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Jan 8, 2019 - Cascade Strategy for Atmospheric Pressure CO2 Fixation to Cyclic Carbonates via Silver Sulfadiazine and Et4NBr Synergistic Catalysis.
Jan 16, 2018 - (20) Though the time is short (1993â2017), studies in this field have been of increasing interest because of their potential practical applications in high-speed computers and high-density magnetic storage devices with the promise of
Jan 16, 2018 - Compound 1 is a Dy6 SMM (1) based on Dy3 triangles, with one CO32- group being derived from atmospheric CO2. The incorporation of an ortho-methoxy substituent into the ligand enables access to double-CO32- bridged Dy6 SMM (2), where tw
Jan 16, 2018 - sium complexes has been complemented with the emergence of a key component, namely, [Dy6(μ4-CO3)3(μ3-OH2)(spch)6-. (MeOH)6(H2O)3]·4MeOH·3H2O (3), and thus four dysprosium-. (III) clusters (1â4) spontaneously fixing one, two, thre
Design of Dysprosium Single-Molecule Magnets ... â¡School of Chemistry and Chemical Engineering, School of Materials Science and Engineering, School of ...
Jan 16, 2018 - This synthetic approach represents an efficient method to develop novel CO32â-bridged lanthanide clusters through spontaneous fixation of ...
Feb 10, 2017 - Hydrogenation of CO2 to Methanol at Atmospheric Pressure over Cu/ .... The calcination was carried out in a furnace Nabertherm. HTC 03/15 ...
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Article
A Cascade Strategy for Atmospheric Pressure CO2 Fixation to Cyclic Carbonates via Silver Sulfadiazine and Et4NBr Synergistic Catalysis Jing-Yuan Li, Li-Hua Han, Qin-Chao Xu, Qing-Wen Song, Ping Liu, and Kan Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05579 • Publication Date (Web): 08 Jan 2019 Downloaded from http://pubs.acs.org on January 13, 2019
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A Cascade Strategy for Atmospheric Pressure CO2 Fixation to Cyclic Carbonates via Silver Sulfadiazine and Et4NBr Synergistic Catalysis Jing-Yuan Li,† Li-Hua Han,† Qin-Chao Xu,‡ Qing-Wen Song,*,† Ping Liu,† and Kan Zhang*,† †State
Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, South Taoyuan Road 27, Taiyuan, 030001, P. R. China
‡Analytical
Instrumentation Center, Institute of Coal Chemistry, Chinese Academy of Sciences, South Taoyuan Road 27, Taiyuan 030001, P. R. China *Email: [email protected], [email protected]
It is of great significance and challenge for highly-efficient catalytic transformation of carbon dioxide into cyclic carbonates especially under low pressure and energy input conditions. In this regard, an efficient silver sulfadiazine/Et4NBr synergistic catalytic system was developed for three-component cascade reaction of propargylic alcohols, CO2, and vicinal diols. The reaction was performed in the absence of any solvent under atmospheric CO2 pressure to afford splendid yields of cyclic carbonates. The excellent performance was ascribed to the simultaneous activation of hydroxyl group in propargylic alcohols/vicinal diols by silver sulfadiazine and synergistic effect between silver species and bulkier Et4N+ in the procedure of intramolecular nucleophilic cyclization confirmed by control experiments and NMR spectra.
INTRODUCTION Carbon dioxide (CO2), a well-known global-warming gas, is widely recognized as an inexpensive, nontoxic, abundant and eco-friendly C1 source for organic synthesis.1,2 Increasing interest is focused on catalytic conversion of CO2 into high-value chemicals for carbon management and sustainable development.3-5 For example, cyclic carbonates generated from CO2 and other reagents were exploited as building blocks for polycarbonates, electrolytes for lithium ion batteries, and inert solvent and so on.6,7 The effective toolkit of organic reactions for the transformation of thermodynamically stable CO2 into cyclic carbonates employs several strategies.8-14 Among them, one of the most famous synthetic route is cycloaddition of CO2 and epoxides to generate five-membered
cyclic carbonates with 100% atom economy.9,15-18 It is, however, limited to the industrial practicality such as high toxicity of epoxides and harsh reaction conditions. In addition, the main use of cyclic carbonates such as ethylene carbonate and propylene carbonate is the preparation of dimethyl carbonate, and meanwhile stoichiometric byproducts i.e. 1,2-diols are produced. Recently, direct condensation of CO2 and vicinal alcohols has been explored as a powerful approach to cyclic carbonates due to the readily available materials and the by-product i.e. water.19-25 The reaction could potentially consume the 1,2-diols and realize the byproduct recycle. Nevertheless, the direct insertion of CO2 into diols is neither kinetically nor thermodynamically-favored (Scheme 1a). Significant advances on metal-catalyzed systems for this reaction have been made including CeO2,23 Mg/MgO,21 Zn-based activation centers.26,27 However, limitations in these systems exist such as the requirement of a large excess of expensive dehydrating agents (e.g. 2-cyanopyridine) and harsh conditions (high temperature and CO2 pressure). In addition, although a few metal-free strategies can achieve the desired transformation of CO2 with high reactivity, co-catalyst scope is limited, that is, almost all of them are based on the strong base such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) assisted insertion of CO2, which remains problematic.28,29 Moreover, DBU and the alkyl halide are often used in large excess (at least equivalent).28 In light of this fact, lately a three-component cascade reaction of propargylic alcohols, CO2 and nucleophiles was put forward by He group, which provides thermodynamically
favorable access to cyclic carbonates.30,31 The reaction of CO2, propargylic alcohols, and vicinal diols undertakes a two-step procedure (Scheme 2). Initially, the intermediate M1 i.e. α-alkylidene cyclic carbonate is obtained through the carboxylative cyclization of propargylic alcohol and CO2. Then, the nucleophilic ring opening of M1 and vicinal diols affords M2, which can further result in cyclic carbonate and α-hydroxyl ketone through intramolecular nucleophilic cyclization. In the process, Ag2CO3/Xantphos complex was demonstrated to be an effective catalyst to produce good yields of cyclic carbonates.31 Recently, we also explored an early transition metal i.e. zinc-based catalyst for the synthesis of carbonates through a variety of alcohols.32 Although great advances have been made, high pressure (> 1.0 MPa CO2) and organic solvent were still inevitable (Scheme 1b). Moreover, excess of propargylic alcohols was necessary for good yields. Therefore, to boost the catalytic activity at ambient conditions e.g. atmospheric pressure of CO2 would be much more promising for CO2 utilization. On the basis of the previous work, silver compounds served as an excellent catalyst capable of activating carbon-carbon triple bonds.33 On the other hand, quaternary ammonium cation was demonstrated able to enhance the nucleophilicity of carbonate intermediate and further promote the intramolecular nucleophilic cyclization of the intermediate.34 We proposed that the coordination of silver and quaternary ammonium
species would greatly boost the catalytic activity for the cascade reaction of propargylic alcohols, CO2 and vicinal diols. Herein, synergistic silver sulfadiazine/Et4NBr catalysis for this three-component reaction was reported to produce cyclic carbonates and αhydroxyl ketones with high efficiency (Scheme 1). Fortunately, satisfactory yields of products were smoothly acquired under atmospheric pressure of CO2 and solvent-free condition via stoichiometric reactant. EXPERIMENTAL SECTION Materials. Carbon dioxide with a purity of 99.99% was commercially available. All raw materials were purchased from Aladdin or Alfa Aesar, and used without further purification. All experiments were performed without any measures to avoid moisture and air. Notably, both silver sulfadiazine (98%) and Et4NBr (98%) were purchased from Aladdin and used without further purification. Analytical Methods. Gas chromatography (GC) analyses were carried out using BEIFEN 3420A equipped with a flame-ionization detector and a capillary column (KB-17, 30 m × 0.25 mm × 0.25 μm). 1H NMR spectra were recorded on a Bruker AVANCE III 400 MHz spectrometer using CDCl3 or DMSO-d6 as solvent referenced to CDCl3 (7.26 ppm) or DMSO-d6 (2.50 ppm).
13C
NMR spectra were recorded at 100.6 MHz in CDCl3 (77.00
ppm). Gas Chromatography-Mass Spectrometer (GC-MS) analyses were conducted on Agilent 7890A-5975C-GC/MSD equipped with a RTX-5MS capillary column at an ionization voltage of 70 eV. X-ray powder diffraction (XRD) was performed through
using Bruker D8 ADVANCE X-ray diffractometer with Cu Ka radiation (λ = 0.15406 nm) at 40 kV and 40 mA. The samples were recorded from 5º and 80º in a rate of 1.2º/min. The XRD patterns of the samples were subsequently analyzed by MDI Jade 6.5. General Procedure for the Synthesis of Propylene Carbonates (PCs, 3a) and 3Hydroxy-3-methylbutan-2-ones (4a) from 1,2-Propanediol, 2-Methyl-3-butyn-2-ol and CO2. As an example, the reaction was conducted in a 10 mL Schlenk tube equipped with magnetic stirring. To begin with, silver sulfadiazine (17.9 mg, 5.00 mol%), Et4NBr (10.5 mg, 5.00 mol%), 1,2-propanediol (76.1 mg, 1.00 mmol) and 2-methyl-3-butyn-2-ol (84.1 mg, 1.00 mmol) with CH3CN (2 mL) were successively added into the Schlenk tube. Then, a balloon filled with CO2 was connected to the Schlenk tube to keep the pressure of CO2 at 0.1 MPa. Subsequently, the reaction mixture was stirred at 80 ºC for the given time. After the reaction, the mixture was purified by column chromatography (silica gel) to provide products 3a and 4a. Compound 3a: colorless liquid, petroleum ether/EtOAc (v/v) 5:1; 1H NMR (400 MHz, CDCl3): δ 4.86-4.78 (m, 1H), 4.54-4.50 (m, 1H), 3.98 (dd, J = 8.4, 7.3 Hz, 1H), 1.44 (d, J = 6.3 Hz, 3H) ppm.
5.00 mol%), 1 (1.00 mmol) and 2 (1.00 mmol) were introduced into a 10 mL Schlenk tube equipped with magnetic stirring. Next, a balloon filled with CO2 was connected to the reaction vessel. The reaction mixture was stirred at 80 ºC for 24 h. After the reaction, it was flushed with CH3CN and concentrated under vacuum. Finally, the residue was purified by column chromatography on silica gel using petroleum ether/EtOAc as eluent to give the products. The reactions under 1.0 MPa CO2 were performed in a 25 mL autoclave with a Teflon vessel inside equipped with magnetic stirring. After introducing silver sulfadiazine (17.9 mg, 5.00 mol%), Et4NBr (10.5 mg, 5.00 mol%), 1 (1.00 mmol) and 2 (1.00 mmol), the autoclave was sealed and filled with CO2 to keep the pressure of CO2 at 1.0 MPa. Then, the reaction mixture was stirred at 80 ºC for 24 h. When the reaction completed, the autoclave was cooled to ambient temperature and residual CO2 was carefully released. Subsequently, the reaction mixture was concentrated under vacuum after being flushed with CH3CN. The obtained residue was purified by column chromatography on silica gel using petroleum ether/EtOAc as eluent to give the products. 4-Ethyl-1,3-dioxolan-2-one (3b)31 Colorless liquid. Yield: 98% (114 mg). Silver sulfadiazine (17.9 mg, 5.00 mol%), Et4NBr (10.5 mg, 5.00 mol%), 1,2-butanediol (90.1 mg, 1.00 mmol) and 2-methyl-3-butyn-2-ol (84.1 mg, 1.00 mmol) were used to synthesize 3b. Petroleum ether/EtOAc (v/v) 5:1. 1H NMR (400 MHz, CDCl3): δ 4.65-4.59 (m, 1H), 4.48 (t, J = 8.2 Hz, 1H), 4.05-4.01 (m, 1H), 1.77-1.67 (m, 2H), 0.95 (t, J = 7.6 Hz, 3H) ppm.
m/z (%) 101 (36), 100 (10), 99 (37), 83 (83), 74 (10), 71 (24), 57 (13), 55 (100), 45 (30), 43 (68), 41 (31), 29 (15), 27 (10). RESULTS AND DISCUSSION Optimization of the Catalytic System Initially, three-component reaction of 1,2-propanediol (1a), 2-methyl-3-butyn-2-ol (2a) and CO2 was chosen as model reaction for the synthesis of propylene carbonate (3a) and 3-hydroxy-3-methylbutan-2-one (α-hydroxyl ketone, 4a) under the given conditions (Table 1). In the absence of any catalyst, the reaction did not take place (entry 1). Furthermore, a series of silver compounds were investigated in combination with nBu
4NBr.
Among them, silver sulfadiazine showed the highest activity with 24% and 29%
yields of 3a and 4a, respectively (entry 2). However, AgSO3CF3 and silver ptoluenesulfonate were inactive (entries 3 and 4). Another interesting finding was that Ag3PO4, AgOAc, Ag2CO3 and Ag2O were also effective in despite of showing low activity in the reaction, while the AgCl, AgI and AgSbF6 displayed no activity (entries 8-11 vs. 57). This is consistent with the fact that Ag3PO4, AgOAc, Ag2CO3 and Ag2O have stronger alkalinity than AgCl, AgI and AgSbF6, which suggested that the alkalinity of silver compounds probably played a vital role in the catalytic cycle, coinciding with the previous work.31 Additionally, it was notably that AgVO3 also showed low activity with 4% and 7% yields of 3a and 4a, respectively (entry 12). Moreover, the key role of silver ion was also demonstrated through blank experiments. As seen from the results, both
sulfadiazine sodium salt and sulfadiazine showed ineffective (entries 13 and 14), indicating that the Ag species makes a big difference on the catalytic activity.
The catalytic performance of co-catalysts with different cations and anions was also studied. In contrast to the reaction conducted in silver sulfadiazine/nBu4NBr, inapparent differences were observed when the quaternary ammonium salt cation was changed (entry 2 vs. entries 15-18). As seen from entry 15, silver sulfadiazine/Et4NBr exhibited the highest efficiency, and nPr4NBr, (nC7H15)4NBr and [BMIM]Br resulted in slightly lower yields of products (entries 16-18). Generally, ion pair separation is easier for these cations with bulkier alkyl substituents because of the weaker electrostatic interactions between cation and anion.34-36 However, bulkier alkyl substituents accompanying with steric hindrance have a negative impact on the coupling of CO2 and propargylic alcohol. Presumably, the best catalytic performance of alkyl substituent in C2 was ascribed to the balance between ion pair separation and steric hindrance. On the other hand, replacing Br- with Cl- led to a reduced yield (entry 19). While Et4NI displayed an equal activity compared with Et4NBr (entry 20 vs. entry 15). In addition, no products were detected when Et4N(NO3) and Et4NBF4 were used as co-catalyst, respectively (entries 21 and 22). These results suggested that anion of quaternary ammonium salt was also a crucial factor in determining the catalytic activity of co-catalyst.37
Furthermore, the individual catalyst silver sulfadiazine or Et4NBr was demonstrated to be ineffective in this reaction (entries 23 and 24). In entries 2-13 and 15-23, silver salts were found not completely soluble in the solvent. Gratifyingly, the most promising result was obtained with 52% 3a yield and 59% 4a yield in the absence of solvent (entry 25). < Figure 1 here> The temperature effect on the reaction was also examined (Figure 1). No target product was detected at room temperature. With increasing temperature from 25 to 120 ºC, the product yield at 80 ºC was remarkably improved. One main reason was that more activated molecules were produced with the increase of energy input, and the reaction rate was also accelerated. Further elevating temperature to 120 ºC gave rise to a sharp decrease of the yield, which was probably attributed to the irreversible deactivation of catalysts at high temperature in the light of the control experiments (Scheme S1, Supporting Information). Accordingly, 80 ºC was finally determined as the optimal temperature for the reaction. Furthermore, almost quantitative yields were successfully obtained by prolonging the reaction time to 24 h under neat conditions (Table 1, entry 26). To the best of our knowledge, this is the first study to concurrently synthesize PCs and α-hydroxyl ketones in high yields under the atmospheric pressure of CO2 and solvent-free conditions via a stoichiometric reactant, with the lowest loading of catalysts among all the reported catalytic systems.
Subsequently, the three-component reaction of CO2 with a wide range of different substituted substrates was investigated in the silver sulfadiazine/Et4NBr catalytic system under atmospheric pressure of CO2 (Table 2). First of all, various substituted propargylic alcohols were introduced into the system. Propargylic alcohols with different alkyl substituents including long-chain alkyl, isopropyl and cyclohexyl gave 3a and the corresponding α-hydroxyl ketones 4a-d in satisfactory yields under the optimal conditions (entries 1-4). Phenyl-substituted propargylic alcohol afforded the product 4e in desired yield when CO2 pressure increased to 1.0 MPa (entry 5). The results could presumably be ascribed to the sterically hindered effect of substituted R1 and R2 which obstruct the carboxylative cyclization of propargylic alcohols and CO2.38 For propargylic alcohol with vinyl substituent, an electron-withdrawing group, doubled catalytic amount was required to obtain improved product yields (Table 2, entry 6 vs. Table S1, entry 2, Supporting Information). Besides, the silver sulfadiazine/Et4NBr was also applicable for 1-octyn-3-ol and gave the target products in high yields (entry 7). In addition, the scope of 1,2-diols was also investigated, and the corresponding cyclic carbonates were acquired for a variety of vicinal diols. When R was methyl, ethyl and propyl in vicinal diols, the yield of the corresponding product could exceed 90% (entries 1, 8 and 9). Nevertheless, for R substituent with C6 chain, the satisfactory yield was
obtained only elevating CO2 pressure to 1.0 MPa (Table 2, entry 10 vs. Table S1, entry 4, Supporting Information). These results revealed that the steric hindrance was induced by increasing length of R alkyl chain.37 Presumably, the stronger steric hindrance slowed down the reaction rate. However, an increased CO2 pressure accelerated the reaction rate of CO2 and propargylic alcohol and therefore further promoted the reaction of M1 and vicinal diol.36 To our delight, sterically congested vicinal diols were also successfully converted into the desired cyclic carbonates 3e and 3f under atmospheric CO2 pressure (entries 11 and 12). Moreover, this protocol was employed to the conversion of glycerol and 1,2,6-hexanetriol, and the corresponding carbonates 3g and 3h were acquired successfully (entries 13 and 14). Mechanism Study As mentioned above, detailed studies on the three-component reaction of CO2, propargylic alcohols, and vicinal diols were reported.31,32 To further explore the catalytic mechanism in the silver sulfadiazine/Et4NBr system, the interaction between catalyst and each reaction component was studied through experimental and NMR methods. As shown in Figure 2, no reaction occurred in the first step when silver sulfadiazine or Et4NBr was individually employed as the catalyst. Interestingly, the yield of α-alkylidene cyclic carbonate could reach 86% in the presence of both silver sulfadiazine and Et4NBr. These results indicated that synergistic catalysis of silver sulfadiazine and Et4NBr exists in the carboxylative cyclization of propargylic alcohols and CO2. In the second step (Figure
3), with silver sulfadiazine as catalyst, 3a was obtained in 30% yield and 35% 4a yield. However, Et4NBr alone showed no activity. In contrast, silver sulfadiazine/Et4NBr catalyst system exhibited synergistic effect with the enhanced yield of 3a and 4a more than 90%. It implied that silver sulfadiazine could catalyze the reaction of 1,2-propanediol and M. Moreover, Et4NBr offered the bulkier quaternary ammonium cation, enhancing the nucleophilicity of oxygen atom in M2, and propelling the followed intramolecular nucleophilic cyclization.34 Besides, the experiments and the XRD patterns demonstrated the precipitation of AgBr in reaction (Figure S5 and Figure S6, Supporting Information). As described in Table 1 (entries 15 and 19), compared with silver sulfadiazine/Et4NCl, silver sulfadiazine/Et4NBr catalyst showed higher activity in the reaction. Therefore, several control experiments were also carried out to study the role of Et4NCl and Et4NBr. As can be seen from Figure 2 and Figure 3, similar to Et4NBr, Et4NCl alone was active neither in the carboxylative cyclization nor during the transesterification. In the first step (Figure 2), silver sulfadiazine/Et4NCl could effectively catalyze the reaction, whereas the yield of α-alkylidene cyclic carbonate was much lower than that of silver sulfadiazine/Et4NBr. However, there was no significant difference on the catalytic performance in the second step (Figure 3). Unquestionably, Et4NBr was more active than Et4NCl in the first step. The reason may be that the stronger electronegativity of Cl- than Br- results in a harder dissociation between cation and anion. In addition, there was hardly any distinction between Et4NCl and Et4NBr in the second step. In other words, it
could be also deduced that the carboxylative cyclization of propargylic alcohols and CO2 was the rate determining step. Furthermore, no significant difference of the catalytic activity between silver sulfadiazine/Et4NBr and sulfadiazine/Et4NI implied that the dissociation capacity of Br- was adequate to the reaction (Table 1, entries 15 and 20). < Figure 2 here> < Figure 3 here> Additionally, there was no reaction occurring between 1,2-propanediol and CO2 under the identical conditions (Scheme 3), suggesting that the direct carboxylation of 1,2propanediol (1a) and CO2 did not take place in the silver sulfadiazine/Et4NBr catalyst system. < Figure 4 here> To further investigate the role of silver sulfadiazine and Et4NBr in the carboxylative cyclization of propargylic alcohols and CO2, the mixture of 2a/silver sulfadiazine and 2a/silver sulfadiazine/Et4NBr was examined through 1H NMR analysis. As seen from Figure 4 (a-d), the peak of 1H signal shifted to 5.31 ppm from 5.29 ppm in the mixture of 2a/silver sulfadiazine or 2a/Et4NBr/silver sulfadiazine. These results indicated that hydroxyl group was activated by silver sulfadiazine. At the same time, the 1H signal of sulfadiazine anion was detected in the mixture of 2a/silver sulfadiazine/Et4NBr, which implied that sulfadiazine was formed in the process (Figure S3, Supporting Information).
< Figure 5 here> Next, the mixture of 1a/silver sulfadiazine or 1a/silver sulfadiazine/Et4NBr was also analyzed by 1H NMR spectrum. The 1H signal of hydroxyl in 1,2-propanediol appeared at δ = 4.41 ppm with a broad peak (Figure 5a). In the mixture of 1a/silver sulfadiazine, the peak of the hydroxyl proton was split into triplet and doublet form, which indicated the interaction between silver sulfadiazine and two kinds of hydroxyl in 1a (Figure 5b). After the introduction of silver sulfadiazine, the intrinsic interaction was broken and the proton exchange velocity reduced. Unlike the single broad peak of -OH in 1a, the 1H signal of -OH was split into two broad doublet peaks in the mixture of 1a/silver sulfadiazine/Et4NBr. This revealed that the strong interaction between silver sulfadiazine and hydroxyl existed, and Et4NBr could adjust the strength of the interaction between silver sulfadiazine and hydroxyls and further influence the hydrogen bond interaction (Figure 5c and d vs. b). By comparison, the small signal shift in figure 4 could be attributed to the steric effect between 2a and silver sulfadiazine. Additionally, similar to the step one, the 1H
signal of sulfadiazine anion was also discovered when silver sulfadiazine and Et4NBr
coexisted. The results indicated the generation of sulfadiazine, which acted as the proton donor (Figure S4, Supporting Information). Based on the results of the above studies and previous works,31,
39
a plausible
mechanism for the three-component reaction of CO2, propargylic alcohols, and vicinal diols by the silver sulfadiazine/Et4NBr catalyst was proposed (Scheme 4). Initially,
attributing to the activation of -OH and carbon-carbon triple bond by the sulfadiazine anion and silver, respectively, the carbonate intermediate A is obtained through the reaction of propargylic alcohol and CO2. Meanwhile, some AgBr is detected, and the remaining catalysts participate in the subsequent process (Figure S5 and S6, Supporting Information). It should be pointed out that Et4N+ is beneficial to stabilize the carbonate intermediate and enhance the nucleophilicity of the oxygen atom. Then, with the participation of a proton donor, i.e. sulfadiazine, an intramolecular nucleophilic cyclization of intermediate A results in the intermediate M1. Subsequently, silver sulfadiazine/Et4NBr catalyzes the nucleophilic attack of the activated -OH from vicinal diol at the carbonyl group from intermediate M1 with the generation of intermediate B. Accompanied by the formation of AgBr (Figure S5 and S6, Supporting Information) and sulfadiazine, intermediate C is obtained. Finally, an intramolecular nucleophilic cyclization of intermediate C gives cyclic carbonate and α-hydroxyl ketone simultaneously. CONCLUSIONS An excellent protocol for the synthesis of cyclic carbonates and α-hydroxyl ketones from propargylic
alcohols,
CO2
and
vicinal
diols
was
developed
through
silver
sulfadiazine/Et4NBr synergistic catalysis. The reaction undertook under atmospheric pressure of CO2 and solvent-free conditions with stoichiometric raw materials. With 5
mol% catalysts and equivalent reactant, the yields of target products could reach up to 99%. Notably, silver sulfadiazine could simultaneously activate the hydroxyl group of propargylic alcohols and vicinal diols. Besides, Et4NBr could not only adjust the interaction between silver sulfadiazine and hydroxyl group, also be in favor of generating bulkier intermediates with stronger nucleophilicity to promote the intramolecular nucleophilic cyclization. This method could be potentially applied in converting CO2 into valuable products under mild reaction conditions. ASSOCIATED CONTENT Supporting Information The following files are available free of charge. Supporting Information including experimental Section, experimental results, and copies of the 1H and 13C NMR spectra for cyclic carbonates 4a−g, 3a−h, and M (PDF) AUTHOR INFORMATION Corresponding Authors *Email: [email protected], [email protected], Tel: 0351-4250105 Funding Sources National Natural Science Foundation of China (21602232) Natural Science Foundation of Shanxi Province (201701D221057)
Notes The authors declare no competing financial interest. ACKNOWLEDGMENT Financial support from the National Natural Science Foundation of China (21602232) and the Natural Science Foundation of Shanxi Province (201701D221057) are gratefully acknowledged. JY Li thanks the Joint Training Project of Shanghai University and Institute of Coal Chemistry, Chinese Academy of Sciences. ABBREVIATIONS CO2, carbon dioxide; DBU, 1,8-diazabicyclo[5.4.0]undec-7-ene; Gas chromatography, GC; PC, propylene carbonate; r.t., room temperature. REFERENCES (1)
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