Metal‐Free Organocatalytic Formylation by CO₂‐Masked Carbene Functionalized Graphene Oxide Nanosheets

Abstract

Despite considerable scientific advancements, there is an urgent need for sustainable, cost‐effective, and efficient methods for chemically transforming CO₂ into valuable chemicals. A stable heterogeneous platform is presented that incorporates four key innovations: 1) the first Tröger's base (TB) chemistry in solids via selective four‐electron reductive functionalization of CO₂, 2) an effective heterogeneous organocatalyst for the chemoselective formylation of both N—H and S—H functionalities with CO₂, 3) a methodology for metal‐free heterogeneous S‐formylation of bioactive thiols, and 4) a direct covalent immobilization of CO₂‐protected N‐heterocyclic carbenes (NHCs) on graphene oxide nanosheets (GONs). The CO₂‐protected catalyst is developed by covalently attaching imidazole (Im) to GONs and functionalizing them with dimethyl carbonate. The resulting CO₂‐protected NHC‐functionalized GONs serves as an effective catalyst for the metal‐free, selective formylation of N—H and S—H bonds under mild conditions. To address gaps in the understanding of TB chemistry in GONs, a metal‐free formylation method is discovered that utilizes an in situ‐generated TB linker produced by converting CO₂ with excess silane. The ability of this catalyst to revert to its CO₂‐protected state enables excellent recyclability. This accessible and efficient platform offers an unprecedented pathway for sustainable CO₂ conversion, supported by both theoretical and experimental evidence.

Here, the authors show the use of an organocatalytic process for the metal‐free N‐/S‐formylation of various N—H and S—H functionalities using a CO₂‐protected NHC‐functionalized graphene oxide nanosheets. The authors discovered the direct N‐formylation of the in situ‐generated Tröger's base linker through reductive catalytic conversion of CO₂.

1. Introduction

Human activities and over‐exploitation of natural resources are relentlessly fueling the emissions of CO₂ in the atmosphere. Carbon dioxide, a well‐known greenhouse gas, is a common waste product, which can act as an inexpensive, abundant, nontoxic, and renewable carbon resource (C1 building block) in organic synthesis for the generation of high value‐added chemicals.^{[ 1} , ² , ^{3 ]} However, the chemical utilization of CO₂ is an uphill task due to its kinetic inertness and thermodynamic stability.^{[ 4} , ^{5 ]} A range of approaches is now urgently needed to avoid the acute environmental impact of the rising concentration of CO₂, which will ultimately lead to climate change.

There are two main routes available to utilize CO₂ effectively, one is its reduction to useful products, such as formic acid, methanol, methane, and so on, and the other one is the functionalization of CO₂ to yield products like cyclic carbonates, polycarbonates, urea, and so on. However, it is to be noted that neither the functionalization nor the reduction alone can satisfy the feedstock of fine petrochemical production. To fill this gap, methods which involve simultaneous reduction and functionalization of CO₂ are needed. Along this line, reductive functionalization of CO₂ was first introduced by Cantat et al. as the “diagonal transformation” (Figure S1, Supporting Information)^{[ 6 ]} and the effective use of this methodology can yield various energy‐storage materials and value‐added chemicals.^{[ 7} , ⁸ , ^{9 ]} Hydrosilylation of CO₂ is one such process, which benefits from the energetically easier addition of Si—H than a H—H bond to CO₂ and the formation of a diverse products with various carbon oxidation states, such as methoxysilanes, silyl formates, methane, and silyl acetals.^{[ 10} , ^{11 ]}

Graphene oxide nanosheets (GONs) have excellent physical and chemical characteristics, like outstanding mechanical strength (130 GPa); great mobility for charge carriers (2 × 10⁵ cm² V⁻¹ s⁻¹); high surface area (≈2600 m² g⁻²); good electrical conductivity; and optical, thermal, and absorption features. Graphene/GO‐based composites are used for multiple applications, like supercapacitors, electrocatalysts, batteries, fuel cells, catalysis, electronic devices, and so on.^{[ 12} , ¹³ , ^{14 ]} Such materials are extensively used as excellent carbon support systems for the generation of nanocatalysts to access the expected stability and performance. GO possesses excellent capability to get anchored by diverse catalytically active species due to the presence of several polar functional groups on the GONs, like basic and acidic functional groups.^{[ 15} , ¹⁶ , ^{17 ]} On the contrary, azolium salts are well‐known to serve as a precursor for N‐heterocyclic carbene (NHC), which finds diverse applications in various fields, like organocatalysis, homogeneous metal‐based catalysis, organometallic chemistry, and so on, because of their strong σ‐donating nature.^{[ 18} , ^{19 ]} Thus, we wondered if the CO₂‐protected NHC‐functionalized GONs could be constructed through a post‐synthetic functionalization of ImGONs with dimethyl carbonate (DMC) for the applications in heterogeneous metal‐free catalytic transformations. The formation of functionalized GO (ImGONs) could be obtained by conducting a simple ring opening of oxirane units on the synthesized GONs. The successful covalent immobilization of the imidazolium units in 1‐(3‐aminopropyl)imidazole onto the GONs surface can be achieved in the presence of 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC) and N‐hydroxysuccinimide (NHS).

Given the toxicity and low‐abundance of transition metals, there is a high demand for the development of metal‐free catalytic systems for the reductive functionalization of CO₂. Along this line, various metal‐free methods for the N‐formylation of amines using carbon dioxide and silane^{[ 20} , ²¹ , ²² , ²³ , ²⁴ , ²⁵ , ^{26 ]} or other reducing agents^{[ 27} , ^{28 ]} have been gradually yet consistently developed in the last few years and NHCs have shown significant promises in this area.^{[ 20} , ²⁹ , ^{30 ]} In this direction, Cantat et al. introduced the first metal‐free platform, a nitrogen‐containing base (1,5,7‐Triazabicyclo[4.4.0]dec‐5‐ene, TBD) as catalyst and silane as a reducing agent, for this reaction.^{[ 6 ]} However, this process requires a very high temperature of 100 °C. To overcome that, the same group utilized an NHC‐based system for the synthesis of formamides from CO₂ and amines at room temperature.^{[ 31 ]} Mandal and coworkers demonstrated some efficient homogeneous catalysts for the N‐formylation of amides under ambient conditions.^{[ 32} , ³³ , ^{34 ]} Intersetingly, this formylation approach generates a new C—N linkage and can be employed in producing core moieties of diverse natural products, such as lansiumamide A and alatamide.^{[ 32 ]}

Recently, an efficient homogeneous organocatalyst for the S‐formylation of thiols using CO₂ and hydrosilane under ambient conditions has been demonstrated (Figure  1E).^{[ 35 ]} However, such methods also have major drawbacks, as homogeneous catalysts are difficult to separate, recover, recycle, and limiting their use. To tackle such challenges, scientific communities have adopted the approach of heterogenizing the homogeneously active catalytic system.^{[ 36 ]} Zhang and coworkers established an elegant approach for the metal‐free reductive conversion of CO₂ using a poly‐NHC‐containing heterogeneous catalytic system, and it is more advantageous to employ this solid recyclable organocatalyst over its homogeneous one because of simplicity, easy purification of the desired product, and separation during the catalyst recycling process. ^[36a] Fei's group first introduced a metal‐free NHC‐based metal–organic framework (MOF) UiO‐68‐NHC by conducting post‐synthetic ligand exchange technique for the reductive conversion of CO₂ with hydrosilane. The most significant positive aspect of this system is the existence of NHC units, which displayed superior CO₂ uptake when compared with pristine UiO‐68.^{[ 37 ]} Some research groups have made an advancement in enabling the formylation of N—H functionalities using CO₂ and hydrosilane by employing efficient heterogeneous catalysts (Figure 1A,B).^{[ 38} , ^{39 ]}

Figure 1.

Background and motivation of reductive functionalization of CO₂. a,b) Previous reports on the catalytic formylation of N—H and S—H functionalities using hydrosilane. c) Our work on heterogeneous organocatalytic formylation of amines, amides, hydrazines, hydrazides, and thiols at ambient conditions.

Inspired by these recent advances, Cao, Huang and coworkers established an unprecedented approach for the facile synthesis of methanol and formamide via hydrosilylative CO₂ reduction using CO₂‐protected NHC‐based covalent organic framework (COF) (Figure 1C).^{[ 40 ]} Recently, Bhaumik and coworkers reported metal‐free activation of CO₂ using NHC‐embedded porous organic hollow nanofibers, which displayed outstanding catalytic activity for the metal‐free N‐formylation reaction (Figure 1D).^{[ 41 ]} Unfortunately, their developed protocols work under harsh conditions, such as extreme temperatures and the use of high‐risk solvents (e.g., N,N‐dimethylformamide [DMF]). This shortcoming needs to be addressed by introducing heterogeneous NHC‐based GONs for the metal‐free reductive conversion of CO₂, in which catalytic activity of the organocatalyst will be retained after repeated use, and this strategy will work under very mild conditions (e.g., solvent‐free, base‐free, atmospheric pressure).

In pursuit of a sustainable and efficient heterogeneous platform, we demonstrate the synthesis and complete characterization of CO₂‐protected NHC‐functionalized graphene oxide nanoparticles. This is accomplished through a post‐synthetic functionalization of ImGONs with DMC. The CO₂‐protected NHC‐functionalized GONs (ImNHC‐CO₂‐GONs) has the remarkable capability of displaying excellent performance on the formylation of diverse N—H/S—H functionalities, such as amines, amides, hydrazines, hydrazides, thiols, and Tröger's base (TB)‐linker containing endomethylene strap under ambient conditions (1 atm. pressure, solvent‐free, and base‐free, Figure 1). It is found to be inexpensive, ecofriendly, and recyclable over five runs without loss of its catalytic performance. Related tests and density functional theory (DFT) calculations are used to explore the reasons behind the high selectivity. This research opens a route for NHC‐functionalized GONs as an intriguing platform to control chemoselective catalysis.

2. Results and Discussion

This study aims to develop an effective platform for converting CO₂ into valuable chemicals. We achieve this through four innovations: 1) the application of TB chemistry in solids through the selective four‐electron reductive functionalization of CO₂, 2) the use of a heterogeneous organocatalyst for the chemoselective formylation of both N—H and S—H functionalities with CO₂, 3) a methodology for metal‐free heterogeneous S‐formylation of bioactive thiols, and 4) a direct covalent immobilization of CO₂‐protected NHCs onto GONs.

2.1. Synthesis and Characterization of Graphene Oxide‐Based Materials

We synthesize three materials, graphene oxide (GO), 1‐(3‐aminopropyl)imidazole functionalized (ImGONs), and CO₂‐protected NHC‐functionalized GONs (ImNHC‐CO₂‐GONs). We synthesize GO by oxidizing graphite powder. We synthesize ImGO by covalent functionalization of 1‐(3‐aminopropyl)imidazole with the epoxide and carboxylic acid functional groups present in GO via amine and amide linkage generation (Figure  2a). We characterize ImGONs and ImNHC‐CO₂‐GONs by several common analytical techniques such as powder X‐ray diffraction (PXRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), field emission scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy, thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), Fourier‐transform infrared spectroscopy (FT‐IR), ultraviolet–visible (UV–Vis) spectroscopy, cross polarization/magic angle spinning nuclear magnetic resonance (solid‐state 13C CP/MAS NMR spectroscopy) and so on. We conduct elemental analyses for the GO and functionalized GONs (for GO, H: 2.4%, C: 53.1%, N: 0.03%; for ImGONs, H: 3.6%, C: 67.7%, N: 9.8%). The existence of nitrogen in ImGONs suggests the successful covalent immobilization of the imidazolium units in 1‐(3‐aminopropyl)imidazole onto the GO surface.

Figure 2.

Structural characterizations of graphene oxide‐based materials. a) The schematic illustration for the synthesis of CO₂‐masked NHC‐functionalized GONs (ImNHC‐CO₂‐GONs). b) PXRD patterns of GO, ImGONs, and ImNHC‐CO₂‐GONs. c) N₂ sorption isotherms of ImGONs, ImNHC‐CO₂‐GONs, and recovered ImNHC‐CO₂‐GONs at 77 K. d) Pore‐size distribution profile of ImGONs, calculated using the QSDFT. e) N₂ sorption isotherm of ImNHC‐GONs upon exposure to air in the absence of CO₂. f) Pore‐size distribution profile of ImGONs, calculated by using BJH method. g) Pore‐size distribution profile of ImNHC‐CO₂‐GONs, calculated by employing BJH method.

Determining the nitrogen content in the functionalized GO is essential for comprehensively quantifying the functional groups attached to GO. The nitrogen content in ImGONs is measured at 9.8%, corresponding to 7 mmol g⁻¹ nitrogen content, which accounts for 2.3 mmol g⁻¹ of 1‐(3‐aminopropyl)imidazole functionalized to GO, as each molecule contains three nitrogen atoms. Figure 2b displays the XRD patterns of GO, ImGONs, and ImNHC‐CO₂‐GONs. The conversion of graphite to graphene oxide (GO) results in a notable shift in the diffraction peak to 11.8° in 2θ, which corresponds to an interlayer spacing (d₀₀₁) of 0.75 nm. This increase in interlayer spacing suggests the effective introduction of oxygen groups between the layers, leading to a more loosely stacked arrangement of the GO sheets. Upon functionalizing GO with 1‐(3‐aminopropyl)imidazole, the 001 diffraction peak shifts to 11.9° in 2θ, resulting in an interlayer spacing (d₀₀₁) of 0.74 nm. This change is accompanied by the appearance of a new broad diffraction peak at 23.0° in 2θ, caused by the (002) plane, highlighting the amorphous characteristics due to the random arrangement of the functionalized GO sheets. Similarly, ImNHC‐CO₂‐GONs displays a 001 diffraction peak located at around 11.8° in 2θ, indicating an interlayer spacing of 0.75 nm. It also demonstrates a new broad diffraction peak centered at 23.0° in 2θ, confirming a random arrangement of the ImNHC‐CO₂‐GONs sheets.^{[ 42 ]}

The presence of mesopores is effectively demonstrated by the N₂ adsorption–desorption isotherms (Figure 2c), which exhibit IV isotherms featuring an H3 hysteresis loop. This observation highlights the typical mesoporous structure of functionalized GO‐based materials.^{[ 43 ]} ImGONs exhibit a BET surface area of 472.1 m² g⁻¹ and pore volume of 0.274 cm³ g⁻¹, while ImNHC‐CO₂‐GONs and recovered ImNHC‐CO₂‐GONs show surface areas of 381.2 and 329.9 m² g⁻¹, respectively. These findings underscore the significant structural differences and potential applications of these materials. The porous property of unstable ImNHC‐GONs (upon exposure to air without maintaining a CO₂ atmosphere after the reaction) is also assessed by N₂ adsorption isotherms measured at 77 K. The ImNHC‐GONs displays a typical Type‐IV behavior, reflecting its dominating mesoporous character (Figure 2e). Further, we evaluate the pore size distribution of ImGONs by the quenched solid‐state functional theory (QSDFT) cylindrical pore model, which displays an obvious distribution peak at 2.8 nm (Figure 2d). Figure 2f presents the pore size distribution of ImGONs calculated using Barrett–Joyner–Halenda (BJH) method, exhibiting a distribution peak at around 3.1 nm. Figure 2g illustrates the pore size distribution of ImNHC‐CO₂‐GONs, assessed using BJH method. The data reveals a significant distribution peak at around 1.9 nm, which provides valuable insights into the material's structural characteristics. This considerable decrease in pore volume and surface area for ImNHC‐CO₂‐GONs (0.203 cm³ g⁻¹ and 381.2 m² g⁻¹, respectively) relative to ImGONs (0.274 cm³ g⁻¹ and 472.1 m² g⁻¹, respectively) can possibly be ascribed to the presence of carboxylate units in ImNHC‐CO₂‐GONs.^{[ 40 ]} Additionally, the surface area of the ImNHC‐CO₂‐GONs drops due to pore blockage in ImGONs after the treatment with DMC. Further, the structural collapse during the course of C‐carboxylation reaction can be a possibility for decreased surface area, and fortunately, it does not happen in this case, as evident from the PXRD results of ImGONs and ImNHC‐CO₂‐GONs (Figure 2b).

The morphological features of the synthesized imidazole‐decorated GONs and CO₂‐masked NHC‐functionalized GONs are then elucidated by TEM and SEM. In order to determine the structural features, morphological (internal morphology) and topographical information of functionalized GO‐based materials, high resolution TEM is used after the treatment of ultrasonic stripping. As shown in Figure  3a, ImGONs displayed a lamellar morphology, and this lamellar morphology is further confirmed by the SEM image (Figure 3c). Importantly, the selected area electron diffraction (SAED) pattern (Figure 3b), having clearly visible electron‐diffraction spots, suggests the presence of the GO, supporting the experimental PXRD data. The SEM image (Figure 3d) of the ImNHC‐CO₂‐GONs displays no noticeable change for the morphology when compared to ImGONs (Figure 3c), which is in line with TEM image of ImNHC‐CO₂‐GONs (Figure 3e).

Figure 3.

Structural characterizations of graphene oxide‐based materials. a) TEM image of ImGONs. b) SAED pattern of ImGONs. c) SEM image of ImGONs. d) SEM image of ImNHC‐CO₂‐GONs. e) TEM image of ImNHC‐CO₂‐GONs. f) Structure of ImNHC‐CO₂‐GONs with top view and side view (made in BIOVIA Material Studio). g) The deconvoluted XPS spectra of C1s (ImNHC‐CO₂‐GONs). h) The deconvoluted XPS spectra of N1s (ImGONs). i) The deconvoluted XPS spectra of N1s (ImNHC‐CO₂‐GONs). j) The deconvoluted XPS spectra of O1s (ImNHC‐CO₂‐GONs). k) TGA of ImGONs.

Next, the XPS is employed to elucidate the surface properties and the interaction between the constituted components in the GONs. The XPS C1s spectrum of ImNHC‐CO₂‐GONs (Figure 3g) can be well deconvoluted into five components at 284.5 eV (assigned to the C=C and C—C bonds), 285.3 eV (assigned to the C—N and C—O bonds), 286.2 eV (assigned to the sp² hybridized carbon of —C=N fragment), 287.2 eV (assigned to the O=C—N bonds), and 288.7 eV (assigned to the O—C=O of imidazolium carboxylate).^{[ 44 ]} Therefore, the XPS C1s spectrum of ImNHC‐CO₂‐GONs confirms the successful post‐synthetic modification of ImGONs in the presence of dimethyl carbonate (DMC). Moreover, the high‐resolution XPS N1s spectrum of ImGONs exhibits two subpeaks with binding energies of 399.7 and 401.6 eV (Figure 3h).

The peak located at 399.7 eV is assigned to the nitrogen atoms of amides, whereas the peak at 401.6 eV is ascribed to the imidazole nitrogen atoms.^{[ 45 ]} Interestingly, the high‐resolution XPS N1s spectrum of ImNHC‐CO₂‐GONs also exhibits two subpeaks with binding energies of 399.8 and 401.9 eV (Figure 3i). The XPS N 1s spectra of ImGONs and ImNHC‐CO₂‐GONs (Figure 3h,i) confirm that the N‐atoms in ImNHC‐CO₂‐GONs show a positive displacement by 0.3 eV (peak at 401.9 eV assigned to imidazolium nitrogen species) when compared to that of ImGONs,^{[ 40} , ^{46 ]} supporting the formation of a stable imidazolium carboxylate upon the exposure of ImGONs to DMC. The XPS O1s spectrum of ImNHC‐CO₂‐GONs exhibits a peak centered at 533.8 eV, confirming the presence of a reasonably stable imidazolium carboxylate in ImNHC‐CO₂‐GONs, as shown in Figure 3j.^{[ 40 ]} Further, the thermal stability of the synthesized ImGONs is assessed by TGA at the temperature range 30–900 °C (Figure 3k), which reveals that ImGONs is thermally stable up to 550 °C. Atomic force microscopy is used to study the thickness of GO‐based materials (Figure S141, S142, and S143, Supporting Information).

2.2. Reaction Development and Scope

After conducting through characterization of the CO₂‐protected NHC‐based GONs, its catalytic performance is evaluated with CO₂‐to‐formamide conversion under very mild reaction conditions. Consequently, at the outset, we use ImNHC‐CO₂‐GONs as an organocatalyst for the N‐formylation of 1a (model substrate) using PhSiH₃ as a hydride source (Table S1, Supporting Information) and to our delight, 99% isolated yield of the expected product formanilide (2a) is attained when we carry out the reaction in acetonitrile at 60 °C for 24 h (entry 3, Table S1, Supporting Information). Nevertheless, to our surprise, the ImNHC‐CO₂‐GONs catalyst delivers the expected formanilide (2a) in 99% under the CO₂ atmosphere (1 bar) and solvent‐free conditions, revealing its excellent performance even without the use of solvent (entry 1, Table S1, Supporting Information). Furthermore, the formylation of N—H bonds was greatly affected by the reaction time and reaction temperature; higher temperature (60–80 °C) has a significant positive impact on the catalytic outcome, yielding 2a in higher yields (99%, entries 1 and 13, Table S1, Supporting Information).

Extending the reaction time promotes the N‐formylation reaction and improves the conversions and yields (entries 10, 11, 20, and 21). Among various hydrosilanes examined, PhSiH₃ is observed to be the most appropriate hydride source for the reaction (Table S1, Supporting Information). Under the same reaction conditions, more sterically congested hydrosilane, like Ph₂SiH₂, is found to be less effective (Table S1, Supporting Information, entry 4). In the presence of polymethylhydrosiloxane (PMHS), the expected formanilide (2a) is not achieved (Table S1, Supporting Information, entry 14). Among various hydrosilanes, PhSiH₃ (the most typical primary silane) is most effective. Alkyl silane or alkoxysilane, such as diethylsilane, triethylsilane, methyldiethoxysilane, trimethoxysilane or triethoxysilane, is found to be inactive for the reaction. Siloxane, such as 1,1,3,3‐tetramethyldisiloxane, is noted to be inactive for this transformation. The lowering of the reaction rate observed with Ph₂SiH₂ supports the calculated S_N ²‐type mechanism for the reduction of CO₂ with silicon hydride. The steric congestion caused by another phenyl ring hinders nucleophilic attack by the anion on the Si center and prevents its activation. We examine various solvents for the N‐formylation reaction and aprotic polar solvents, like MeCN, DMF, or DMSO, are detected to be appropriate, yielding the desired product in excellent yield (entries 3, 5, and 6), while THF serves as an inferior solvent (entry 7). Therefore, the best outcome is achieved when we perform the reaction under solvent‐free conditions at 60 °C using PhSiH₃ as a hydride source. More screening parameters are summarized in the Supporting Information.

Under the optimized conditions, we expanded the reaction scope to a series of amines and a simple summary is provided in Table  1 . The substrates containing electron‐donating and ‐withdrawing functional groups at all the positions (ortho‐, meta‐, and para‐) on the benzene ring (2b–n and 2r–u) are all tolerated, providing the desired N‐formylated products in 51%–96% yields, which offer an opportunity for further exploration. Nevertheless, the substrates containing strongly electron‐withdrawing functional groups, such as NO₂ and CN, at para‐ or ortho‐position afford the corresponding products in comparatively lower yields (2d and 2n, 51%–56%), consistent with the lower nucleophilic nature of the amine systems. It is reported that less nucleophilic substrate 4‐nitroaniline (1d) fails to deliver the desired formylated product (2d, yield <0%) by employing TBAF·3H₂O (higher catalyst loading, 10 mol%) as a catalyst under 1 bar CO₂ pressure at room temperature, whereas our catalytic system displays good performance for 1d, providing facile access to the corresponding product (2d) in 56% yield.^{[ 22 ]}

Table 1.

Metal‐Free catalytic N‐formylation of amines with CO₂.^a)

^a)Reaction conditions: catalyst ImNHC‐CO₂‐GONs (30 mg), amine (0.3 mmol), PhSiH₃ (0.6 mmol, 2 equiv. of “Si—H” relative to amines), 1 bar CO₂, 60 °C, 24 h. All are isolated yields. ^b)PhSiH₃ (1.2 mmol).

It should be noted that the reductive dehalogenation is not detected for halogen‐substituted amines. It is worth mentioning that aliphatic primary amines like the (substituted)benzyl amines and cyclohexylamine are also observed to be compatible with the developed protocol, delivering the corresponding formamides in 65%–79% yields (2o‐q and 2f’). Inspired by these obtained results, we next turn to explore the reaction of heterocycles. Notably, the primary amines containing heterocycles including pyridine and quinoline are also suitable substrates and afford the desired formamides in good yields (62%, 2z and 66%, 2y). Specifically, in the case of diamines such as the clinically important drug Dapsone,^{[ 47 ]} both the amine functional groups are monoformylated to deliver the diformylated products (2a’, 2b’, and 2d’) in >60% yields. We detect that our catalytic system has a great influence on chemoselectivity. More interestingly, ImNHC‐CO₂‐GONs can promote chemoselective formylation of 1a’’ containing both primary and secondary amines to access 2a’’ with high yield (84%) keeping the secondary amine moiety intact, in which the primary amine is selectively monoformylated, although less nucleophilic than the secondary one. Reductive cyclization of o‐diamine derivatives leads to benzimidazole systems having biological and pharmacological activities.^{[ 48 ]} More interestingly, the o‐diaminobenzene delivers benzimidazole (2c’) in 74% isolated yield via reductive cyclization, while the 2,3‐diaminopyridine (1e’) is an unreactive substrate.^{[ 38 ]} Moreover, unprotected carboxylic acid is tolerated under the same reaction conditions, providing an opportunity for further elaborations, and the reaction of 3,4‐diaminobenzoic acid provides 5‐benzimidazolecarboxylic acid (2c’’) in 71% yield. Additionally, the cyclic secondary amines (for example, 1f’) yield the desired N‐formylated products (2f’) in good yields, whereas a similar kind of synthetic protocol was previously reported by using glycine betaine (GB; 1‐carboxy‐N,N,N‐trimethylmethanaminium inner salt) as a metal‐free catalyst system under 10 bar CO₂ pressure at 50 °C with diphenylsilane in moderate yield of about 41%.^{[ 24 ]}

We explore the reaction of the secondary amines and the desired N‐formylated products (2g’–l’) are delivered without the generation of any byproduct like the corresponding N‐methylated products. Cyclic amines, for example, 1‐(‐2‐pyrimidyl)piperazine and pyrrolidine, are readily N‐formylated to the desired formamides (2g’: 82%; 2h’: 72%), however, imidazole is noted to be unreactive (2n*). Additionally, the acyclic aliphatic and aromatic secondary amines including the sterically crowded ones, such as diisopropylamine, N‐methylaniline, and diphenylamine, deliver the formylated products in good yields (2i’‐2l’, 59%–71%). It should be noted that a synthetic protocol for the generation of 2j’ is previously developed by employing lecithin as proficient organocatalyst at 5 bar CO₂ pressure, and unfortunately, the methodology is unsuccessful, while our greener approach affords the desired 2j’ in good yield (71%) under very mild conditions.^{[ 26 ]} Overall, a wide variety of reactive functional groups, such as ether (2v), —O₂ (2d/2i), —CN (2n), —SO₂ (2a’), and even the very reactive —OH (2m’), are all tolerated in the N‐formylation reaction under the reaction conditions, offering an opportunity for further elaborations, which establishes the potential of our present catalytic systems.

We also explore the N‐formylation reaction of various amides using CO₂, however, the methodology is comparatively difficult than amines as amides having pKa ≈−0.5 have lesser nucleophilic nature due to the conjugation of the carbonyl (—C=O) group with nitrogen lone pair in amide system. Nevertheless, inspired by the previous reports,^{[ 32} , ^{49 ]} we further explore the metal‐free N‐formylation of amides, and benzamide (3a) is selected as a model substrate for the optimization study. A simple summary of our optimization study with a selected set of amides is provided in Table S2, Supporting Information. Pleasingly, our present ImNHC‐CO₂‐GONs after treatment with PhSiH₃ under solvent‐ and base‐free conditions delivers the corresponding monoformylated product 4a (59%) in 12 h at 60 °C (entry 2, Table S2, Supporting Information), which is further increased to 72% by prolonging reaction time to 24 h (entry 3, Table S2, Supporting Information). Nevertheless, the ImGONs is inactive for the synthesis of formylated product (entries 9 and 10, Table S2, Supporting Information), which further demonstrates that the carbon center present in a —CHO moiety comes from CO₂.

With the optimized reaction conditions in hand, we set out to explore the scope of N‐formylation reaction of various amides (Table  2 ). Interestingly, as depicted in Table 2, a variety of substituents on the aromatic ring, both electron‐releasing (e.g., methoxy, 3b,e) and electron‐withdrawing (e.g., chloride, 3c), are well tolerated so that the corresponding formylated products 4b,c, and 4e can be isolated in good yields (63%–69%). We investigate the strongly electron‐withdrawing para‐nitro‐substituted benzamide (3d) and heterocycle containing amide like nicotinamide but unfortunately fail to deliver the corresponding formylated products (4d and 4f) under the optimized conditions. Moreover, different types of N—H functionalities, like hydrazines or hydrazides, are formylated effectively employing our metal‐free catalytic protocol resulting in the monoformylated products in good yields (4g‐j, 62%–73%). Furthermore, Li and coworkers reported the use of DMSO as an efficient metal‐free catalyst to generate the compound (4i) in lower yield, whereas our metal‐free system offers superior results (i.e., 73% isolated yield).^{[ 23 ]} Pleasingly, for the substrate having both amine and amide groups, only amine group is chemoselectively formylated keeping the amide unit intact and the desired product (4k) is isolated in 71% yield. Interestingly, our developed organocatalyst is capable of formylating the amine moiety selectively keeping ortho‐amide group (4L, 56%) unaffected.

Table 2.

Scope for the metal‐free formylation of diverse NH₂ functionalities using in situ generated CO₂.^a)

^a)Reaction conditions: catalyst ImNHC‐CO₂‐GONs (30 mg), amide/hydrazine/hydrazide (0.3 mmol), PhSiH₃ (0.6 mmol, 2 equiv. of “Si—H” relative to NH₂ functionalities), 1 bar CO₂. All are isolated yields. ^b)PhSiH₃ (1.2 mmol).

Inspired by these obtained outcomes, we set out to explore the scope of the metal‐free S‐formylation reaction of diverse thiols (Table  3 ). The S‐formylation of thiols plays a vital role in numerous essential biological processes.^{[ 35 ]} Upto now, there has been a lack of any heterogeneous catalytic chemical process for this biologically significant transformation. Benzyl thiols with electron‐donating groups at the para position of the phenyl ring yield the corresponding S‐formylated products with high yields (6a, 88%), as detailed in Table 3. The heteroaryl benzyl thiols, such as furan‐2‐ylmethanethiol (5c) and thiophen‐2‐ylmethanethiol (5d), reliably produce excellent yields of the corresponding S‐(furan‐2‐ylmethyl) methanethioate (6c) and S‐(thiophen‐2‐ylmethyl) methanethioate (6d) under the optimized reaction conditions, with impressive results of 91% and 93% for 6c and 6d, respectively (Table 3). Moreover, we thoroughly examine the chemoselectivity of our current approach for the S‐formylation of thiols that contain reducible groups, such as —CN. The substrate (5b) effectively produces the desired S‐formylated thiols (6b) with 69% yield while maintaining the integrity of the —CN group. The cyclic thiol (6e) shows interesting result with 52% isolated yield under our reaction protocol. 2‐Phenylethane‐1‐thiol (5f) and 2‐(pyrazin‐2‐yl)ethane‐1‐thiol (5g) are successfully transformed into the formylated products with high yields of 90% (6f) and 82% (6g), respectively, as detailed in Table 3. Interestingly, we are able to convert the thiol (5i) derived from natural terpenoid into the corresponding formyl product with good yield of 79% (6i), as described in Table 3. In addition, we successfully synthesize the S‐formyl derivative of α‐tocopherol (vitamin E), 6j, achieving 92% yield under metal‐free conditions (Table 3).

Table 3.

Scope for the metal‐free S‐formylation of thiols using in situ generated CO₂ ^a).

^a)Reaction conditions: catalyst ImNHC‐CO₂‐GONs (30 mg), thiol (0.3 mmol), PhSiH₃ (0.6 mmol, 2 equiv. of “Si—H” relative to thiols), 1 bar CO₂. All are isolated yields.

On the contrary, Farha, Cui and coworkers introduced TB chemistry in solution and in Zr(IV)‐containing MOFs.^{[ 50 ]} Motivated by the in situ strap elimination and formylation of the dicarboxylate‐functionalized TB linker (H₂L) facilitated by the presence of formic acid in solution, we decide to explore this intriguing chemistry within solid‐state material, focusing specifically on NHC‐based GONs. This research holds the potential to uncover new insights and applications in the field. Most interestingly, the overlooked strap‐clipped TB chemistry in functionalized GONs has left a gap in our knowledge. We have made a promising discovery involving a novel formylation of the in situ‐generated TB linker through the reductive conversion of CO₂ using excess silane (Figure  4c). This finding opens new avenues for enhancing our understanding in this field.

Figure 4.

a) TB chemistry in solution, b) Zr(IV)‐based MOFs, and c) CO₂‐masked NHC‐containing GONs. ^aReaction conditions: catalyst ImNHC‐CO₂‐GONs (30 mg), p‐aminoethylbenzoate (0.6 mmol), PhSiH₃ (10.2 mmol, 17 equiv. of “Si—H” relative to p‐aminoethylbenzoate), 1 bar CO₂. All are isolated yields.

2.3. Mechanistic Investigations

In order to gain more insights into the mechanism of the metal‐free formylation of N—H and S—H functionalities using in situ generated CO₂, we design several control experiments and detailed computational studies. Understanding the mechanistic routes of the metal‐free N‐formylation reaction facilitated by NHC is crucial from the viewpoint of its application in developing other synthetic protocols. Keeping the ImGONs structure in mind, a monomeric fragment (5a’) is synthesized in order to comprehend the role of the actual catalytic system, which is easier to understand at a molecular level. Accordingly, the corresponding NHC‐CO₂ adduct (6a) is synthesized through functionalization of 5a’ with DMC (Figure  5a) and it was characterized by liquid‐state nuclear magnetic resonance (NMR) spectroscopy (δ = 163.0 ppm for the carboxylate C=O moiety) and high‐resolution mass spectrometry (HRMS, see Supporting Information). Similarly, the reaction between the ImGONs and DMC in the absence of base is carried out and the generation of an NHC‐CO₂ adduct is confirmed by the CO₂ temperature‐programed desorption data (CO₂‐TPD), ¹³C CP/MAS solid‐state NMR, XPS, and FT‐IR spectroscopy (Figure 5b).

Figure 5.

Control experiments for the reaction mechanism.

In the ¹³C solid‐state NMR spectrum of the obtained compound, a new peak centered at around δ = 166 ppm can be assigned to the carboxylate C=O moiety of the generated NHC‐CO₂ adduct in addition to a peak located at around δ = 175 ppm (also appears for the starting ImGONs) corresponding to the carbon atoms of amide functional groups present in the GONs backbone (Figure  6a).^{[ 36 ]} The NHC‐CO₂ adduct in ImNHC‐CO₂‐GONs is confirmed by a peak at 1669 cm^{− 1}, which shows the stretching vibration of the COO⁻ group (Figure 6b). We also confirm the presence of NHC‐CO₂ adduct in ImNHC‐CO₂‐GONs using CO₂‐TPD. This data illustrates how CO₂ is released from ImNHC‐CO₂‐GONs as the temperature changes.

Figure 6.

a) ¹³C CP‐MAS NMR spectra of ImGONs and ImNHC‐CO₂‐GONs adduct. b) FT‐IR spectra of GO, ImGONs, and ImNHC‐CO₂‐GONs adduct. c) CO₂‐TPD profiles of ImGONs and ImNHC‐CO₂‐GONs. d,e) The ¹³C{¹H} and ¹H NMR spectra of the reaction mixture, in which the reaction of aniline with 6a (10 mol%) under CO₂ atmosphere at 120 °C lead to the generation of formoxysilane. f) The reaction of aniline with 6a (10 mol%) in which color change is accompanied.

As shown in Figure 6c, there is a peak around 160 °C that indicates CO₂ is released from ImNHC‐CO₂‐GONs. In contrast, we do not detect a CO₂ peak for the parent ImGONs. To confirm the participation of such NHC‐CO₂ adduct in the catalytic cycle, a standard aniline N‐formylation reaction was performed using 6a as catalyst and gratifyingly, the desired product 2a was obtained in 42% yield (Figure 5c), supporting the involvement of such species in the present catalytic process. We then react the ImNHC‐CO₂‐GONs adduct with Ph₂SiH₂ in the absence of CO₂ in CD₃CN and monitor the resulting reaction mixture using ¹H and ¹³C{¹H} NMR spectroscopy. A singlet centered at δ = 8.17 ppm (¹H NMR, Figure S129, Supporting Information) and a peak at around δ = 163.0 ppm (¹³C{¹H} NMR, Figure S130, Supporting Information) are indicative of a —CHO moiety of formoxysilane (Figure 5d) as described in the literature.^{[ 32} , ⁵¹ , ^{52 ]}

Following the reaction of aniline with 6a (10 mol%) under CO₂ atmosphere, NMR analysis reveals two new ¹H NMR signals (singlets) located at 8.70 and 7.95 ppm (Figure 6e). These signals are attributed to C2‐H of the imidazolium cation and N—H of the carbamate anion, respectively. Furthermore, a ¹³C{¹H}NMR resonance centered at around 163.3 ppm (Figure 6d), corresponding to C=O of a carbamate moiety, is observed. These findings strongly support the formation of a carbamate complex in the reaction mixture, resulting from the coupling of aniline and CO₂ (Figure 6f). The high‐resolution mass spectrometry (HRMS) coupled with electrospray ionization also endorsed the presence of a carbamate moiety and azolium unit (Figure S140, Supporting Information), establishing our detailed theoretical studies, which suggested the activation mode E (Figure  7e) that proceeds through the [NHCH]⁺[carbamate]⁻ intermediate as the most favorable pathway. These observations indicate that the NHC carbene carbon does not interact directly with the Si atom of hydrosilane rather the in situ‐generated NHC center reacts with free amine and CO₂ to form the carbamate complex, [NHCH]⁺[Carbamate]⁻, the key catalytic intermediate. Further, the catalytic activities of the related one or two catalytically active site containing imidazolium carboxylates (6a and 6b) are compared with our heterogeneous ImNHC‐CO₂‐GONs catalyst. It is worth mentioning that they displayed much lower activities (isolated yields of the desired product, 2a at 120 °C: 42% for 6a and 62% for 6b, Figure 5c,f, respectively) than that of ImNHC‐CO₂‐GONs. The high efficiency of our heterogeneous catalytic system (ImNHC‐CO₂‐GONs) can be attributed to the combination of the gas enrichment (or storage) effect owing to the advantageous mesopore structure, which helps to increase in‐pore concentrations of the substrates, and also the presence of several azolium units in the heterogeneous system.

Figure 7.

The H‐transfer mechanism of all the possible activation modes. a–e) H‐transfer from PhSiH₃ to in situ‐generated CO₂ at the ImNHC‐GONs active site following all the possible activation modes: Mode A, B, C, D, and E, showing the (I) reactant, (I’) TS, and (II) product states. f) H‐transfer from PhSiH₃ to CO₂ at the double ‘Im’ group functionalized ImNHC‐GONs active site following activation “Mode E” showing the (I) reactant, (I’) TS, and (II) product states. Color code: C (black), N (blue), H (white), Si (yellow), and O (red). Bond lengths are in Å unit.

In order to gain further insights of the possible routes for the reductive functionalization of CO₂ in presence of amine and hydrosilane, we conduct the detailed DFT calculations.^{[ 53} , ^{54 ]} Various H‐transfer mechanisms from hydrosilane (PhSiH₃) to CO₂ are first computed to realize the most favorable formylation route. Considering the estimated activation barriers for the H‐transfer mechanism of all the possible activation modes (“Mode A, B, C, D, and E”, Figure 7), “Mode E” (Figure 7e) is found to be the most favorable one. In this mode, the ‘O’ atom of CH₃NH‐CO₂ ⁻, stabilized by the imidazolium unit of the catalyst, interacts with the Si center of PhSiH₃, which triggers the transfer of an H atom to a second molecule of CO₂ to form CH₃NHCOO‐SiPhH₂ and HCOO⁻. The activation barrier for this CH₃NH assisted indirect H transfer at the GONs active site is calculated to be 18.2 kcal mol⁻¹, the lowest among all the H‐transfer activation modes studied here. Following the most favorable H‐transfer through “Mode E” (Figure 7e), the energy profile of the present N‐formylation reaction between CH₃NH₂, a model amine substrate, and in situ‐generated CO₂ at the active site of ImNHC‐GONs (a smaller fragment with one imidazolium unit is chosen for the ease of calculation) is shown in Figure  8 . The reaction energy for the H‐transfer step leading to the formation of ‘CH₃NHCOO‐SiPhH₂‐HCOO’ (Figure 8b) is calculated to be exothermic by −20.2 kcal mol⁻¹.

Figure 8.

DFT‐computed reaction pathways. DFT‐calculated reaction energy profile for the N‐formylation of CH₃NH₂, representative substrate, using in situ‐generated CO₂ over the active site of ImNHC‐GONs. The probable intermediates and TS along the reaction pathway are shown. The energy values and bond lengths given in the figure are in kcal mol⁻¹ and Å units, respectively.

In the next step, the ‘O’ atom of the HCOO⁻ attacks the Si center of the CH₃NHCOO‐SiPhH₂ adduct (Figure 8b,c), which leads to the breakage of O—Si bond generating CH₃NHCOO and PhH₂Si‐O(CH)O (Figure 8c). The activation barrier and reaction energy for this step are calculated to be 12.3 kcal mol⁻¹ and endothermic by 5.6 kcal mol⁻¹, respectively. Removal of CO₂ from the CH₃NHCOO⁻ species of intermediate (c) results in a new intermediate (d), where the H atom from the carbene C of ImNHC‐COF active site is transferred back to the CH₃NH regenerating the starting amine CH₃NH₂.^{[ 54 ]} In the next step (d)→(e), the N atom of the CH₃NH₂ attacks the carbonyl moiety of PhH₂Si‐O(CH)O, resulting in the formation of an N—C bond in intermediate (e), where the HCOO⁻ moiety of CH₃NH‐HCOO⁻ interacts with the Si of PhSiH₂ in a bidentate chelating fashion, forming a four‐membered structure (Figure 8e). Notably, the highest activation barrier for the whole step (c)→(e) is calculated to be 33.8 kcal mol⁻¹ because state (d) is just an intermediate in the barrier. The intermediate (e) finally undergoes C—O bond cleavage to generate the N‐formylated product, N‐Methyl formamide (NMF) under the formation of PhSi(O)H₂. From the complete N‐formylation reaction of CH₃NH₂ with CO₂, the obtained activation barrier (19.3 kcal mol⁻¹), detected for the initial H‐transfer from PhSiH₃ to CO₂, indicates that the reaction is facile over the present ImNHC‐GONs catalyst under the moderate experimental condition. The actual catalytic sites of ImNHC‐GONs have several imidazolium moieties and so, to understand the effect of the second imidazolium moiety, if at all, on the H‐transfer energetics, the most favored activation “Mode E” is also simulated with a model having two imidazolium groups (Figure 7f) and the activation barrier (18.4 kcal mol⁻¹) as well as reaction energy (−21.5 kcal mol⁻¹) for the H‐transfer reaction is found to be similar to the ones obtained with ImNHC‐GONs model with single imidazolium group.

Based on these comprehensive DFT studies and various control experiments, we propose a plausible mechanistic pathway for the present metal‐free N‐formylation reaction (Figure  9 ). The in situ‐generated [NHCH‐GONs]⁺[Carbamate]⁻ species directly interacts (through its carbamate oxygen) to the Si center of PhSiH₃, which triggers the hydride transfer to in situ‐generated CO₂. Based on the DFT calculation, it is found that the NHC carbene carbon of the NHC‐GONs (not an active catalyst) does not interact with the Si atom of PhSiH₃ rather the in situ‐generated active NHC center reacts with amine and CO₂ to produce the carbamate complex, [NHCH‐GONs]⁺[Carbamate]⁻.

Figure 9.

A possible mechanism of the N‐formylation reaction promoted by ImNHC‐CO₂‐GONs.

It can be justified as follows: the active site of the NHC‐GONs, that is, the carbene C atom, is shielded by the large functional units on the N centers (clear from the Figure 7c,e), whereas in the case of loose contact ion pair complex [NHCH‐GONs]⁺[Carbamate]⁻, the active site shifts to the carbamate O atom, which is obviously far away from the big and bulky arms of the NHC unit and thus, capable of acting as an effective nucleophile for the activation of a Si—H linkage of PhSiH₃ without experiencing any steric effect. This promising activation mode displays the “S_N ²@Si‐Acceptor” pattern, where the Si—H linkage is activated through a concerted backside S_N ² nucleophilic attack by the carbamate O⁻ center and subsequently, a free CO₂ accepts the leaving hydride. The C center of a CO₂ molecule is more electrophilic when compared with the CO₂ units present in ImNHC‐CO₂‐GONs adduct and can serve as a more potential hydride acceptor. This “S_N ²@Si‐Acceptor” model justifies the higher performance of PhSiH₃ among the investigated silanes (Table S1, Supporting Information) based on the steric requirement and the presence of three Si—H bonds, which can function as a hydride source after activation for the reductive functionalization of CO₂.^{[ 22} , ⁵³ , ^{55 ]}

In the next step, the formoxysilane intermediate is formed, which is also confirmed from the ¹H and ¹³C{¹H} NMR spectra (Figure S129, S130, Supporting Information, respectively). Subsequently, the desired N‐formylated product is obtained from the reaction of amine, activated via interaction with free NHC (Figure 9), with the generated formoxysilane under the possible elimination of PhSiH₂OH as a byproduct.^{[ 55} , ^{56 ]} Overall, we can reasonably conclude that in this present N‐formylation reaction, the NHC‐GONs does not function as a silane activator instead it promotes the N‐formylation of N—H bonds by generating a new thermodynamically stable complex (i.e., [NHCH‐GONs]⁺[Carbamate]⁻).^{[ 57 ]} This mechanistic understanding offers new insight of the NHC‐GONs promoted N‐formylation reaction, and thus, we believe that it would help to design/synthesize new effective ecofriendly NHC‐GONs catalytic system in near future for the improved transformation of CO₂. In order to assess the catalyst's reusability, we recover the ImNHC‐CO₂‐GONs catalyst from the reaction mixture after the N‐formylation reaction under CO₂ atmosphere. This is done through centrifugation, followed by washing with organic solvents and drying in vacuo. It is important to mention that the ImNHC‐CO₂‐GONs can be reused over five times (Figure  10 ), and the PXRD pattern of the recovered catalyst system confirms the retention of its original structural integrity (Figure 2b and S4e, Supporting Information). Pore‐blockage on the GONs surface after the 5th run, which reduces active‐site accessibility, likely contributes to the apparent loss of catalytic activity. Additionally, there is no structural failure, as evidenced by the PXRD pattern of the recovered catalyst system. Furthermore, the morphological features of the recovered ImNHC‐CO₂‐GONs catalyst are assessed by TEM and SEM. TEM images of the recovered catalytic system, as presented in Figure S4a, Supporting Information, confirm that the morphology of the recovered ImNHC‐CO₂‐GONs catalyst remains the same as that of the fresh catalytic system. This finding is supported by the SEM images of the reused catalyst after the 5th run (Figure S4c,d, Supporting Information), aligning with the PXRD pattern of the reused catalytic system.

Figure 10.

Recyclability chart of ImNHC‐CO₂‐GONs. Catalyst recycling for the reductive functionalization of in situ‐generated CO₂ in the presence of thiophen‐2‐ylmethanethiol (5d) by the ImNHC‐CO₂‐GONs catalyst. Recyclability chart of ImNHC‐CO₂‐GONs up to five runs for the catalytic reductive functionalization of CO₂ to (6d) under the optimized conditions. Error bars indicate the standard deviation of the reaction results obtained from three independent replicates.

3. Conclusions

We have successfully developed new pre‐NHC‐decorated GONs for the effective metal‐free reductive functionalization of CO₂. Intriguingly, the imidazolium‐derived GONs (ImNHC‐CO₂‐GONs) can promote the metal‐free chemoselective formylation of various N—H and S—H functionalities (amines, amides, hydrazines, hydrazides, and thiols) with PhSiH₃ under mild conditions. Most interestingly, the strap‐clipped TB chemistry in functionalized GONs presents an opportunity to expand our knowledge in this field that has been overlooked. Further, we could demonstrate that the heterogenization of metal‐free NHC‐based homogeneous catalysts can make the process sustainable, cost‐effective, and environment‐friendly with good recyclability (especially, the first direct covalent immobilization of imidazolium carboxylates onto the GONs, offering fast, low‐cost production of high‐quality material). The detailed DFT calculations and control experiments establish that NHC serves as a precursor of the [NHCH‐GONs]⁺[Carbamate]⁻ complex, which activates silane. This study introduces a stable heterogeneous platform for the efficient transformation of CO₂ without using metals. This platform presents an innovative pathway for sustainable CO₂ conversion.

Conflict of Interest

The authors declare no conflict of interest.

Supporting information

Supplementary Material

Ghosh Swarbhanu, Ariya Parisa A.. ChemSusChem. 2025; 18:e202500986. 10.1002/cssc.202500986

Data Availability Statement

The data that support the findings of this study are available in the supplementary material of this article.