The present invention relates to the field of chemical sciences. The present invention generally relates to a simple, economic and effective process for the conversion of carbon dioxide to methanol under mild reaction conditions. In particular, the present invention relates to processes for the conversion of carbon dioxide to methanol in the presence of carbenes or their derivatives/adducts under mild reaction conditions. BACKGROUND OF THE INVENTION

Carbon dioxide (CO2), a major greenhouse gas, and its contribution to global warming is widely recognized by the scientific community and is eventually affecting the well-being of humans. Increase in global energy demand fuelled by fossil fuel utilization has led to a mount in CO2 concentration in the atmosphere and global warming. Removal of CO2 from industrial sources or from the atmosphere (carbon capture), jointly with cutbacks in fossil fuel use, is essential to stabilize and possibly reduce overall CO2 concentration in the atmosphere. While carbon capture and sequestration (CCS) has been projected to tackle this problem, another desirable pathway is the carbon capture and recycling (CCR) approach, where CO2 is recycled back to fuels and materials. Arresting CO2 from the air, where its concentration is 0.04%, might well seem premature, given that there is still no power plant in which CO2 is captured from the full exhaust stream. Carbon dioxide is an attractive, economical, renewable and nontoxic Ci source for the production of chemicals and fuels. However, the high thermodynamic stability of CO2 strongly limits the scope of chemical transformation of CO2 into a fuel such as methanol. This uphill task can only be managed by using efficient reactants in the presence of a hydride source. In particular, the conversion of CO2 into methanol is considered to be an important chemical transformation as it can address two global issues simultaneously: reducing global warming and providing methanol as a synthetic fuel to combat the current energy crisis. Most of the current catalysts known to catalyze the reduction of CO2 into valuable products employ transition metals in the presence of 99.995% pure CO2. Recently Olah, Prakash and coworkers developed an efficient homogeneous Ru-based catalyst for the production of CH3OH from air (400 ppm CO2) and H2 using a polyamine at 125-165°C in an ethereal solvent. But in the long term, sustainable technologies for the reduction of CO2 must take into account the availability of such metal ions as well as their cost and toxicity. Metal-free reactions are often an attractive surrogate to metal-catalyzed processes given their low cost and environmentally benign nature. The possibility of using metal-free systems for the CO2 reduction to methoxyborane under ambient conditions and under low concentration remains an open challenge. Moreover, understanding the mechanistic pathways for this important chemical transformation by isolating and characterizing the catalytically active species has been extremely limited in the current literature.

Although the process of conversion of CO2 into methanol is already known in the art, these methods have limitations, such as, availability of such metal ions, the cost and toxicity. Thus, there is a need for better and simpler processes for the conversion of CO2 into methanol. The present invention overcomes drawbacks of the prior art to provide improved, effective, economical and scalable routes for the conversion of CO2 into methanol.

SUMMARY OF THE INVENTION

The present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting carbene or its adduct with borane derivative in presence of CO2 to obtain methoxy borane derivative; and

b) hydrolyzing the methoxy borane derivative to obtain methanol.

The invention further provides a process for preparing formic acid from CO2 comprising the steps of:

a) reacting a carbene with a borane to obtain carbene borane adduct;

b) reacting carbene borane adduct with CO2 to obtain carbene borane adduct formate;

c) reacting formate with sodium hydroxide to obtain sodium formate; and d) hydrolysing the sodium formate to obtain formic acid.

The present invention further provides a process for preparing compound 2 comprising the step of reacting compound 1 with 9-borabicyclo[3.3.1]nonane (9-BBN) to obtain the compound 2.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood and put into practical effect, reference is made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where: Figure 1. Longevity test of compound 3b. This was tested by monitoring the time required for complete consumption of substrate by 1H NMR spectroscopy in three consecutive reaction cycles.

Figure 2. Fixation and isolation of CO2 from air, compound 6' as a reaction intermediate.

Figure 3. Capture of carbon dioxide from air in solid state by compound 2 with the formation of a bicarbonate compound 4.

Figure 4. Reduction of carbon dioxide from air with compound 6'.

Figure 5. Isolation of borondiformate compound 6 as a reaction intermediate during the reduction of 99.995% pure carbon dioxide with compound 3a and 3b.

Figure 6. Reduction of carbon dioxide into methoxyborane or sodiumformate in air. a) Synthesis of abnormal N-heterocyclic carbene 9-borabicyclo(3.3.1)nonane adduct (αNHC- 9BBN) of compound 2. b) Fixation of carbon dioxide from air with the formation of compound 3. c) Reduction of carbon dioxide into methoxyborane in air. d) Reduction of carbon dioxide into sodium formate in air. Figure 7. Replacement of formate anion and carbon dioxide fixation from air in solid state, a) Replacement of formate anion with ion-exchange resin.

Figure 8. Proposed mechanism for the reduction of CO2 into methoxyborane or sodium formate with compound 2 in air. DETAILED DESCRIPTION OF THE INVENTION

The present invention addresses the unmet needs of the art and provides improved processes for preparing methanol from CO2 with enhanced yield using carbene or its adduct under milder reaction conditions. The present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting a carbene or its adduct with a borane derivative in presence of CO2 to obtain a methoxy borane derivative; and

b) hydrolyzing the methoxy borane derivative to obtain methanol.

In an embodiment of the present invention, the carbene or its adduct of step (a) is a N- heterocyclic carbene (NHC) or its adduct.

As described herein, N-heterocyclic carbenes (NHC) comprises normal N-heterocyclic carbene (nNHC) and abnormal N-heterocyclic carbene (αNHC). Normal N-heterocyclic carbene (nNHC) are carbene compounds wherein carbene center is located between the two heteroatoms. Abnormal N-heterocyclic Carbene (αNHC) are carbene compounds wherein carbene center is no longer located between the two heteroatoms. Further, the abnormal N-heterocyclic carbenes (αNHC) also comprise mesoionic carbenes (MIC) such as 1, 2,3 -Triazolylidene-based carbene.

In another embodiment of the present invention, the heterocyclic carbene or its adduct is an abnormal heterocyclic carbene (αNHC) or its adduct. In yet another embodiment of the present invention, the abnormal heterocyclic carbene adduct is selected from a group consisting of abnormal heterocyclic carbene CO2 adduct, abnormal heterocyclic carbene borane adduct, and combinations thereof. In still another embodiment of the present invention, the abnormal heterocyclic carbene or its adduct of step a) is compound 3a, compound 3b, compound 3b ¹ (Scheme 1) or a combination thereof.

Scheme 1 : Carbene based compounds for the reduction of CO2 to methoxyborane with hydroboranes in the presence of various CO2 sources under ambient conditions.

In still another embodiment of the present invention, the abnormal heterocyclic carbene or its adduct of step a) is compound I, compound II, compound III (Scheme 2) or a combination thereof.

Scheme 2: Carbene based compounds for the reduction of CO2 to methoxyborane with hydroboranes in the presence of various CO2 source under ambient conditions.

In still another embodiment of the present invention, the abnormal heterocyclic carbene or its adduct of step a) is compound 1, compound 2, compound 3, compound 6 (Scheme 2a) or a combination thereof.

Scheme 2a: Carbene based compounds for the reduction of CO2.

In a further non-limiting embodiment, the concentration of carbene or its adduct ranges from about 0.02 to about 5 mol %.

In another embodiment, the concentration of carbene or its adduct ranges from about 0.08 to about 3 mol %. In a further embodiment, the concentration of carbene or its adduct is about 0.1 mol%.

In an embodiment of the present invention, the borane derivative of step (a) is selected from a group consisting of catecholborane (HBcat), pinacolborane (HBpin), 9- borabicyclo[3.3.1]nonane (9-BBN), BH3 SMe ₂ , BH3 THF, NH3BH3 and combinations thereof. These borane derivatives act as reductants.

In another embodiment, the borane derivative is 9-borabicyclo[3.3.1]nonane (9-BBN). In still another non-limiting embodiment, concentration of the borane derivative ranges from about 2 to about 5 mmol.

In a further embodiment, concentration of the borane derivative ranges from about 2.5 to about 4 mmol.

In a still further embodiment, concentration of the borane derivative is about 3.4 mmol.

In another embodiment of the present invention, the methoxy borane derivative of step step (a) is beta-methoxy-4,4,5,5-tetramethyl-[l,3,2]dioxaborolane (9BBNOMe), beta- methoxy-catecholborane (CatBOMe), beta-methoxy -4,4,5, 5-tetramethyl-

[l,3,2]dioxaborolane (PinBOMe), trimethyl borate.dimethyl sulfide ((CH ₃ OBO) ₃ .SMe2) or trimethyl borate.tetrahydrofuran ((CH ₃ OBO) ₃ .THF). In an embodiment of the present invention, step a) of the process as described above is carried out in the presence of a solvent selected from a group consisting of tetrahydrofuran (THF), toluene, benzene, bromobenzene, acetonitrile, dimethylsulfoxide (DMSO), dimethylformamide (DMF) and combinations thereof. In an embodiment of the present invention, step b) of the process as described above is carried out in presence solvent selected from a group consisting of water, THF, Toluene, Benzene, Bromobenzene, Acetonitrile, DMSO, DMF and combinations thereof.

In an embodiment of the present invention, the process is carried out in the presence of an internal standard, preferably hexamethylbenzene.

In still another embodiment of the present invention, the reaction mixture of containing carbene or it's adduct, solvent and internal standard of step a) of the above said process is degassed before introducing CO2 into the reaction mixture.

In still another embodiment of the present invention, step a) of said process is carried out under pressure ranging from about 1 atm to about 5 atm of CO2. In yet another embodiment, step a) of said process is carried out under pressure ranging from about 1 atm to about 3 atm of CO2.

In another embodiment, step a) of said process is carried out under pressure of about 1 atm of C0 ₂ .

In still another embodiment of the present invention, the carbon dioxide purity ranges from about 50% to about 99.999%. In yet another embodiment, the carbon dioxide purity is about 99%.

In another embodiment, the carbon dioxide purity is about 99. 995%.

In still another embodiment of the present invention, step a) of said process is carried out in a tube.

In still another embodiment of the present invention, step a) of said process is carried out in a J. Young tube. In still another embodiment of the present invention, step a) of said process is carried out under heating conditions.

In still another embodiment of the present invention, steps a) and b) of said process are carried out at a temperature ranging from about 20°C to about 50°C.

In yet another embodiment of the present invention, said process is carried out for a time period ranging from about 2 hours to about 10 hours.

In a further embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting a carbene or its adduct with a borane derivative in the presence of CO2 to obtain a methoxy borane derivative; and

b) hydrolyzing the methoxy borane derivative to obtain methanol. In another embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting a heterocyclic carbene or its adduct with a borane derivative in the presence of CO2 to obtain a methoxy borane derivative; and

b) hydrolyzing the methoxy borane derivative to obtain methanol.

In yet another embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting an abnormal heterocyclic carbene or its adduct with a borane derivative in the presence of CO2 to obtain a methoxy borane derivative; and b) hydrolyzing the methoxy borane derivative to obtain methanol.

In still another embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting an abnormal heterocyclic carbene or its adduct with 9- borabicyclo[3.3.1]nonane (9-BBN) in the presence of CO2 to obtain a methoxy borane derivative; and

b) hydrolyzing the methoxy borane derivative in the presence of solvent(s) to obtain methanol.

In still another embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting an abnormal heterocyclic carbene 3a with 9-borabicyclo[3.3.1]nonane (9-BBN) in the presence of CO2 to obtain beta-methoxy-9- borabicyclo(3.3.1)nonane; and

b) hydrolyzing the methoxy borane derivative in the presence of water and tetrahydrofuran to obtain methanol. In still another embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of: a) reacting an abnormal heterocyclic carbene adduct 3b with 9- borabicyclo[3.3.1]nonane (9-BBN) in the presence of CO2 to obtain beta- methoxy-9-borabicyclo(3.3. l)nonane; and

b) hydrolyzing the methoxy borane derivative in the presence of water and tetrahydrofuran to obtain methanol.

In still another embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting an abnormal heterocyclic carbene adduct 3b ¹ with 9- borabicyclo[3.3.1]nonane (9-BBN) in the presence of CO2 to obtain beta- methoxy-9-borabicyclo(3.3. l)nonane; and

b) hydrolyzing the methoxy borane derivative in the presence of water and tetrahydrofuran to obtain methanol. In still another embodiment, the present invention relates to a process for preparing methanol from CO2, said process comprising the steps of:

a) reacting an abnormal heterocyclic carbene or its adducts I, II or III with 9- borabicyclo[3.3.1]nonane (9-BBN) in the presence of CO2 to obtain a methoxy borane derivative; and

b) hydrolyzing the methoxy borane derivative in the presence of solvent(s) to obtain methanol.

In still another embodiment, the process for preparing methanol from CO2 further comprises isolation and purification steps of the corresponding products, wherein said isolation and purification is carried out by acts selected from a group consisting of addition of solvent, quenching, filtration, extraction, and combination of acts thereof.

In an embodiment, the obtained methanol by the aforesaid process of the present invention has a purity greater than about 90 %.

In a preferred embodiment of the present invention, the obtained methanol has a purity ranging from about 90 % to about 95 %. The abnormal cyclic carbene (3a), carbene-CO ₂ adduct (3b) and carbene-borane adduct (3b') and their activity was studied at room temperature for reduction of carbon dioxide with 9-BBN (9-borabicyclo[3.3.1]nonane) as a benchmark hydroborane to optimize the best conditions. The formation of methoxyborane (CH3OBBN) was confirmed by multinuclear NMR spectroscopy ¹ H NMR (δ = 3.44 ppm in C ₆ D ₆ ), ¹³ C NMR (δ = 53.3 ppm) as well as ¹¹ B NMR (δ = 56 ppm). During the catalytic reaction, after 1 hour at room temperature, a white precipitate settles at the bottom of the tube, which was further characterized as 2,2'-oxydibenzo[d][l,3,2]dioxaborole (catBOBcat), [in case of catecholborane] on the basis of ¹ H, ¹³ C and ¹¹ B (δ = 22.4 ppm) NMR spectroscopic data. A control experiment confirmed that a carbene or its adduct was needed to promote the reduction of CO2 to CH3OBBN. Hydrolysis of CH3OBBN by using an excess of water in tetrahydrofuran (THF) affords a solution of methanol.

Table 1 : Reduction of 99.995% pure carbon dioxide with various hydroboranes using compound 3b. ^[a]

[ ^aI Reactions was performed in a 25 mL Schlenk tube equipped with a J. Young valve: 2.0 mg of compound 3b (0.0034 mmol; 0.1 mol %), 9-BBN (3.4 mmol) and hexamethylbenzene in 2 mL of C ₆ D ₆ under 1 atm pressure of 99.995% pure carbon dioxide at r.t (room temperature) for 6 hours. ^Based on the integration of methoxy group of CH ₃ OBR ₂ , determined by ¹ H NMR spectroscopy using hexamethylbenzene as an internal standard. It was observed that in terms of efficiency, compound 3b was comparable with compound 3a in the presence of 99.995% pure carbon dioxide gas. Reaction conditions were optimized (C ₆ D6, and 1 atm. CO2) for a number of hydroboranes at room temperature with good Turn Over Numbers (TONs) (Table 1). Treatment of a solution of compound 3b with 1000 equivalents of catecholborane (HBcat) at room temperature under one atmosphere pressure of CO2 resulted in a TON of 200 within about 6 hours (Table 1, entry 1). Under similar conditions, BH ₃ .SMe2 proved to be an excellent hydrogen source, providing (CH ₃ OBO) ₃ with a TON of 290 in about 6 hours (Table 1, entry 2). The addition of 1000 equivalents of Pinacolborane (HBpin) to a solution of compound 3b under one atmosphere pressure of CO2 at room temperature produced the desired product in about 6 hours period with a TON of 210 (Table 1, entry 3). The lower activity of HBpin compared to BH ₃ .SMe2 was not surprising since it was known that HBpin was less reactive for the hydroboration reaction. The reaction worked efficiently for BH ₃ .THF as well (Table 1, entry 5).

To check the stability of the carbene active species, in situ recycling experiment was performed. Three successive reaction runs for reduction of carbon dioxide to methoxyborane with 0.1 mol% of carbene compound loading in the presence of 9-BBN as reductant under ambient conditions were performed. The reaction was continued for three successive cycles after loading the carbene only once during the first cycle. However, after each reaction cycle, a fresh batch of 9-BBN and hexamethylbenzene was added. The result of this experiment indicated a sustained activity of compound 3b for three successive cycles with complete consumption of substrate (Figure 1).

Interestingly, when compounds 3a, 3b and 3b' were exposed overnight to air with C ₆ D6, a sharp color change for compound 3a (green to red) and compound 3b' (light yellow to green) (Figure 2) was observed, but there was no color change for compound 3b. From NMR spectroscopy ( ¹ H) it was confirmed that compounds 3a and 3b were decomposed. Surprisingly, in the case of compound 3b', after exposing it to air, two extra singlets at δ = 8.53 and 8.55 ppm with 1 : 1 signal intensity ratio were observed. These two signals were attributed to formate group and C5-H of carbene fragments, respectively, implying the formation of a formate compound 6' (Figure 2). These assignments were further substantiated by the corresponding ¹³ C NMR signal at δ = 169.2 ppm (C=0 of formate) and δ= 122.7 ppm (C5 of carbene). Based on all these NMR evidences, the formation of compound 6' was proposed (Figure 2). Compound 6' was obtained as colorless crystals from C ₆ D6 at 51% yield upon crystallization under open atmosphere. The single crystal X- ray study of compound 6' confirmed its formulation (Figure 2), in which a CO2 molecule was formulated as formate, hydroborane fragment was hydrolyzed to boric acid and C5 carbon of the carbene was protonated. Further, it was also observed that abnormal heterocyclic carbene borane adduct i.e. compound 3b' was capable to capture the CO2 in solid state within 3 days to produce compound, 6', which was confirmed with NMR spectroscopy ( ¹ H, ¹³ C and ¹¹ B) (Figure 3). During this process, color changes from light green to off white color were also observed (Figure 3). To further establish compound 6' as a bonafide carbene intermediate, it was reacted with 10 equivalents of hydroboranes (9- BBN) in the presence of air, affording the corresponding CH3OBR2 product with 10% yield after about 6 hours (Figure 4). The addition of hydroboranes to compound 6' was carried out with the help of a glove box or Schlenk line technology, since hydroboranes were highly moisture sensitive. After successful addition, the vial was closed and a sharp color change from green to red was observed (Figure 4) with the formation of 9BBN-OMe (in case of 9BBN), which was confirmed with NMR spectroscopy ( ¹ H, ¹³ C and ¹¹ B). Accordingly, it was concluded that compound 3b' captures CO2 from air (400 ppm CO2) to furnish compound 6' with the functionalization of CO2 as a formate ion and reduction of CO2 from air to methoxyborane at room temperature. The yield of methoxyborane in the presence of air was 10%, likely due to lower concentration (0.04%) of carbon dioxide in air. Increased supply of carbon dioxide in the reaction chamber was thus expected to increase the yield.

Table 2: Reduction of 99.995%) pure carbon dioxide with various hydroboranes using compound 6'. ^[a]

^[aI Reactions were performed in a 25 mL Schlenk tube equipped with a J. Young valve: 2.0 mg of compound 6', 9-BBN and hexamethylbenzene in 2 mL of C ₆ D ₆ under 1 atm pressure of 99.995% pure carbon dioxide at r.t for 6 hours. ^Based on the integration of methoxy group of CH ₃ OBR ₂ , determined by ¹ H NMR spectroscopy using hexamethylbenzene as an internal standard. Several hydroboranes were tested at room temperature (Table 2) in the presence of 99.995%) pure carbon dioxide instead of air (0.04 %> CO2). Treatment of a solution of compound 6' with BH ₃ .SMe2 at room temperature under one atmosphere pressure of CO2, resulted in 62%> yield within about 6 hours (Table 2, entry 1). In order to understand the mechanistic pathway for the reduction of carbon dioxide (99.995% pure) with compound 3a, several stoichiometric reactions were carried out. The combination of compound 3a and 3 equivalents of hydroborane in toluene under 1 atm. pressure of CO2 at room temperature for about 2 hours, resulted in a sharp color change from green to colorless with the formation of a new product as evidenced by ¹ H NMR spectroscopy. Two singlets appeared at δ = 8.51 and 8.33 ppm with 2: 1 signal intensity ratio. These two signals were attributed to formate group of R3(OCOH)2 and C5-H of carbene fragments, respectively implying the formation of a borondiformate compound 6 (Figure 5). These assignments were further substantiated by the corresponding ¹³ C NMR signal at δ= 167.7 ppm (C=0 of formate) and δ= 122.7 ppm (C5 of carbene). Further, to know the source of C5-H of carbene fragment, the reaction was performed with the above stoichiometric reaction with toluene-d ₈ instead of its proton analogue, when an exactly identical compound was formed indicating that the source of hydrogen was hydroborane. Based on NMR evidence, the formation of compound 6 is proposed (Figure 5). Compound 6 was obtained as colorless crystals from toluene/hexane mixture at 70% yield upon crystallization under inert atmosphere.

Table 3 : Reduction of 99.995%) pure carbon dioxide with hydroborane (9BBN) using

reaction intermediate 6 with different loading. ^[a]

^[aI Reactions were performed in a 25 mL J-Young Schlenk tubes: 2.0 mg of catalyst 6 (0.0026mmol), 9-BBN (2.6 mmol) and hexamethylbenzene in 2 mL of CeDe under 1 atm pressure of pure carbon dioxide at r.t. ^Based on the integration of methoxy group of CH ₃ OBR ₂ , determined by ¹ H NMR spectroscopy using hexamethylbenzene as an internal standard. The single crystal X-ray study of compound 6 confirmed its formulation (Figure 5), in which a CO2 molecule was incorporated into a formal B-H bond. To further establish compound 6 as a bonafide carbene intermediate, it was reacted with CO2 in the presence of 1000 equivalents of the hydroboranes (9-BBN), affording the corresponding CH3OBR2 product with a TON of 380 after about 6 hours (Table 3). Such a high conversion activity of compound 6 prompted us to interrogate further whether it can still be functional even under lower catalyst loading. The carbene loading test was performed using 9-BBN as reductant under ambient conditions (Table 3). It was observed that compound 6 was active for reduction of carbon dioxide to methoxyborane with a miniscule carbene loading down to 0.005 mol % resulting in a TON value as high as 6000 after 12 hours (Table 3, entry 3). Importantly, carbene 6 exhibits the highest TON, (6000, Table 3) under ambient reaction conditions for the reduction of CO2 to methoxyborane among any of the compounds reported to date under ambient conditions. Apart from this, during the course of the experiment, a gas was evolved which upon ¹ H NMR spectroscopic analysis was determined to be dihydrogen {δ= 4.47 ppm).

On the basis of the above experimental results, a mechanism for the reduction of carbon dioxide to methoxyborane with carbene 3a was proposed as shown in Scheme 3. In the presence of carbon dioxide and carbene 3a, the carbene-C02 adduct 3b was first formed, which further undergoes a nucleophilic reaction with hydroborane, resulting in compound 3c. In compound 3c, the B-H bond becomes activated for further reaction with carbon dioxide since it was attached with a strong σ donating abnormal carbene. Subsequent insertion reaction of carbon dioxide into the B-H bond of compound 3c resulted in a four coordinate compound 3d. Compound 3d on further reaction with hydroborane generated borondiformate salt, 6 as zwitterions with the elimination of a B-O-B dimer compound 7a. Compound 6 was thoroughly characterized (by X-ray and NMR spectroscopy). The formation of compound 7a was confirmed by NMR spectroscopy ( ¹ H, ¹³ C and ¹¹ B) in case of pinacolborane (HBpin) by performing stoichiometric experiment between αNHC (compound 3a) and 3 equivalents of HBpin under CO2 atmosphere which showed exclusive formation of compounds 7a and 6. Another molecule of hydroborane was further reacted with 6 regenerating the free carbene (3a), boron formate (7b) and hydrogen gas (evidenced by ¹ H NMR spectroscopy). The boronformate7b was reduced to its acetal form H2C(OR ₃ )2 (compound 8) in the presence of hydroborane. The formation of compound 8 was confirmed from its characteristic chemical shift (δ = 5.34 ppm in C6D ₆ ) upon analysis of the reaction mixture by ¹ H NMR spectroscopy. As probed earlier, compound 3a could furnish compound 3b in the presence of carbon dioxide and compound 3b can react further with hydroborane reproducing compound 3c in the cycle. Finally compound 8 was reduced to methoxide derivative 5d in the presence of 3c with the elimination of the RBOBR dimer (compound 7a), where compound 3c remains unchanged after the reduction of compound 8. The formation of RBOBR dimer (compound 7a) in case of catecholborane was confirmed by ¹ H, ¹³ C and ¹¹ B (δ= 22.4 ppm) NMR spectroscopic analysis.

Scheme 3: Proposed mechanism for abnormal NHC (compound 3a) based CO2 reduction (99.995% pure CO ₂ ) with 9-BBN. In step 6, the aNHC (compound 3a) reacts with CO ₂ to form the CO2 adduct of aNHC (compound 3b). *The source of oxygen in compound 7a (Step 4) was CO2. On the other hand, to gain information on the mechanistic pathways for the reduction of carbon dioxide with carbene 3b' in the presenceof air (400 ppm carbon dioxide), several control reactions were carried out. When the compound 3b' was exposed in air with C ₆ D6 for overnight (12 hours) the functionalization of CO2 as formate (compound 6') was observed, which was confirmed through NMR spectroscopy ( ¹ H, ¹³ C and ¹¹ B) and X-ray study (Figure 2). The combination of carbene 6' and 2 equivalents of hydroborane in C ₆ D6, in the presence of air at room temperature for about 2 hours under closed system formed a new product as observed by ¹ H NMR spectroscopy. The formation of product was confirmed as acetal form H ₂ C(OR3) ₂ (compound 8). Apart from this, during the course of experiment with air under closed system, a gas was evolved which upon ¹ H NMR spectroscopic analysis was revealed as dihydrogen (δ = 4.47 ppm). On the basis of the above experimental results, a cycle for the reduction of carbon dioxide (from air) to methoxyborane with carbene 3b' can be proposed as shown in Scheme 4. In the presence of air and compound 3b', it first arrest the CO2 from air into the B-H bond of 3b' resulting a four coordinate compound 3d'. Compound 3d' on further reaction with moisture could generate formate salt, 6' as zwitterions with the complete hydrolysis of hydroborane fragment as boric acid. Compound 6' was thoroughly characterized (by X-ray and NMR spectroscopy). Another molecule of hydroborane further reacts with 6' generating the free carbene (3a), boron formate (7b) and hydrogen gas (evidenced by ¹ H NMR spectroscopy). The boronformate 7b was reduced to its acetal form H ₂ C(OR3) ₂ (compound 8) in the presence of hydroborane. The formation of compound 8 was confirmed from its characteristic chemical shift (δ = 5.34 ppm in C6D ₆ ) upon analysis of the reaction mixture by ¹ H NMR spectroscopy. Compound 3a reacts with hydroborane to reproduce compound 3b' in the cycle of reactions. Finally compound 8 was reduced to methoxide derivative 5d in the presence of compound 3b' with the elimination of the RBOBR dimer (compound 7a), where compound 3b' remains unchanged after the reduction of compound 8.

Scheme 4: Proposed mechanism for compound 3b' CO2 reduction from air with 9-BBN. In step 4, the aNHC (compound 3a) reacts with 9BBN to form the 9BBN adduct of aNHC (compound 3b').

The present invention also relates to a process for preparing compound 2, wherein said process consists of reacting compound 1 with 9-borabicyclo[3.3.1]nonane (9BBN) to obtain the compound 2.

In an embodiment of the present invention the above said process is carried out under heating conditions. In an embodiment of the present invention the above said process of present compound 2 is carried out at a temperature ranging from 25°C to 50°C, preferably at temperature 40 °C.

In an embodiment of the present invention the above said process for conversion of compound 1 to compound 2 is carried out in the presence of a solvent, wherein said solvent is toluene, benzene, tetrahydrofuran and combinations thereof.

The present invention also provides a process for preparing formic acid from CO2 comprising the steps of:

a. reacting a carbene with a borane to obtain carbene borane adduct;

b. reacting carbene borane adduct with CO2 to obtain carbene borane adduct formate;

c. reacting formate with sodium hydroxide to obtain sodium formate; and d. hydrolysing the sodium formate to obtain formic acid.

In an embodiment of the present invention the above said process for preparing formic acid from CO2 is carried out for a time period ranging from about 28 hours to 42 hours at a temperature ranging from about 20°C to about 50°C.

In another embodiment of the present invention the above said process for preparing formic acid from CO2

step a), b) are carried out in solvent selected from a group comprising toluene, benzene, tetrahydrofuran (THF) and combinations thereof;

step c) is carried out in solvent selected from a group comprising toluene, benzene, tetrahydrofuran (THF), water and combinations thereof; and

step d) is carried out in water.

In an embodiment of the present invention the above said process of step a) for preparing formic acid from CO2 was carried out by reacting a carbene with a borane at 40°C in the presence of toluene for 2 hours to obtain carbene borane adduct. In another embodiment of the present invention the above said process of step b) for preparing formic acid from CO2 was carried out by reacting carbene borane adduct with CO2 at room temperature in the presence of toluene for 6 hours to obtain carbene borane adduct formate.

In yet another embodiment of the present invention the above said process of step c) for preparing formic acid from CO2 was carried out by reacting formate with sodium hydroxide in the presence of mixture of water and THF at a ratio of 10: 1 at room temperature to obtain sodium formate.

In still another embodiment of the present invention the above said process of step d) for preparing formic acid from CO2 was carried out by hydrolysing the sodium formate in presence of water at room temperature for 12 hours to obtain formic acid. As used herein the term "comprising" or "comprises" is used in reference to compositions, methods, and respective component(s) thereof, that are essential to the method or composition, yet open to the inclusion of unspecified elements, whether essential or not.

The singular terms "a," "an," and "the" include plural referents unless context clearly indicates otherwise. Similarly, the word "or" is intended to include "and" unless the context clearly indicates otherwise. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of this invention, suitable methods and materials are described below. The abbreviation, "e.g." is derived from the Latin exempli gratia, and is used herein to indicate a non-limiting example. Thus, the abbreviation "e.g." is synonymous with the term "for example."

The description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while method steps or functions are presented in a given order, alternative embodiments may perform functions in a different order, or functions may be performed substantially concurrently. The teachings of the invention provided herein can be applied to other procedures or methods as appropriate. The various embodiments described herein can be combined to provide further embodiments. Aspects of the invention can be modified, if necessary, to employ the compositions, functions and concepts of the above references and application to provide yet further embodiments of the invention. These and other changes can be made to the invention in light of the detailed description. All such modifications are intended to be included within the scope of the appended claims.

Specific elements of any of the foregoing embodiments can be combined or substituted for elements in other embodiments. Furthermore, while advantages associated with certain embodiments of the invention have been described in the context of these embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. EXAMPLES

General considerations

All manipulations were performed under a dry and oxygen-free atmosphere (argon) using standard Schlenk techniques or inside a glovebox maintained below 0.1 ppm of O2 and H2O levels. Glassware were dried for overnight at 130 °C before use. THF, toluene, pentane and benzene were dried over a sodium/enzophenone mixture and distilled before use. CH3CN and CH2CI2 were dried over CaH2 and distilled before use. Carbon dioxide was purchased from Praxair in a 5.5 purity gas cylinder with 99.995% purity. The ¹ H and ¹³ C NMR spectra were recorded on 400 and 500 MHz NMR spectrometers with residual undeuterated solvent as an internal standard. ¹¹ B NMR spectra were obtained by using a Bruker Avance 500 MHz NMR spectrometer. Chemical shifts for ¹¹ B NMR spectra were referenced using Et20 BF ₃ as an external standard. Chemical shifts (δ) were given in ppm, and J values were given in Hz. Elemental analyses were performed in a Perkin-Elmer 2400, Series II, CHNS/O analyzer. The melting point was measured in a sealed glass tube on a Biichi B-540 melting point apparatus. All solid reagents or substrates were purchased (Sigma-Aldrich, Merck and Spectrochem) and used as received. Unless otherwise noted, liquid chemicals were purchased from commercial suppliers (Sigma-Aldrich, Merck and Spectrochem) and dried over molecular sieves (4 A) prior to use. The molecular sieves (4 A, Merck) were dried under a dynamic vacuum at 250 °C for 48 hours prior to use. Isolated abnormal N-heterocyclic carbene (compound 3a) and abnormal N-heterocyclic carbene CO2 adduct (compound 3b) were prepared according to the literature procedures described by Bertrand and coworkers. During the reaction, freeze-pump-thaw cycle was performed to remove N2 gas from J. Young tube and next it was waited until the temperature of J. Young tube reached to room temperature. Then the reaction mixture was exposed to atmospheric pressure of CO2 gas and the J. Young tube was sealed to perform the reaction.

Example 1: Reduction of carbon dioxide with carbenes:

Compound 4d was treated with carbon dioxide in presence of carbenes (either with compound 3a or compound 3b) and solvent at a specified temperature (mentioned in Table 4) to obtain compound 5d.

Table 4: Optimization studies for carbon dioxide reduction with carbenes 3a and 3b. ^[a]

[a] Reactions were performed in a 25 mL Schlenk tube equipped with a J. Young valve: 2.0 mg of carbene 3a (0.0037 mmol) or 3b (0.0034 mmol), 9-BBN (1000 equivalent) and hexamethylbenzene in 2 mL of solvent under 1 atm pressure of carbon dioxide, [b] Based on the integration of methoxy group of CH3OBR2, determined by ¹ H NMR integration using hexamethylbenzene as an internal standard.

A mixture of 9-BBN and carbene 3a in a 1000: 1 ratio (i.e., 0.1 mol % carbene loading) under an atmosphere of CO2 gas produced the methoxyborane derivative CH3OBBN resulting in a TON (turnover number) of 100 after 6 hours at room temperature in anhydrous THF (Table 4, entry 1). Solvent optimization revealed that the reaction was more efficient in benzene or bromobenzene (Table 4, entries 3 and 4). A TON of 290 or 280 was observed after 6 hours at room temperature using benzene or bromobenzene as a solvent. It was observed that in terms of carbene efficiency, the carbene 3b was almost comparable with the carbene 3a (Table 4, entries 3 and 5). Almost similar TON (~ 300) was observed after 6 hours at room temperature. At higher temperature (40 °C), the rate of the reaction was fast with a TON of 310 was observed after 2 hour (Table 4, entry 7). A control experiment confirmed that a carbene was needed to promote this transformation (Table 4, entry 8).

Example 2: Synthesis of l,3-bisf2,6-diisopropylphenyl)-2,4-diphenylimidazolidine-9- borabicvclo[3.3.11 nonan-9-diformate ( compound 6)

A 25 mL Schlenk flask equipped with a stirring bar was charged with compound 3a (272.0 mg, 0.50 mmol, lequivalent), 9-BBN (3 equivalents) and toluene (10 mL) at -40 °C in the presence of carbon dioxide atmosphere (1 atm). After 30 minutes, the reaction mixture was warmed to room temperature and stirred for 2 hours in the presence of 1 atmosphere pressure CO2. The solution became transparent within 1 hour at room temperature. A white solid formed during the evaporation of the solvent. The resulting solid was washed with hexane (3 x 5 mL) and dried under reduced pressure to afford compound 6 (269 mg, 0.35 mmol, 70%). X-ray quality crystals were grown from toluene/hexane in a NMR tube inside the glovebox at room temperature. ¹ H NMR (400 MHz, CDCI ₃ , 25 °C, TMS): «5 = 8.51 (s, 2H), 8.33 (s, 1H), 7.66-7.58 (m, 2H), 7.45-7.41 (m, 2H), 7.38-7.30 (m, 6H), 7.22 (t, 4H, J = 7 Hz), 6.94 (d, 2H, J= 7.3 Hz), 2.51 (q, 2H, J= 6.7 Hz), 2.43 (q, 2H, J= 6.7 Hz), 1.83- 1.82 (m, 6H), 1.54-1.53 (m, 4H), 1.40-1.39 (m, 2H), 1.31 (d, 6H, J= 6.7 Hz), 1.02 (d, 6H, J = 6.7 Hz), 0.86 (t, 12H, J = 6.1 Hz), 0.75 (s, 2H) ppm; ¹³ C NMR (100 MHz, 25 °C, TMS): δ = 167.83, 145.7, 144.8, 144.4, 137.3, 133.2, 133.0, 132.7, 131.2, 130.0, 129.6, 129.4, 128.4, 126.3, 125.6, 124.3, 122.7, 120.6, 31.4, 29.6, 29.3, 25.5, 25.1, 23.8, 23.4, 22.6 ppm; ¹¹ B NMR (120 MHz, CDCh, 25 °C, TMS) δ = 9.1 ppm; Elemental analysis: Calcd. for C50H67BN2O4: C 77.90, hours8.76, N 3.63; found: C 79.43, hours8.80, N 2.32. Example 3: Synthesis of 13-bis(2,6-diisopropylphenyl)-2,4-diphenylimidazolidine, 2,2-bisfformyloxy)-4,4,5,5-tetramethyl-l,3.,2-dioxaborolan-2 -uide salt (compound 6') and 2,2'-oxybis(4.,4,5,5-tetramethyl-l,3.,2-dioxaborolane) (compound 7a )

Scheme 5: Capture of PinB-O-BPin dimer during the transformation of compound 3d to compound 6. A 25 mL Schlenk flask equipped with a stirring bar was charged with compound 3a (272.0 mg, 0.50 mmol, lequiv), PinBH (3 equivalents) and toluene (10 mL) at -40 °C in the presence of carbon dioxide atmosphere (1 atm). After 30 minutes, the reaction mixture was warmed to room temperature and stirred for 2 hours in the presence of 1 atmosphere pressure CO2. A white solid formed during the evaporation of the solvent. The resulting solid was washed with hexane (3 x 5 mL) and dried under reduced pressure to afford the mixture of compounds 6' and 7a'.

Example 4: Hydroboration of CO2 with isolated abnormal N-heterocyclic carbene (compound 3a)

Under an argon atmosphere, a 25 mL Schlenk tube equipped with a J. Young valve was charged with compound 3a (2.0 mg, 0.0037 mmol), borane (3.7 mmol, 1000 equivalent) and C ₆ D6 (2 mL). To this solution, hexamethylbenzene was added as an internal standard. The mixture was degassed by a freeze-pump-thaw cycle and placed under 1 atm of CO2 at room temperature. After 1 hour at room temperature, a small white precipitate was formed and allowed to settle at the bottom of the tube. The progress of the reaction was monitored by ¹ H NMR spectroscopic integration and the TON was calculated based on the integration of methoxy group of CH3OBR2 with respect to internal standard. All reported TON of products were an average of at least two runs.

Example 5: Hydroboration of CO2 with abnormal N-heterocyclic carbene CO2 adduct (compound 3b)

Under an argon atmosphere, a 25 mL Schlenk tube equipped with a J. Young valve was charged with compound 3b (2.0 mg, 0.0034 mmol), borane (3.4 mmol, 1000 equiv) and C ₆ D6 (2 mL). To this solution, hexamethylbenzene was added as an internal standard. The mixture was degassed by a freeze-pump-thaw cycle and placed under 1 atm of CO2 at room temperature. After 1 hour at room temperature, a small white precipitate was formed and allowed to settle at the bottom of the tube. The progress of the reaction was monitored by ¹ H NMR spectroscopic integration and the TON was calculated based on the integration of methoxy group of CH3OBR2 with respect to internal standard. All reported TON of products were an average of at least two runs.

Example 6: Hydroboration of CO2 with l,3-bis(2,6-diisopropylphenyl)-2,4- diphenylimidazolidine-9-borabicyclo[3.3.11nonan-9-diformate (compound 6)

In a glovebox, a 25 mL Schlenk tube equipped with a J. Young valve was charged with carbene compound 6 (2.0 mg, 0.0026 mmol), 9-BBN (2.6 mmol) and C6D ₆ (2 mL). For low carbene loading experiment (beyond 0.1 mol %), a stock solution of carbene 6 was prepared. Known amount of hexamethylbenzene was added as an internal standard. The resulting mixture was degassed by freezing the sample with liquid N2 followed by the evacuation under vacuum. While the solution was allowed to thaw at room temperature, the tube was charged with 1 atm of CO2. The progress of the reaction was monitored by ¹ H NMR spectroscopic integration and the TON was calculated based on the integration of methoxy group of CH3OBR2 with respect to internal standard. All reported TON of products were an average of at least two runs.

Example 7: Procedure for carbene longevity experiment with 9-BBN as reductant In a glovebox, a 25 mL J. Young tube was charged with compound 3b (2.0 mg, 0.0034 mmol), 9-BBN (3.4 mmol, 1000 equiv) and C ₆ D6 (2 mL). Known amount of hexamethylbenzene was added as an internal standard. The resulting mixture was degassed by freezing the sample with liquid N2 followed by the evacuation under vacuum. While the solution was allowed to thaw at room temperature, the J. Young tube was charged with 1 atm of CO2 at room temperature. The progress of the reaction was monitored by ¹ H NMR spectrum of the solution, which showed that starting 9-BBN is consumed completely within 8 hours. Again a fresh batch of 9-BBN and hexamethylbenzene were added for the next carbene cycle without adding any further carbene into the reaction vessel. This procedure was repeated for a total of three consecutive runs of the reaction with carbene.

Example 8: Typical procedure for the conversion of carbon dioxide to methanol

In a glove box, a 25 mL J. Young tube was charged with compound 3b (2.0 mg, 0.0034 mmol), 9-BBN (0.34 mmol, 100 equiv) and C ₆ D6 (1 mL). To this solution, known amount of hexamethylbenzene was added as an internal standard. The mixture was degassed by a freeze-pump-thaw cycle and placed under 1 atm of CO2 at room temperature. After 1 hour at room temperature, a small white precipitate was formed and allowed to settle at the bottom of the tube. The mixture was left to react at room temperature for the specified amount of time (4 hours) after which the solvent was removed under reduced pressure. Then tetrahydrofuran (THF) was added and H2O (2 mL) was injected to the reaction mixture. The reaction mixture was stirred for 3 hours to afford a solution of methanol in THF. The formation of methanol (δ= 3.15 ppm in C6D ₆ ) was determined by using ¹ H NMR spectroscopy with C ₆ D6 as the solvent and hexamethylbenzene as an internal standard.

Characterization of catBOBcat (7a") dimer formation

Under an argon atmosphere, a 2.5 mL NMR tube equipped with a J. Young valve was charged with compound 3b (2.0 mg, 0.0034 mmol), catecholborane (0.34 mmol, 100 equiv) and C ₆ D6 (0.6 mL). The mixture was degassed by a freeze-pump-thaw cycle and placed under 1 atm of CO2 at room temperature. After 1 hour at room temperature, a small white precipitate was formed and allowed to settle at the bottom of the tube. Then the solution was transferred to another tube and the precipitate was washed with hexane. The precipitate was characterized as catBOBcat on the basis of ¹ H, ¹³ C and ¹¹ B spectroscopic comparison. ¹ H NMR (500 MHz, CDCh, 25 °C, TMS): δ = 7.29-7.27 (m, 4H), 7.16-7.14 (m, 4H) ppm; ¹³ C NMR (100 MHz, 25 °C, TMS): δ= 147.4, 123.0, 112.6 ppm; ¹¹ B NMR (120 MHz, CDCh, 25 °C, TMS) δ= 22.4 ppm. Example 9: Synthesis of Compound 2 and Compound 3

The abnormal N-heterocyclic carbene (αNHC) (compound 1) was prepared according to literature procedure and αNHC-9BBN adduct (compound 2) was prepared with 75% isolated yield upon reaction between compound 1 and 9-BBN at 1 : 1 ratio in toluene at 40 °C for 2 hours (Figure 6a). The formation of compound 2 was confirmed from NMR evidence [ ¹¹ B NMR (δ = -16 ppm) in C ₆ D6] . When a solution of compound 2 in C ₆ D6 was left open to ambient air for overnight, a sharp color change from light yellow to green (Figure 6b) was observed with the formation of a new product (compound 3) as evidenced by ¹ H NMR spectroscopy. The isolated yield of this product 3 was 40 % after hexane wash. Two significant singlets appeared at δ = 8.53 and 8.55 ppm with a 1 : 1 signal intensity ratio in CDCh. These two signals at δ = 8.53 and 8.55 ppm were attributed to formate anion and C5-H of αNHC cation, respectively. The presence of the signal attributed to formate anion in ¹ FINMR spectroscopy indicates that the CO2 might have been fixed during such transformation and the source of such formate anion must be CO2 present in air. These assignments were further substantiated by the corresponding ¹³ C NMR signals at δ =169.2 ppm (assigned to C=0 of formate) and (5=125.4 ppm (C5 of αNHC). The ¹³ C NMR spectroscopy further confirms the presence of a formate anion in compound 3. Next, to know the fate of boron containing 9-BBN backbone during this transformation, ¹¹ B NMR was recorded, which revealed a singlet at δ = 20.8ppm. This ¹¹ B chemical shift matched with that arising from free boric acid {B(OH) ₃ }. Based on all these NMR evidences, the formulation of compound 3 was proposed. To check further reactivity of the captured CO2, compound 3 was treated with a boron hydride. The compound 3 was reacted with 10 equivalents of the hydroboranes (9-BBN) in the presence of air, to obtain the corresponding CFbOBBN product with full consumption of compound 3 within 6 hours in C ₆ D6 (Figure 6c). The formation of methoxyborane (CFbOBBN) was confirmed by NMR spectroscopy [ ¹ H NMR (δ =3.44 ppm), ¹³ C NMR (δ = 53.3 ppm), and ¹¹ B NMR (δ =56 ppm) in C ₆ D6] . During the course of reaction, a gas evolution was observed, which was confirmed as hydrogen by ¹ H NMR spectroscopy (δ = 4.46 ppm). Example 10: Synthesis of formic acid via formation of sodium formate

In the presence of 5 mL 2(M) NaOH solution and 0.5 mL TFIF at room temperature, compound 3 (Figure 6d) was fully consumed signifying the formation of sodium formate. The formation of sodium formate (HCOONa) was confirmed by NMR spectroscopy [¾ NMR (δ =8.24 ppm) in D2O]. The formed sodium formate was hydrolysed to obtain formic acid. Next, it was interesting to check if the captured CO2 from air could be expelled from compound 3 which will enable reuse of the carbene scaffold for further CO2 capture.

Example 11: Reusability of carbene scaffold for capturing CO2

Upon heating at 150 °C for 12 hours, compound 3 looses its formate anion, when a sharp color change from colorless to chocolate color was observed with formation of a new product as evidenced by ¹ H NMR spectroscopy. As stated previously, in compound 3, two singlets (in ¹ H NMR spectrum) in downfield region with δ = 8.53 and 8.55 ppm having a 1 : 1 signal intensity ratio in CDCh were observed. After heating the compound 3 at 150 °C for 12 hours, tiWH NMR spectrum of the resulting compound revealed only a new singlet (δ = 8.35 ppm) and the other singlet in ¹ H NMR spectrum vanished which indicates that the formate anion might have been lost during the heating process. To further support this ¹³ C NMR spectroscopic experiment was performed, wherein the peak in ¹³ C NMR spectrum in CDCh revealed that the singlet in downfield region at δ = 169.2 ppm disappeared completely, which further confirmed the loss of formate counter anion. Based on the NMR evidence, it was evident that upon heating at 150 °C, compound 3 looses its captured carbon dioxide molecule (which was present as a formate anion). Furthermore, it is possible to replace the formate anion from compound 3, with chloride ion, when compound 3 is simply passed through a DOWEX chloride ion-exchange resin. On passing through the ion-exchange column, compound 5 with 50% isolated yield was formed (Figure 7a). The formation of compound 5 was confirmed by NMR studies. After passing the compound 3 through an ion-exchange column, the ¹ H NMR spectrum of resulting compound displayed only one singlet at δ = 10.75 ppm and in ¹³ C NMR spectrum no signal beyond 144.45 ppm in CDCh was observed, confirming the absence of any formate ion. Based on these NMR evidences, the formation of compound 5 was proposed (Figure 7a). Based on the above experiments (heating and exchanging ion with resin), it was demonstrated that the captured CO2 from the air can be expelled out to regenerate the starting αNHC salt which in principle can be reused to prepare αNHC carbene borane adduct to further capture CO2 from air. Additionally, when the compound 2 was exposed in air in solid state (as a fine powder in a petri dish) for 7 days, a sharp color change from brown to off white was observed (Figure 3) with formation of a new product as evidenced by the ¹ H NMR spectroscopy. Two singlets appeared at δ = 8.58 and 8.76 ppm with a 1 : 1 signal intensity ratio in CDCh at room temperature. These two signals at δ = 8.58 and 8.76 ppm (which were different from those observed for compound 3) were attributed to a bicarbonate anion and C5-H of cationic αNHC fragment, respectively. These assignments were further substantiated by the corresponding ¹³ C NMR spectroscopic signal at δ = 169 ppm (C=0 of bicarbonate) and δ =125.4 ppm (C5 of αNHC). Furthermore, the ¹¹ B NMR spectrum of compound 4 revealed a singlet at δ = 21 ppm, which matches with free boric acid {B(OH) ₃ } . Based on all these NMR evidences, the formation of compound 4 was proposed (Figure 3).

To gain further information on the mechanistic pathways of reduction of the captured of carbon dioxide, several stoichiometric reactions were carried out. On the basis of experimental results, a mechanistic path for the reduction of CO2 to methoxyborane and sodium formate with compound 2 in air was proposed as shown in Figure 8. The combination of compound 1 and same equivalents of 9-BBN in toluene at 40 °C furnishes compound 2. The formation of compound 2 was confirmed through NMR. The compound 2 can serve as a hydride donor during the course of the reaction. So, B-H bond of compound 2 becomes activated for further reaction, since it is attached with a strong σ- donating αNHC. In the presence of air, CO2 molecule is selectively incorporated into a B- H bond to form the compound 2a. Because of moisture in air, the compound 2a is hydrolyzed to compound 3, where carbene borane bond collapsed to protonate the carbene as a positive charge and formate is generated as a negative charge to stabilize the whole compound as a zwitterion During this process, 9BBN fragment is hydrolyzed to boric acid with the elimination of cyclooctane. Formation of cyclooctane was confirmed from reaction mixture ¹ H NMR (δ = 1 ,5 ppm in C6D ₆ ). The compound 3 was characterized with NMR spectroscopy and elemental analysis. The compound 3 can react with NaOH solution to furnish sodium formate (compound 10), which was confirmed through NMR analysis. On the other hand, another molecule 9-BBN reacts with compound 3 to regenerate free αNHC (compound 1) with the formation of a boronformate (compound 6) via hydrogen gas liberation. In the presence of air, it is difficult to stabilize the regenerated free carbene 1 since this carbene is highly moisture sensitive. The boronformate 6 can be reduced to if s acetal form H2C(OBBN)2 (compound 7) in the presence of 9-BBN. The formation of compound 7 was confirmed from its characteristic chemical shift (δ =5.34 ppm in C6D ₆ ) upon analysis of the reaction mixture by ¹ HNMR spectroscopy. Finally, compound 7 was reduced to methoxide derivative (compound 8) in the presence of compound 2 with the elimination of compound 9. Example 12: Synthesis of methanol from carbon dioxide in the presence of carbenes compounds I, II and III

In summary, the role of an abnormal N-heterocyclic carbenes (αNHC) or adducts such as αNHC-9BBN adduct (compound 2) for capturing carbon dioxide from air and it's reduction into methoxyborane or sodium formate under ambient conditions was established. The CO2 trapped intermediate such as {αNHC-H, OCOH, B(OH) ₃ } (compound 3) was characterized to unequivocally establish the capture of carbon dioxide from air. It was further shown that such capture of CO2 from a low concentrated source of CO2 (such as air) is possible in solid state also. The compound 3 can act as a carbon dioxide reservoir; where CO2 containing anion can be released by heating at 150 °C or with an ion exchange column regenerating the starting carbene salt for reuse. This study opens up the possibility of CO2 capture from air followed by its reduction into methanol or formic acid without employing any metal and under very mild conditions.

The process of the present invention describing CO2 conversion to methanol in the presence of carbene or its derivative s/adducts has several advantages including but not limiting to the process being simple, economic, efficient, high purity of obtained methanol, and the process is also devoid of usage of toxic metal reagents, and also the TON value of carbenes being high in the presence of 99.995% pure carbon dioxide which shows that carbene is active even under low amounts of loading, and minimal side product was formed indicating that the reaction is clean.