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Article

Catalytic Behavior of NHC–Silver Complexes in the Carboxylation of Terminal Alkynes with CO2

by
Assunta D’Amato
1,
Marco Sirignano
1,
Francesco Viceconte
2,
Pasquale Longo
1 and
Annaluisa Mariconda
2,*
1
Department of Chemistry and Biology, University of Salerno, Via Giovanni Paolo II, 132, 84084 Fisciano, Italy
2
Department of Science, University of Basilicata, Viale dell’Ateneo Lucano, 10, 85100 Potenza, Italy
*
Author to whom correspondence should be addressed.
Inorganics 2024, 12(11), 283; https://doi.org/10.3390/inorganics12110283
Submission received: 4 September 2024 / Revised: 23 October 2024 / Accepted: 28 October 2024 / Published: 30 October 2024
(This article belongs to the Special Issue N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications, 2nd Edition)
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Abstract

:
A number of N-heterocyclic carbene–silver compounds (NHCs)AgX were tested in the direct carboxylation of terminal alkynes using carbon dioxide as the C1 carbon feedstock. The reactions proceed at a pressure of 1 atm of CO2 at room temperature, in the presence of Cs2CO3, and using silver–NHC complexes as catalysts. Thus, phenylacetylene and several alkynes are converted to the corresponding propiolic acids in good to high conversions. The activity of the catalysts is strongly influenced by the substituents on the NHC backbone and the nature of the counterion. Specifically, the most active compound exhibits iodide as the counterion and is stabilized by a benzimidazole derivative. After 24 h of reaction, a quantitative conversion is obtained utilizing DMF as the solvent and phenylacetylene as the substrate.

Graphical Abstract

1. Introduction

The widespread use of fossil fuels has resulted in a considerable increase in CO2 levels in the atmosphere, hence enhancing the greenhouse effect. Carbon dioxide is currently one of the most fascinating reagents for organic chemistry because it is inexpensive and non-toxic. It is thermodynamically stable and chemically inert, so the activation of this molecule to use it as a reagent requires the use of specific catalysts or particularly drastic reaction conditions, generally high pressures, temperatures higher than room temperatures, or completely anhydrous conditions [1,2,3]. In recent years, research has achieved significant results, also from the point of view of sustainable chemistry, in the exploitation of this important raw material with catalytic transformation into chemical substances with high added value, e.g., the reaction of CO2 with epoxides to obtain cyclic carbonates [4,5,6] or polycarbonates [7,8], the carboxylation of ethylene and methyl iodide to form acrylates [9,10,11,12], and that of alkynes to give carboxylic acids or esters [13,14]. Among the several reactions that activate CO2, the carboxylation of terminal alkynes has shown to be particularly noteworthy since it yields propiolic acids. They are essential intermediates for the production of fine chemicals, medicines, bioactive compounds, synthetic fibers, and conductive polymers [13,15,16,17,18,19,20,21], as well as substrates for other reactions such as hydroarylations, decarboxylative couplings, and cycloadditions [18,19,20,21,22,23,24,25,26,27,28] (Scheme 1). The latter can give heterocycles such as butyrolactones, flavonoids, furanone, and pyranone [29,30,31,32,33].
Significant contributions in the carboxylation of terminal alkynes have been made by many research groups [34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49].
This reaction can happen in the absence of catalysts and at a high temperature [50]. In the presence of copper(I) and silver(I) halide complexes that have shown good activity in catalyzing the carboxylation of various alkynes in the presence of a strong base [51,52,53,54], it can occur under mild conditions. The mechanism of this reaction, as proposed by C. Liu et al. [55] or J. Jover et al. [56], who corroborated their findings with DFT calculations, involves the reaction of CsCO3− with (NHC)AgX to form the anionic complex (a), which represents the catalytically active species (see Scheme 2). Coordination of the alkyne to the metal center (b), followed by its deprotonation, assisted by the cesium carbonate as a base, produces silver acetylide (c). Then, the interaction of CO2 with the C(sp)-Ag (d) and its subsequent insertion into the C-metal bond (e) after acidification with CsHCO3 produces the propiolic acid (see Scheme 2) [56,57].
The reactivity of group 11 metals in low oxidation states (0 or 1) in this type of reaction is attributed to their tendency to act as carbophilic Lewis acids, allowing them to interact with triple C-C bonds. The p-complexation produces the activation of both the C-C and the C(sp)-H bonds, facilitating the coupling [58,59,60,61]. Among the many copper(I)- or silver(I)-based complexes employed in this catalytic process, N-heterocyclic carbenes showed great activity and good stability [36,37,62,63,64,65]. Zhang et al. [36,62] reported the carboxylation of terminal alkynes with CO2 (1 atm) using poly-NHC–Cu(I) or poly-NHC–Ag(I) catalysts, which showed high activity and stability, yielding functionalized propiolic acids effectively under ambient conditions with Cs2CO3. Similarly, Fang et al. [63] described the synthesis and catalytic activity of N-benzyl-substituted NHC–Ag complexes in the same reaction, also achieving high activity and stability with good to excellent yields (up to 83%—TOF 519 h−1) under similar experimental conditions. Verpoort et al. [37,64] documented excellent data on isolated and in situ-generated silver-based catalysts with sulfonated NHC ligands for the direct carboxylation of terminal alkynes under mild conditions with high yields. It is worth noting that gold(I) complexes display lower activity than silver analogs due to the different electronegativities of the two metals: 1.9 for silver and 2.4 for gold. This difference makes the M-C≡C-R bond more stable and, consequently, the carbon that must interact with the CO2 less nucleophilic.
Recently, some of us developed and characterized several novel silver and gold complexes stabilized by asymmetrically nitrogen-substituted N-heterocyclic carbene ligands, such as N-(2-hydroxyethyl)-N’-(2-hydroxy-2-phenyl)ethyl-2-ylidene. In this study, various silver complexes were investigated in the carboxylation reaction with CO2 of numerous terminal alkynes to produce propiolic acids. A kinetic study was carried out to assess the effects of the following: (i) different substituents on the backbone of the imidazole ring, (ii) different metal counterions, and (iii) different reaction solvents.

2. Results

2.1. Synthesis and Characterization of Complexes

The NHC metal complexes 1a [66], 2a, 3a [67], and 4a [68] were synthesized as reported in the literature. Complexes 4b and 4c were synthesized by slightly modifying the literature procedure (Scheme 3). The first step is the synthesis of N-2-phenyl-2-hydroxyethyl-benzimidazole (S4), which was obtained by the reaction of benzimidazole with styrene oxide. The opening of the epoxide generates a hydroxyl group, which was introduced in order to increase the solubility of the catalyst in a polar reaction media. S4b and S4c were obtained with the reaction of S4 with 2-iodoethanol or benzyl bromide (see Scheme 3). Complex 4b was synthesized by mixing a solution of imidazolium salt S4b with 0.6 eq. of Ag2O at room temperature and in the dark. The reaction of imidazolium salt S4c with Ag2O leads to the formation of the (NHC)AgBr complex. Complex 4c was obtained by a counterion metathesis reaction of (NHC)AgBr with sodium iodide (see Supplementary Materials).
The iodide complexes were characterized by means of 1H- and 13C-NMR spectroscopy, mass spectrometry (MALDI), and the elemental analysis technique. Influences of the imidazole’s backbone on the σ-donation properties of the ligand were evaluated, according to Nolan and Huynh [69,70], for proligands S1a, S2a, and S4a, measuring one-bond CH J-coupling (DMSO-d6, 150 MHz). 1JC–H were coherent with increasing σ-donation in the order S2a < S1a < S4a (229.92 Hz, 222.84 Hz, 221.56 Hz).
The iodide counterion of complex 4a undergoes exchange when it reacts with the appropriate silver or sodium salt due to the precipitation of silver iodide. Thus, 4a.1, 4a.2, and 4a.3 were obtained using silver acetate, silver hexafluorophosphate, and silver nitrate, respectively (Scheme 4). Chloride complex 4a.4 was obtained by the reaction of 4a with an excess of NaCl. The main evidence of the counterion exchange is due to the shift of the carbenic carbon in the 13C NMR spectra of 4a.1, 4a.2, 4a.3, and 4a.4, whereas the rest of the spectra remain mostly unaltered. Table 1 shows the chemical shifts of these carbon atoms, which are at lower ppm (upfield shifted), as the σ-donor capacity of the NHC decreases [71].
As can be noticed by observing the data in Table 1, the σ donation of the carbene ligand follows the order 4a > 4a.2 > 4a.1 > 4a.3 > 4a.4, i.e., to NHCAgX complexes with X equal to I−, NO3−, OAc− PF6−, and Cl−, respectively [69,72,73].
The main evidence of the counterion exchange is due to the shift of the carbenic carbon in the 13C NMR spectra of 4a.1, 4a.2, 4a.3, and 4a.4, whereas the rest of the spectra remain mostly unaltered.
The two signals attributable to the carbenic carbon of the complex with PF6− may be due to two species present in the solution. In fact, as frequently observed both by diffractometric and by mass spectrometry analysis of similar compounds [74,75,76,77], silver complexes with N-heterocyclic carbenic ligands give rise to two possible species due to the silver following equilibrium in solution:
[(NHC)2Ag]+[AgX2]−⇄2(NHV)AgX
Thus, while for X = I−, NO3−, −OAc, and Cl−, the equilibrium is more shifted towards the formation of the neutral species and is faster than the NMR time scale, for the PF6− ion the equilibrium is probably slower, and, therefore, two carbenic signals are visible, i.e., at 191.4 and 188.3 ppm due to carbenic carbon of [(NHC)2Ag]+ and (NHC)AgPF6, respectively. Alternatively, the presence of a doublet attributable to Ccarbene in the spectrum of the silver complex with PF6− could be due to the coupling constant of Ccarbene and Ag, whose two natural isotopes have both nuclear spin ½, and therefore they are NMR active, with a narrow coupling constant of 55 Hz.
It is worth recalling that it is known from the literature that the pattern of carbene carbons bonded to silver (Ccarbene-Ag) can present itself in three distinct ways, i.e., (i) no splitting (sharp or broad singlet), (ii) doublet of doublets (coupling constants with each silver isotope 107Ag and 109Ag), and (iii) no peak attributable to the carbene carbon [76].

2.2. Catalytic Carboxylation of Alkynes with CO2

The catalytic activity of silver complexes (1% mol) was evaluated in the coupling reaction of phenylacetylene and CO2 at atmospheric pressure, carrying out the reactions at room temperature in DMSO for 16 h in the presence of cesium carbonate [64].
For the catalysis conditions, we were inspired by the work of Fang et al. [63]. In this work, the carboxylation of terminal alkynes with CO2 (1 atm) with NHC–Ag complexes was tested using different bases (Cs2CO3, DBU, K2CO3, KOtBu, NaOtBu, NaOH) and solvents (DMF, DMSO, CH2Cl2, CH3CN, THF).
The best catalysis conditions were found using Cs2CO3 as a base and DMF as a solvent.
Table 2 reports the obtained results. It is worth noting that the silver complexes are needed to obtain propiolic acid [63]. In fact, a reaction carried out under our experimental conditions (run 18) using the imidazolium salt S4a (1.0 mmol), Cs2CO3 (1.2 mmol), and phenylacetylene (100 mmol) under the pressure of 1.0 atm of CO2 did not produce the carboxylic acid. Comparing the data from runs 1–4 reveals that the substituents on the backbone of the imidazole ring have a considerable influence on the catalyst’s activity. Indeed, these complexes differ only for these substituents, with 4a being the most active, having a condensed arene ring, and the least active having two chlorine atoms in positions 4 and 5 of the ring. This suggests that the inductive effect of the substituents is important; clearly, those that give electron density to the carbenic carbon and, consequently, to the metal center favor the formation of the acetylide and make the C bonded to the metal center more nucleophilic, thus more reactive towards CO2 carbonilic carbon. The choice of dry DMSO as the reaction solvent was made on the basis of the results reported by Velázquez [64], and since then, high conversions in the carboxylation of alkynes with CO2 with catalysts based on silver–NHC complexes were obtained by Zhang [78] in dry DMF as the solvent, whereby complex 2a and 4a, the least and most active, respectively, were tested in DMF as well (see Table 2, runs 5 and 6). Furthermore, complex 4a was tested with a series of solvents of different polarity (see Table 2, runs 7–11). As is evident from the data in Table 2, solvents with low dipole moments (dioxane, THF, and CH2Cl2) give very low conversions (0–15%), those with high dipole moments and weakly acids (DMSO and DMF) give very high conversions (≈90%), while those with high dipole moments and weakly basic (CH3CN) or with intermediate polarity (CH3COOEt) give more modest conversions (≈30–40%). The best solvent for carrying out the carboxylation reaction of phenylacetylene with these catalytic systems was dimethylformamide.
Thus, by performing runs 6, 12, and 13 in DMF, we confirmed that having higher electron density on the carbenic carbon makes the silver complexes more catalytically active. The catalysts used in these tests differ in only one substituent on nitrogen, i.e., methyl for 4a, 2-hydroxyethyl for 4b, and benzyl for 4c. Complex 4a has the greatest activity, while the one with the least activity is complex 4b, the latter having the most electron-withdrawing substituent. Having established that the best ancillary ligand of tested complexes is N-2-phenyl-2-hydroxyethyl-N’-methyl-benzimidazole-2-ylidene, we tried to determine the possible effect of the ancillary ligand. In runs 6 and 14-17, the activities of the Ag(I) complexes with the just-mentioned NHC ligand and iodide, acetate, nitrate, hexafluoro phosphate, and chloride are compared. The catalyst showing the highest activity is 4a (run 6), while the one with the lowest is 4a.4 (run 17). Complex 4a.4 has chloride as the counterion and has the carbene with the lowest σ-donating capacity, while complex 4a has iodide as the counterion and has the carbene with the highest σ-donating capacity, as demonstrated by the 13C NMR resonances of the carbene ligands (see above). This causes the silver iodide bond to be weaker than the silver chloride bond and, thus, more likely to leave the coordination site free for the alkyne.
It is worth noting that the reaction is highly selective since no by-product is obtained, and the whole reaction contains only the propiolic acid and the unreacted alkyne.
The catalytic activity of complex 4a was evaluated by monitoring the carboxylation reaction of phenylacetylene carried out at room temperature in DMF under a CO2 atmosphere. The kinetic data are reported, and the corresponding kinetic profile is shown in Scheme 5. The conversions/time curve was determined with 1H-NMR spectroscopy using the integration of the signals of the aromatic protons and that of the alkynyl proton of the residual phenylacetylene at δ 3.14 ppm.
As seen in the kinetic plot, catalyst 4a is extremely efficient, achieving approximately 50% conversion in 5 h and allowing for the quantitative reaction of phenylacetylene with CO2 in 24 h.
Thus, because our catalytic system is particularly effective, we decided to investigate various alkynes in this reaction with both alkyl and aryl substituents. Table 3 reports the results obtained performing the reaction at room temperature in the presence of 1% mol of complex 4a and 1.2% mol of Cs2CO3 under an atmosphere of CO2, using DMF as solvent.
All products were isolated and characterized by 1H and 13C-NMR, elemental analysis (See Supplementary Materials), and GC-MS, obtaining a correspondence between conversion (obtained through 1H NMR) and yield of the isolated product very close to each other. The differences found were less than 4%.
Alkylacetylenes are more reactive than arylacetylenes, e.g., n-butyl- and tert-butyl-acetylene give conversion higher than 90% in 16 h. Instead, the arylacetylenes have a conversion between 55 and 70% in 16 h. This is easily understood given that alkyls have a higher electron-donating capacity than aryls, which means they have a better coordinating ability to the metal center. It is worth noting that the different para substituents on the aryl acetylenes have little impact on the reactivity, probably because of their contrasting effect, i.e., (i) electron-withdrawing groups increase the acidity of the alkyne but make the C(sp) less nucleophilic and thus less reactive towards the CO2 carbon; and (ii) electron donating groups decrease the acidity of the alkyne and thus make it less reactive towards the metal center to give the acetylide, which, however, has the more nucleophilic C(sp) and therefore is more reactive towards the carbon of the CO2.

3. Materials and Methods

3.1. Synthesis of Catalysts 1–4a–c and 4a.1–4a.4

Detailed information regarding the synthesis and characterization of metal complexes 1–4a–c and 4a.1–4a.4 is reported in the Supplementary Materials.

3.2. General Procedure for Carboxylation of Alkynes

Catalyst (1.0 mol%), Cs2CO3 (390 mg, 1.2 mmol), and freshly dried solvent (1.0 mL) were added to a 10 mL Schlenk tube under an inert atmosphere. The tube was evacuated and filled with CO2. The alkyne (1.0 mmol) was added under a stream of carbon dioxide, and the resulting mixture was stirred at room temperature and ambient pressure. After 16 h, the mixture was quenched using 1.0 mL of CH2Cl2, and then it was treated with 10 mL of solution 2N of K2CO3 and stirred for 30 min. The mixture was extracted with dichloromethane (3 × 10 mL). The aqueous portion was acidified with HCl until Ph = 1 and extracted with diethyl ether (3 × 10 mL). The two organic portions were dried with MgSO4. The corresponding carboxylic compound was obtained with filtration and removal of the solvent in vacuo.
A characterization of the product carboxylic acids is reported in the Supplementary Materials.

4. Conclusions

The catalytic behavior of silver–NHC complexes in the selective carboxylation process between carbon dioxide and phenylacetylene and other terminal alkynes was investigated in this work. The catalyst structure affects the phenylacetylene carboxylation conversion. The most active complex is stabilized by an NHC benzimidazole derivative, while the least performing is an NHC derivative of 4,5-dichloroimidazole. On the other hand, the substitution of one of the nitrogen atoms with a methyl group rather than a (2-hydroxyethyl) moiety provides a more performing catalyst. This shows that complexes with electron-donating groups on the nitrogen and backbone of NHC ligands provide a higher electron density on the carbenic carbon and, as a result, on the metal center, increasing the catalyst’s activity. This is because the increased electron density on the metal center causes the carbon bonded to the metal center to become more nucleophilic, which in turn increases its reactivity with the carbon of CO2. Catalysis tests were conducted with 4a in different solvents, and the highest conversion was obtained when DMF was used, becoming quantitative after 24 h. Furthermore, we evaluated the function of the counterion under optimal catalytic circumstances. Tested under solvent-optimized circumstances, the combination containing the iodide ion proved to be the most active. Lastly, compound 4a exhibited good to high conversions of activity in the carboxylation of various terminal alkynes.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/inorganics12110283/s1, In the Supplementary materials are reported the synthesis and characterization (1H-NMR, 13C-NMR, mass spectrometry and elemental analysis) of the new salts and metal complexes. The characterization of propiolic acids obtained in catalysis tests is also reported. The authors have cited additional references within the Supplementary Materials [79,80,81].

Author Contributions

Conceptualization, P.L. and A.M.; methodology, A.D. and M.S.; investigation, A.D. and M.S.; data curation, A.D., M.S. and F.V.; writing—original draft preparation, A.D. and A.M.; writing—review and editing, P.L. and A.M.; supervision, P.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the Next Generation EU–Italian NRRP, Mission 4, Component 2, Investment 1.5, call for the creation and strengthening of ‘Innovation Ecosystems’, building ‘Territorial R&D Leaders’ (Directorial Decree n. 2021/3277)—project Tech4You—Technologies for climate change adaptation and quality of life improvement, n. ECS0000009. This work reflects only the authors’ views and opinions; neither the Ministry for University and Research nor the European Commission can be considered responsible for them.

Data Availability Statement

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Huang, K.; Sun, C.-L.; Shi, Z.-J. Transition-Metal-Catalyzed C–C Bond Formation through the Fixation of Carbon Dioxide. Chem. Soc. Rev. 2011, 40, 2435. [Google Scholar] [CrossRef] [PubMed]
  2. Federsel, C.; Jackstell, R.; Beller, M. State-of-the-Art Catalysts for Hydrogenation of Carbon Dioxide. Angew. Chem. Int. Ed. 2010, 49, 6254–6257. [Google Scholar] [CrossRef] [PubMed]
  3. Maeda, C.; Miyazaki, Y.; Ema, T. Recent Progress in Catalytic Conversions of Carbon Dioxide. Catal. Sci. Technol. 2014, 4, 1482. [Google Scholar] [CrossRef]
  4. Decortes, A.; Castilla, A.M.; Kleij, A.W. Salen-Complex-Mediated Formation of Cyclic Carbonates by Cycloaddition of CO2 to Epoxides. Angew. Chem. Int. Ed. 2010, 49, 9822–9837. [Google Scholar] [CrossRef] [PubMed]
  5. Whiteoak, C.J.; Kielland, N.; Laserna, V.; Escudero-Adán, E.C.; Martin, E.; Kleij, A.W. A Powerful Aluminum Catalyst for the Synthesis of Highly Functional Organic Carbonates. J. Am. Chem. Soc. 2013, 135, 1228–1231. [Google Scholar] [CrossRef]
  6. Du, G.-F.; Guo, H.; Wang, Y.; Li, W.-J.; Shi, W.-J.; Dai, B. N-Heterocyclic Carbene Catalyzed Synthesis of Dimethyl Carbonate via Transesterification of Ethylene Carbonate with Methanol. J. Saudi Chem. Soc. 2015, 19, 112–115. [Google Scholar] [CrossRef]
  7. Lu, X.-B.; Darensbourg, D.J. Cobalt Catalysts for the Coupling of CO2 and Epoxides to Provide Polycarbonates and Cyclic Carbonates. Chem. Soc. Rev. 2012, 41, 1462–1484. [Google Scholar] [CrossRef]
  8. Darensbourg, D.J. Making Plastics from Carbon Dioxide: Salen Metal Complexes as Catalysts for the Production of Polycarbonates from Epoxides and CO2. Chem. Rev. 2007, 107, 2388–2410. [Google Scholar] [CrossRef]
  9. Bernskoetter, W.H.; Tyler, B.T. Kinetics and Mechanism of Molybdenum-Mediated Acrylate Formation from Carbon Dioxide and Ethylene. Organometallics 2011, 30, 520–527. [Google Scholar] [CrossRef]
  10. Zhang, Y.; Hanna, B.S.; Dineen, A.; Williard, P.G.; Bernskoetter, W.H. Functionalization of Carbon Dioxide with Ethylene at Molybdenum Hydride Complexes. Organometallics 2013, 32, 3969–3979. [Google Scholar] [CrossRef]
  11. Bruckmeier, C.; Lehenmeier, M.W.; Reichardt, R.; Vagin, S.; Rieger, B. Formation of Methyl Acrylate from CO2 and Ethylene via Methylation of Nickelalactones. Organometallics 2010, 29, 2199–2202. [Google Scholar] [CrossRef]
  12. Lee, S.Y.T.; Cokoja, M.; Drees, M.; Li, Y.; Mink, J.; Herrmann, W.A.; Kühn, F.E. Transformation of Nickelalactones to Methyl Acrylate: On the Way to a Catalytic Conversion of Carbon Dioxide. ChemSusChem 2011, 4, 1275–1279. [Google Scholar] [CrossRef]
  13. Manjolinho, F.; Arndt, M.; Gooßen, K.; Gooßen, L.J. Catalytic C–H Carboxylation of Terminal Alkynes with Carbon Dioxide. ACS Catal. 2012, 2, 2014–2021. [Google Scholar] [CrossRef]
  14. Bonne, D.; Dekhane, M.; Zhu, J. Modulating the Reactivity of α-Isocyanoacetates: Multicomponent Synthesis of 5-Methoxyoxazoles and Furopyrrolones. Angew. Chem. 2007, 119, 2537–2540. [Google Scholar] [CrossRef]
  15. Maeda, K.; Goto, H.; Yashima, E. Stereospecific Polymerization of Propiolic Acid with Rhodium Complexes in the Presence of Bases and Helix Induction on the Polymer in Water. Macromolecules 2001, 34, 1160–1164. [Google Scholar] [CrossRef]
  16. D’Souza, D.M.; Kiel, A.; Herten, D.-P.; Rominger, F.; Müller, T.J.J. Synthesis, Structure and Emission Properties of Spirocyclic Benzofuranones and Dihydroindolones: A Domino Insertion–Coupling–Isomerization–Diels–Alder Approach to Rigid Fluorophores. Chem.-Eur. J. 2008, 14, 529–547. [Google Scholar] [CrossRef] [PubMed]
  17. Nurhanna Riduan, S.; Ying, J.Y.; Zhang, Y. Carbon Dioxide Mediated Stereoselective Copper-Catalyzed Reductive Coupling of Alkynes and Thiols. Org. Lett. 2012, 14, 1780–1783. [Google Scholar] [CrossRef] [PubMed]
  18. Moon, J.; Jang, M.; Lee, S. Palladium-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylic Acids and Aryl Halides. J. Org. Chem. 2009, 74, 1403–1406. [Google Scholar] [CrossRef]
  19. Trost, B.M.; Toste, F.D.; Greenman, K. Atom Economy. Palladium-Catalyzed Formation of Coumarins by Addition of Phenols and Alkynoates via a Net C−H Insertion. J. Am. Chem. Soc. 2003, 125, 4518–4526. [Google Scholar] [CrossRef]
  20. Jia, W.; Jiao, N. Cu-Catalyzed Oxidative Amidation of Propiolic Acids Under Air via Decarboxylative Coupling. Org. Lett. 2010, 12, 2000–2003. [Google Scholar] [CrossRef]
  21. Moon, J.; Jeong, M.; Nam, H.; Ju, J.; Moon, J.H.; Jung, H.M.; Lee, S. One-Pot Synthesis of Diarylalkynes Using Palladium-Catalyzed Sonogashira Reaction and Decarboxylative Coupling of Sp Carbon and Sp2 Carbon. Org. Lett. 2008, 10, 945–948. [Google Scholar] [CrossRef]
  22. Yeom, H.-S.; Koo, J.; Park, H.-S.; Wang, Y.; Liang, Y.; Yu, Z.-X.; Shin, S. Gold-Catalyzed Intermolecular Reactions of Propiolic Acids with Alkenes: [4 + 2] Annulation and Enyne Cross Metathesis. J. Am. Chem. Soc. 2012, 134, 208–211. [Google Scholar] [CrossRef]
  23. Tartaggia, S.; De Lucchi, O.; Gooßen, L.J. Practical Synthesis of Unsymmetrical Diarylacetylenes from Propiolic Acid and Two Different Aryl Bromides. Eur. J. Org. Chem. 2012, 2012, 1431–1438. [Google Scholar] [CrossRef]
  24. Bararjanian, M.; Balalaie, S.; Rominger, F.; Movassagh, B.; Bijanzadeh, H.R. Six-Component Reactions for the Stereoselective Synthesis of 3-Arylidene-2-Oxindoles via Sequential One-Pot Ugi/Heck Carbocyclization/Sonogashira/Nucleophilic Addition. J. Org. Chem. 2010, 75, 2806–2812. [Google Scholar] [CrossRef]
  25. Jacobsen, M.J.; Funder, E.D.; Cramer, J.R.; Gothelf, K.V. β-Olefination of 2-Alkynoates Leading to Trisubstituted 1,3-Dienes. Org. Lett. 2011, 13, 3418–3421. [Google Scholar] [CrossRef]
  26. Meng, L.-G.; Ge, N.-L.; Yang, M.-M.; Wang, L. Cyclization Reaction of 2-Azido-1-(2-Hydroxyphenyl)Ethanones with Terminal Alkynoates Catalyzed by 4-Dimethylaminopyridine (DMAP): Synthesis of 2-Aminobenzofuran-3(2H)-One Derivatives. Eur. J. Org. Chem. 2011, 2011, 3403–3406. [Google Scholar] [CrossRef]
  27. Feng, H.; Ermolat’ev, D.S.; Song, G.; Van Der Eycken, E.V. Synthesis of Symmetric 1,4-Diamino-2-Butynes via a Cu(I)-Catalyzed One-Pot A3-Coupling/Decarboxylative Coupling of a Propiolic Acid, an Aldehyde, and an Amine. J. Org. Chem. 2012, 77, 5149–5154. [Google Scholar] [CrossRef]
  28. Feng, H.; Ermolat’ev, D.S.; Song, G.; Van der Eycken, E.V. Synthesis of Oxazolidin-2-Ones via a Copper(I)-Catalyzed Tandem Decarboxylative/Carboxylative Cyclization of a Propiolic Acid, a Primary Amine and an Aldehyde. Adv. Synth. Catal. 2012, 354, 505–509. [Google Scholar] [CrossRef]
  29. Mohammadi-Khanaposhtani, M.; Jalalimanesh, N.; Saeedi, M.; Larijani, B.; Mahdavi, M. Synthesis of Highly Functionalized Organic Compounds through Ugi Post-Transformations Started from Propiolic Acids. Mol. Divers. 2020, 24, 855–887. [Google Scholar] [CrossRef] [PubMed]
  30. Idris, M.A.; Lee, S. Recent Advances in Decarboxylative Reactions of Alkynoic Acids. Synthesis 2020, 52, 2277–2298. [Google Scholar] [CrossRef]
  31. Chen, C.; Wu, J.; Yan, G.; Huang, D. Recent Advances of Propiolic Acids in Organic Reactions. Tetrahedron Lett. 2020, 61, 151415. [Google Scholar] [CrossRef]
  32. Du, X.; Yu, J.; Gong, J.; Zaman, M.; Pereshivko, O.P.; Peshkov, V.A. Gold-Catalyzed Post-Ugi Cascade Transformation for the Synthesis of 2-Pyridones: Gold-Catalyzed Post-Ugi Cascade Transformation for the Synthesis of 2-Pyridones. Eur. J. Org. Chem. 2019, 2019, 2502–2507. [Google Scholar] [CrossRef]
  33. Fraile, A.; Parra, A.; Tortosa, M.; Alemán, J. Organocatalytic Transformations of Alkynals, Alkynones, Propriolates, and Related Electron-Deficient Alkynes. Tetrahedron 2014, 70, 9145–9173. [Google Scholar] [CrossRef]
  34. Arndt, M.; Risto, E.; Krause, T.; Gooßen, L.J. C–H Carboxylation of Terminal Alkynes Catalyzed by Low Loadings of Silver(I)/DMSO at Ambient CO2 Pressure. ChemCatChem 2012, 4, 484–487. [Google Scholar] [CrossRef]
  35. Boogaerts, I.I.F.; Fortman, G.C.; Furst, M.R.L.; Cazin, C.S.J.; Nolan, S.P. Carboxylation of N–H/C–H Bonds Using N-Heterocyclic Carbene Copper(I) Complexes. Angew. Chem. Int. Ed. 2010, 49, 8674–8677. [Google Scholar] [CrossRef]
  36. Yu, D.; Zhang, Y. Copper- and Copper–N-Heterocyclic Carbene-Catalyzed C─H Activating Carboxylation of Terminal Alkynes with CO2 at Ambient Conditions. Proc. Natl. Acad. Sci. USA 2010, 107, 20184–20189. [Google Scholar] [CrossRef]
  37. Yuan, Y.; Chen, C.; Zeng, C.; Mousavi, B.; Chaemchuen, S.; Verpoort, F. Carboxylation of Terminal Alkynes with Carbon Dioxide Catalyzed by an In Situ Ag2O/N-Heterocyclic Carbene Precursor System. ChemCatChem 2017, 9, 882–887. [Google Scholar] [CrossRef]
  38. Kim, S.H.; Kim, K.H.; Hong, S.H. Carbon Dioxide Capture and Use: Organic Synthesis Using Carbon Dioxide from Exhaust Gas. Angew. Chem. Int. Ed. 2014, 53, 771–774. [Google Scholar] [CrossRef]
  39. Liu, X.-H.; Ma, J.-G.; Niu, Z.; Yang, G.-M.; Cheng, P. An Efficient Nanoscale Heterogeneous Catalyst for the Capture and Conversion of Carbon Dioxide at Ambient Pressure. Angew. Chem. 2015, 127, 1002–1005. [Google Scholar] [CrossRef]
  40. Cheng, H.; Zhao, B.; Yao, Y.; Lu, C. Carboxylation of Terminal Alkynes with CO2 Catalyzed by Bis(Amidate) Rare-Earth Metal Amides. Green Chem. 2015, 17, 1675–1682. [Google Scholar] [CrossRef]
  41. Correa, A.; Martín, R. Metal-Catalyzed Carboxylation of Organometallic Reagents with Carbon Dioxide. Angew. Chem. Int. Ed. 2009, 48, 6201–6204. [Google Scholar] [CrossRef] [PubMed]
  42. Köster, F.; Dinjus, E.; Duñach, E. Electrochemical Selective Incorporation of CO2 into Terminal Alkynes and Diynes. Eur. J. Org. Chem. 2001, 2001, 2507–2511. [Google Scholar] [CrossRef]
  43. Zhang, L.; Zhang, W.; Shi, L.; Ren, X.; Lü, X. Sequential Ag-Catalyzed Carboxylative Coupling/Ru-Catalyzed Cross-Metathesis Reactions for the Synthesis of Functionalized 2-Alkynoates. Chin. J. Catal. 2013, 34, 1179–1186. [Google Scholar] [CrossRef]
  44. Yu, B.; Xie, J.-N.; Zhong, C.-L.; Li, W.; He, L.-N. Copper(I)@Carbon-Catalyzed Carboxylation of Terminal Alkynes with CO2 at Atmospheric Pressure. ACS Catal. 2015, 5, 3940–3944. [Google Scholar] [CrossRef]
  45. Xie, Y.; He, B.F.; Huang, N.Y.; Deng, W.Q. The Direct Carboxylation of Terminal Alkynes with Carbon Dioxide Using Copper-Conjugated Microporous Polymer as Catalyst. Adv. Mater. Res. 2013, 634–638, 612–615. [Google Scholar] [CrossRef]
  46. Wang, X.; Lim, Y.N.; Lee, C.; Jang, H.-Y.; Lee, B.Y. 1,5,7-Triazabicyclo[4.4.0]Dec-1-Ene-Mediated Acetylene Dicarboxylation and Alkyne Carboxylation Using Carbon Dioxide. Eur. J. Org. Chem. 2013, 2013, 1867–1871. [Google Scholar] [CrossRef]
  47. Bhanja, P.; Modak, A.; Bhaumik, A. Supported Porous Nanomaterials as Efficient Heterogeneous Catalysts for CO2 Fixation Reactions. Chem.-Eur. J. 2018, 24, 7278–7297. [Google Scholar] [CrossRef]
  48. Molla, R.A.; Ghosh, K.; Banerjee, B.; Iqubal, M.A.; Kundu, S.K.; Islam, S.M.; Bhaumik, A. Silver Nanoparticles Embedded over Porous Metal Organic Frameworks for Carbon Dioxide Fixation via Carboxylation of Terminal Alkynes at Ambient Pressure. J. Colloid Interface Sci. 2016, 477, 220–229. [Google Scholar] [CrossRef] [PubMed]
  49. Song, Q.-W.; Zhou, Z.-H.; He, L.-N. Efficient, Selective and Sustainable Catalysis of Carbon Dioxide. Green Chem. 2017, 19, 3707–3728. [Google Scholar] [CrossRef]
  50. Dingyi, Y.; Yugen, Z. The Direct Carboxylation of Terminal Alkynes with Carbon Dioxide. Green Chem. 2011, 13, 1275. [Google Scholar] [CrossRef]
  51. Inamoto, K.; Asano, N.; Kobayashi, K.; Yonemoto, M.; Kondo, Y. A Copper-Based Catalytic System for Carboxylation of Terminal Alkynes: Synthesis of Alkyl 2-Alkynoates. Org. Biomol. Chem. 2012, 10, 1514. [Google Scholar] [CrossRef] [PubMed]
  52. Tsuji, Y.; Fujihara, T. Carbon Dioxide as a Carbon Source in Organic Transformation: Carbon–Carbon Bond Forming Reactions by Transition-Metal Catalysts. Chem. Commun. 2012, 48, 9956. [Google Scholar] [CrossRef] [PubMed]
  53. Li, F.-W.; Suo, Q.-L.; Hong, H.-L.; Zhu, N.; Wang, Y.-Q.; Han, L.-M. DBU and Copper(I) Mediated Carboxylation of Terminal Alkynes Using Supercritical CO2 as a Reactant and Solvent. Tetrahedron Lett. 2014, 55, 3878–3880. [Google Scholar] [CrossRef]
  54. Finashina, E.D.; Tkachenko, O.P.; Startseva, A.Y.; Krasovsky, V.G.; Kustov, L.M.; Beletskaya, I.P. Incorporation of Carbon Dioxide into Molecules of Acetylene Hydrocarbons on Heterogeneous Ag-Containing Catalysts. Russ. Chem. Bull. 2015, 64, 2796–2801. [Google Scholar] [CrossRef]
  55. Liu, C.; Luo, Y.; Zhang, W.; Qu, J.; Lu, X. DFT Studies on the Silver-Catalyzed Carboxylation of Terminal Alkynes with CO2: An Insight into the Catalytically Active Species. Organometallics 2014, 33, 2984–2989. [Google Scholar] [CrossRef]
  56. Jover, J.; Maseras, F. Computational Characterization of the Mechanism for Coinage-Metal-Catalyzed Carboxylation of Terminal Alkynes. J. Org. Chem. 2014, 79, 11981–11987. [Google Scholar] [CrossRef]
  57. Zhang, X.; Zhang, W.-Z.; Ren, X.; Zhang, L.-L.; Lu, X.-B. Ligand-Free Ag(I)-Catalyzed Carboxylation of Terminal Alkynes with CO2. Org. Lett. 2011, 13, 2402–2405. [Google Scholar] [CrossRef]
  58. Bakhoda, A.; Okoromoba, O.E.; Greene, C.; Boroujeni, M.R.; Bertke, J.A.; Warren, T.H. Three-Coordinate Copper(II) Alkynyl Complex in C–C Bond Formation: The Sesquicentennial of the Glaser Coupling. J. Am. Chem. Soc. 2020, 142, 18483–18490. [Google Scholar] [CrossRef]
  59. Moglie, Y.; Mascaró, E.; Gutierrez, V.; Alonso, F.; Radivoy, G. Base-Free Direct Synthesis of Alkynylphosphonates from Alkynes and H -Phosphonates Catalyzed by Cu2O. J. Org. Chem. 2016, 81, 1813–1818. [Google Scholar] [CrossRef]
  60. Kim, J.; Stahl, S.S. Cu-Catalyzed Aerobic Oxidative Three-Component Coupling Route to N-Sulfonyl Amidines via an Ynamine Intermediate. J. Org. Chem. 2015, 80, 2448–2454. [Google Scholar] [CrossRef]
  61. Mondal, S.; Yashmin, S.; Ali, R.; Soundaram, R.; Ghosh, S.S.; Khan, A.T. Synthesis of Biologically Active Fused 1,4-Oxathiin Derivatives from 4-Hydroxydithiocoumarins, Arylacetylenes and Dimethyl Sulfoxide by Cu(i)-Catalyzed C–H Functionalization and Cross-Dehydrogenative C–S Coupling Reactions. Org. Biomol. Chem. 2021, 19, 5818–5826. [Google Scholar] [CrossRef] [PubMed]
  62. Yu, D.; Tan, M.X.; Zhang, Y. Carboxylation of Terminal Alkynes with Carbon Dioxide Catalyzed by Poly(N-Heterocyclic Carbene)-Supported Silver Nanoparticles. Adv. Synth. Catal. 2012, 354, 969–974. [Google Scholar] [CrossRef]
  63. Li, S.; Sun, J.; Zhang, Z.; Xie, R.; Fang, X.; Zhou, M. Carboxylation of Terminal Alkynes with CO2 Using Novel Silver N-Heterocyclic Carbene Complexes. Dalton Trans 2016, 45, 10577–10584. [Google Scholar] [CrossRef]
  64. Díaz Velázquez, H.; Wu, Z.-X.; Vandichel, M.; Verpoort, F. Inserting CO2 into Terminal Alkynes via Bis-(NHC)-Metal Complexes. Catal. Lett. 2017, 147, 463–471. [Google Scholar] [CrossRef]
  65. D’Amato, A.; Sirignano, M.; Russo, S.; Troiano, R.; Mariconda, A.; Longo, P. Recent Advances in N-Heterocyclic Carbene Coinage Metal Complexes in A3-Coupling and Carboxylation Reaction. Catalysts 2023, 13, 811. [Google Scholar] [CrossRef]
  66. Napoli, M.; Saturnino, C.; Cianciulli, E.I.; Varcamonti, M.; Zanfardino, A.; Tommonaro, G.; Longo, P. Silver(I) N-Heterocyclic Carbene Complexes: Synthesis, Characterization and Antibacterial Activity. J. Organomet. Chem. 2013, 725, 46–53. [Google Scholar] [CrossRef]
  67. Mariconda, A.; Sirignano, M.; Costabile, C.; Longo, P. New NHC- Silver and Gold Complexes Active in A3-Coupling (Aldehyde-Alkyne-Amine) Reaction. Mol. Catal. 2020, 480, 110570. [Google Scholar] [CrossRef]
  68. Sirignano, M.; D’Amato, A.; Costabile, C.; Mariconda, A.; Crispini, A.; Scarpelli, F.; Longo, P. Hydroamination of Alkynes Catalyzed by NHC-Gold(I) Complexes: The Non-Monotonic Effect of Substituted Arylamines on the Catalyst Activity. Front. Chem. 2023, 11, 1260726. [Google Scholar] [CrossRef]
  69. Meng, G.; Kakalis, L.; Nolan, S.P.; Szostak, M. A Simple 1H NMR Method for Determining the σ-Donor Properties of N-Heterocyclic Carbenes. Tetrahedron Lett. 2019, 60, 378–381. [Google Scholar] [CrossRef]
  70. Teng, Q.; Vinh Huynh, H. A Unified Ligand Electronic Parameter Based on 13C NMR Spectroscopy of N-Heterocyclic Carbene Complexes. Dalton Trans. 2017, 46, 614–627. [Google Scholar] [CrossRef]
  71. Lummiss, J.A.; Higman, C.S.; Fyson, D.L.; McDonald, R.; Fogg, D.E. The Divergent Effects of Strong NHC Donation in Catalysis. Chem. Sci. 2015, 6, 6739–6746. [Google Scholar] [CrossRef] [PubMed]
  72. Jacobsen, H.; Correa, A.; Poater, A.; Costabile, C.; Cavallo, L. Understanding the M(NHC) (NHC = N-Heterocyclic Carbene) Bond. Coord. Chem. Rev. 2009, 253, 687–703. [Google Scholar] [CrossRef]
  73. Sirignano, M.; Costabile, C.; Mariconda, A.; Longo, P. Effect of Counterion on the Catalytic Activity of NHC-Gold(I) in A3 Coupling Reactions. Results Chem. 2023, 6, 101198. [Google Scholar] [CrossRef]
  74. Lin, I.J.B.; Vasam, C.S. Preparation and Application of N-Heterocyclic Carbene Complexes of Ag(I). Coord. Chem. Rev. 2007, 251, 642–670. [Google Scholar] [CrossRef]
  75. Hintermair, U.; Englert, U.; Leitner, W. Distinct Reactivity of Mono- and Bis-NHC Silver Complexes: Carbene Donors versus Carbene–Halide Exchange Reagents. Organometallics 2011, 30, 3726–3731. [Google Scholar] [CrossRef]
  76. Garrison, J.C.; Youngs, W.J. Ag(I) N-Heterocyclic Carbene Complexes:  Synthesis, Structure, and Application. Chem. Rev. 2005, 105, 3978–4008. [Google Scholar] [CrossRef]
  77. Mariconda, A.; Grisi, F.; Costabile, C.; Falcone, S.; Bertolasi, V.; Longo, P. Synthesis, Characterization and Catalytic Behaviour of a Palladium Complex Bearing a Hydroxy-Functionalized N-Heterocyclic Carbene Ligand. New J Chem 2014, 38, 762–769. [Google Scholar] [CrossRef]
  78. Zhang, Z.-Z.; Mi, R.-J.; Guo, F.-J.; Sun, J.; Zhou, M.-D.; Fang, X.-C. 1,3-Bis(4-Methylbenzyl)Imidazol-2-Ylidene Silver(I) Chloride Catalyzed Carboxylative Coupling of Terminal Alkynes, Butyl Iodide and Carbon Dioxide. J. Saudi Chem. Soc. 2017, 21, 685–690. [Google Scholar] [CrossRef]
  79. Sirignano, M.; Mariconda, A.; Vigliotta, G.; Ceramella, J.; Iacopetta, D.; Sinicropi, M.S.; Longo, P. Catalytic and Biological Activity of Silver and Gold Complexes Stabilized by NHC with Hydroxy Derivatives on Nitrogen Atoms. Catalysts 2021, 12, 18. [Google Scholar] [CrossRef]
  80. Mariconda, A.; Iacopetta, D.; Sirignano, M.; Ceramella, J.; Costabile, C.; Pellegrino, M.; Rosano, C.; Catalano, A.; Saturnino, C.; El-Kashef, H.; et al. N-Heterocyclic Carbene (NHC) Silver Complexes as Versatile Chemotherapeutic Agents Targeting Human Topoisomerases and Actin. ChemMedChem 2022, 17, e202200345. [Google Scholar] [CrossRef]
  81. Atif, M.; Bhatti, H.N.; Haque, R.A.; Iqbal, M.A.; Ahamed Khadeer, M.B.; Majid, A.M.S.A. Synthesis, Structure, and Anticancer Activity of Symmetrical and Non-Symmetrical Silver(I)-N-Heterocyclic Carbene Complexes. Appl. Biochem. Biotechnol. 2020, 191, 1171–1189. [Google Scholar] [CrossRef] [PubMed]
Inorganics 12 00283 sch001
Scheme 1. Examples of conversion reactions of propiolic acids in organic synthesis.
Scheme 1. Examples of conversion reactions of propiolic acids in organic synthesis.
Inorganics 12 00283 sch001
Inorganics 12 00283 sch002
Scheme 2. Hypothesized mechanism for the silver–NHC catalyzed carboxylation of terminal alkynes.
Scheme 2. Hypothesized mechanism for the silver–NHC catalyzed carboxylation of terminal alkynes.
Inorganics 12 00283 sch002
Inorganics 12 00283 sch003
Scheme 3. Synthesis of NHC–silver(I) complexes 1–3a and 4a–c.
Scheme 3. Synthesis of NHC–silver(I) complexes 1–3a and 4a–c.
Inorganics 12 00283 sch003
Inorganics 12 00283 sch004
Scheme 4. Synthetic routes for the exchange of the counterion.
Scheme 4. Synthetic routes for the exchange of the counterion.
Inorganics 12 00283 sch004
Inorganics 12 00283 sch005
Scheme 5. Kinetic profile of 4a in the reaction.
Scheme 5. Kinetic profile of 4a in the reaction.
Inorganics 12 00283 sch005
Table 1. Chemical Shift of carbenic carbon of silver–NHC complexes 4a (NHC)AgX.
Table 1. Chemical Shift of carbenic carbon of silver–NHC complexes 4a (NHC)AgX.
ComplexXδC (DMSO-d6)
Ag-C (ppm)
4aI−191.1
4a.1AcO−188.4
4a.2NO3−189.9
4a.3PF6−191.4–188.3
4a.4Cl−184.6
Table 2. Carboxylation reaction of phenylacetylene.
Table 2. Carboxylation reaction of phenylacetylene.
Inorganics 12 00283 i001
Run [a]CatalystSolventConversion (%) [b]TOF (h−1)
11aDMSO75469
22aDMSO54338
33aDMSO82513
44aDMSO87544
52aDMF75469
64aDMF92575
74aCH3CN30188
84aTHF--
94aDioxane744
104aCH2Cl21594
114aEthylacetate40250
124bDMF52325
134cDMF63394
144a.1DMF75469
154a.2DMF40250
164a.3DMF37231
174a.4DMF25156
18S4aDMF--
[a] Reaction conditions: phenylacetylene 1.0 mmol; CO2 (1 atm); Cs2CO3 1.2 mmol; dry solvent—1 mL, 16 h, room temperature. [b] Conversions: calculated using 1H-NMR spectroscopy with the integration of the signals of aromatic protons with respect to CH the signal of residual phenylacetylene (δ = 3.14 ppm in CD2Cl2).
Table 3. Alkynes scope in the carboxylation reaction with 4a.
Table 3. Alkynes scope in the carboxylation reaction with 4a.
Inorganics 12 00283 i002
Run [a]RConversion (%) [b]
1n-C4H999
2t-C4H990
3CH2Ph70
4Inorganics 12 00283 i00370
5Inorganics 12 00283 i00470
6Inorganics 12 00283 i00568
7Inorganics 12 00283 i00665
8Inorganics 12 00283 i00755
[a] Reaction conditions: alkyne 1.0 mmol; CO2 (1 atm); Cs2CO3 1.2 mmol; dry DMF—1 mL, 16 h, room temperature. [b] Conversions: calculated using 1H-NMR spectroscopy with the integration of the signals of aromatic protons with respect to the CH signal of residual alkyne.
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D’Amato, A.; Sirignano, M.; Viceconte, F.; Longo, P.; Mariconda, A. Catalytic Behavior of NHC–Silver Complexes in the Carboxylation of Terminal Alkynes with CO2. Inorganics 2024, 12, 283. https://doi.org/10.3390/inorganics12110283

AMA Style

D’Amato A, Sirignano M, Viceconte F, Longo P, Mariconda A. Catalytic Behavior of NHC–Silver Complexes in the Carboxylation of Terminal Alkynes with CO2. Inorganics. 2024; 12(11):283. https://doi.org/10.3390/inorganics12110283

Chicago/Turabian Style

D’Amato, Assunta, Marco Sirignano, Francesco Viceconte, Pasquale Longo, and Annaluisa Mariconda. 2024. "Catalytic Behavior of NHC–Silver Complexes in the Carboxylation of Terminal Alkynes with CO2" Inorganics 12, no. 11: 283. https://doi.org/10.3390/inorganics12110283

APA Style

D’Amato, A., Sirignano, M., Viceconte, F., Longo, P., & Mariconda, A. (2024). Catalytic Behavior of NHC–Silver Complexes in the Carboxylation of Terminal Alkynes with CO2. Inorganics, 12(11), 283. https://doi.org/10.3390/inorganics12110283

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