1,3 bis(4 methylbenzyl)imidazol 2 ylidene silver(i) chloride catalyzed carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide

1,3 Bis(4 methylbenzyl)imidazol 2 ylidene silver(I) chloride catalyzed carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide Accepted Manuscript Original article 1,3 Bis(4 methyl[.]

Accepted Manuscript Original article 1,3-Bis(4-methylbenzyl)imidazol-2-ylidene silver(I) chloride catalyzed carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide Zhi-Zhi Zhang, Rui-Jie Mi, Fang-Jie Guo, Jing Sun, Ming-Dong Zhou, XiangChen Fang PII: DOI: Reference: S1319-6103(17)30025-X http://dx.doi.org/10.1016/j.jscs.2017.02.001 JSCS 856 To appear in: Journal of Saudi Chemical Society Received Date: Revised Date: Accepted Date: January 2017 February 2017 February 2017 Please cite this article as: Z-Z Zhang, R-J Mi, F-J Guo, J Sun, M-D Zhou, X-C Fang, 1,3-Bis(4methylbenzyl)imidazol-2-ylidene silver(I) chloride catalyzed carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide, Journal of Saudi Chemical Society (2017), doi: http://dx.doi.org/10.1016/j.jscs 2017.02.001 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain Manuscript for Journal of Saudi Chemical Society 2017 02.07 1,3-Bis(4-methylbenzyl)imidazol-2-ylidene silver(І) chloride catalyzed carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide Zhi-Zhi Zhang,1,3 Rui-Jie Mi,2 Fang-Jie Guo,2 Jing Sun,2 Ming-Dong Zhou,2* XiangChen Fang1,3* State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China Email: fxc@ecust.edu.cn School of Chemistry and Materials Science, Liaoning Shihua University, Dandong Road 1, Fushun 113001, China E-mail: mingdong.zhou@lnpu.edu.cn Fushun Research Institute of Petroleum and Petrochemicals, Sinopec Group, Fushun 113001, China Abstract The N-heterocyclic carbene silver(I) complex 1,3-bis(4-methylbenzyl)imidazol-2ylidene silver chloride was applied as the effective catalyst for the three-component carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide The reaction proved to be highly efficient when using mol% of 1,3-bis(4methylbenzyl)imidazol-2-ylidene silver(І) chloride as the catalyst in the presence of 1.5 equiv of Cs2CO3 as the base in DMF This reaction shows good selectivity and substituent-loading capability, in which various functionalized 2-alkynoates were obtained in good yields under very mild conditions Keywords: Carboxylative coupling; 2-Alkynoates; Carbon dioxide; N-heterocyclic carbene silver (I) complex Introduction Catalytic transformation of CO2 into value-added chemicals has been regarded as one of perspective research field in terms of sustainable chemistry In the last decade, great efforts have been made both in academia and chemical industry [1-4] Some remarkable progresses include the cyclic addition of CO2 to epoxide, copolymerization of CO2 and epoxides, hydrogenation of CO2, the carboxylation of alkynes with CO2 and so forth [5-7] Among various catalytic transformations, the carboxylation of alkynes with CO2 to produce functionalized propiolic acids or 2alkynoates has been received considerable attentions owing to the importance of Manuscript for Journal of Saudi Chemical Society 2017 02.07 propiolic acids and 2-alkynoates in organic synthesis [8-11] Nolan [12,13], Grooβen [14-16], Zhang [17-19], Lu [20-22], He [23-26], and other groups [27,28] have made significant efforts in this rapidly emerging field Generally, such a transformation can be smoothly proceeded by using copper(I) or silver(I) as the catalyst in the presence of a strong base such as Cs2CO3 or K2CO3 under mild conditions Comparing to copper(I), silver(I) seems to be more advantageous as it is more stable and active Moreover, the catalyst loading can also be highly reduced when using silver(I) instead of copper(I) On the other hand, it has been found that the involvement of Nheterocyclic carbene (NHC) ligands to the catalytic carboxylation system can widen the substrate scope, since NHC ligands may be helpful to activate the CO2 molecule via the formation of an intermediate CO2 adduct [29-32] Nevertheless, the study concerning Ag(I) - or Cu(I)-NHC catalyzed carboxylation of terminal alkynes with CO2 is unfortunately rather limited In this regard, several novel Ag-NHC complexes have been prepared in our laboratory and they have been successfully applied as the catalyst for the carboxylation of aryl / alkyl terminal alkynes with CO2 to afford various functionalized propiolic acids [33] Previous studies indicated that 1,3-bis(4methylbenzyl)imidazol-2-ylidene silver(І) chloride is one of the most effective catalyst among various examined Ag-NHC complexes In continuation our study on the carboxylation of CO2, we have further investigated the carboxylative coupling of terminal alkynes, butyl iodide and CO2 to produce 2-alkynoates To our delight, 1,3bis(4-methylbenzyl)imidazol-2-ylidene silver(І) chloride also displayed excellent catalytic activity towards this transformation Moreover, the reaction could be also proceeded under rather mild conditions (40ºC, 1atm) Therefore, we wish to report our findings of this work herein Experimental Section 2.1 General Remarks All manipulations were performed using standard Schlenk techniques under a dry nitrogen or CO2 atmosphere All the experiments were performed in flame-dried Schlenk tubes NMR spectra were obtained on a Bruker Ascend HD 500 (1H NMR, 500 MHz; 13C NMR, 125 MHz) spectrometer using CDCl3 or DMSO-d as solvents IR spectra were recorded on a Spectrum GX FT-IR spectrometer HRMS (ESI) determinations were carried out on a Bruker Daltonics McriOTOF II mass spectrometer The spectra were collected from 55 to 600m/z at an acquisition rate of 1- s per scan The product (10 mg) was dissolved in acetonitrile (200 mL) The Manuscript for Journal of Saudi Chemical Society 2017 02.07 samples were injected at a flow rate of 1.1 mL·min-1 of 80 % acetonitrile + 0.1% HCOOH for the MS detection under the basic conditions The cesium carbonate was dried for 12 h in vacuo at 120 °C prior to use CO2 (99.999%) was dried by 4Å molecular sieves before use Solvents before used were dehydration under standard methods and stored under N2 Silver(I) salt and other reagents of analytical grade were used as received 2.2 General procedure for the carboxylative coupling reaction A 50 mL oven dried Schlenk flask was charged with Ag-NHC (8.4 mg, 0.01 mmol), Cs2CO3 (488 mg, 1.5 mmol), nBuI (137 µL, 1.2 mmol), and alkyne (1.0 mmol) and mL dry DMF Then, the reaction mixture was stirred at 40oC for 48 h under an atmosphere of CO2 (99.999%, balloon) After the reaction, water was added to the mixture, then extracted with diethyl ether (3×10 mL) The combined organic layer was further washed with saturated aqueous NaCl, dried with anhydrous MgSO4, filtered, and finally concentrated in vacuo The pure products were obtained by column chromatography (ethyl acetate/petroleum ether=1:50) Butyl 3-phenylpropiolate (2a) [25] H NMR (CDCl3, 500 MHz) δ (ppm): 7.57-7.53 (m, 2H),7.44-7.39 (m, 1H), 7.37-7.32 (m, 2H), 4.23 (t, J=6.5 Hz, 2H), 1.72-1.64 (m, 2H), 1.47-1.37 (m, 2H), 0.95 (t, J=7.5 Hz, 3H); IR (cm-1) (KBr) 2959, 2212, 1710, 1602, 1489 Butyl 3-(p-tolyl)propiolate (2b) [25] H NMR (CDCl3, 500 MHz) δ (ppm): 7.48 (d, J=8.0 Hz, 2H), 7.17 (d, J=7.5 Hz, 2H), 4.23 (t, J=6.5 Hz, 2H), 2.37 (s, 3H), 1.73-1.66 (m, 2H), 1.48-1.40 (m, 2H), 0.96 (t, J=7.5 Hz, 3H); IR (cm-1) (KBr) 2959, 2228, 1709, 1472 Butyl 3-(4-Propylphenyl)propiolate (2c) H NMR (CDCl3, 500 MHz) δ (ppm): 7.50 (d, J=8.5 Hz, 2H), 7.17 (d, J=8.5 Hz, 2H), 4.23 (t, J=6.5 Hz, 2H), 2.60 (t, J=7.5 Hz, 2H), 1.72-1.60 (m, 4H), 1.46-1.40 (m, 2H), 0.98-0.90 (m, 6H); 13 C NMR (CDCl3, 125 MHz) δ (ppm): 154.30, 145.86, 132.94, 128.68, 116.72, 86.57, 80.33, 65.79, 38.01, 30.43, 24.12, 19.00, 13.66, 13.60; IR (cm1 ) (KBr) 2933, 2225, 1717, 1606, 1597, 1466; HRMS (ESI, m/z) calcd for C16H21O2 [M+H]+: 245.1536, found:245.1548 Butyl 3-([1,1'-biphenyl]-4-yl)propiolate (2d) H NMR (CDCl3, 500 MHz) δ (ppm): 7.65 (d, J=8.5 Hz, 2H), 7.60-7.56 (m, 4H), 7.47-7.41 (m, 2H), 7.40-7.34 (m, 1H), 4.25 (t, J=6.5 Hz, H), 1.74-1.66 (m, 2H),1.49-1.40 (m, 2H), 0.97 (t, J=7.0 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ (ppm): Manuscript for Journal of Saudi Chemical Society 2017 02.07 154.19, 139.72, 133.41, 128.90, 128.07, 127.14, 127.05, 118.32, 86.03, 81.28, 65.90, 30.43, 19.02, 13.61; IR (cm-1) (KBr) 2960, 2220, 1710, 1606, 1509, 1466; HRMS (ESI, m/z) calcd for C19H19O2 [M+H]+: 279.1380, found: 279.1385 Butyl 3-(4-methoxyphenyl)propiolate (2e) [25] H NMR (CDCl3, 500 MHz) δ (ppm): 7.54 (d, J=9.0 Hz, 2H), 6.88 (d, J=9.0 Hz, 2H), 4.23 (t, J=6.5 Hz, 2H), 3.83 (s, 3H), 1.72-1.66 (m, 2H),1.46-1.40 (m, 2H), 0.96 (t, J=7.5 Hz, 3H); IR (cm-1) (KBr) 2959, 2212, 1706, 1605, 1509, 1464 Butyl 3-(4-fluorophenyl)propiolate (2f) [25] H NMR (CDCl3, 500 MHz) δ (ppm): 7.61-7.55 (m, 2H), 7.10-7.04 (m, 2H), 4.24 (t, J=6.5 Hz, 2H), 1.72-1.67 (m,2H), 1.47-1.40 (m, 2H), 0.96 (t, J=7.5 Hz, 3H); IR (cm-1) (KBr) 2959, 2216, 1709, 1601, 1597, 1509, 1471 Butyl 3-(3-fluorophenyl)propiolate (2g) H NMR (CDCl3, 500 MHz) δ (ppm): 7.39-7.31 (m, 2H), 7.30-7.25 (m, 1H), 7.19- 7.12 (m, 1H), 4.25 (t, J=6.5 Hz, 2H), 1.74-1.66 (m, 2H), 1.49-1.39 (m, 2H), 0.96 (t, J=7.5 Hz, 3H) ;13C NMR (CDCl3, 125MHz) δ (ppm): 162.15 (d, J=246.4 Hz), 153.81, 130.26 (d, J=9.1 Hz), 128.78 (d, J=3.6 Hz), 121.48, 119.57, (d, J=23.5 Hz), 118.02 (d, J=20.8 Hz), 84.16 (d, J=3.5 Hz), 81.16, 66.04, 30.38, 18.99, 13.58; IR (cm-1) (KBr) 2961, 2225, 1715, 1606, 1583, 1487, 1469; HRMS (ESI, m/z) calcd for C13H14FO2 [M+H]+: 221.0972, found: 221.0976 Butyl 3-(4-chlorophenyl)propiolate (2h) [25] H NMR (CDCl3, 500 MHz) δ (ppm):7.51 (d, J=8.5 Hz, 2H), 7.35 (d, J=8.5 Hz, 2H), 4.24 (t, J=6.5 Hz, 2H), 1.73-1.65 (m, 2H), 1.48-1.38 (m, 2H), 0.96 (t, J=7.5 Hz, 3H); IR (cm-1) (KBr) 2959, 2224, 1710, 1590, 1489 Butyl 3-(4-cyanophenyl)propiolate (2i) [28] H NMR (CDCl3, 500 MHz) δ (ppm): 7.68 (s, 4H), 4.26 (t, J=6.5 Hz, 2H),1.74-1.67 (m, 2H), 1.48-1.41 (m, 2H), 0.96 (t, J=7.5 Hz, 3H); IR (cm-1) (KBr) 2926, 1741, 1717, 1464 Butyl 3-(4-(trifluoromethyl)phenyl)propiolate (2j) H NMR (CDCl3, 500 MHz) δ (ppm): 7.69 (d, J=8.0 Hz, 2H), 7.64 (d, J=8.0 Hz, 2H), 4.26 (t, J=6.5 Hz, 2H),1.73-1.67 (m, 2H), 1.48-1.41 (m, 2H), 0.97 (t, J=7.5 Hz, 3H); 13 C NMR (CDCl3,125 MHz) δ (ppm): 153.61, 133.05, 132.07 (q, J=32.5 Hz), 125.43 (q, J=3.6 Hz), 123.49 (q, J=270.9 Hz), 123.48, 83.65, 82.28, 66.10, 30.36, 18.95, 13.49; IR (cm-1) (KBr) 2917, 1703, 1523, 1469; HRMS (ESI, m/z) calcd for C14H13F3O2 [M+H]+: 271.0940, found:271.0944 Manuscript for Journal of Saudi Chemical Society 2017 02.07 Butyl hept-2-ynoate (2k) [34] H NMR (CDCl3, 500 MHz) δ (ppm): 4.19-4.13 (m, 2H), 2.37-2.31 (m, 2H), 1.70- 1.61 (m, 2H), 1.60-1.55 (m, 2H), 1.48-1.37 (m, 4H), 0.97-0.90 (m, 6H); IR (cm-1) (KBr) 2962, 2236, 1715, 1470 Butyl non-2-ynoate (2l) [25] H NMR (CDCl3, 500 MHz) δ (ppm): 4.08 (t, J=6.5 Hz, 2H), 2.25 (t, J=7.0 Hz, 2H), 1.62-1.46 (m, H), 1.37-1.28 (m, 4H), 1.27-1.17 (m, 4H), 0.89-0.80 (m, 6H); IR (cm1 ) (KBr) 2962, 2236, 1711, 1466 Results and discussion 1,3-bis(4-methylbenzyl)imidazol-2-ylidene silver(І) chloride (Ag-NHC) was synthesized according to the published procedures [33] Scheme represents the molecular structure of 1,3-bis(4-methylbenzyl)imidazol-2-ylidene silver(І) chloride (Ag-NHC) X-ray single crystal diffraction data indicates a dinuclear solid-state structure [33], however it exists as a monomer in the presence of polar solvents owing to the weak bridging Ag…Cl bond of the dimer [35, 36] The Ag-NHC complex was applied as the catalyst for the carboxylative coupling of terminal alkynes, butyl iodide and CO using Cs2CO as the effective base (Table 1) The terminal alkyne 1-phenylethyne 1a was initially examined as the substrate for reaction optimizations Blank experiments showed that the reaction could not proceed in the absence of the metal catalyst or the base (Table 1, entries 1, 2) The reaction was firstly studied using different dry solvents under the condition of mol% catalyst, 1.5 equiv of Cs2CO at 40 ºC and atmospheric pressure of CO2 The reactions afforded good yields of the desired butyl 3-phenylpropiolate 2a in DMF, CH3CN and DMSO, in accordance with most carboxylative coupling reactions reported in the literatures (entries 3-5) [23-26, 28] However, the reaction could not proceed in CH 2Cl2, whereas moderate yield was obtained in THF (entries 6, 7) When reducing the catalyst loading from to mol%, the product yield was also significantly reduced (entry 8) Increasing the amount of catalyst to mol%, the reaction only led to a similar yield as that of mol% (entry 9) Moreover, the amount of Cs2CO also affected the reaction efficiency, and the application of 1.5 equiv of Cs2CO3 proved to be necessary to complete the reaction (entries 10-12) Finally, the examined three-component carboxylative coupling reaction proved to be favorable at 40 oC Continue increasing the reaction temperature only Manuscript for Journal of Saudi Chemical Society 2017 02.07 led to a significant decrease of 2a yield, which may due to the low concentration of CO2 in solution at higher temperatures Based on the above studies, the scope of this carboxylation reaction was then further examined under the condition of atmospheric pressure of CO2, 1.5 equiv of Cs2CO3 and mol% of Ag-NHC in DMF at 40oC for 48 h To our delight, the reaction proved to be applicable for terminal aryl alkynes bearing various functional groups on the phenyl ring Good to excellent 2-alkynoateyields were obtained for terminal aryl alkynes bearing electron-donating groups such as methyl, propyl phenyl and methoxy groups (2b-2e) Halo (F or Cl) substituted terminal aryl alkynes also resulted in satisfactory yields of desired 2-alkynoates (2f-2h) Comparable good yields were also achieved for strong electron-withdrawing group -CN or CF3 substituted terminal aryl alkynes (2i, 2j) Finally, the reaction was also found to be applicable for linear alkyl terminal alkynes (2k, 2l) Therefore, this reaction shows good substituent-loading capability Notably, all the reactions resulted in the formation of as the only isolated products, thus showing a good selectivity Based on the literature precedents [24, 33, 37], a possible catalytic mechanism outlined in Scheme is proposed The coordination of alkyne to Ag-NHC is assumed to occur at first, thus leading to a more acidic alkyne The subsequent deprotonation of alkyne by strong basic Cs2CO3 affords a CsCO3- ligated intermediate Such an intermediate may undergo the removal of CsHCO3 to generate a desired silver(I) acetylide The following insertion of CO2 into Ag-C bond of the silver(I) acetylide affords a silver(I) propiolate intermediate Finally, silver(I) propiolate might interact with butyl iodide to afford the desired 2-alkynoate product, regenerating the Ag-NHC catalyst Conclusions The three-component carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide were successfully achieved using 1,3-bis(4-methylbenzyl)imidazol-2ylidene silver(І) chloride as the catalyst and Cs2CO3 as the base in DMF under ambient temperature and atmospheric pressure of CO2 Good to excellent yields of various 2-alkynoates were afforded as the isolated products The possible reaction mechanism is also discussed Manuscript for Journal of Saudi Chemical Society 2017 02.07 Acknowledgements M.D.Z thanks the National Science Foundation of China (21101085), Natural Science Foundation of Liaoning Province (2015020196), Fushun Science & Technology Program (FSKJHT 201423), and Liaoning Excellent Talents Program in University (LJQ2012031) for the financial supports References [1] M Cokoja, C Bruckmeier, B Rieger,W A Herrmann, F E Kühn, Angew Chem Int Ed 50 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Manuscript for Journal of Saudi Chemical Society 2017 02.07 Table 1．Optimization of reaction conditions.a Entry Ag-NHC(mol%) Cs2CO3(equiv.) Solvent Yield(%)b - 1.5 DMF 2 - DMF 1.5 DMF 92 1.5 CH3CN 90 1.5 DMSO 87 1.5 CH2Cl2 1.5 THF 46 1.5 DMF 45 1.5 DMF 90 10 1.0 DMF 20 11 1.2 DMF 81 12 2.0 DMF 92 13 c 1.5 DMF 39 14 d 1.5 DMF 75 Manuscript for Journal of Saudi Chemical Society 15 e a 2017 02.07 1.5 DMF 69 The reactions were carried out using 1a (1.0 mmol), nBuI (1.2 mmol), CO2 (99.999%, balloon), Cs2CO3 and Ag-NHC insolvent (5 mL) at 40oC for 48 h; b Isolated yield c 25oC; d 60oC; e 85oC Table 2.The carboxylative coupling of various terminal alkynes, butyl iodidewith CO2.a,b 2a, 92% 2b, 94% 2c, 77% 2d, 81% 2e, 91% 2f, 82% 2g, 85% 2h, 86% 2i, 84% 10 Manuscript for Journal of Saudi Chemical Society 2j, 81% a 2017 02.07 2k,82% 2l,80% The reactions were carried out using (1.0 mmol), nBuI (1.2 mmol), CO2 (99.999%, balloon), Cs2CO3 (1.5 mmol) and Ag-NHC (2 mol%) in DMF (5 mL) at 40oC for 48 h; b Isolated yields 11 Manuscript for Journal of Saudi Chemical Society 2017 02.07 Scheme Monomeric structure of 1,3-bis(4-methylbenzyl)imidazol-2-ylidene silver(І) chloride Scheme The proposed mechanism 12 ... Journal of Saudi Chemical Society 20 17 02. 07 1,3- Bis(4- methylbenzyl)imidazol- 2- ylidene silver(І) chloride catalyzed carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide. .. alkynes, butyl iodidewith CO2.a,b 2a, 92% 2b, 94% 2c, 77% 2d, 81% 2e, 91% 2f, 82% 2g, 85% 2h, 86% 2i, 84% 10 Manuscript for Journal of Saudi Chemical Society 2j, 81% a 20 17 02. 07 2k, 82% 2l,80% The... for Journal of Saudi Chemical Society 20 17 02. 07 154.19, 139. 72, 133.41, 128 .90, 128 .07, 127 .14, 127 .05, 118. 32, 86.03, 81 .28 , 65.90, 30.43, 19. 02, 13.61; IR (cm-1) (KBr) 29 60, 22 20, 1710, 1606,