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Article

Photocatalytic N-Formylation of CO2 with Amines Catalyzed by Diethyltriamine Pentaacetic Acid

by
Xuexin Yuan
1,
Qiqi Zhou
1,
Yu Chen
1,
Hai-Jian Yang
1,*,
Qingqing Jiang
1,
Juncheng Hu
1 and
Cun-Yue Guo
2,*
1
Key Laboratory of Catalysis and Energy Materials Chemistry of Ministry of Education & Hubei Key Laboratory of Catalysis and Materials Science, College of Chemistry and Materials Science, South-Central Minzu University, Wuhan 430074, China
2
School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing 101408, China
*
Authors to whom correspondence should be addressed.
C 2024, 10(3), 62; https://doi.org/10.3390/c10030062
Submission received: 9 June 2024 / Revised: 1 July 2024 / Accepted: 9 July 2024 / Published: 11 July 2024
(This article belongs to the Section CO2 Utilization and Conversion)
Browse Figures
Versions Notes

Abstract

:
In the present work, inexpensive and commercially available diethyltriamine pentaacetic acid (DTPA) was used as an initiator to catalyze the N-formylation reaction of CO2 with amines via the construction of C-N bonds in the presence of xanthone as the photosensitizer and PhSiH3 as the reducing agent. After a systematic study of various factors, the optimal conditions for the photocatalytic reaction were obtained: 2.5 mmol of amine, 2.5 mmol of PhSiH3, 10 mol% of DTPA, 20 mol% of xanthone, 1 mL of dimethylsulfoxide (DMSO), atmospheric pressure, and 35 W UV lamp irradiation for 48 h. Under the optimal conditions, the catalyst system afforded high performance for the N-formylation of amines (primary and secondary amines) and CO2, and the yields of the N-formylated products of dialkylamines were above 70%. Further studies exhibit that the catalytic system has a wide scope of substrate applications. For various alicyclic secondary amines, heterocyclic secondary amines, aliphatic primary amines, and aromatic primary amines, the corresponding N-formylation products can be obtained efficiently. In addition, the catalyst can be recycled by simple precipitation and filtration. After five cycles of recycling, there was no significant change in the catalytic and structural properties of DTPA. Finally, a possible reaction mechanism is proposed.

Graphical Abstract

1. Introduction

With the development of industrial societies, the amount of carbon dioxide in the atmosphere has increased year over year. Carbon dioxide, which accounts for about 82% of all greenhouse gases, is thought to be the main cause of global warming. However, climate change due to global warming could be one of the major threats to modern civilization. Therefore, the reduction of CO2 emissions and the utilization of CO2 has become an urgent issue [1].
Utilization of CO2, or, better to say, “chemical fixation of CO2”, can be obtained via a simple reaction between CO2 and various compounds, such as epoxides, amines, and so forth. The N-formylation reaction of amines with CO2 is one of the attractive routes to high value-added formamide chemicals. Formamide is widely used in the synthesis of chemicals. It is not only a key intermediate in the synthesis of isocyanates [2,3], drugs [4,5,6], and pesticides [7] but also a solvent for organic synthesis reactions such as N,N-dimethylformamide or N,N-dimethylacetamide [8,9,10]. Traditionally, the synthesis of formamide generally requires the use of CO, which has a high degree of toxicity, as a carbonylation reagent to react with the amine. In contrast, the use of CO2 with amines to generate formamide or methylamine via N-formylation and N-methylation reactions is a green, safe, and more attractive production strategy. However, the schemes reported so far use either homogeneous catalysts [11,12,13], heterogeneous catalysis [14,15], or higher reaction temperatures [16,17]. Therefore, N-formylation of amines and CO2 using visible light under mild reaction conditions is a promising but less explored approach. However, although many catalyst systems have been adopted successfully to catalyze the N-formylation between CO2 and amines under traditional chemothermal conditions, few successful works under photocatalyzed conditions have been reported [18,19].
In 2017, Han’s group used glycine betaine, the carboxylate ammonium salt, as a catalyst for the reduction reaction of CO2 and amine to generate formamide, amine acetal, and methylamine [20]. In 2018, Yu’s team used Ir(ppy)2(dtbbpy) PF6 as a photosensitizer and benzyl quaternary ammonium salt as a substrate to realize the coupling of CO2 with benzyl to form the corresponding benzyl formate without needing external addition of a single-electron donor [21]. This work inspired our interest in the area of photocatalyzed N-formylation of amines and CO2. In most reported photocatalysis, expensive metal compounds and photosensitizers were used. So, in the present work, cheap and commercially available diethyltriamine pentaacetic acid (DTPA, a good electron-donating reagent with 3 N) was used as a non-metal organic photocatalyst to catalyze the N-formylation reaction of CO2 with amines in the presence of relative cheap xanthone as the photosensitizer.

2. Materials and Methods

2.1. Reagents and Instruments

The following reagents are purchased from Aladdin Reagents Ltd. and used without further purification: diethylenetriaminepentaacetic acid (99% purity), xanthone (99% purity), dimethyl sulfoxide (99.7% purity), 2-ethylbutan-1-amine (99% purity), di-n-butylamine (99% purity), dihexylamine (99% purity), di-isopropylamine (99.5% purity), pyrrolidine (99% purity), piperidine (99% purity), 2-methylpiperidine (99% purity), polymer-bound (99% purity), thiomorpholine (98% purity), aniline (99.5% purity), 4-fluoroaniline (99% purity), 4-chloroaniline (99% purity), 4-bromoaniline (99% purity), 4-nitroaniline (99% purity), p-toluidine (99% purity), 4-ethylaniline (99% purity), 4-butylaniline (98% purity), 4-isopropylaniline (98% purity), 2-ethylaniline (98% purity), 2,6-dimethylbenzenamine (98% purity), 2,6-diethylaniline (98% purity), 2,6-diisopropylaniline (90% purity), and CO2 (99.99% purity) with all reagents are purchased from Aladdin Reagents Ltd. and used without further purification. Reaction conversions and selectivity were determined with a Bruker Al-400 MHz NMR instrument (Bruker Technologies Ltd., Migdal HaEmek, Israel) and a LED UV lamp (Zhonglian UV Optical Factory) with a wavelength of 365 nm.

2.2. Preparation of Formamide

Weighed reagents and magnets were added to a 50 mL dry Schlenk flask, and carbon dioxide was used to displace the air in the reaction flask at least three times. Then, the reaction flask is connected to a balloon filled with carbon dioxide, thus ensuring that there is enough carbon dioxide to fully react with the substrate. Subsequently, a quantitative amount of liquid reagent was added into the reaction vial via syringe. The reaction was initiated by turning on the 35 W UV lamp (365 nm). When the reaction finished in set time, a small amount of the mixture was taken for NMR test and calculation of the conversion yield.

2.3. Catalyst Recycling Procedure

After each experiment, 25 mL of ethyl acetate was added to the reaction mixture to induce the precipitation, and then filtered and dried in vacuum for 2 h. Then, the collected catalyst was used for next run.

3. Results and Discussion

3.1. Optimization of Reaction Conditions

The formylation of N-methylaniline and CO2 was chosen as the model reaction to screen the optimal conditions with DTPA as the catalyst, and xanthone as the photosensitizer (Figure 1).

3.1.1. Light Intensity Effect on the Reaction

First, the reaction of N-methylaniline and CO2 was carried out without light, and almost no product was obtained even at 80 °C (entry 1, Table 1). Then, the wattage of the LED lamp was adjusted. When a 35 W UV lamp was used as the light source, the conversion of N-methylaniline reached 92%, and the N-formylated product was obtained with 93% selectivity (entry 3, Table 1). As the wattage continues to increase, both conversion rate and selectivity further decreases. The increase in wattage will lead to an increase in temperature (<10 °C), and higher temperature is favorable for the generation of N-methylation products, and this trend is also observed in the non-photocatalytic systems [22,23,24,25].

3.1.2. Screening of Amount of DTPA and Xanthone and Reaction Time

The amounts of DTPA and xanthone were calculated according to substrate N-methylaniline. As shown in Table 2, when DTPA dosage increased from 5 mol% to 10 mol% while keeping the xanthone amount at 20 mol%, the conversion of substrate increased sharply from 48% to 92%, and a much better selectivity of 93% for the N-formylated product was obtained (entries 1 and 2, Table 2). However, a further increase of DTPA amount to 20 mol% did not result in a significant change in yield and selectivity (entry 3, Table 2). When the xanthone amount decreased from 20 mol% to 10 mol% with a DTPA amount of 10 mol%, the conversion of substrate decreased dramatically from 92% to 51%, and the selectivity for N-formylated product also dropped (entry 4, Table 2). A further decrease in the xanthone amount to 5 mol% resulted in a lower yield. A longer reaction time than 48 h did not result in a significant increase in yield but much worse selectivity (entry 7, Table 2), and a shorter reaction time of 24 h resulted in a dramatic decrease in yield.

3.1.3. Screening of Solvents

The polarity of the solvent also has a strong influence on this reaction system (Figure 2). When the polar DMSO and DMF were used as solvents, the conversion of the reactants reached 92% and 93%, respectively. However, when DMF was used as a solvent, the selectivity of the N-formylated product decreased to 68% dramatically. When slightly less polar acetonitrile was used as the solvent, the conversion decreased to 64%, and the selectivity of the N-formylation product was 82%. When the solvent was changed to the less polar THF, the conversion of N-methylaniline was further reduced to 58%, and the selectivity of the formylated product was only 54%. Overall, the polarity of the solvent has a greater effect on the reaction, with greater polarity favoring the N-formylation reaction [26,27].

3.1.4. Screening of Reducing Agents and Their Dosages

In the formylation of amines with carbon dioxide, the choice of a reducing agent plays an important role in improving the yield and selectivity (Table 3). In the screening of phenylhydrosilanes, the selectivity of the N-formylated product reached 100% as the number of phenyls increased. However, there was a significant decrease in the conversion of N-methylaniline from 92% (entry 1, Table 3) to 50% (entry 2, Table 3) and 26% (entry 3, Table 3). Overall, the fewer the number of hydrogens in the reductant hydrosilane, the bigger the steric hindrance of the substituent and the lower the conversion of the substrate.
The amount of reducing agent also significantly affects the yield of this reaction. When 1.25 mmol of PhSiH3 was used, the conversion was only 48% (entry 5, Table 3). When 3.75 mmol of PhSiH3 was used in the reaction, there was no significant increase in the conversion, while the selectivity for the formylated product decreased slightly (entry 6, Table 3). Therefore, 2.5 mmol of PhSiH3 was chosen as the optimal amount of reducing agent.
In summary, the optimal photocatalytic conditions were screened as 20 mol% xanthone, 10 mol% DTPA, 35 W, 48 h, and 2.5 mmol PhSiH3.

3.2. Studies on the Suitability of N-Formylated Substrates for Secondary Amines

The application scope of catalytic systems has been widely tested under optimal photocatalytic conditions. As shown in Table 4, for most of the secondary amines, the corresponding formamide products were obtained in good to excellent yields (70–95%). Good yields of 88.5%, 79.4%, and 77.0% were also obtained when dialkylamines, such as di-n-propylamine, di-n-butylamine, di-n-hexylamine, and di-isopropylamine, were used as substrates for the reaction, respectively. The yield decreases gradually with the increase in carbon chain length, probably due to the increase in viscosity and steric hindrance. In most cases of cyclic secondary amines, hexagonal ring compounds of piperidines with CO2 formed corresponding N-formylated products in good to excellent yields of 72.9–92.6%. However, when pentacyclic pyrrolidine was used as substrates, a yield of only 45.2% was obtained, probably due to their larger ring tension. Heterocyclic amines, such as morpholine and thiomorpholine with electron-rich atoms O or S, can easily react with CO2 to yield N-formylated products with excellent yields (>95%). Higher-molecular-weight secondary amine compounds with aromatic phenyl group can also react with CO2 in high yields (>90%) when catalyzed by the present photocatalytic system.

3.3. Studies on the Suitability of N-Formylated Substrates for Primary Amines

3.3.1. Investigation of Aromatic Primary Amine Substrate Suitability

Aromatic primary amines were also explored under the optimal reaction conditions. As can be seen from Table 5, N-formylation for most of the aromatic primary amines and CO2 showed good selectivity: more than 99% of the products are monosubstituted formamide products, and almost no double-substituted or methylamine products were produced. Aniline containing halogen atoms (e.g., -F, -Br, -Cl) in the para position gave moderate yields of 79.4%, 75.8%, and 73.5%, respectively. When p-nitroaniline was used as the substrate, the yield of the product was only 53.5% due to the strong electron-withdrawing effect. Primary amines with electron-donating groups such as methyl, ethyl, n-butyl, and isopropyl in the para position of aniline have progressively lower yields as the carbon chain grows. In the case of ethylaniline, the corresponding yield of o-ethylaniline was much higher than that of para-ethylaniline, probably indicating the existence of an intermolecular steric hindrance of substrates to N-formylation. However, for ortho-substituted anilines, such as 2,6-dimethylaniline, 2,6-diethylaniline, and 2,6-diisopropylaniline, which have larger steric hindrance, spatial potential barrier effect was not so notable, and the efficiency of the N-formylation reaction in yield ranges from 86.2 to 91.7%.

3.3.2. Study of the Suitability of Aliphatic Primary Amine Substrates

Subsequently, aliphatic primary amines were explored. As shown in Table 6, aliphatic primary amines showed higher reactivity than aromatic primary amines. Primary amines with different alkyl chains, e.g., n-butylamine, n-hexylamine, and n-octylamine, provided N-formylated products with excellent yields (85–90%). It was also found that the product yield decreased with the growth of the carbon chain. This phenomenon is consistent with the data reported by Zhang et al. [28] using nano Pd/C catalyst at 105 °C for 24 h to generate N-formylation. The yields in N-formylation of tert-butylamine and cyclohexylamine with larger steric hindrance were only 50.9% and 40.3%, respectively, after 48 h of reaction. Substituted benzylamines, with both electron-donating (-OCH3) and electron-withdrawing (-F) groups, have higher yields compared to benzylamines (38.0%). Extension of the carbon chain between the benzene ring and the amino group resulted in excellent yield of N-formylated compound (98.0%). When using alkyne propylamine as a substrate, the alkyne group was not reduced even in the presence of the reducing agent PhSiH3, and N-formylation occurred only on the amino group during the whole reaction period; similar reports have been presented in the literature [29].

3.4. Catalyst Recycling

In order to test the stability of the catalyst, catalyst recycling experiments were conducted under optimal reaction conditions (Figure 3). After each cycle, ethyl acetate (25 mL) was added to the reaction mixture to induce precipitation of the reactants; then, after filtration and drying in a vacuum for 2 h, the catalyst was used repeatedly. The results show that there was no significant loss of DTPA activity after five cycles of recycling.
In addition, comparing the IR spectra (Figure 4) of DTPA after five cycles of recycling with that of fresh DTPA finds that the structure of DTPA was still maintained, indicating good stability and recyclability of DTPA.

3.5. CO2 Photocatalytic Reaction Mechanism

Based on previous literature reports [30,31,32,33], a possible catalytic mechanism was proposed in Figure 5. Firstly, the xanthone acts as a photocatalyst (PC) to form the excited state of PC* under the irradiation of light. PC* undergoes single electron transfer (SET) with DTPA to form a DTPA radical cation. Reaction of DTPA+ with phenylsilane forms phenylsilyl radicals and releases H+. Meanwhile, CO2 reacts with aniline to form the carbamate anion (I). Then, carbamate anion reacts with phenylsilyl radicals to form radical anions (II). Subsequent decomposition of radical anions can generate the carbamoyl radical (III). Carbamoyl radical can undergo a hydrogen atom transfer process, which ultimately produces the desired product formamide.

4. Conclusions

Commercially available DTPA as a catalyst and relatively inexpensive xanthone as a photocatalyst have been used to form a photocatalytic system to promote the photocatalytic N-formylation of amines with CO2 efficiently. Under the optimal conditions, N-formylated products were obtained in moderate to good yields with high selectivity. In addition, the catalyst exhibited high stability and good recyclability via simple precipitation and filtration. No significant changes in the catalytic properties and structure of DTPA were observed after five cycles of recycling. The present photocatalytic catalytic system does not require high reaction temperature and CO2 pressure, manifesting an environmentally friend and non-toxic catalytic system with potential application for the industrial synthesis of formamide.

Author Contributions

Conceptualization, X.Y. and Y.C.; methodology, Q.Z.; software, Q.Z.; validation, X.Y., Y.C. and Q.Z.; formal analysis, Q.Z.; investigation, X.Y. and Q.J.; resources, Q.Z.; data curation, X.Y., J.H.; writing—original draft preparation, X.Y.; writing—review and editing, H.-J.Y.; visualization, X.Y.; supervision, H.-J.Y. and C.-Y.G.; project administration, C.-Y.G.; funding acquisition, H.-J.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China (grant number 51073175) and the Fund for Academic Innovation Teams of South-Central Minzu University (No. XTZ24016).

Data Availability Statement

All data have been shown in the main text. The data presented in this study are available on request from the corresponding author Professor Yang.

Conflicts of Interest

The authors declare no conflicts of interest.

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Carbon 10 00062 g001
Figure 1. Photocatalyzed CO2 N-formylation reaction.
Figure 1. Photocatalyzed CO2 N-formylation reaction.
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Figure 2. Effect of solvent on the N-formylation of N-methylaniline with CO2. Reaction conditions: N-methylaniline (2.5 mmol), xanthone (20 mol%), DTPA (10 mol%), solvent (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, and 48 h. The yield was determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard.
Figure 2. Effect of solvent on the N-formylation of N-methylaniline with CO2. Reaction conditions: N-methylaniline (2.5 mmol), xanthone (20 mol%), DTPA (10 mol%), solvent (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, and 48 h. The yield was determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard.
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Figure 3. Recycling experiment of DTPA-catalyzed N-formylation reaction of CO2 with aniline.
Figure 3. Recycling experiment of DTPA-catalyzed N-formylation reaction of CO2 with aniline.
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Figure 4. Infrared comparison spectra of DTPA before and after 5 times of reuse.
Figure 4. Infrared comparison spectra of DTPA before and after 5 times of reuse.
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Figure 5. Reaction mechanism of CO2 with aniline N-formylation.
Figure 5. Reaction mechanism of CO2 with aniline N-formylation.
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Table 1. Effect of light intensity on the N-formylation reaction of N-methylaniline with CO2.
Table 1. Effect of light intensity on the N-formylation reaction of N-methylaniline with CO2.
EntryLED (W)Conversion (%) a,bSelectivity (%) b
(2a:2b)
1 c-trace-
2208896:4
3359293:7
4508593:7
5808190:10
61008088:12
a Reaction conditions: N-methylaniline (2.5 mmol), xanthone (20 mol%), DTPA (10 mol%), DMSO as solvent (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, and 48 h. b The yield was determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard. c Without LED light, 0.1 MPa CO2 pressure, 80 °C.
Table 2. Effect of DTPA/xanthone amount and reaction time on the N-formylation reaction of N-methylaniline with CO2.
Table 2. Effect of DTPA/xanthone amount and reaction time on the N-formylation reaction of N-methylaniline with CO2.
EntryDTPA (mol%)Xanthone (mol%)Yield(%) a,bSelectivity (%) b
(2a:2b)
15204885:15
210209293:7
320209392:8
410105190:10
51054390:10
6 c10203793:7
7 d10209478:12
a Reaction conditions: N-methylaniline (2.5 mmol), DMSO as solvent (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, and 48 h. b The yields were determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard. c 24 h. d 72h.
Table 3. Effect of reducing agents and their amounts on the N-formylation of N-methylaniline with CO2.
Table 3. Effect of reducing agents and their amounts on the N-formylation of N-methylaniline with CO2.
EntryHydrosilaneDosage (mmol)Conversion (%) a,bSelectivity (%) b
(2a:2b)
1PhSiH32.592100:0
2Ph2SiH22.550100:0
3Ph3SiH2.526100:0
4Me2PhSiH2.5trace-
5Et3SiH2.524100:0
6 cPhSiH31.254885:15
7 dPhSiH33.759391:9
a Reaction conditions: N-methylaniline (2.5 mmol), xanthone (20 mol%), DTPA (10 mol%), DMSO (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, and 48 h. b The yields were determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard. c PhSiH3 (1.25 mmol) 48 h. d PhSiH3 (3.75 mmol).
Table 4. N-formylation of secondary amines.
Table 4. N-formylation of secondary amines.
Carbon 10 00062 i001
EntrySubstrateProductYield (%) a,b
1Carbon 10 00062 i002Carbon 10 00062 i00388.5
2Carbon 10 00062 i004Carbon 10 00062 i00579.4
3Carbon 10 00062 i006Carbon 10 00062 i00777.0
4Carbon 10 00062 i008Carbon 10 00062 i00998.0
5Carbon 10 00062 i010Carbon 10 00062 i01145.2
6Carbon 10 00062 i012Carbon 10 00062 i01392.6
7Carbon 10 00062 i014Carbon 10 00062 i01588.5
8Carbon 10 00062 i016Carbon 10 00062 i01772.9
9Carbon 10 00062 i018Carbon 10 00062 i01996.5
10Carbon 10 00062 i020Carbon 10 00062 i02195.2
11Carbon 10 00062 i022Carbon 10 00062 i02392.6
12Carbon 10 00062 i024Carbon 10 00062 i02590.1
a Reaction conditions: Substrate (2.5 mmol), xanthone (20 mol%), DTPA (10 mol%), DMSO (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, 35 W, and 48 h. b The yields were determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard.
Table 5. Aromatic primary amine N-formylation reactions.
Table 5. Aromatic primary amine N-formylation reactions.
Carbon 10 00062 i026
EntrySubstrateProductYield (%) a,b
1Carbon 10 00062 i027Carbon 10 00062 i02882.6
2Carbon 10 00062 i029Carbon 10 00062 i03079.4
3Carbon 10 00062 i031Carbon 10 00062 i03275.8
4Carbon 10 00062 i033Carbon 10 00062 i03473.5
5Carbon 10 00062 i035Carbon 10 00062 i03653.5
6Carbon 10 00062 i037Carbon 10 00062 i03869.0
7Carbon 10 00062 i039Carbon 10 00062 i04053.5
8Carbon 10 00062 i041Carbon 10 00062 i04239.4
9Carbon 10 00062 i043Carbon 10 00062 i04448.8
10Carbon 10 00062 i045Carbon 10 00062 i04694.3
11Carbon 10 00062 i047Carbon 10 00062 i04891.7
12Carbon 10 00062 i049Carbon 10 00062 i05086.2
13Carbon 10 00062 i051Carbon 10 00062 i05287.7
a Reaction conditions: Substrate (2.5 mmol), xanthone (20 mol%), DTPA (10 mol%), DMSO (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, 35 W, and 48 h. b The yields were determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard.
Table 6. N-formylation reaction of aliphatic primary amines.
Table 6. N-formylation reaction of aliphatic primary amines.
Carbon 10 00062 i053
EntrySubstrateProductYield (%) a,b
1Carbon 10 00062 i054Carbon 10 00062 i05590.1
2Carbon 10 00062 i056Carbon 10 00062 i05787.0
3Carbon 10 00062 i058Carbon 10 00062 i05985.5
4Carbon 10 00062 i060Carbon 10 00062 i06150.9
5Carbon 10 00062 i062Carbon 10 00062 i06340.3
6Carbon 10 00062 i064Carbon 10 00062 i06538.0
7Carbon 10 00062 i066Carbon 10 00062 i06753.5
8Carbon 10 00062 i068Carbon 10 00062 i06946.1
9Carbon 10 00062 i070Carbon 10 00062 i07198.0
10Carbon 10 00062 i072Carbon 10 00062 i07348.8
a Reaction conditions: Substrate (2.5 mmol), xanthone (20 mol%), DTPA (10 mol%), DMSO (1 mL), CO2 (0.1 MPa), PhSiH3 (2.5 mmol), rt, 35 W, and 48 h. b The yields were determined by 1H NMR spectra analysis using 1,3,5-trimethoxybenzene as an internal standard.
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MDPI and ACS Style

Yuan, X.; Zhou, Q.; Chen, Y.; Yang, H.-J.; Jiang, Q.; Hu, J.; Guo, C.-Y. Photocatalytic N-Formylation of CO2 with Amines Catalyzed by Diethyltriamine Pentaacetic Acid. C 2024, 10, 62. https://doi.org/10.3390/c10030062

AMA Style

Yuan X, Zhou Q, Chen Y, Yang H-J, Jiang Q, Hu J, Guo C-Y. Photocatalytic N-Formylation of CO2 with Amines Catalyzed by Diethyltriamine Pentaacetic Acid. C. 2024; 10(3):62. https://doi.org/10.3390/c10030062

Chicago/Turabian Style

Yuan, Xuexin, Qiqi Zhou, Yu Chen, Hai-Jian Yang, Qingqing Jiang, Juncheng Hu, and Cun-Yue Guo. 2024. "Photocatalytic N-Formylation of CO2 with Amines Catalyzed by Diethyltriamine Pentaacetic Acid" C 10, no. 3: 62. https://doi.org/10.3390/c10030062

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