Synthesis of aniline from dinitrogen and benzene mediated by magnesium oxide supported sodium hydride

Domain: physics
Published: 2026-04-09
Editorial outcome: minor_revision

Abstract
The activation and valorization of inert molecules (e.g., dinitrogen (N ), alkanes, and alkenes) for the
synthesis of nitrogen-containing organic compounds have long been a highly sought-after goal in
chemistry. However, it remains a formidable challenge, stemming from the inherent chemical inertness
of the robust N≡N and C-H bonds, as well as the competitive adsorption and activation of reactants.
Consequently, examples of direct C-N bond formation using N and alkanes/alkenes as feedstocks
2
remain exceptionally scarce. Herein, we report that sodium hydride supported on magnesium oxide
(NaH/MgO) possesses unique multiple reactive sites, which enable the conversion of N and
2
unactivated arenes and facilitate C-N bond formation. The synergistic interplay between sodium,
magnesium, and hydride species at the NaH/MgO interface plays a pivotal role in the reduction of N
2
to NH species. These reactive NH intermediates then deprotonate the aryl C-H bond, attack the
x x
alkali-interacted aryl ring, and drive the formation of sodium anilide on the surface. Subsequent
protonation of sodium anilide yields aniline with high selectivity (>90%). This work demonstrates the
feasibility of transforming N and simple arenes into key nitrogen-containing organic compounds via a
2
solid surface-mediated process, thereby opening ample room for developing heterogeneous catalysts
for the transformation of N and organic substrates.
2

Introduction
The direct transformation of N into value-added nitrogen-containing products poses a formidable
2
scientific challenge because of its inert nature. At present, almost all organic nitrogen-containing
compounds are synthesized using ammonia or amine as the nitrogen source. The well-established
industrial ammonia synthesis process (Haber-Bosch process) is energy intensive and of high carbon
footprint. In recent years, on one hand, the development of more efficient catalysts for ammonia
synthesis and alternative N fixation methods such as electrochemical, photochemical, plasma-
2
catalytic, and chemical looping routes have been received much attention1-6. On the other hand, the
direct transformation of N into organic nitrogen-containing compounds including amines, nitriles,
2
alkaloids etc., has also piqued significant interest7-12. Although heterogeneous, homogeneous, and
biological catalysts are known for their roles in catalytic nitrogen fixation to ammonia, the (catalytic)
synthesis of more complex nitrogen-containing organic molecules has far less precedent.

The pioneering research efforts regarding the conversion of N into organic compounds have
2
largely concentrated on molecular transition metal complexes because of their versatile and well-
defined compositions and structures, flexible chemical environments, as well as diversified
coordination modes for both N and organic substrates8,13-19. Although there are some cases of the
2
coupling of N with aryllithium or aryl halides, mediated by transition metals, to yield N-containing
2
compounds20-23, research on the reactions of N with arenes without prior functionalization remains
2
scarce. Holland et al. reported an iron β-diketiminate complex that mediates the coupling of N and
2
arenes to yield aniline derivatives24. The key C-N bond formation step occurs after partial silylation of
coordinated N on the Fe site. Tian et al. reported a plasma-enabled, catalyst-free approach to the
2
direct coupling of benzene and N into arylamines at the plasma-liquid interface, leveraging the high-
2
energy environment for N activation25. Very recently, Wei and Xi et al. reported a chromium-mediated
2
synthetic cycle for the direct conversion of N into multi-substituted hydrazines via aryl migration, here
2
termed the Xi Cycle, thereby representing a landmark advance in N functionalization26. The synthesis
2
of organic nitrogen-containing compounds from N and inert hydrocarbon sources on a solid surface,
2
hitherto, has rarely been reported.

Metal hydrides, existing in diverse structural and compositional forms, have played crucial roles
in many fundamental chemical transformations27-30. It has recently been demonstrated that alkali and
alkaline earth metal hydrides, including lithium hydride (LiH), barium hydride (BaH ), and sodium
2
hydride (NaH), can enable N fixation and subsequent hydrogenation to form N-H bonds, driven by
2
thermal energy, plasma, or ultraviolet light illumination31-35. Beyond N activation, hydride species (H‾)
2
have also been shown to mediate the activation of inert C-H bonds, such as that in benzene, under
mild conditions36-38. Taken together, these insights suggest the potential of hydrides to enable the
synergistic activation of N≡N and C-H bonds, thereby facilitating direct C-N bond formation. Herein,
we demonstrate the direct construction of C-N bond from inert N and unactivated arenes mediated
2
by sodium hydride supported on MgO. This transformation proceeds through three key steps: N
2
fixation via mechanochemistry, C-N bond formation under thermochemical conditions, and protonation
or hydrogenation to yield aniline. Anilines are obtained as dominant products with high selectivity
(>90%). Notably, the one-pot synthesis of nitrogen-containing organic compounds from N and simple
2
arenes can also be achieved under heating at 200°C. Different from molecular transition metal
complexes reported previously, this study reveals the intriguing role of alkali (and alkaline earth) metal
hydrides in the activation of N≡N and C-H bonds, along with the formation of the C-N bond.
Interestingly, the introduction of iron species exerts a pronounced promotional effect on N≡N bond
activation and subsequent C-N bond construction. This work could create substantial opportunities for
the advancement of heterogeneous materials aimed at converting N and hydrocarbon sources into
2
valuable organic nitrogen-containing compounds.

Results
N fixation by NaH/MgO
2
While neat NaH has been reported to fix a negligible amount of N species under normal thermal
2
conditions33, we found that when dispersed on the MgO support, it is capable to fix N . Firstly, we
2
investigated thermal N fixation by NaH/MgO, which was prepared by ball-milling a mixture of NaH
2
(10wt%) and MgO powders in a commercial tungsten carbide (WC) jar. The N -temperature-
2
programmed reaction (N -TPR) profile of NaH/MgO shows H formation upon heating under a N flow,
2 2 2
with a signal intensity significantly higher than that in Ar-temperature-programmed decomposition
reaction (Ar-TPD) (Figure S1a), indicating N reduction by the hydride material31,39. In contrast, control
2
experiments confirmed that bare MgO produced no detectable H signal (Figure S1b). Moreover, the
2
NaH/MgO sample collected after heating in an N atmosphere exhibits the significant N-H bond
2
stretching vibrations at 3263 and 3217 cm-1 (Figure S2), confirming the formation of surface NH (x=1,
x
2) species. These results show that the ball-milled NaH/MgO can activate N and promote its
2
hydrogenation to form N-H bonds.

To simplify precursor preparation for N fixation, we explored a streamlined, one-pot process using
2
readily available Na metal pellets and MgO powder under H and N pressures to afford the N-fixed
2 2
samples. That is, Na, and MgO were co-feed and ball milled in a WC jar with variable N /H
2 2
pressures,
affording a solid product (denoted as Na-N-H/MgO). The X-ray diffraction (XRD) pattern (Figure S3),
high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image, and
energy-dispersive X-ray (EDX) mapping (Figure 2a) showed that Na species is evenly dispersed on
the MgO support at the (sub)nanometer scale. Diffuse reflectance infrared Fourier transform (DRIFT)
spectra (Figure 2b) showed several bands around 3277, 3244, and 3220 cm-1 which are assigned to
stretching vibrations of NH (x=1 and 2) species, a clear indication of N≡N bond cleavage followed by
x
hydrogenation to N-H bonds. Isotope experiments using 15N and D also confirmed that these bands
2 2
can be assigned to the stretching vibrations of NH (Figure S4). Noted that the observed vibrational
x
modes closely resemble those of NaNH and Mg(NH ) albeit with slight shifts, suggesting that the
2 2 2
NH species could be bonded with both Na and Mg atoms on the surface. Time-of-flight secondary-
x
ion mass spectrometry (ToF-SIMS) with negative mode (Figure 2c) detected cluster ions containing
NH species (NH‾, NaNH‾, NaNH ‾, and MgNH ‾), confirming NH formation and N bonding with Na
x 2 2 x
and/or Mg.

The amount of fixed nitrogen over Na-N-H/MgO was further quantified via hydrolysis with water
vapor, where protonation of the fixed nitrogen yielded NH as the sole N-containing product (Figure
3
S5); for example, after ball milling under a N (15 bar)-H (15 bar) atmosphere, the amount of fixed
2 2
nitrogen was determined to be 0.35 mmol g-1 (Figure S6b). Additionally, we observed that the
adventitious Fe introduced from the milling jar material significantly affects the amount of nitrogen fixed
during ball milling. As shown in Figures 2d and S6a, the amount of fixed nitrogen reaches 1.2 mmol g-
1 in a stainless-steel jar, approximately 3 times that in a WC jar. The XRD pattern reveals the presence
of Fe nanoparticles after ball-milling of Na and MgO in a stainless-steel jar (Figure S7). It is well-known
that Fe metal is catalytically active for ammonia synthesis from N and H . We therefore propose iron
2 2
species plays an important role in this system, and accordingly prepared the nitrogen-fixed material
comprising Na/MgO and Fe (denoted as Na-N-H/MgO-Fe). The amount of fixed N increases with
2
increasing N partial pressure, with a maximum of 2.17 mmol g-1 achieved over the Na/MgO-Fe sample
2
under N (25 bar)-H (10 bar) conditions (Figure 2d). These results demonstrate the efficacy of one-pot
2 2
mechanochemical methods in boosting N activation and conversion by NaH/MgO.

Coupling of fixed nitrogen species with benzene
We then examined the reaction of fixed NH species with benzene to see whether C-H bond activation
x
and C-N bond formation could take place. The Na-N-H/MgO-Fe samples were reacted with benzene
at 200 °C for 3 hours. The solid products were partially dissolved in DMSO, and the resulting solution
was analyzed by proton nuclear magnetic resonance (1H NMR) (Figure 3a). Distinct up-field chemical
shifts were observed at 5.35, 5.77, and 6.37 ppm, compared to typical aniline signals (6.48, 6.55, and
6.99 ppm). Similar proton resonance was observed in sodium anilide (C H -NHNa)40,41 (Figure S8),
6 5
which was synthesized via the reaction of NaH with aniline. These results indicate the formation of
sodium anilide salt species on the surface of Na-N-H/MgO-Fe. Moreover, the negative ToF-SIMS
spectrum (Figure S9) showed the formation of a series of C-N bond-containing species such as
C H NNa‾ and C H N‾ etc., further verifying the formation of anilide salts on Na-N-H/MgO.
6 5 6 5
The resulting anilide salts were further protonated with aqueous solutions, and the organic
products were extracted into organic solvents. GC-MS analysis identified aniline as the predominant
nitrogen-containing product, accompanied by the formation of other N-containing compounds
including phenylenediamine, aminobiphenyl, and benzidine, as well as the homocoupling side product
biphenyl (Figure S10).

Notably, Na-N-H/MgO sample synthesized in a WC jar (without Fe) also produced aniline via
reaction with benzene followed by protonation, albeit with a lower yield of 1.41 μmol g-1 (Figure 3b).
This result substantiates that Na-N-H/MgO is intrinsically capable of mediating C-H bond activation
and C-N bond formation in the absence of transition metals. In contrast, the reference Fe-N-MgO
sample without NaH failed to produce aniline upon reaction with benzene, underscoring the critical
role of the NaH/MgO interface in activating the arene C-H bond and enabling C-N bond formation.
Remarkably, when Fe was present, the Na-N-H/MgO achieved an aniline yield of 214 μmol g-1 at
200 °C (Figure 3b and Table S1). The specific prominent role of iron or other transition metals will be
investigated in a separate study.

The reaction of Na-N-H/MgO-Fe samples with benzene was conducted at different temperatures
(Figures 3c, 3d, and S11). Figure 3c reveals a volcano-shaped correlation between the amount of fixed
nitrogen and the reaction temperature, with the maximum at 200 °C. Lower conversion at higher
temperatures may be attributed to the decomposition of NH or decomposition/conversion of anilide
x
salts. Figure S11b shows the product distribution after reactions conducted at different temperatures.
Notably, the selectivity for total N-containing products was higher than 95% below 200 °C (Figure
S11a). More interestingly, the selectivity of aniline among N-containing products exceeded 90%
typically below 180 °C (Figure 3d), whereas aniline selectivity declined at higher temperatures,
suggesting over-reactions between benzene and the solid surface. Through the optimization of
reaction temperature, ball milling time, and loading of Na, a maximum conversion (ca. 26.3%) of fixed
N in the 10 wt% Na/MgO sample was achieved at 200 °C (Figure 3c and Table S1). The yields of
aniline and total N-containing compounds were 214 and 310 μmol g-1, respectively. Furthermore, to
verify aniline originated from N rather than nitrogen contaminates, Na-15N-H/MgO-Fe was
2
synthesized using 15N , and then reacted with benzene under the same conditions. GC-MS analysis
2
confirmed 15N-labelled aniline as the main product (Figure 3e), confirming N as the nitrogen source.
2

While hydrolysis offers a straightforward route to convert anilide salts to aniline, it results in the
concomitant hydration of Na/MgO, leading to loss of reactivity. This prompted us to explore
hydrogenation of anilide salts to produce aniline and regenerate NaH/MgO, potentially completing the
synthetic cycle. To verify this, neat sodium anilide was synthesized and subjected to hydrogenation
under a H flow. As shown in Figure 3f, sodium anilide undergoes the desorption of unreacted aniline
2
at lower temperature (ca. 80 °C), followed by hydrogenation to release additional aniline upon heating
to 275 °C. In contrast, Ar-TPD confirmed only the lower-temperature aniline desorption signal,
validating the hydrogenation process (Figure S12). Similarly, the surface-bonded sodium anilide
species on Na/MgO can also be hydrogenated to aniline, albeit with lower signal intensity. No aniline
formation was observed under argon atmosphere shown in Figure S13. These observations highlight
the potential to close the chemical cycle via hydrogenation treatment, warranting further investigation
to fully explore this process.

Conversion of N and benzene
2
Building on the successful stepwise synthesis of surface anilide, we further investigated the feasibility
of one-pot C-N bond formation. NaH/MgO-Fe samples were employed as the mediator, over which
benzene and N were introduced at specific pressures in a sealed system at 200 °C (Figure S14).
2
Aniline was obtained after protonation treatment, albeit with relatively low yield of 109 μmol g-1 under
20 bar N pressure, attributed to competitive adsorption of benzene and N on NaH/MgO-Fe.
2 2
Additionally, the one-step reaction was further evaluated in a flow reactor, where N served as both
2
the reactant gas and the carrier gas to bring benzene vapor to the NaH/MgO-Fe. Aniline was formed
after reaction at 200 °C under ambient pressure, followed by hydrolysis treatment (Figure S15). Overall,
the results present a pioneering protocol for the direct formation of C-N bonds from N and benzene,
2
in particular providing a viable strategy for the one-step transformation of N and arenes into nitrogen-
2
containing organic compounds.

Mechanistic studies
The reaction mechanism of Na/MgO for the activation of N and C H , as well as the subsequent C-N
2 6 6
bond formation was investigated by DFT calculations. Since neither NaH nor MgO alone functions for
this process, the synergy between NaH and MgO is crucial for activating H , N , and C H molecules,
2 2 6 6
as well as for facilitating C-N bond formation. TEM and ToF-SIMS results, revealed the presence of
sub-nanosized sodium cluster (Na -Na ) species (Figure S16). DFT calculation results further
1 5
indicated that a Na cluster model featuring a quasi-square planar geometry exhibits the optimal
4
interfacial binding energy, significantly superior to that of the Na -Na and Na clusters (Figure S17).
1 3 5
Accordingly, the Na /MgO(100) model was selected for the subsequent mechanistic study (Figure
4
S18).

On the Na /MgO model, H undergoes heterolytic dissociation into Na-H-Mg and O-H species,
4 2
with an energy barrier of merely 0.22 eV. N preferentially adsorbs in a side-on configuration at the
2
Na-Mg-Na triangular site, with the N-N bond elongated to 1.17 Å. Subsequently, the hydride at the Na-
H-Mg ensemble transfers to the adsorbed N , producing the *N H intermediate by 1.45 eV via a
2 2
reductive protonation pathway. Migration of surface *OH species to the Na-Mg site to regenerate Na-
H-Mg is exothermic; this replenishment of hydride facilitates the subsequent hydrogenation of *N H to
2
*N H , ultimately forming the surface species Na-NH -Mg and Na-N-Mg. These findings are supported
2 2 2
by experimental results from DRIFTS and ToF-SIMS.

After N fixation at the Na-H-Mg interface, benzene preferentially adsorbs at surface Na sites via
2
cation-π interaction, adopting an η6 configuration. Deprotonation of benzene occurs upon attack by *N
species, generating a surface-stabilized absorbed phenyl species on the Na-cluster surface (denoted
as Na-C H *) and Na-NH-Mg species. This step is significantly exothermic (ΔE = −1.00 eV) with a
6 5
moderate activation energy barrier (E = 0.36 eV), indicating favorable kinetics. Subsequently, surface
a
*C H was attacked by the nucleophilic *NH at the interface, yielding *C H NH . Subsequently,
6 5 2 6 5 2
*C H NH preferentially interacts with Na, accompanied by hydrogen transfer, to yield
6 5 2
thermodynamically stable C H NH-Na and OH species in strongly exothermic step (-0.87 eV).
6 5

Scope of arenes
The successful synthesis of aniline from N and benzene inspired us to investigate C-N bond formation
2
in reactions of N with a series of aromatic substrates bearing various functional groups using the
2
Na/MgO sample. As shown in Figure 4, a range of aniline derivatives were obtained under the general
reaction conditions. Monoalkylated arenes reacted with surface-bound NH species to afford the
x
corresponding amination products (2-11) in moderate to good yields. Meta-substituted N-containing
products predominate in these reactions, in contrast to conventional synthetic routes where
substitution typically occurs at the ortho- and para- positions, often guided by directing groups. For
example, m-toluidine (2) was the predominant product from toluene with a yield of 108 μmol g-1, with
trace amounts of p-toluidine (Figure S19). Arenes bearing ethyl, propyl and butyl groups similarly gave
exclusively meta-substituted amines (3-9) in appreciable yields, although their overall fixed-nitrogen
conversions were lower than those observed with benzene. The preference for reaction at electron-
deficient positions implies a process involving nucleophilic attack by NH species.
x

For bulkier arenes, 3-aminobiphenyl and 3-(2-phenylethyl) benzenamine (10 and 11) were
obtained in yields of 161 μmol g-1 and 81 μmol g-1, respectively. For dialkyl-substituted substrates, m-
xylene was converted to 3,5-dimethylaniline (12) with a relatively low yield of 22 μmol g-1. That is
attributed to electron-donating methyl groups enhancing the electron density of the aromatic ring,
thereby weakening its reactivity. In contrast, m-terphenyl afforded 3-amino-m-terphenyl (14) in a higher
yield of 93 μmol g-1. Despite lower yields, 1-aminofluorene (13) (13 μmol g-1) and 4-amino-p-terphenyl
(15) (12 μmol g-1) were also successfully synthesized. The amination method was also compatible with
polycyclic aromatic hydrocarbons. In these cases, naphthalene underwent amination at the β-position
(16). Similarly, both anthracene and phenanthrene underwent amination at β-sites (17 and 18), in
contrast to the typical electrophilic substitution patterns. Quinoline was also effectively transformed
into aminoquinoline (19) with a yield of 98 μmol g-1, consistent with the Chichibabin reaction pathway.
Reactions of halogenated benzenes with Na-N-H/MgO yielded aniline (20a-23a), diphenylamine (20b-23b), and triphenylamine (20c-23c) instead of the corresponding haloanilines, suggesting a
dehalogenative amination process analogous to the Buchwald-Hartwig cross-coupling42. Additionally,
the surface anilide salts can react with chlorotrimethylsilane (TMSCl) to afford silylated aniline
derivates (Figure S20).

Methods
Chemicals and materials
Sodium block (99.7%) was purchased from Aladdin. MgO with a high specific surface area (ca. 170
m2 g-1) was synthesized according to a literature report43. Benzene (99.7%) was purchased from
Aladdin and then was dried by 3 Å zeolite before use. N (99.999%) and H (99.999%) were purchased
2 2
from Dalian Special Gas Co., Ltd. Ar (99.999%) was purchased from Dalian Junfeng Gases Co. Ltd.
15N (98%) was purchased from Cambridge Isotope Laboratories. All materials were handled inside a
2
glove box filled with purified argon (O , H O <1 ppm), owing to the air- and moisture-sensitivity of the
2 2
reagents and samples.

Materials synthesis
(1) Fabrication of Na/MgO
Na/MgO with a Na loading of 10 wt% was prepared as follows. The MgO was pretreated under an
argon flow at 580 °C for 8 h. Subsequently, metallic sodium (55.6 mg) and MgO (500 mg) were mixed
and ball milled in either a tungsten carbide jar or stainless-steel jar at 200 revolutions per minute (rpm)
for 12 hours.

(2) Fabrication of Na-N-H/MgO
Metallic sodium (55.6 mg) and MgO (500 mg) were mixed and ball milled in a tungsten carbide jar
under a N /H atmosphere at 200 rpm for 12 hours. The obtained sample was denoted as Na-N-
2 2
H/MgO.

(3) Fabrication of Na-N-H/MgO-Fe
Metallic sodium (55.6 mg) and MgO (500 mg) were mixed and ball milled in a stainless-steel jar under
a N /H atmosphere at 200 rpm for 12 hours. The obtained sample was denoted as Na-N-H/MgO-Fe.
2 2

(4) Fabrication of Fe-N/MgO
MgO (500 mg) was ball milled in a stainless-steel jar under a N /H atmosphere at 200 rpm for 12
2 2
hours. The obtained sample was denoted as Fe-N/MgO.

(5) Fabrication of NaH/MgO
NaH/MgO with a NaH loading of 10 wt% was also synthesized by ball milling NaH (44.4 mg) and MgO
(400 mg) in a tungsten carbide jar at 200 rpm for 8 hours.

After ball milling, the solid products were collected and stored in an Ar-filled glove box.

Quantification of fixed-N on Na-N-H/MgO samples
The active nitrogen species on Na-N-H/MgO were converted to ammonia by hydrolysis treatment and
quantified using a conductivity meter. Water vapor carried by argon was introduced into the reaction
tube to react with the Na-N-H/MgO. Then the exhaust gas was bubbled through dilute sulfuric acid,
and the change of the conductivity meter was tracked to determine the mounts of ammonia
discharge31,44,45, corresponding to the amount of nitrogen fixation of the sample.

General procedure of the reaction between Na-N-H/MgO and benzene
The reaction of Na-N-H/MgO with benzene was conducted in a home-made stainless-steel sealed
reactor with a quartz lining. In a typical experiment, 50 mg of Na-N-H/MgO and 200 μL of benzene
were added into the reactor in a glove box filled with argon. Then the reactor was heated to the desired
temperature for several hours (such as at 200 °C for 3 hours). After reaction, the solid-liquid mixtures
were collected for further characterization.

One-pot procedure for aniline synthesis
The one-pot reaction of benzene and N over Na/MgO was conducted in a custom-designed stainless-
2
steel sealed reactor with quartz lining. The Na/MgO was loaded into the quartz tube, while benzene
was introduced into the reactor outside the tube, and N pressurized to desired values. Once the
2
reaction temperature reached 200 °C, gaseous benzene and N were co-converted over Na/MgO.
2
After reaction, the solid residues were hydrolyzed by an NH Cl aqueous solution followed by extraction
4
with ethyl acetate. The liquid products were then collected and analyzed by GC-MS.
In addition, in the flow system, benzene vapor, carried by N was co-fed to Na/MgO at 200 °C under
2
ambient pressure. After reaction, the mixtures were treated and analyzed by gas chromatography-
mass spectrometry (GC-MS) as described above.

Quantitative analysis of aniline
50 mg of the solid products was hydrolyzed using 2 mL saturated ammonium chloride solution at room
temperature, followed by extraction with 2mL of ethyl acetate. Notably, aniline and other N-containing
organics were typically obtained as the sole products after the demetalation treatment Quantitative
analysis of anilines was performed using gas chromatography with flame ionization detection (GC-FID)
employing dodecane as the internal standard. The conversion of fixed-N to N-containing compounds
was calculated according to the following formula:
Nmole of N in N-contaning organics
Conversion of fixed N (%) = ×100% (1)
mole of fixed N
The selectivity of N-containing compounds was calculated based on the following formula:
mole of N-contaning organics
Selectivity of N-containing organics (%) = ×100% (2)
mole of N-contaning organics + mole of biphenyl
The selectivity of aniline was calculated based on the following formula:
mole of aniline
Selectivity of aniline (%) = ×100% (3)
mole of N in N-contaning organics

Characterizations
Power X-ray diffraction (PXRD) patterns were recorded on a PANalytical X’pert diffractometer in a
home-made sample cell sealed by KAPTON film to avoid air and moisture contamination.
Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) measurements were conducted
on a Brucker Tensor II unit in diffuse reflection mode with a scan resolution of 4 cm-1 and an
accumulation of 32 scans each time.
Solution NMR spectroscopy was performed on a Bruker AVANCE III 400 MHz NMR spectrometer (9.4
T) at room temperature. Solution 1H NMR were conducted with DMSO as the deuterated reagent.
Transmission electron microscopy (TEM), high-angle annular dark field scanning transmission
electron microscopy (HAADF-STEM) and energy-dispersive X-ray (EDX) mapping measurements
were carried out on a JEOL JEM-ARM 300F field-emission electron microscope operated at 200 kV
acceleration voltage.
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) profiles were obtained by using a ToF-
SIMS 5-100 (Ion-ToF GmbH) instrument in positive and negative mode, which was equipped with Ar-
gas cluster sputtering ion source (5 keV) and Bi + ion beam as the analysis beam (30 keV). The
3
analyzed area and the sputtered area were 100*100 μm2 and 300*300 μm2, respectively.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Please also see the attached report doc file for your convenience.\nThis work successfully realized the concurrent activation of two chemically inert molecules of N2 and benzene being\ntransformed into aniline with C-N bond coupling. By taking advantage of the special properties of metal hydrides for nitrogen\nfixation as previously reported by the same authors, they further demonstrate the feasibility of NaH/MgO for C-N coupling\ndirectly from molecular N2, even without transition metal catalysts and under relatively mild conditions. Various factors\naffecting the reaction were investigated and mechanism was explored. The work itself is important, and represents one of\nthe rare examples to realize aniline synthesis directly from N2 and benzene, albeit in a stepwise manner. However, the\nworks suffers from a few important drawbacks, which I believe need to be addressed.\n1)Conversion of fixed N was reported as in Figure 3c, which is important. On the other hand, conversion of benzene is\nnecessary as well for a complete evaluation of the performance. Based on the 200 uL benzene used and the N-containing\nproduct (as in Fig. 3c), the conversion rate in terms of N-product (or aniline itself) seems to be pretty low. Has the authors\ntried to reduce the amount of benzene used in a single reaction?\n2)Following the above question, biphenyl is the major byproduct as stated in the manuscript; yet, the biphenyl yield was not\nclearly quantified. More detailed information about that may be helpful for a better understanding of the reaction process.\n3)In Figure 3b, “WC-Fe(addintion)” is hard to understand. I can not find any experiment information about that in the\nmanuscript and in the supplementary file.\n4)With respect the mass spectrometry (Fig. 3a), the accurate mass should be shown for both the experiment values and\ntheoretical values.\n5)Part of experimental section in the manuscript was repeated in the supplementary file.\n6)In the manuscript: “attacked by the nucleophilic *NH2 at the interface, yielding *C6H5NH2”; while in Fig. S17, the\nintermediate species seems to be C6H5-NH*. Please check that.", "reviewer_2": "As a whole, this is a good paper worth publishing in Nat.Comm. However, there are several drawbacks and ambiguities to\nbe modified before the acceptance as listed below:\n1. “Hydride-mediated co-activation of N2 and benzene” looks not reflecting the mechanism.\nCertainly, N2 is activated to some extent by hydride but the effective activator of benzene is by sodium atom cluster\naccording to the authors claim. In addition, N2 activation is much enhanced by iron metal. So, the role of hydride is\noverestimated.\n2. NaH works for N2 activation but is there any evidence for active role of MgH for this activation?\n3. Mechanism: substitution reactions of benzene occur by electrophilic species, i.e., cationic benzene is an intermediate\nspecies, in general. The authors claim C6H5Na is formed by deprotonation, i.e., benzene anion, which is unstable. Is there\nany evidence to justify this claim? This is a key question in this paper.\n4. Miscellaneous:\na. Is Na3N or Na3NHx formed ? The formation of Na3N was reported in JACS 143 69(2020. Why sodium metal cluster are\nformed ?\nb. When Na-anilide is converted into aniline with the reaction with water, the control of stoichiometric reaction looks so\ndifficult due to highly active the Na-anilide. Some description to follow this reaction is required.\nc. Fig.3 a. Is the sample for the NMR solution?\nf. The vertical axis looks incorrect because this is TDS of H2.", "reviewer_3": "This manuscript by Guo, Chen and co-workers describes the activation of N2 and benzene and their transformation into\naniline derivatives using a NaH/MgO system. One-pot C-N bond formation from N2 and benzene is achieved with\nNaH/MgO-Fe samples. Mechanistic insights are provided by computational studies, which propose that the activated\nnitrogen species deprotonate benzene to form PhNa and -NH species, followed by nucleophilic attack of the NH2 species\non the phenyl unit to form C-N bond. The scope of arenes has also been examined using the Na/MgO samples. The\nchemistry presented in this paper is intriguing; however, several issues must be addressed before a decision can be made.\nPlease address the following points.\n1.As the authors mention, the presence of transition metals strongly influences the activity of the samples. The sample\npreparation was carried out using stainless-steel or tungsten carbide jars. The authors should instead use a transition metal\nfree jar, such as an agate jar etc. for sample preparation.\n2.Regarding the scope of the alkali metals, combinations such as LiH or BaH2 with MgO should also be examined.\n3.For the characterization of N-H bond stretching vibrations, 15N-labeled and D-labeled isotopologues (15N-H and N-D,\netc.) should also be prepared and characterized.\n4.In the mechanistic studies, I am wondering whether the nucleophilic NH2 species attacks the deprotonated C6H5- unit.\n5.The DFT calculations should be performed with iron metals included in the model.\n6.ref21 “K. Hori, M. Mori. Synthesis of…”"}, "author_response": "Response to Reviewers’ Comments\nReviewer #1 (Remarks to the Author):\nPlease also see the attached report doc file for your convenience.\nThis work successfully realized the concurrent activation of two chemically inert molecules\nof N and benzene being transformed into aniline with C-N bond coupling. By taking\n2\nadvantage of the special properties of metal hydrides for nitrogen fixation as previously\nreported by the same authors, they further demonstrate the feasibility of NaH/MgO for C-\nN coupling directly from molecular N , even without transition metal catalysts and under\n2\nrelatively mild conditions. Various factors affecting the reaction were investigated and\nmechanism was explored. The work itself is important, and represents one of the rare\nexamples to realize aniline synthesis directly from N and benzene, albeit in a stepwise\n2\nmanner. However, the works suffers from a few important drawbacks, which I believe need\nto be addressed.\nResponse: We sincerely appreciate the referee for recognizing the scientific\nsignificance of this work and providing valuable and insightful suggestions. In response,\nwe have conducted additional experiments and prepared a detailed, point-by-point\nresponse to all the comments. The corresponding revisions are described as follows.\nComment 1: Conversion of fixed N was reported as in Figure 3c, which is important. On\nthe other hand, conversion of benzene is necessary as well for a complete evaluation of\nthe performance. Based on the 200 uL benzene used and the N-containing product (as in\nFig. 3c), the conversion rate in terms of N-product (or aniline itself) seems to be pretty low.\nHas the authors tried to reduce the amount of benzene used in a single reaction?\nResponse: We thank the referee for this kind suggestion. Indeed, benzene has been\nintentionally used in excess in our reaction system. This is because benzene with a\nrelatively low boiling point is prone to vaporization and condensation on the reactor walls\nunder reaction conditions, which lead to mass-transfer limitations and fluctuations in its\neffective concentration in the reaction zone. As suggested by the referee, we systematically\nreduced the amount of benzene to evaluate its effect on benzene conversion. As shown in\nFigure R1, decreasing the benzene amount from 200 μL to 25 μL resulted in a pronounced\ndecline in the yield of N-containing products, which dropped to ~50 μmol g-1 at 25 μL. The\ncorresponding benzene conversion increased from 0.54% (200 μL) to 0.88% (25 μL).\nAlthough a higher apparent benzene conversion was observed at lower benzene loading,\nthis was accompanied by a substantial loss in product yield. These results indicate that\nexcess benzene not only alleviates mass-transfer issues but also increases the effective\nbenzene partial pressure, thereby sustaining kinetically favorable conditions and enabling\nhigher overall N-product formation.\n1 / 17\nFigure R1. The yield of N-containing products and conversion of benzene as a function of\ndose of benzene. Reaction conditions: sample mass, 50 mg; Reaction temperature and\ntime, 200 °C for 3 h.\nComment 2: Following the above question, biphenyl is the major byproduct as stated in the\nmanuscript; yet, the biphenyl yield was not clearly quantified. More detailed information\nabout that may be helpful for a better understanding of the reaction process.\nResponse: As the referee suggested, we have provided quantitative data for biphenyl\ntogether with other N-containing products at different reaction temperatures (Figure R2). It\ncan be seen that negligible biphenyl was produced below 200 °C, indicating high selectivity\ntoward N-containing products under mild conditions. When reaction temperature exceeded\n200 °C, the biphenyl yield increased markedly. This increase is attributed to the\ndecomposition of active NHₓ species at elevated temperatures, which suppresses N-\nincorporation pathways and promotes benzene coupling side reactions.\n2 / 17\nFigure R2. Product distributions for the reaction of Na-N-H/MgO with benzene at different\ntemperatures.\nThe related figure and corresponding descriptions are added into Supplementary\nInformation (Page 13) and Revised manuscript (Page 6), respectively:\nIn Supplementary Information:\n“Figure S11. (a) Selectivity of N-containing products as a function of temperature in\nthe range of 150 °C to 250 °C. The only side product was biphenyl. (b) Yields of products\nincluding aniline, phenylenediamine, aminobiphenyl, benzidine and biphenyl as a function\nof temperature in the range of 150°C to 250 °C.”\nIn revised manuscript:\n“Figure S11a shows the product distribution after reactions conducted at different\ntemperatures. Notably, the selectivity for total N-containing products was higher than 95%\nbelow 200 °C (Figure S11b).”\n3 / 17\nComment 3: In Figure 3b, “WC-Fe(addition)” is hard to understand. I can not find any\nexperiment information about that in the manuscript and in the supplementary file.\nResponse: We sincerely apologize for the confusion caused by the incorrect insertion\nof Fig. 3b. The originally displayed panel was inserted in error. And the corrected version\nis provided as Figure R3. Na-N-H/MgO was synthesized by ball milling in a tungsten\ncarbide jar under an N /H atmosphere to eliminate the effect of iron. Instead, the sample\n2 2\nprepared under identical conditions using a stainless-steel jar was denoted as Na-N-\nH/MgO-Fe. For comparison, Fe/N-MgO was synthesized following the same procedure but\nin the absence of sodium. As shown in Figure R3, the results demonstrate Na-Mg-N-H\ninterfacial structure plays a critical role in arene C-H bond activation and subsequent C-N\nbond formation, while iron exerts a promotional effect.\nFigure R3 (Figure 3b). Effect of Fe on aniline yield over Na-N-H/MgO.\nWe thank the referee again for pointing out this oversight. We have corrected Figure\n3b in the Revised manuscript (Page 7) and the preparation procedures for the various\nsamples have been added to the manuscript (Page 12):\n1) Fabrication of Na-N-H/MgO\nMetallic sodium (55.6 mg) and MgO (500 mg) were mixed and ball milled in a tungsten\ncarbide jar under a N /H atmosphere at 200 rpm for 12 hours. The obtained sample was\n2 2\ndenoted as Na-N-H/MgO.\n2) Fabrication of Na-N-H/MgO-Fe\nMetallic sodium (55.6 mg) and MgO (500 mg) were mixed and ball milled in a stainless-\nsteel jar under a N /H atmosphere at 200 rpm for 12 hours. The obtained sample was\n2 2\ndenoted as Na-N-H/MgO-Fe.\n3) Fabrication of Fe-N/MgO\nMgO (500 mg) was ball milled in a stainless-steel jar under a N /H atmosphere at 200 rpm\n2 2\nfor 12 hours. The obtained sample was denoted as Fe-N/MgO.\n4 / 17\nComment 4: With respect the mass spectrometry (Fig. 3a), the accurate mass should be\nshown for both the experiment values and theoretical values.\nResponse: Figure 3a shows the 1H-NMR spectra, rather than a mass spectrum. We\nare sorry for the confusion caused by ambiguous labeling. To clarify this point, we have\nexplicitly labeled the chemical shift of each peak in the spectra (Figure R4). Figure 3a\nhas also been updated accordingly in the revised manuscript.\nFigure R4 (Figure 3a). 1H-NMR spectra of product from reaction between Na-N-H/MgO\nand benzene.\nComment 5: Part of experimental section in the manuscript was repeated in the\nsupplementary file.\nResponse: We thank the referee for pointing this out. We have removed the redundant\ncontent from the revised Supplementary Information file.\nComment 6. In the manuscript: “attacked by the nucleophilic *NH at the interface, yielding\n2\n*C H NH ”; while in Fig. S17, the intermediate species seems to be C H -NH*. Please\n6 5 2 6 5\ncheck that.\nResponse: We thank the referee for the careful comment. In the originally proposed\nmechanism, C-N bond formation was considered as a concerted process, in which NH *\n2\nattacks C H * to form C H NH * followed by dehydrogenation to generate anilide salts.\n6 5 6 5 2\nThat is to say, two step was included in this pathway: (1) C H * + NH * →C H NH * and\n6 5 2 6 5 2\n(2) C H NH * → C H NH* + H*. As noted by the referee, the present mechanistic route\n6 5 2 6 5\nwas not fully shown in Figure S18, leading to ambiguity in the mechanistic interpretation.\nIn response, we have re-examined the separated reaction pathways and identified a more\nreasonable process, which is now presented in Figure R5. In the revised pathway, the\nreaction is initiated by nucleophilic attack of NH * on C H * to form C H NH * , overcoming\n2 6 5 6 5 2\nan energy barrier of 1.27 eV. Subsequently, C H NH * preferentially interacts with Na,\n6 5 2\naccompanied by hydrogen transfer, to yield thermodynamically stable C H NH-Na* and\n6 5\n5 / 17\nOH* species in strongly exothermic step (-0.87 eV).\nFigure R5. Free energy diagram of the reaction pathway for the synthesis of aniline from\nN and benzene on Na /MgO(100) cluster model\n2 4\nThe revised calculated pathways and corresponding description have been added to\nthe Supplementary Information (Page 20) and Main text (Page 8), respectively.\nIn Supplementary Information:\n“Figure S18. Free energy diagram of the reaction pathway for the synthesis of aniline from\nN and benzene on Na /MgO(100) cluster model.”\n2 4\nIn revised manuscript:\n“Subsequently, surface *C H was attacked by the nucleophilic *NH at the interface,\n6 5 2\nyielding *C H NH , overcoming an energy barrier of 1.27 eV. Subsequently, *C H NH\n6 5 2 6 5 2\npreferentially interacts with Na, accompanied by hydrogen transfer, to yield\nthermodynamically stable C H NH-Na and OH species in strongly exothermic step (-0.87\n6 5\neV).”\n6 / 17\nReviewer #2 (Remarks to the Author):\nAs a whole, this is a good paper worth publishing in Nat.Comm. However, there are several\ndrawbacks and ambiguities to be modified before the acceptance as listed below:\nResponse: We sincerely thank the reviewer for his or her encouraging support for\npublication in Nature Communications. We have carefully considered all comments and\naddressed the raised concerns accordingly (vide infra).\nComment 1. “Hydride-mediated co-activation of N and benzene” looks not reflecting the\n2\nmechanism.\nCertainly, N is activated to some extent by hydride but the effective activator of benzene\n2\nis by sodium atom cluster according to the authors claim. In addition, N activation is much\n2\nenhanced by iron metal. So, the role of hydride is overestimated.\nResponse: We thank the reviewer for raising the thoughtful concern. We agree that\nthe original wording could imply that both N and benzene are directly activated at hydride\n2\nsites, which does not fully reflect our presented mechanistic understanding. Experimentally,\nNaH/MgO reacts with N to generate Na-N-H/MgO under both stainless-steel and tungsten\n2\ncarbide milling conditions. In contrast, in the absence of sodium hydride, N fixation is\n2\nnegligible even in the presence of Fe. This clearly demonstrates that hydride species are\nindispensable for N activation in our system. Mechanistic investigations further indicate\n2\nthat hydride species within the Na-H-Mg ensemble transfer to adsorbed N , forming *N H\n2 2\nintermediates via a reductive protonation pathway. Therefore, hydrides constitute the key\nsites responsible for N activation and the generation of reactive NHₓ species. In current\n2\nmechanism, benzene adsorption most likely occurs on sodium cluster sites, and that C-N\nbond formation proceeds via reaction between activated benzene species and surface Na-\nNHₓ intermediates. Thus, hydride does not directly activate benzene but plays a decisive\nupstream role by enabling N fixation and generating the reactive nitrogen species required\n2\nfor subsequent coupling. We note that this mechanistic proposal represents one plausible\npathway, and further studies are ongoing to elucidate the specific role of hydride species\nin the C-N bond formation process.\nRegarding Fe, we acknowledge that iron enhances N activation to some extent.\nthree times lower than NaH/MgO. More importantly, the Fe-containing samples do not\nproduce C-N coupling products upon reaction with benzene. This suggests that Fe-derived\nnitrogen species are not competent for subsequent C-N bond formation, whereas hydride-\nmediated NH species bound to sodium are accessible.\nx\nIn response to the referee’s suggestion and to avoid mechanistic overstatement, we\nhave revised the title to: “Hydride-mediated conversion of dinitrogen and benzene for C–\nN bond formation.”\nComment 2. NaH works for N activation but is there any evidence for active role of MgH\n2\nfor this activation?\nResponse: Based on experimental and mechanistic study, Na-Mg-H interfacial\nstructure is formed upon reaction of NaH with MgO, which serves as the primary active site\n7 / 17\nfor N activation. To directly access whether MgH contributes toN fixation or subsequent\n2 2\nC-N bond formation, control experiments were carried out using MgH and MgO.\n2 2 2\nconditions identical to those used for Na-N-H/MgO, and the resulting material was denoted\nas Mg-N-H/MgO. The amount of fixed nitrogen over Mg-N-H/MgO was only 0.08 mmol g-1\n(Figure R6a), which is more than an order of magnitude lower than that of Na-N-H/MgO\n(1.2 mmol g-1), indicating that MgH is not the main contributor for N fixation.\nwas formed (Figure R6b). Collectively, these experimental results demonstrate that MgH\nplay a negligible role in role in either N activation or C-N bond formation. Instead, Na-H-\ntransformation.\nFigure R6. (a) Amount of fixed nitrogen in the 10 wt% Mg-N-H/MgO sample, determined\nby the conductivity method used in this work. (b) GC spectrum of products after hydrolysis.\nDodecane was used as an internal standard.\nComment 3. Mechanism: substitution reactions of benzene occur by electrophilic species,\ni.e., cationic benzene is an intermediate species, in general. The authors claim C6H5Na is\nformed by deprotonation, i.e., benzene anion, which is unstable. Is there any evidence to\njustify this claim? This is a key question in this paper.\nResponse: We thank the referee for raising this important mechanistic point. We do\nnot propose the formation of a “free benzene anion”. Rather, we suggest that benzene is\nadsorbed and activated on sodium cluster sites, followed by C-H cleavage to generate a\nsurface-stabilized adsorbed phenyl species (denoted as Na–C H *). Such species should\n6 5\nbe regarded as surface-bound organosodium intermediates rather than discrete, free\nC H ‾ anions. Although direct spectroscopic observation of Na-C H * is experimentally\n6 5 6 5\nchallenging due to its high reactivity, alkali metal compounds (e.g., K, KH) have been\nreported to deprotonate benzene under strongly reducing conditions, forming metal-phenyl\nintermediates (Morton, A. K., Lanpher, E. J. J. Org. Chem. 1958, 23, 1639- 1642.; Murphy\nJ. A. et al., J. Am. Chem. Soc. 2018, 140, 11510−11518). Given the strongly reducing\nenvironment and elevated temperature (200 °C) in our system, formation of a surface-\nstabilized Na-C H * species is chemically plausible.\n6 5\nImportantly, both experimental and theoretical results support a nucleophilic\n8 / 17\nsubstitution pathway. As shown in Figure 4, the alkylbenzene substrates exclusively yield\nthe corresponding meta-alkylated anilines, rather than ortho- or para-substituted products.\nThis regioselectivity is consistent with nucleophilic attack of electron-deficient sites by\nsurface NH ‾ species, as further supported by the DFT results in Figure S18.\nshown as follows:\nAfter N fixation at the Na-H-Mg interface, benzene preferentially adsorbs at surface\noccurs upon attack by *N species, generating a surface-stabilized absorbed phenyl species\non the Na-cluster surface (denoted as Na-C H *) and Na-NH-Mg species. This step is\n6 5\nsignificantly exothermic (ΔE = −1.00 eV) with a moderate activation energy barrier (E =\na\n0.36 eV), indicating favorable kinetics.\nComment 4. Miscellaneous:\na. Is Na N or Na NH formed? The formation of Na N was reported in JACS 143 69(2020.\n3 3 x 3\nWhy sodium metal cluster are formed?\nResponse: We thank the referee for this thoughtful question regarding the possible\nformation of Na N/Na NH species and the origin of Na cluster.\n3 3 x\nFirstly, for the nature of Na cluster, the precise dispersion state of sodium species is difficult\nto unambiguously resolve using current characterization techniques. Nevertheless, no\nsodium lattice fringes or crystalline particles were detected by STEM or XRD, respectively,\nindicating that sodium is present in a highly dispersed, non-bulk form. Consistently, SIMS\nanalysis reveals Na -Na species, supporting the presence of atomically dispersed or sub-\n1 4\nnanometer sodium clusters rather than bulk metallic sodium. Moreover, our previous\nstudies have shown that alkaline earth or rare-earth metal hydrides tend to disperse on\nMgO as sub-nanostructured species (Guo J. et al., Nat. Commun., 2025, 16, 1, 1868; Guo\nJ. et al., Angew. Chem. Int. Ed., 2025, 64, 50, e202517421). By analogy, sodium species\nformed upon reaction of NaH with MgO are expected to adopt a similarly dispersed\ninterfacial or cluster-like configuration on the MgO surface.\nFor the formation of Na N or Na NH, as noted by the referee, bulk Na N formation\n3 3 3\nfrom Na and N has only been reported under highly non-equilibrium conditions, such as\n2\nplasma-assisted synthesis (see Fischer D. et al., Angew. Chem. Int. Ed., 2002, 41, 10,\n1755-1756; Hosono H. et al., J. Am. Chem. Soc., 2021, 143, 69-72). Under the present\nball-milling and thermal reaction conditions, the formation of bulk Na N is therefore highly\n3\nhard.\nWe have indeed considered the possibility of surface Na-N or Na-NH species. NH\nx x\nspecies coordinated with sodium and magnesium are easily characterized by IR\nspectroscopy (see Figure 2b), whereas direct identification of the surface N species\nremains experimentally challenging. To evaluate whether Na N species form and\nx\nparticipate in C-N coupling, Na/MgO was treated under 30 bar of N at 450 °C and\n2\nsubsequently reacted with benzene. After hydrolysis, negligible amounts of fixed N species\nwere detected, indicating that the formation of Na N under these conditions is highly\nx\nunfavorable. Furthermore, the treated samples exhibited no measurable reactivity toward\n9 / 17\nbenzene and yielded no detectable aniline, demonstrating that such NaₓN species, if\npresent, are not sufficient to enable C-N bond formation.\nb. When Na-anilide is converted into aniline with the reaction with water, the control of\nstoichiometric reaction looks so difficult due to highly active the Na-anilide. Some\ndescription to follow this reaction is required.\nResponse: We thank the referee for the kind suggestion. Indeed, the produced Na-\nanilide salt after reaction was also highly dispersed on MgO surface. Importantly, the\nhydrolysis treatment induces demetalation of the Na-anilide rather than decomposition of\nthe organic products. Taken together, the entire hydrolysis and workup procedure is well\ncontrolled and can be conducted safely. To clarify this point, we have supplemented\nadditional details in the Supplementary Information.\nThe corresponding descriptions in manuscript (Page 14, highlighted in yellow) are\nshown as follows:\n“50 mg of the solid products was hydrolyzed using 2 mL saturated ammonium chloride\nsolution at room temperature, followed by extraction with 2mL of ethyl acetate. Notably,\naniline and other N-containing organics were typically obtained as the sole products after\nthe demetalation treatment. Quantitative analysis of anilines was performed using gas\nchromatography with flame ionization detection (GC-FID) employing dodecane as the\ninternal standard.”\nc. Fig.3 a. Is the sample for the NMR solution?\nResponse: The 1H-NMR spectra in Figure 3a was indeed performed in solution. After\nthe reaction between Na-N-H/MgO and benzene, the residue was dispersed in DMSO-d .\ndirectly recorded by 1H-NMR spectroscopy.\nf. The vertical axis looks incorrect because this is TDS of H .\n3f does not show H -TDS data. Instead, it presents H temperature-programmed reaction\n2 2\n(H -TPR) profiles monitored by online mass spectrometry (MS), during which aniline\n2\nevolution was tracked in the hydrogenation of sodium anilide. Accordingly, the vertical axis\ncorresponds to the MS signal intensity of aniline (Figure R7).\n10 / 17\nFigure R7. H -TPR-MS profiles of Na-N-H/MgO-Fe following reaction with benzene, and of\n2\nas-prepared Na-anilide.\n11 / 17\nReviewer #3 (Remarks to the Author):\nThis manuscript by Guo, Chen and co-workers describes the activation of N and benzene\n2\nand their transformation into aniline derivatives using a NaH/MgO system. One-pot C-N\nbond formation from N and benzene is achieved with NaH/MgO-Fe samples. Mechanistic\n2\ninsights are provided by computational studies, which propose that the activated nitrogen\nspecies deprotonate benzene to form PhNa and -NH species, followed by nucleophilic\nattack of the NH species on the phenyl unit to form C-N bond. The scope of arenes has\n2\nalso been examined using the Na/MgO samples. The chemistry presented in this paper is\nintriguing; however, several issues must be addressed before a decision can be made.\nPlease address the following points.\nResponse: We sincerely thank the reviewer for this kind comment. We are also\nparticularly intrigued by the chemistry underlying the activation of small molecules, such\nas dinitrogen and benzene.\nComment 1. As the authors mention, the presence of transition metals strongly influences\nthe activity of the samples. The sample preparation was carried out using stainless-steel\nor tungsten carbide jars. The authors should instead use a transition metal free jar, such\nas an agate jar etc. for sample preparation.\nResponse: We fully agree with the referee that excluding transition-metal\ncontamination is essential. Initially, control experiments were attempted using agate jars\nwithout introduction of transition metals. However, the agate jars available in our laboratory\ncannot be safely pressurized and exhibit insufficient gas tightness, rendering them\nunsuitable for reactions under high N /H pressure.\n2 2\nTo achieve the N fixation under completely transition-metal-free conditions, we\n2\ntherefore adopted an alternative thermochemical synthesis route. MgO and metallic\nsodium were physically mixed in a quartz linear, and the mixture was reacted at 300 °C\nunder a 30 bar N /H atmosphere in the calcination tube. The resulting solid product was\n2 2\nsubsequently characterized by IR spectroscopy, and its reactivity toward benzene was\nevaluated.\nAs shown in Figure R8a, after reaction under N /H pressure, the IR spectrum exhibits\n2 2\ndistinct NH vibrational bands at 3265, 3220, and 1558 cm-1, which are attributable to the\nx\nsymmetric stretching, asymmetric stretching, and bending modes of NH species,\nx\nrespectively. This result confirms the occurrence of nitrogen fixation in the absence of\ntransition metals. Furthermore, the nitrogen-fixed sample was then reacted with benzene\nat 200 °C. Aniline was detected by GC analysis after hydrolysis, serving as direct evidence\nthat the system enables both nitrogen fixation and C-N bond coupling without the\ninvolvement of transition metals.\n12 / 17\nFigure R8. a) DRIFT spectrum of Na/MgO after nitrogen fixation. b) GC spectrum of the\nproducts after hydrolysis.\nComment 2. Regarding the scope of the alkali metals, combinations such as LiH or BaH\n2\nwith MgO should also be examined.\nResponse: We are thankful to the referee for the constructive suggestion. Beyond\nsodium, we have also extended our investigation to other alkali and alkaline earth metals\nto evaluate their capabilities in nitrogen fixation and C-N bond formation. The results are\nsummarized in Table R1. Li, K, and Ca, alongside Na, were active for C-N coupling. Among\nthem, lithium afforded nitrogen-containing products with a yield of 72 μmol g-1 after nitrogen\nfixation and subsequent reaction with benzene. In contrast, Ba and Mg were inactive, with\nno aniline detected. Among these tested alkali and alkaline earth metals, Na/MgO exhibits\nthe optimal performance. Elucidating the underlying reasons for the distinct behaviors of\nthese metals is part of our future studies.\nTable R1. Various supported alkali and alkaline earth metals mediated C-N coupling\nComment 3. For the characterization of N-H bond stretching vibrations, 15N-labeled and\nD-labeled isotopologues (15N-H and N-D, etc.) should also be prepared and characterized.\nResponse: We thank the referee for this valuable suggestion. To unambiguously\nassign the N-H vibrational features, we performed isotopic labeling experiments using 15N\n2\nor D . Na-N-D/MgO and Na-15N-H/MgO samples were synthesized via ball milling Na and\n2 2 2 2\nsolid samples were collected for further DRIFT characterizations. The vibration frequency\n13 / 17\nin wavenumbers (ν) for a diatomic bond like (N-H, N-D, or 15N-H) in the sample harmonic\noscillator model is:\n1 𝑘\n𝜈 = √\n2𝜋𝑐 𝜇\nWhere: ν is the vibration frequency, c is the speed of light, k is the force constant of\nbond (assumed identical for N-H, N-D and 15N-H), μ is the reduced mass of the bonded\natoms. For a bond A-B, the formula of μ is as follows:\n𝑚 ∙𝑚\n𝐴 𝐵\n𝜇 =\n𝑚 +𝑚\n𝐴 𝐵\nFor N-H, μ =0.933u, μ =1.75u, μ =0.938u. So, the frequency ratio relationships\nNH ND 15NH\nare as follows:\n𝜈(15𝑁−𝐻) 𝜇(𝑁−𝐻)\n=√ =0.997\n𝜈(𝑁−𝐻) 𝜇(15𝑁−𝐻)\n𝜈(𝑁−𝐷) 𝜇(𝑁−𝐻)\n=√ =0.73\n𝜈(𝑁−𝐻) 𝜇(𝑁−𝐷)\nAs shown in Figure R9, Na-N-H/MgO synthesized under N /H atmosphere exhibits\n2 2\nN-H stretching vibration at 3277, 3244, and 3220 cm-1, respectively. Upon replacing 14N\n2\nwith 15N , the corresponding 15N-H stretching bands shift to 3274, 3238, and 3215 cm-1.\nFurthermore, while synthesizing Na-N-D/MgO under N /D atmosphere, distinct N-D\n2 2\nstretching bands are observed at 2410, 2384, and 2350 cm-1, which also closely match the\nvalues calculated from isotopic mass substitution. These observations thereby provide\nstrong and direct evidence that the assigned bands originate from genuine N-H (or N-D)\nvibrational modes.\nFigure R9. DRIFT spectra of samples under different isotopic gas atmospheres.\n14 / 17\nThe related figure and corresponding descriptions are added into Supplementary\nInformation (Page 6) and Revised manuscript (Page 4), respectively:\nIn revised manuscript:\n“Isotope experiments using 15N and D also confirm that these bands can be assigned\n2 2\nto the stretching vibrations of NH (Figure S4)”\nx\nIn Supplementary Information:\n“Figure S4. DRIFT spectra of samples under different isotopic gas atmospheres.”\nComment 4. In the mechanistic studies, I am wondering whether the nucleophilic NH\n2\nspecies attacks the deprotonated C H - unit.\n6 5\nResponse: Yes, according to our proposed mechanism, deprotonation of benzene occurs\non the strongly reducing sodium cluster surface, generating a surface-stabilized phenyl\nspecies (denoted as Na-C H *). Subsequently, the surface NH species formed via\n6 5 2\nhydride-mediated N activation, serves as a nucleophile and attacks the activated phenyl\n2\nintermediate, leading to C-N bond formation.\nComment 5. The DFT calculations should be performed with iron metals included in the\nmodel.\nResponse: We are very thankful to the referee for the constructive suggestion.\nFollowing the reviewer’s suggestion, we explicitly incorporated Fe metal sites into our\nDFT models to evaluate their influence on N fixation and the subsequent C-N bond\n2\ncoupling pathway. Despite the limited revision time, we constructed two representative Fe-\ncontaining models. Specifically, we developed a Fe-Na model by anchoring a single Fe\natom on the Na cluster surface to simulate the reaction microenvironment involving Fe\nactive sites (Figure R10a). In addition, on the other hand, a second structural model with\nFe substituting Mg was also considered to clarify the roles of different Fe incorporation\nmodes (Figure R10b).\n15 / 17\nFigure R10. Structural model of a) a single Fe atom anchored on Na cluster surface. b) Fe-\nsubstituting Mg site. Color scheme: Na, purple; Fe, grey; Mg, green; O, red.\nAs shown in Figure R11, when Fe was anchored on Na cluster surface, the results\nshow that N preferentially adsorbs at the Fe-Na bridge site in a side-on configuration.\nwith ~1.10 Å in gas-phase N , indicating substantial weakening of the N≡N bond. We\n2\nsubsequently examined the direct dissociation pathway of the adsorbed N . This step is\n2\nkinetically accessible with an energy barrier of 1.40 eV, and is thermodynamically favorable,\nbeing exothermic by 1.79 eV. The dissociation yields surface-bound N* species, which can\nbe further hydrogenated to form NH* intermediates that are thermodynamically stable.\nUpon introduction of benzene into the model, benzene preferentially adsorbs at the Fe site\nand undergoes C-H activation, assisted by adjacent N* species, to form a surface-bound\nphenyl intermediate (C H *) along with NH*. Then NH* acts as a nucleophile and attacks\n6 5\nthe C H * intermediate to form the C-N coupling product. This step is only mildly\n6 5\nendothermic, with a reaction energy of 0.13 eV, indicating that C-N bond formation is\nthermodynamically feasible under the reaction conditions.\nSimilarly, when Fe substitutes for Mg, the hydride-mediated N activation pathway is also\n2\npromoted (Figure R12). The calculated endothermicity for the N * → NNH* step decreases\n2\nfrom 1.45 eV to 1.13 eV, indicating a reduced thermodynamic barrier for this key N\n2\nactivation process. The overall pathway of nitrogen fixation and subsequent C-N bond\nformation in this model closely resembles that of the iron-free system. Notably, although\nbenzene deprotonation exhibits a slightly higher activation barrier (1.27 eV) compared to\nthe Fe-free model, the resulting intermediates are thermodynamically more stable. This\nsuggests that Fe incorporation does not alter the fundamental mechanism but provides\nadditional stabilization along the reaction coordinate, rendering the C-N coupling pathway\nthermodynamically more favorable.\nOverall, these results demonstrate that Fe loading markedly improves the kinetic and\nthermodynamic feasibility of the key N activation, thereby promoting nitrogen fixation and\n2\nfacilitating the subsequent hydrogenation/amination steps leading to aniline formation.\nNevertheless, constrained by the available time and computational capacity, the present\nfindings only suggest a possible mechanism. Therefore, the mechanism of iron’s role in\nthe construction of C-N bond will also be the focus of our next research.\n16 / 17\nFigure R11. Free energy diagram of the reaction pathway for the synthesis of aniline from\nN and benzene on Fe-anchored Na /MgO(100) cluster model\n2 4\nFigure R12. Free energy diagram of the reaction pathway for the synthesis of aniline from\nN and benzene on Fe-substituted Na /MgO(100) cluster model\n2 4\nComment 6. ref21 “K. Hori, M. Mori. Synthesis of…”\nResponse: We thank the referee for the careful review. We have carefully reviewed\nthe references and corrected the errors. All changes have been highlighted in yellow in the\nrevised manuscript.\n17 / 17"}, {"round": 2, "reviewer_comments": {"reviewer_1": "Thanks to the authors for the careful revisions and additional experiments. All of my questions and concerns have been fully\naddressed. I recommend acceptance of the manuscript in its present form.", "reviewer_2": "I think most of the version are within the authors' responsibility.\nThe remaining drawback is the title. Hydride-mediated C-N bond formation leads to a possibility of misleading for the\nreaders: Hydrides activates N2 but does not directly contribute to activation of aromatics.\nA title reflecting the real events is required such as \"NaH-activated......\".", "reviewer_3": "The authors have carefully addressed the comments raised by the reviewer and provided additional experimental and\ncomputational data in the revised manuscript. The responses are clear and satisfactory, and the manuscript has been\nimproved accordingly. Therefore, I consider that the concerns have been sufficiently addressed and recommend the\nmanuscript for publication in its present form."}, "author_response": "Responses to Reviewers’ Comments\nReviewer #1 (Remarks to the Author):\nThanks to the authors for the careful revisions and additional experiments. All of my\nquestions and concerns have been fully addressed. I recommend acceptance of the\nmanuscript in its present form.\nResponse: We appreciate the referee very much for the positive recommendation.\nReviewer #2 (Remarks to the Author):\nI think most of the version are within the authors' responsibility. The remaining drawback is\nthe title. Hydride-mediated C-N bond formation leads to a possibility of misleading for the\nreaders: Hydrides activates N but does not directly contribute to activation of aromatics.\nResponse: We understand the consideration from the referee. The original wording\nmay overemphasize a mechanistic aspect, specifically the role of hydride. As noted above,\nthe proposed mechanism represents one plausible pathway and requires further\ninvestigation. Our work is primarily centered on the direct synthesis of aniline from two\nabundant yet inert feedstocks, N and benzene, via a solid-state, surface-mediated\n2\nprocess. To better reflect this key advance, we have revised the title to: “Synthesis of aniline\nfrom dinitrogen and benzene mediated by magnesium oxide supported sodium hydride”.\nWe believe the revised title more accurately captures the core contribution of the work\nwhile avoiding potential overinterpretation of mechanistic aspects.\nReviewer #3 (Remarks to the Author):\nThe authors have carefully addressed the comments raised by the reviewer and provided\nadditional experimental and computational data in the revised manuscript. The responses\nare clear and satisfactory, and the manuscript has been improved accordingly. Therefore,\nI consider that the concerns have been sufficiently addressed and recommend the\nmanuscript for publication in its present form.\nResponse: We appreciate the referee very much for the positive recommendation."}]

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