isotope-labeled nitrous oxide N 15 NO from the reaction of N 2 H 4 •H 2 O + {[Cu II ] -( 15 NO 2 )} + rules out the possible coupling or dimerization of NO/HNO generated from nitrite. 63,64 In an alternative mechanism, we propose a nucleophilic attack of N 2 H 4 on the N-site of the copper(II)-bound nitrite leading to the generation of NH 2 −NH−N=O, which decays to NH 3 and NNO (Figure 8).…”

“…Electrocatalytic NO 3 – reduction by [Cr­(cyclam)­Cl 2 ] + has been proposed to involve the [Cr V ]-oxo intermediate . A set of recent reports illustrates deoxygenation of NO 3 – at relatively less oxophilic transition metal sites (e.g., Co and Ni) typically in the presence of a wide range of oxophilic reagents including CO, (Bpin) 2 (pyrazine), and VCl 3 . − While the reduction of NO 3 – at late transition metal sites remains rare and commonly realized with the usage of oxophilic reagents, − the developments of metal-based NO 3 – reducing processes are challenging due to weakly coordinating and the chemically inert nature of NO 3 – . In contrast, NO 2 – anion exhibits stronger binding affinity toward metal and offers more diverse reactivity patterns in comparison to NO 3 – . − Accordingly, the reductions of nitrite at metal sites have been demonstrated in the presence of a wide range of reducing agents including thiols, − H 2 S, phosphines, − phenols, − and ene-diols. − It is noteworthy that the reaction of hydrazine (N 2 H 4 ) and nitrate in the presence of copper­(II) salts has been known in the literature for several decades. , More specifically, N 2 H 4 in alkaline conditions leads to copper­(II)-mediated transformation of nitrate to nitrite in good yield, thereby enabling estimation of nitrate in water samples .…”

Thiol and H2S-Mediated NO Generation from Nitrate at Copper(II)

“…Alternatively, OAT from nitrate may occur directly to a reductant. In some cases, carbon monoxide, phosphines, or the silyl-based Mashima reagent can abstract an O atom from a bound nitrate to give CO 2 , R 3 PO, or TMS-O-TMS. ,− Moreover, intramolecular O-atom transfer between metal-bound nitrate and nitrosyl can form nitrogen dioxide or nitrite. , Other methods include hydrazine-mediated nitrate reduction as well as electrocatalytic nitrate reduction using molecular complexes in homogeneous or heterogenized forms. ,− …”

Sequential Deoxygenation of CO2 and NO2– via Redox-Control of a Pyridinediimine Ligand with a Hemilabile Phosphine

“…Typical strategies for O atom extraction from nitrogen oxyanions via the Mashima or borylating reagents, as well as through oxygen-deficient polyoxo-clusters, have recently been shown to be viable for selective deoxygenation of NO x – . Several NO x – conversions have been reported utilizing transition metal complexes; − however, few are reported to produce value-added chemicals. − …”