Activation and Deactivation of Benzylic C−H Bonds Guided by Stereoelectronic Effects in Hydrogen Atom Transfer from Amides and Amines to Alkoxyl Radicals

Kinetic and product studies on the reactions of tert-alkoxyl radicals with secondary and tertiary alkanamides bearing benzylic α-C−H bonds, isoindoline, tetrahydroisoquinoline and the corresponding N-acetyl derivatives were carried out. Product studies on the reactions with the tert-butoxyl radical (tBuO⋅) point toward exclusive HAT from the benzylic α-C−H bonds. Comparison of the k_H values measured for reaction with the cumyloxyl radical (CumO⋅) with those obtained previously for the corresponding reactions of N-alkyl- and N,N-dialkylalkanamides, are indicative of a lack of benzylic activation and the operation of steric and stereoelectronic effects. Compared to N-methyl and N-ethyl groups, the presence of N-benzyl groups increases the barrier required to reach the optimal conformation for HAT, where the α-C−H bond to be cleaved is perpendicular to the plane of the amide, precluding concurrent overlap with the phenyl π-system. When the benzylic α-C−H bonds are in a conformation that allows for optimal overlap with both the phenyl π-system and the amide π-system or amine nitrogen lone pair, as in the isoindoline and tetrahydroisoquinoline derivatives, increases in k_H that exceed 2-orders of magnitude were observed, highlighting the strong contribution provided by stereoelectronic activation to these HAT processes.     

In Silico Partial N2 to NH3 Conversion with a Light Atom Molecule

N₂ can be stepwise converted in silico into one molecule NH₃ and a secondary amide with a bond activator molecule consisting only of light main group elements. The proposed N₂-activating pincer-related compound carries a silyl ion (Si⁽⁺⁾) center as well as three Lewis acidic (−BF₂) and three Lewis basic (−PMe₂) sites, providing an efficient binding pocket for gaseous N₂ within the framework of intramolecular frustrated Lewis pairs (FLP). In addition, it exhibits supportive secondary P−B and F⋅⋅⋅B contacts, which stabilize the structure. In the PSi⁽⁺⁾−N−N−BP environment the N≡N triple bond is extended from 1.09 Å to remarkable 1.43 Å, resembling a N−N single bond. The strongly activated N−N-fragment is prone to subsequent hydride addition and protonation steps, resulting in the energy efficient transfer of two hydrogen equivalents. The next hydride added causes the release of one molecule NH₃, but leaves the ligand system as poisoned R₃Si⁽⁺⁾−NH₂−PMe₂ or R₃Si⁽⁺⁾−NH₃ dead-end states behind. The study indicates that approximately tetrahedral constrained SiBP₂-pockets are capable to activate N₂, whereas the acid-rich SiB₃- and SiB₂P-pocktes, as well as the base-rich SiP₃-pockets fail, hinting towards the high relevance of the acid-base proportion and relative orientation. The electronic structure of the N₂-activated state is compared to the corresponding state of a recently published peri-substituted bond activator molecule featuring a PSi⁽⁺⁾−N−N−Si⁽⁺⁾P site (S. Mebs, J. Beckmann, Physical Chemistry Chemical Physics 2022 , 24, 20953–20967).     

Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

Catalysts for the oxidation of NH₃ are critical for the utilization of NH₃ as a large‐scale energy carrier. Molecular catalysts capable of oxidizing NH₃ to N₂ are rare. This report describes the use of [Cp*Ru(P^tBu₂N^Ph₂)(¹⁵NH₃)][BAr^F₄], (P^tBu₂N^Ph₂=1,5‐di(phenylaza)‐3,7‐di(tert‐butylphospha)cyclooctane; Ar^F=3,5‐(CF₃)₂C₆H₃), to catalytically oxidize NH₃ to dinitrogen under ambient conditions. The cleavage of six N?H bonds and the formation of an N≡N bond was achieved by coupling H⁺ and e^? transfers as net hydrogen atom abstraction (HAA) steps using the 2,4,6‐tri‐tert‐butylphenoxyl radical (^tBu₃ArO^.) as the H atom acceptor. Employing an excess of ^tBu₃ArO^. under 1 atm of NH₃ gas at 23 °C resulted in up to ten turnovers. Nitrogen isotopic (¹⁵N) labeling studies provide initial mechanistic information suggesting a monometallic pathway during the N???N bond‐forming step in the catalytic cycle.     

Tritopic NHC Precursors: Unusual Nickel Reactivity and Ethylene Insertion into a C(sp3)–H Bond

The imidazolium chloride [C₃H₃N(C₃H₆NMe₂)N{C(Me)(=NDipp)}]Cl ( 1 ; Dipp=2,6‐diisopropyl phenyl), a potential precursor to a tritopic N^imineC^NHCN^amine pincer‐type ligand, reacted with [Ni(cod)₂] to give the Ni^I‐Ni^I complex 2 , which contains a rare cod‐derived η³‐allyl‐type bridging ligand. The implied intermediate formation of a nickel hydride through oxidative addition of the imidazolium C−H bond did not occur with the symmetrical imidazolium chloride [C₃H₃N₂{C(Me)(=NDipp)}₂]Cl ( 3 ). Instead, a Ni−C(sp³) bond was formed, leading to the neutral N^imineCHN^imine pincer‐type complex Ni[C₃H₃N₂{C(Me)(=NDipp)}₂]Cl ( 4 ). Theoretical studies showed that this highly unusual feature in nickel NHC chemistry is due to steric constraints induced by the N substituents, which prevent Ni−H bond formation. Remarkably, ethylene inserted into the C(sp³)−H bond of 4 without nickel hydride formation, thus suggesting new pathways for the alkylation of non‐activated C−H bonds.     

Low-Temperature Isolation of a Labile Silylated Hydrazinium-yl Radical Cation, [(Me3Si)2N−N(H)SiMe3].+

The oxidation of silylated hydrazine, (Me₃Si)₂N−N(H)SiMe₃, with silver salts led to the formation of a highly labile hydrazinium-yl radical cation, [(Me₃Si)₂N−N(H)SiMe₃]^.+, at very low temperatures (decomposition > −40 °C). EPR, NMR, DFT and Raman studies revealed the formation of a nitrogen-centered radical cation along the N−N unit of the hydrazine. In the presence of the weakly coordinating anion [Al{OCH(CF₃)₂}₄]⁻, crystallization and structural characterization in the solid state were achieved. The hydrazinium-yl radical cation has a significantly shortened N−N bond and a nearly planar N₂Si₃ framework, in contrast to the starting material. According to DFT calculations, the shortened N−N bond has a total bond order of 1.5 with a π-bond order of 0.5. The π bond can be regarded as a three-π-electron, two-center bond.     

Influence of the Flexibility of Nickel PCP-Pincer Complexes on C−H and P−C Bond Activation and Ethylene Reactivity: A Combined Experimental and Theoretical Investigation

Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium C_sp2−H bond with [Ni(cod)₂] affording a carbanionic ligand in [NiCl(PC_sp3^HP)] ( 8 ) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PC^NHCP)]PF₆ ( 9 ) upon halide abstraction; 3) ethylene insertion into the Ni−H bond of the latter and ethyl migration to the N−C−N carbon atom of the heterocycle in [Ni(PC^EtP)]PF₆ ( 10 ); and 4) an unprecedented C−P bond activation transforming the P−C^NHC−P pincer ligand of 8 in a C−C^NHC−P pincer and a terminal phosphanido ligand in [Ni(PPh₂)(CC^NHCP)] ( 15 ). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.     

(6‐Oxido‐2‐oxo‐1,2‐dihydropyrimidine‐5‐carboxylato‐κ2O5,O6)bis[2‐(2‐pyridyl)‐1H‐benzimidazole‐κ2N2,N3]manganese(II) monohydrate

In the title compound, [Mn(C₅H₂N₂O₄)(C₁₂H₉N₃)₂]·H₂O, the Mn^II centre is surrounded by three bidentate chelating ligands, namely, one 6‐oxido‐2‐oxo‐1,2‐dihydropyrimidine‐5‐carboxylate (or uracil‐5‐carboxylate, Huca²⁻) ligand [Mn—O = 2.136 (2) and 2.156 (3) Å] and two 2‐(2‐pyridyl)‐1H‐benzimidazole (Hpybim) ligands [Mn—N = 2.213 (3)–2.331 (3) Å], and it displays a severely distorted octahedral geometry, with cis angles ranging from 73.05 (10) to 105.77 (10)°. Intermolecular N—H...O hydrogen bonds both between the Hpybim and the Huca²⁻ ligands and between the Huca²⁻ ligands link the molecules into infinite chains. The lattice water molecule acts as a hydrogen‐bond donor to form double O...H—O—H...O hydrogen bonds with the Huca²⁻ O atoms, crosslinking the chains to afford an infinite two‐dimensional sheet; a third hydrogen bond (N—H...O) formed by the water molecule as a hydrogen‐bond acceptor and a Hpybim N atom further links these sheets to yield a three‐dimensional supramolecular framework. Possible partial π–π stacking interactions involving the Hpybim rings are also observed in the crystal structure.     

Non-Interacting Ni and Fe Dual-Atom Pair Sites in N-Doped Carbon Catalysts for Efficient Concentrating Solar-Driven Photothermal CO2 Reduction

Solar-to-chemical energy conversion under weak solar irradiation is generally difficult to meet the heat demand of CO₂ reduction. Herein, a new concentrated solar-driven photothermal system coupling a dual-metal single-atom catalyst (DSAC) with adjacent Ni−N₄ and Fe−N₄ pair sites is designed for boosting gas-solid CO₂ reduction with H₂O under simulated solar irradiation, even under ambient sunlight. As expected, the (Ni, Fe)−N−C DSAC exhibits a superior photothermal catalytic performance for CO₂ reduction to CO (86.16 μmol g⁻¹ h⁻¹), CH₄ (135.35 μmol g⁻¹ h⁻¹) and CH₃OH (59.81 μmol g⁻¹ h⁻¹), which are equivalent to 1.70-fold, 1.27-fold and 1.23-fold higher than those of the Fe−N−C catalyst, respectively. Based on theoretical simulations, the Fermi level and d-band center of Fe atom is efficiently regulated in non-interacting Ni and Fe dual-atom pair sites with electronic interaction through electron orbital hybridization on (Ni, Fe)−N−C DSAC. Crucially, the distance between adjacent Ni and Fe atoms of the Ni−N−N−Fe configuration means that the additional Ni atom as a new active site contributes to the main *COOH and *HCO₃ dissociation to optimize the corresponding energy barriers in the reaction process, leading to specific dual reaction pathways (COOH and HCO₃ pathways) for solar-driven photothermal CO₂ reduction to initial CO production.     

Trivalent Rare-Earth Metal Amide Complexes as Catalysts for the Hydrosilylation of Benzophenone Derivatives with HN(SiHMe2)2 by Amine-Exchange Reaction

The rare-earth metal complexes Ln( L¹ )[N(SiHMe₂)₂](thf) (Ln=La, Ce, Y; L¹ =N,N′′-bis(pentafluorophenyl)diethylenetriamine dianion) were synthesized by treating Ln[N(SiHMe₂)₂]₃(thf)₂ with L¹ H₂. The lanthanum and cerium derivatives are active catalysts for the hydrosilylation of benzophenone derivatives with HN(SiHMe₂)₂. An amine-exchange reaction was revealed as a key step of the catalytic cycle, in which Ln−Si−H β-agostic interactions are proposed to promote insertion of the carbonyl moiety into the Si−H bond.     

Building up Strain in One Step: Synthesis of an Edge-Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion

The exhaustive trichlorosilylation of hexachloro-1,3-butadiene was achieved in one step by using a mixture of Si₂Cl₆ and [nBu₄N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu₄N]₂[ 1 ] was isolated in 36 % yield after recrystallization. The negative charges of [ 1 ]²⁻ are mainly delocalized across its two carbanionic (Cl₃Si)₂C termini (α-effect of silicon) such that the central bond possesses largely C=C double-bond character. Upon treatment with 4 equiv of HCl, [ 1 ]²⁻ is converted into neutral 1,2,3,4-tetrakis(trichlorosilyl)but-2-ene, 3 . The Cl⁻ acceptor AlCl₃, induces a twofold ring-closure reaction of [ 1 ]²⁻ to form a six-membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4 , which was structurally characterized by X-ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.     

Bond dissociations in hypervalent ammonium radicals prepared by collisional neutralization of protonated six-membered nitrogen heterocycles

Hypervalent organic ammonium radicals were generated by collisional neutralization with dimethyl disulfide of protonated 1,4-diazabicyclo[2.2.2]octane (1H⁺), N,N′-dimethylpiperazine (2H⁺) and N-methylpiperazine (3H⁺). The radicals dissociated completely on the 5.1 μs time-scale. Radical 1H^• underwent competitive N−H and N−C bond dissociations producing 1,4-diazabicyclo[2.2.2]octane and small ring fragments. Dissociations of radical 2H^• proceeded by N−H bond dissociation and ring cleavage, whereas N−CH₃ bond cleavage was less frequent. Radical 3H^• underwent N−H, N−CH₃ and N−C_ring bond cleavages followed by post-reionization dissociations of the formed cations. The pattern of bond dissociations in the hypervalent ammonium radicals derived from six-membered nitrogen heterocycles is similar to those of aliphatic ammonium radicals. © 1997 John Wiley & Sons, Ltd.     

Poly[diaqua(μ‐4,4′‐bipyridine‐κ2N:N′)bis(μ‐cyanido‐κ2C:N)bis(cyanido‐κC)nickel(II)copper(II)]: a metal–organic cyanide‐bridged framework

The structure of the title compound, [NiCu(CN)₄(C₁₀H₈N₂)(H₂O)₂]_n or [{Cu(H₂O)₂}(μ‐C₁₀H₈N₂)(μ‐CN)₂{Ni(CN)₂}]_n, was shown to be a metal–organic cyanide‐bridged framework, composed essentially of –Cu–4,4′‐bpy–Cu–4,4′‐bpy–Cu– chains (4,4′‐bpy is 4,4′‐bipyridine) linked by [Ni(CN)₄]²⁻ anions. Both metal atoms sit on special positions; the Cu^II atom occupies an inversion center, while the Ni^II atom of the cyanometallate sits on a twofold axis. The 4,4′‐bpy ligand is also situated about a center of symmetry, located at the center of the bridging C—C bond. The scientific impact of this structure lies in the unique manner in which the framework is built up. The arrangement of the –Cu–4,4′‐bpy–Cu–4,4′‐bpy–Cu– chains, which are mutually perpendicular and non‐intersecting, creates large channels running parallel to the c axis. Within these channels, the [Ni(CN)₄]²⁻ anions coordinate to successive Cu^II atoms, forming zigzag –Cu—N[triple‐bond]C—Ni—C[triple‐bond]N—Cu– chains. In this manner, a three‐dimensional framework structure is constructed. To the authors' knowledge, this arrangement has not been observed in any of the many copper(II)–4,4′‐bipyridine framework complexes synthesized to date. The coordination environment of the Cu^II atom is completed by two water molecules. The framework is further strengthened by O—H...N hydrogen bonds involving the water molecules and the symmetry‐equivalent nonbridging cyanide N atoms.     

Bis(2‐{1‐[(2,4,6‐trimethylphenyl)imino]ethyl}pyrrol‐1‐ido‐κ2N,N′)nickel(II): a supramolecular structure formed by C—H...π(arene) hydrogen bonds

<!?tlsb=‐0.2pt>Nitrogen‐based polydentate ligands are of interest owing to their flexible complexation to transition metal atoms. For the title compound, [Ni(C₁₅H₁₇N₂)₂], a transition metal complex formed by the coordination of two identical N,N′‐bidentate mono(imino)pyrrolyl ligands to an Ni^II centre, an X‐ray crystal diffraction study indicates that the two ligands show an inverted arrangement with respect to one another around the Ni^II centre, which is located on a crystallographic inversion centre. The planes of the aromatic substituents at the imine N atoms of the ligands show dihedral angles of 85.91 (5)° with respect to the NiN₄ plane. The Ni—N bond lengths are in the range 1.9072 (15)–1.9330 (15) Å and the N_imino—Ni—N_pyrrole bite angles are 83.18 (6)°. The Ni—N_pyrrole bond is substantially shorter than the Ni—N_imino bond. Molecules are linked into an extensive network by means of intermolecular C—H...π(arene) hydrogen bonds in which every molecule acts both as hydrogen‐bond donor and acceptor. The supramolecular assembly takes the form of an infinite two‐dimensional sheet.     

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)-Centre: Labile Mono- and Bis(hydridogallyl)zinc Complexes

In the presence of TMEDA (N,N,N’,N’-tetramethylethylenediamine), partially deaggregated zinc dihydride as hydrocarbon suspensions react with the gallium(I) compound [(BDI)Ga] ( I , BDI={HC(C(CH₃)N(2,6-iPr₂-C₆H₃))₂}⁻) by formal oxidative addition of a Zn−H bond to the gallium(I) centre. Dissociation of the labile TMEDA ligand in the resulting complex [(BDI)Ga(H)−(H)Zn(tmeda)] ( 1 ) facilitates insertion of a second equiv. of I into the remaining Zn−H to form a thermally sensitive trinuclear species [{(BDI)Ga(H)}₂Zn] ( 2 ). Compound 1 exchanges with polymeric zinc dideuteride [ZnD₂]_n in the presence of TMEDA, and with compounds I and 2 via sequential and reversible ligand dissociation and gallium(I) insertion. Spectroscopic and computational studies demonstrate the reversibility of oxidative addition of each Zn−H bond to the gallium(I) centres.     

Electrocatalytic Reduction of Nitrogen to Ammonia Using Tiara-like Phenylethanethiolated Nickel Cluster

The fixing of N₂ to NH₃ is challenging due to the inertness of the N≡N bond. Commercially, ammonia production depends on the energy-consuming Haber-Bosch (H−B) process, which emits CO₂ while using fossil fuels as the sources of hydrogen and energy. An alternative method for NH₃ production is the electrochemical nitrogen reduction reaction (NRR) process as it is powered by renewable energy sources. Here, we report a tiara-like nickel-thiolate cluster, [Ni₆(PET)₁₂] (where, PET=2-phenylethanethiol)] as an efficient electro-catalyst for the electrochemical NRR at ambient conditions. Ammonia (NH₃: 16.2±0.8 μg h⁻¹ cm⁻²) was the only nitrogenous product over the potential of −2.3 V vs. F_c⁺/F_c with a Faradaic efficiency of 25%±1.7. Based on theoretical calculations, NRR by [Ni₆(PET)₁₂] proceeds through both the distal and alternating pathways with an onset potential of −1.84 V vs. RHE (i.e., −2.46 V vs. F_c⁺/F_c) which corroborates with the experimental findings.     

Alkoxy-1,3,5-triazapentadien(e/ato) copper(II) complexes: template formation and applications for the preparation of pyrimidines and as catalysts for oxidation of alcohols to carbonyl products

Template combination of copper acetate (Cu(AcO)₂?H₂O) with sodium dicyanamide (NaN(C≡N)₂, 2 equiv) or cyanoguanidine (N≡CNHC(=NH)NH₂, 2 equiv) and an alcohol ROH (used also as solvent) leads to the neutral copper(II)–(2,4‐alkoxy‐1,3,5‐triazapentadienato) complexes [Cu{NH?C(OR)NC(OR)?NH}₂] (R=Me ( 1 ), Et ( 2 ), nPr ( 3 ), iPr ( 4 ), CH₂CH₂OCH₃ ( 5 )) or cationic copper(II)–(2‐alkoxy‐4‐amino‐1,3,5‐triazapentadiene) complexes [Cu{NH?C(OR)NHC(NH₂)?NH}₂](AcO)₂ (R=Me ( 6 ), Et ( 7 ), nPr ( 8 ), nBu ( 9 ), CH₂CH₂OCH₃ ( 10 )), respectively. Several intermediates of this reaction were isolated and a pathway was proposed. The deprotonation of 6 – 10 with NaOH allows their transformation to the corresponding neutral triazapentadienates [Cu{NH?C(OR)NC(NH₂)?NH}₂] 11 – 15 . Reaction of 11 , 12 or 15 with acetyl acetone (MeC(?O)CH₂C(?O)Me) leads to liberation of the corresponding pyrimidines NC(Me)CHC(Me)NC NHC(?NH)OR, whereas the same treatment of the cationic complexes 6 , 7 or 10 allows the corresponding metal‐free triazapentadiene salts {NH₂C(OR)?NC(NH₂)?NH₂}(OAc) to be isolated. The alkoxy‐1,3,5‐triazapentadiene/ato copper(II) complexes have been applied as efficient catalysts for the TEMPO radical‐mediated mild aerobic oxidation of alcohols to the corresponding aldehydes (molar yields of aldehydes of up to 100 % with >99 % selectivity) and for the solvent‐free microwave‐assisted synthesis of ketones from secondary alcohols with tert‐butylhydroperoxide as oxidant (yields of up to 97 %, turnover numbers of up to 485 and turnover frequencies of up to 1170 h^?1).     

Reaction Mechanism and Kinetics study on Addition of CCl4 to 1-hexene Catalyzed by Mo-Mo Quintuply-bond

Transition metal-catalyzed atom transfer radical addition (ATRA) reactions are an effective and versatile strategy for constructing carbon–carbon bonds in organic synthesis. Typically, the metal center in this metal-assisted radical transformation undergoes a reversible redox process. In this work, a quintuply-bonded dinuclear complex, Mo₂(N^∧N)₂ {N^∧N = μ-κ²-CH[N(2,6-iPr₂C₆H₃)]₂}, has been investigated as potential catalyst for radical addition of CCl₄ to 1-hexene by performing density functional theory (DFT) calculations. The study shows that the Mo₂(N^∧N)₂-mediated radical addition reaction is computationally predicted to occur with acceptable activation energies, indicating that the Mo-Mo quintuple bond can be applied as an effective catalyst for this transformation under mild conditions. The whole reaction involves 3 steps, two of which are metal-mediated. Firstly, the C-Cl bond activiation catalyzed by Mo₂(N^∧N)₂ to obtain Mo₂(N^∧N)₂Cl and ·CCl₃ radical; Then the ·CCl₃ radical interacts with 1-hexene to get an addition, the addition product reacts with the Mo₂(N^∧N)₂Cl to get the last product and regenerate the catalyst Mo₂(N^∧N)₂. Both the thermodynamic and kinetic study show that the second step is the rate-determine step. When coordinating solvent pyridine is added to the catalytic reaction, the reaction is suppressed due to their high energies barriers, which is consistent with experimental results.     

Copper-Catalyzed Chemo- and Enantioselective Radical 1,2-Carbophosphonylation of Styrenes

The copper-catalyzed enantioselective radical difunctionalization of alkenes from readily available alkyl halides and organophosphorus reagents possessing a P−H bond provides an appealing approach for the synthesis of α-chiral alkyl phosphorus compounds. The major challenge arises from the easy generation of a P-centered radical from the P−H-type reagent and its facile addition to the terminal side of alkenes, leading to reverse chemoselectivity. We herein disclose a radical 1,2-carbophosphonylation of styrenes in a highly chemo- and enantioselective manner. The key to the success lies in not only the implementation of dialkyl phosphites with a strong bond dissociation energy to promote the desired chemoselectivity but also the utilization of an anionic chiral N,N,N-ligand to forge the chiral C(sp³)−P bond. The developed Cu/N,N,N-ligand catalyst has enriched our library of single-electron transfer catalysts in the enantioselective radical transformations.     

Electrocatalytically Activating and Reducing N2 Molecule by Tuning Activity of Local Hydrogen Radical

Decarbonizing N₂ conversion is particularly challenging, but essential for sustainable development of industry and agriculture. Herein, we achieve electrocatalytic activation/reduction of N₂ on X/Fe−N−C (X=Pd, Ir and Pt) dual-atom catalysts under ambient condition. We provide solid experimental evidence that local hydrogen radical (H*) generated on the X site of the X/Fe−N−C catalysts can participate in the activation/reduction of N₂ adsorbed on the Fe site. More importantly, we reveal that the reactivity of X/Fe−N−C catalysts for N₂ activation/reduction can be well adjusted by the activity of H* generated on the X site, i.e., the interaction between the X−H bond. Specifically, X/Fe−N−C catalyst with the weakest X−H bonding exhibits the highest H* activity, which is beneficial to the subsequent cleavage of X−H bond for N₂ hydrogenation. With the most active H*, the Pd/Fe dual-atom site promotes the turnover frequency of N₂ reduction by up to 10 times compared with the pristine Fe site.