Nitrite Reduction Cycle on a Dinuclear Ruthenium Complex Producing Ammonia

Enhanced p-d Orbital Coupling in Unconventional Phase RhSb Alloy Nanoflowers for Efficient Ammonia Electrosynthesis in Neutral Media

Phase control provides a promising approach for physicochemical property modulation of metal/alloy nanomaterials toward various electrocatalytic applications. However, the controlled synthesis of alloy nanomaterials with unconventional phases remains challenging, especially for those containing both p- and d-block metals. Here, we report the one-pot synthesis of ultrathin RhSb alloy nanoflowers (NFs) with an unconventional 2H phase. Using 2H RhSb NFs as an electrocatalyst for nitrite reduction reaction in neutral media, the optimal NH3 Faradaic efficiency and yield rate can reach up to 96.8% and 47.2 mg h-1 mgcat -1 at -0.3 and -0.6 V (vs. reversible hydrogen electrode), respectively. With 2H RhSb NFs as a bifunctional cathode catalyst, the as-assembled zinc-nitrite/methanol batteries deliver a high energy efficiency of 96.4% and improved rechargeability with 120-h stable running. Ex/in situ characterizations and theoretical calculations have demonstrated that the phase change of RhSb from face-centered cubic (fcc) to 2H has optimized the electronic structure through stronger interactions between Rh and Sb by p-d orbital couplings, which improves the adsorption of key intermediates and reduces the reaction barriers of nitrite reduction to guarantee the efficient electrocatalysis. This work offers a feasible strategy of boosting the electrocatalytic performance of alloy nanostructures by integrating phase control and p-d orbital coupling.

Selective Stepwise Reduction of Nitrate and Nitrite to Dinitrogen or Ammonia

This study reports a method for the selective reduction of NO3- and NO2- to N2 or NH3, extending prior work in our lab where NO3- was reduced to NO by [N(afaCy)3Fe]OTf2 (N(afaCy)3 = tris(5-cyclohexyl-amineazafulvene-2-methyl)amine, OTf = triflate). The first pathway involves the reduction of NO2- to N2, where the NO generated in the initial step is transformed to N2O by PPh3 and further reduced to N2 by the [N(afaCy)3Fe]OTf2 complex. An alternative pathway showcases the reduction of the bound NO complex, [N(afaCy)3Fe(NO)]2+, to NH3 using chemical reductants, albeit with a modest yield of 29%. Confirmation of the nitrogen source as NO is established through 15N labeling studies. Hydroxylamine (NH2OH) is proposed as a plausible intermediate in the reduction of bound NO, supported by independent NH2OH reduction experiments and computational studies. Nature employs a well-orchestrated, stepwise process involving several enzymes to reduce N-containing oxyanions, and this approach provides valuable insights into the stepwise reduction mechanisms of nitrate and nitrite, yielding NH3 or N2 as the product.

Advanced Ruthenium-Based Electrocatalysts for NOx Reduction to Ammonia

Ammonia (NH3) is widely recognized as a crucial raw material for nitrogen-based fertilizer production and eco-friendly hydrogen-rich fuels. Currently, the Haber-Bosch process still dominates the worldwide industrial NH3 production, which consumes substantial energy and contributes to enormous CO2 emission. As an alternative NH3 synthesis route, electrocatalytic reduction of NOx species (NO3 -, NO2 -, and NO) to NH3 has gained considerable attention due to its advantages such as flexibility, low power consumption, sustainability, and environmental friendliness. This review timely summarizes an updated and critical survey of mechanism, design, and application of Ru-based electrocatalysts for NOx reduction. First, the reason why the Ru-based catalysts are good choice for NOx reduction to NH3 is presented. Second, the reaction mechanism of NOx over Ru-based materials is succinctly summarized. Third, several typical in situ characterization techniques, theoretical calculations, and kinetics analysis are examined. Subsequently, the construction of each classification of the Ru-based electrocatalysts according to the size of particles and compositions is critically reviewed. Apart from these, examples are given on the applications in the production of valuable chemicals and Zn-NOx batteries. Finally, this review concludes with a summary highlighting the main practical challenges relevant to selectivity and efficiency in the broad range of NOx concentrations and the high currents, as well as the critical perspectives on the fronter of this exciting research area.

A terpyridine-based copper complex for electrochemical reduction of nitrite to nitric oxide

In biological systems, nitrite reductase enzymes (NIRs) are responsible for reduction of nitrite (NO2-) to nitric oxide (NO). These NIRs have mostly Cu- or Fe-containing active sites, surrounded by amine-containing ligands. Therefore, mononuclear Cu complexes with N-donor ligands are highly relevant in the development of NIR model systems and in the mechanistic investigation of the nitrite reduction reaction. Herein, we report on a terpyridine-based CuII complex with square planar geometry for H+-assisted electrochemical reduction of NO2-. Through electrochemical measurements, spectroscopic characterization and isotope-labelling experiments we propose a mechanistic reaction pathway involving an unstable HNO2 state. The CuI intermediate, formed electrochemically, was isolated and its molecular structure was deduced, showing linkage isomerism of the nitrite ligand. Moreover, qualitative and quantitative product analysis by GC-MS shows N2O formed as a side product along with the main product NO. Furthermore, by obtaining single crystals and conducting structural analysis we were able to determine the structural arrangement and redox state of the complex after electrochemical treatment.

Tetrapodal iron complexes invoke observable intermediates in nitrate and nitrite reduction

This study investigates the mechanistic pathways of nitrate and nitrite reduction by the tetrapodal iron complex [Py2Py(afamcyp)2Fe]OTf2, revealing key intermediates to elucidate the reaction process. Using UV-Vis, IR, mass and NMR spectroscopies, stable binding of oxyanions to the iron centre was observed, supporting the formation of the iron(iii)-hydroxide intermediate [Py2Py(afamcyp)2Fe(OH)]OTf2. This intermediate is less stable than in previous systems, providing insights into the behaviour of metalloenzymes. A bimetallic mechanism is proposed for nitrogen oxyanion reduction where additional iron is required to drive the complete reaction, resulting in the formation of the final nitrosyl complex, Py2Py(pimcyp)2Fe(NO), and water. Our findings enhance the understanding of iron-based reduction processes and contribute to the broader knowledge of oxyanion reduction mechanisms.

Electrodegradation of nitrogenous pollutants in sewage: from reaction fundamentals to energy valorization applications

The excessive accumulation of nitrogen pollutants (mainly nitrate, nitrite, ammonia nitrogen, hydrazine, and urea) in water bodies seriously disrupts the natural nitrogen cycle and poses a significant threat to human life and health. Electrolysis is considered a promising method to degrade these nitrogenous pollutants in sewage, with the advantages of high efficiency, wide generality, easy operability, retrievability, and environmental friendliness. For particular energy devices, including metal-nitrate batteries, direct fuel cells, and hybrid water electrolyzers, the realization of energy valorization from sewage purification processes (e.g., valuable chemical generation, electricity output, and hydrogen production) becomes feasible. Despite the progress in the research on pollutant electrodegradation, the development of electrocatalysts with high activity, stability, and selectivity for pollutant removal, coupled with corresponding energy devices, remains a challenge. This review comprehensively provides advanced insights into the electrodegradation processes of nitrogenous pollutants and relevant energy valorization strategies, focusing on the reaction mechanisms, activity descriptors, electrocatalyst design, and actuated electrodes and operation parameters of tailored energy conversion devices. A feasibility analysis of electrodegradation on real wastewater samples from the perspective of pollutant concentration, pollutant accumulation, and electrolyte effects is provided. Challenges and prospects for the future development of electrodegradation systems are also discussed in detail to bridge the gap between experimental trials and commercial applications.

Electrokinetics of Nitrite to Ammonia Conversion in the Neutral Medium Over A Platinum Surface

Polycrystalline Pt electrode was employed to selectively convert nitrite ions (N O 2 - ${{{\rm N}{\rm O}}_{2}^{-}}$ ) into useful nitrogenous compound through electrochemical reduction reaction in neutral medium. According to adsorptive stripping analysis, the reduction process produced nitric oxide (NO) on the surface of Pt electrode. The spectroscopic test and gas chromatographic studies discovered the presence of ammonia (NH3) in the electrolyzed solution, suggesting the transformation of adsorbed NO into NH3 during the reverse scan. Scan rate dependent investigation was performed to elucidate kinetic information relating to this reaction on Pt surface. From Ep vs scan rate (υ) and jp vs υ (logarithmic plot), it was found that the conversion ofN O 2 - ${{{\rm N}{\rm O}}_{2}^{-}}$ ion into NO is an irreversible reaction which relies on the diffusion ofN O 2 - ${{{\rm N}{\rm O}}_{2}^{-}}$ ions to electrode surface. The Tafel analysis unveiled that the first electron transfer sets the overall reaction rate, having formal reduction potential, E0'=-0.46 V and standard heterogeneous rate constant, k0=1 . 07 × 10 - 2 ${1.07\times {10}^{-2}}$ cm s-1. Reductive transfer coefficient (α) is another kinetics parameter, which was found to be approximate 0.77 from the difference between Ep and Ep/2 of the voltammograms obtained over scan rate range 0.005 V s-1 to 0.250 V s-1, indicating a stepwise process. According to temperature-dependent voltammograms, the nitrite reduction reaction on Pt had a calculated activation energy of about 19.8 kJ mol-1 and a pre-exponential factor of about 8.39×103 mA cm-2.

Distinctive p-d Orbital Hybridization in CuSb Porous Nanonetworks for Enhanced Nitrite Electroreduction to Ammonia

Electrochemical nitrite reduction reaction (NO 2 - RR ${\mathrm{NO}}_{\mathrm{2}}^{\mathrm{ - }}{\mathrm{RR}}$ ), as a green and sustainable ammonia synthesis technology, has broad application prospects and environmental friendliness. Herein, an unconventional p-d orbital hybridization strategy is reported to realize the fabrication of defect-rich CuSb porous nanonetwork (CuSb PNs) electrocatalyst forNO 2 - RR ${\mathrm{NO}}_{\mathrm{2}}^ - {\mathrm{RR}}$ . The crystalline/amorphous heterophase structure is cleverly introduced into the porous nanonetworks, and this defect-rich structure exposes more atoms and activated boundaries. CuSb PNs exhibit a large NH3 yield (r N H 3 ${{r}_{{\mathrm{N}}{{{\mathrm{H}}}_{\mathrm{3}}}}}$ ) of 946.1 µg h-1m cat - 1 ${\mathrm{m}}_{{\mathrm{cat}}}^{ - {\mathrm{1}}}$ and a high faradaic efficiency (FE) of 90.7%. Experimental and theoretical studies indicate that the excellent performance of CuSb PNs results from the defect-rich porous nanonetworks structure and the p-d hybridization of Cu and Sb elements. This work describes a powerful pathway for the fabrication of p-d orbital hybrid defect-rich porous nanonetworks catalysts, and provides hope for solving the problem of nitrogen oxide pollution in the field of environment and energy.

Platinum group nanoparticles doped BCN matrix: Efficient catalysts for the electrocatalytic reduction of nitrate to ammonia

The effective treatment of nitrate (NO3-) in water as a nitrogen source and electrocatalytic NO3- reduction to ammonia (NH3) (NRA) have become preferred methods for NO3--to-NH3 conversion. Achieving efficient NO3--to-NH3 conversion requires the design and development of electrode materials with high activity and efficiency for the electrocatalytic NRA reaction. Herein, based on the special properties of dodecahydro-closo-dodecaborate anions, a BCN matrix, loaded with platinum-group nanoparticles (namely, Pd/BCN, Pt/BCN, and Ru/BCN), was prepared using a simple method for the electrocatalytic NRA reaction. Results showed that Pd/BCN exerts the best catalytic effect on the NRA reaction. The NH3 production rate reached 12.71 mg h-1 mgcat.-1 at -1.0 V vs. RHE. Faraday efficiency reached 91.79 %, which can be attributed to the more uniform distribution of the nanoparticles. Furthermore, Pd/BCN exhibited high cycling stability and resistance to ionic interference. Moreover, the density functional theory calculations indicated that small and well-distributed Pd nanoclusters in the BCN matrix have a large active surface area and promote the catalytic process. This study provides a new strategy to design catalysts for green ammonia synthesis.

C≡N and N≡O Bond Cleavages of Acetonitrile and Nitrosyl Ligands at a Dimolybdenum Center to Render Ethylidyne and Acetamidinate Ligands

Extended reduction of [Mo2Cp2(μ-Cl)(μ-PtBu2)(NO)2] (1) with Na(Hg) in acetonitrile (MeCN) at room temperature resulted in an unprecedented full cleavage of the C≡N bond of a coordinated MeCN molecule to yield the vinylidene derivative Na[Mo2Cp2(μ-PtBu2)(μ-CCH2)(NO)2], which upon protonation with (NH4)PF6 gave the ethylidyne complex [Mo2Cp2(μ-PtBu2)(μ-CMe)(NO)2] [Mo1-Mo2 = 2.9218(2) Å] in a selective and reversible way. Controlled reduction of 1 at 273 K yielded instead, after protonation, the 30-electron acetamidinate complex [Mo2Cp2(μ-PtBu2)(μ-κN:κN'-HNCMeNH)(μ-NO)]PF6 [Mo1-Mo2 = 2.603(2) Å], in a process thought to stem from the paramagnetic MeCN-bridged intermediate [Mo2Cp2(μ-PtBu2)(μ-NCMe)(NO)2], followed by a complex sequence of elementary steps including cleavage of the N≡O bond of a nitrosyl ligand.

Stepwise Sulfite Reduction on a Dinuclear Ruthenium Complex Leading to Hydrogen Sulfide

Sulfite reduction by dissimilatory sulfite reductases is a key process in the global sulfur cycle. Sulfite reductases catalyze the 6e- reduction of SO32- to H2S using eight protons (SO32- + 8H+ + 6e- → H2S + 3H2O). However, detailed research into the reductive conversion of sulfite on transition-metal-based complexes remains unexplored. As part of our ongoing research into reproducing the function of reductases using dinuclear ruthenium complex {(TpRu)2(μ-Cl)(μ-pz)} (Tp = HB(pyrazolyl)3), we have targeted the function of sulfite reductase. The isolation of a key SO-bridged complex, followed by a sulfite-bridged complex, eventually resulted in a stepwise sulfite reduction. The reduction of a sulfite to a sulfur monoxide using 4H+ and 4e-, which was followed by conversion of the sulfur monoxide to a disulfide with concomitant consumption of 2H+ and 2e-, proceeded on the same platform. Finally, the production of H2S from the disulfide-bridged complex was achieved.

Sustainable removal of nitrite waste to value-added ammonia on Cu@Cu2O core-shell nanostructures by pulsed laser technique

The biochemical reduction of nitrite (NO₂^-) ions to ammonia (NH₃) requires six electrons and is catalyzed by the cytochrome c NO₂^- reductase enzyme. This biological reaction inspired scientists to explore the reduction of nitrogen oxyanions, such as nitrate (NO₃^-) and NO₂^- in wastewater, to produce the more valuable NH₃ product. It is widely known that copper (Cu)-based nanoparticles (NPs) are selective for the NO₃^- reduction reaction (NO₃^-RR), but the NO₂^-RR has not been well explored. Therefore, we attempted to address the electrocatalytic conversion of NO₂^- to NH₃ using Cu@Cu₂O core-shell NPs to simultaneously treat wastewater by removing NO₂^- and producing valuable NH₃. The Cu@Cu₂O core-shell NPs were constructed using the pulsed laser ablation of Cu sheet metal in water. The core-shell nanostructure of these particles was confirmed by various characterization techniques. Subsequently, the removal of NO₂^- and the ammonium (NH₄⁺)-N yield rate were estimated using the Griess and indophenol blue methods, respectively. Impressively, the Cu@Cu₂O core-shell NPs exhibited outstanding NO₂^-RR activity, demonstrating a maximum NO₂^- removal efficiency of approximately 94% and a high NH₄⁺-N yield rate of approximately 0.03 mmol h^-1.cm^-2 at -1.6 V vs. a silver/silver chloride reference electrode under optimal conditions. The proposed NO₂^-RR mechanism revealed that the (111) facet of Cu favors the selective conversion of NO₂^- to NH₃ via a six-electron transfer. This investigation may offer a new insight for the rational design and detailed mechanistic understanding of electrocatalyst architecture for the effective conversion of NO₂^- to NH₄⁺.

Ni nanoparticle-decorated biomass carbon for efficient electrocatalytic nitrite reduction to ammonia

Electrocatalytic nitrite (NO₂^-) reduction to ammonia (NH₃) can not only synthesize value-added NH₃, but also remove NO₂^- pollutants from the environment. However, the low efficiency of NO₂^--to-NH₃ conversion hinders its applications. Here, Ni nanoparticle-decorated juncus-derived biomass carbon prepared at 800 °C (Ni@JBC-800) serves as an efficient catalyst for NH₃ synthesis by selective electroreduction of NO₂^-. This catalyst shows a remarkable NH₃ yield of 4117.3 μg h^-1 mg_cat.^-1 and a large faradaic efficiency of 83.4% in an alkaline electrolyte. The catalytic mechanism is further investigated by theoretical calculations.

Chemistry of a Nitrosyl Ligand κ:η-Bridging a Ditungsten Center: Rearrangement and N–O Bond Cleavage Reactions

The novel nitrosyl-bridged complex [W₂Cp₂(μ-P^tBu₂)(μ-κ:η-NO)(CO)(NO)](BAr₄) [Ar = 3,5-C₆H₃(CF₃)₂] was prepared in a multistep procedure starting from the hydride [W₂Cp₂(μ-H)(μ-P^tBu₂)(CO)₄] and involving the new complexes [W₂Cp₂(μ-P^tBu₂)(CO)₄](BF₄), [W₂Cp₂(μ-P^tBu₂)(CO)₂(NO)₂](BAr₄), and [W₂(μ-κ:η⁵-C₅H₄)Cp(μ-P^tBu₂)(CO)(NO)₂] as intermediates, which follow from reactions with HBF₄·OEt₂, NO, and Me₃NO·2H₂O, respectively. The nitrosyl-bridged cation easily added chloride upon reaction with [N(PPh₃)₂]Cl, with concomitant NO rearrangement into the terminal coordination mode, to give [W₂ClCp₂(μ-P^tBu₂)(CO)(NO)₂], and underwent N–O and W–W bond cleavages upon the addition of CN^tBu to give the mononuclear phosphinoimido complex [WCp(NP^tBu₂)(CN^tBu)₂](BAr₄). Another N–O bond cleavage was induced upon photochemical decarbonylation at 243 K, which gave the oxo- and phosphinito-bridged nitrido complex [W₂Cp₂(N)(μ-O)(μ-OP^tBu₂)(NO)](BAr₄), likely resulting from a N–O bond cleavage step following decarbonylation.

The π binding of the NO ligand in the cation [W₂Cp₂(μ-P^tBu₂)(μ-κ:η-NO)(CO)(NO)]⁺ facilitates the addition of ligands with concomitant rearrangement of the bridging nitrosyl into the terminal coordination mode and also facilitates cleavage of the N−O bond of that ligand at low temperature possibly in two different ways: either through the oxidative addition of this ligand to the dimetal center or through deoxygenation by another ligand.

High-Efficiency Ammonia Electrosynthesis on Anatase TiO2-x Nanobelt Arrays with Oxygen Vacancies by Selective Reduction of Nitrite

Electrocatalytic reduction of nitrite to NH₃ provides a new route for the treatment of nitrite in wastewater, as well as an attractive alternative to NH₃ synthesis. Here, we report that an oxygen vacancy-rich TiO_2-x nanoarray with different crystal structures self-supported on the Ti plate can be prepared by hydrothermal synthesis and by subsequently annealing it in an Ar/H₂ atmosphere. Anatase TiO_2-x (A-TiO_2-x) can be a superb catalyst for the efficient conversion of NO₂^- to NH₃; a high NH₃ yield of 12,230.1 ± 406.9 μg h^-1 cm^-2 along with a Faradaic efficiency of 91.1 ± 5.5% can be achieved in a 0.1 M NaOH solution containing 0.1 M NaNO₂ at -0.8 V, which also exhibits preferable durability with almost no decay of catalytic performances after cycling tests and long-term electrolysis. Furthermore, a Zn-NO₂^- battery with such A-TiO_2-x as a cathode delivers a power density of 2.38 mW cm^-2 as well as a NH₃ yield of 885 μg h^-1 cm^-2.

A 3D FeOOH nanotube array: an efficient catalyst for ammonia electrosynthesis by nitrite reduction

Nitrite (NO₂^-) is a detrimental pollutant widely existing in groundwater sources, threatening public health. Electrocatalytic NO₂^- reduction settles the demand for removal of NO₂^- and is also promising for generating ammonia (NH₃) at room temperature. A nanotube array directly grown on a current collector not only has a large surface area, but also exhibits improved structural stability and accelerated electron transport. Herein, a self-standing FeOOH nanotube array on carbon cloth (FeOOH NTA/CC) is proposed as a highly active electrocatalyst for NO₂^--to-NH₃ conversion. As a 3D catalyst, the FeOOH NTA/CC is able to attain a surprising faradaic efficiency of 94.7% and a large NH₃ yield of 11937 μg h^-1 cm^-2 in 0.1 M PBS (pH = 7.0) with 0.1 M NO₂^-. Furthermore, this catalyst also displays excellent durability in cyclic and long-term electrolysis tests.

A TiO2-x nanobelt array with oxygen vacancies: an efficient electrocatalyst toward nitrite conversion to ammonia

Electrocatalytic nitrite reduction not only holds significant potential in the control of nitrite contamination in the natural environment, but also is an attractive approach for sustainable ammonia synthesis. In this communication, we report that a TiO_2-x nanobelt array with oxygen vacancies on a titanium plate is able to convert nitrite into ammonia with a high faradaic efficiency of 92.7% and a large yield of 7898 μg h^-1 cm^-2 in alkaline solution. This monolithic catalyst also shows high durability with the maintenance of its catalytic activity for 12 h. Theoretical calculations further reveal the critical role of oxygen vacancies in nitrite electroreduction.

Recent advances in electrocatalytic nitrite reduction

Electrocatalytic nitrite reduction is of great significance for wastewater treatment and value-added chemicals synthesis. This review highlights the latest progress in electrochemical nitrite reduction to produce two types of products, including gaseous products (NO, N₂O, N₂) and liquid products (NH₂OH and NH₄⁺). The heterogeneous and homogeneous catalysts used in the corresponding reduction processes are introduced, with emphasis on the product selectivity regulation and reaction mechanism understanding. Finally, the challenges and opportunities in this field are analyzed as well. This review can provide guidelines for designing electrochemical systems with high efficiency and specificity for nitrite reduction.

Ni2P nanosheet array for high-efficiency electrohydrogenation of nitrite to ammonia at ambient conditions

Ammonia (NH₃) plays an important role in agriculture and industry. The industry-scale production mainly depends on the Haber-Bosch process suffering from issues of environment pollution and energy consumption. Electrochemical reduction can degrade nitrite (NO₂^-) pollutants in the environment and convert it into more valuable NH₃. Here, Ni₂P nanosheet array on nickel foam is proposed as a 3D electrocatalyst for high-efficiency electrohydrogenation of NO₂^- to NH₃ under ambient reaction conditions. When tested in 0.1 M phosphate buffer saline with 200 ppm NO₂^-, such Ni₂P/NF is able to obtain a large NH₃ yield rate of 2692.2 ± 92.1 μg h^-1 cm^-2 (3282.9 ± 112.3 μg h^-1 mg_cat.^-1), a high Faradic efficiency of 90.2 ± 3.0%, and selectivity of 87.0 ± 1.7% at -0.3 V versus a reversible hydrogen electrode. After 10 h of electrocatalytic reduction, the conversion rate of NO₂^- achieves near 100%. The catalytic mechanism is further investigated by density functional theory calculations.

N-O Bond Activation and Cleavage Reactions of the Nitrosyl-Bridged Complexes [M2Cp2(μ-PCy2)(μ-NO)(NO)2] (M = Mo, W)

The title complexes (1a,b) were prepared in two steps by first reacting the hydrides [M₂Cp₂(μ-H)(μ-PCy₂)(CO)₄] with [NO](BF₄) in the presence of Na₂CO₃ to give dinitrosyls [M₂Cp₂(μ-PCy₂)(CO)₂(NO)₂](BF₄), which were then fully decarbonylated upon reaction with NaNO₂ at 323 K. An isomer of the Mo₂ complex having a cisoid arrangement of the terminal ligands ( cis-1a) was prepared upon irradiation of toluene solutions of 1a with visible-UV light at 288 K. The structure of these trinitrosyl complexes was investigated using X-ray diffraction and density functional theory (DFT) calculations, these revealing a genuine pyramidalization of the bridging NO that might be associated in part to an increase of charge at the N atom and anticipated a weakening of the N-O bond upon reaction with bases or reducing reagents. Complexes 1a,b reacted with [FeCp₂](BF₄) to give first the radicals [M₂Cp₂(μ-PCy₂)(μ-NO)(NO)₂](BF₄) according to CV experiments, which then underwent H-abstraction to yield the nitroxyl-bridged complexes [M₂Cp₂(μ-PCy₂)(μ-κ¹:η²-HNO)(NO)₂](BF₄), alternatively prepared upon protonation with HBF₄·OEt₂. The novel coordination mode of the nitroxyl ligand in these products was thermodynamically favored over its tautomeric hydroximido form, according to DFT calculations, and similar nitrosomethane-bridged cations [M₂Cp₂(μ-PCy₂)( μ-κ¹:η²-MeNO)(NO)₂]⁺ were prepared by reacting 1a,b with CF₃SO₃Me or [Me₃O]BF₄. Complexes 1 reacted with M(Hg) (M = Zn, Na) in tetrahydrofuran to give the amido-bridged derivatives [M₂Cp₂(μ-PCy₂)(μ-NH₂)(NO)₂] with retention of stereochemistry, a transformation also induced by using mild O atom scavengers such as CO and phosphites in the presence of water. In the absence of water, phosphites accomplished a deoxygenation of the bridging NO of the Mo₂ complexes to yield the phosphoraniminato-bridged derivatives [Mo₂Cp₂(μ-PCy₂){μ-NP(OR)₃}(NO)₂] (R = Et, Ph), also with retention of stereochemistry.