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In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/analyst Page 1 of 5 Please do notAnalyst adjust margins 1 2 3 4 Journal Name 5 6 7 ARTICLE 8 9 10 11 High Sensitive Detection of Carbon Dioxide by Pyrimido[1,2- 12 13 a]benzimidazole derivative: Combining Experimental and 14 Received 00th January 20xx, Theoretical Studies Accepted 00th January 20xx 15 16 DOI: 10.1039/x0xx00000x Guomin Xia, Chengyan, Ruan, Hongming Wang* 17 www.rsc.org/ In present paper, a “light-up” chemsensor with a highly specificity for carbon dioxide detection using Pyrimido[1,2- 18 a]benzimidazole derivative (P1H) in liquid media has been developed. The results show that the P1H reacts with carbon 19 dioxide activated by basic ion to form carboxylic acid compound (P1-COOH). These results provide a possible method for 20 carboxylation reactions of P1H using carbon dioxide based on vinyl carbanion as well. The complete reaction mechanism 21 cycle was described by DFT calculation as well. 22 23 synthesis via using CO 2 as the electrophile and other 24 1. Introduction organometallic reagents as nucleophile. 12 Typically, nucleophile such as organolithium, organozinc and 25 With the deterioration of global warming and its secondary organic manganese are universally taken as precursors, and 26 induced disasters, researches on greenhouse gases chemistry 1 this method is always limited by low catalytic performances, Manuscript 27 have caught urgent attention. The capture and utilization of harsh reaction conditions, and restricted substrate scope. 13 28 these gases have been greatly promoted in both laboratorial 2-3 Photosynthesis in nature is a process utilized by plants and 29 and industrial application for the last decades. Among those other organisms to convert light energy to chemical energy via 30 researches, the detection, capture and conversion of the reaction between carbon dioxide and water in mild condition 31 abundant, easily available and renewable carbon dioxide as 14 . The key step of photosynthesis is that RuBP enzyme reacts 32 green C1 feedstock have been considered as a sustainable with carbon dioxide which leads to the atmospheric carbon 33 strategy, seeking to balance the industrial development 4-5 dioxide fixation at its C2 center in the carboxylation 34 and environmental protection. reactions(figure 1). 15 The reaction proceeds through several 35 Because of the inherent kinetic stability, carbon dioxide hardly elemental steps, including enolization and deprotonation, 36 reacts directly with the organic reactants without being 6 yielding the 2,3-enediolate, a carbanion that contains double activated by potent catalyst systems. It is well known that the Accepted 37 phosphate ester and is the substrate of carbon dioxide catalyst systems like metal-containing complexes, nitrogen- 38 addition(figure 1). 16 These researches indicate that the base (e.g. frustrated amidine and guanidines) and task-specific 39 carbanion hold an efficient capture and acivation for carbon ionic liquids can activate the carbon dioxide 40 7 dioxide, and transfer carbon dioxide to efficiently. Among those catalysts, some special nitrogen- 41 carboxylic acid compound. 42 based basic precursors including N-heterocyclic carbenes (NHCs) 8, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) 9 and 1,5,7- 43 10-11 44 triazabicyclo[4.4.0] dec-5-ene (TBD) are able to active and react with carbon dioxide to form zwitterionic adducts under 45 Analyst CO atmosphere. Unfortunately, these base-CO adducts have 46 2 2 been proved to be extremely unstable and unobtainable in the 47 presence of ambient moisture. Strict operation condition, such 48 as the water-free and oxygen-free conditions, is necessary for 49 these reactions 12 . For example, direct carboxylation of C-H Figure 1. Suggested multistep mechanism for the carboxylation reaction catalyzed by 50 bond with carbon dioxide is an important reaction in organic rubiso. 51 52 It has been said that nature is the best teacher. As a 53 consequence, discovering a biomimetic precursor, such as 54 carbanion, which is able to directly and blandly detection, 55 capture and convert unactivated CO 2 to generate ambient 56 stable chemicals rather than zwitterionic adducts, was [16] 57 intensively desired in mild reaction condition. Herein, 58 59 60 This journal is © The Royal Society of Chemistry 20xx J. Name ., 2013, 00 , 1-3 | 1 Please do not adjust margins Please do notAnalyst adjust margins Page 2 of 5 ARTICLE Journal Name 1 2 taking inspiration from nature, we report an high effective chloroform as eluent) to give P1H in 41% yield (563mg, 3 method for sensitive detection of carbon dioxide using 2.08mmol) M.P. 252-253 ℃. 1H NMR (400 MHz, DMSO-d ) ppm 4 6 carbanion in mild condition. The results indicate that the P1H 10.08 (s, 1H), 8.39 (d, J = 8.22 Hz, 1H), 7.94 (d, J = 8.26 Hz, 1H), 5 can react with carbon dioxide rapidly and sensitively in the 7.70-7.46 (m, 2H), 4.49 (q, J = 7.11 Hz, 2H), 1.46-1.32 (m, 3H). 6 - 13 presence of excess F ion to form the carboxylation product. C-NMR (400 MHz, DMSO-d6), 163.35(1C), 152.60(1C), 7 The reaction mechanism was confirmed by its spectroscopic 147.44(1C), 145.28(1C), 137.23(1C), 127.60(1C), 127.38(1C), 8 analysis. Furthermore, theoretical calculations provided 123.23(1C), 120.24(1C), 113.93(1C), 110.99(1C), 63.15(1C), 9 detailed explanations to the phenomena. 14.45(1C). Anal. Calcd for P1H: C, 56.64; H, 3.66; N, 15.24. 10 Found: C, 56.60; H, 3.70; N, 15.21. 11 2.4 Computational detailed 12 2. Experimental All the theoretical calculations were performed with Gaussian 13 2.1 Chemicals and reagents 09 suite programs. 17 Geometrical optimization, including 14 All commercially available reagents and solvents were transition structure searches were performed by the hybrid 15 density functional B3LYP methods 18,19 and standard 6– 16 purchased from commercial suppliers and used without further purification unless otherwise stated. Absorption 311G(d,p) basis set. All reactants and intermediate had no 17 imaginary frequency, and the transition states were 18 spectrometry was performed using Gold S54T spectrophotometer of Lengguang Company, and fluorescence ascertained by vibrational analysis with only one imaginary 19 spectrometry was performed using F-7000 FL frequency mode. The zero-point energy was calculated by 20 Spectrophotometer of Hitachi. Melting points were using the vibrational frequencies. In the case of transition 21 1 13 determined in open capillaries. H NMR and C NMR spectra states, the vibration was associated with a movement in the 22 were recorded with a Bruker AVANCE 500 spectrometer with direction of the reaction coordinate. Intrinsic reaction 23 use of the deuterated solvoent as the lock and TMS as an coordinate calculations, at the same level of theory, were 24 internal reference. Elemental analysis was performed on performed to ensure that the transition states led to the 25 Elementar Vario vario EL III. Mass spectra were acquired using expected reactants and products. The solvent effects have 26 a triple quadrupole mass spectrometer (6430 QqQLC/MS been considered using a relatively simple self-consistent 27 system; Agilent Technologies, USA) equipped with an reaction field (SCRF) method, based on the polarizable Manuscript 20 28 orthogonal ESI source.The crystals for X-ray diffraction continuum model (PCM). The solvent used in this calculation 29 analyses were grown in dichloromethane by adding n-hexane is DMF. The values of the relative energies with zero-point 30 to slow diffuse. The X-ray diffraction experiment was carried energy correction (∆E0) were calculated and used on the basis 31 out using Bruker SMART APEX-II Single-crystal diffractometer. of the total energies of the stationary points. 32 Tetrabutylammonium salts (F -, AcO -, Cl -, Br - and I -) were all 33 >98% pure and the solutions used in titrations were prepared 3. Results and discussion 34 in fresh dry acetonitrile (CH 3CN). 35 At the beginning, a yellow solid P1H with luminescence was 36 H Cl synthesized inadvertently by adding an EtOH solution of 2- N O O O O O Accepted 37 O NH2 aminobenzimidazole into fresh squaric acid dichloride under DMF N N + N O vigorous stirring (Scheme 1). The X-ray crystal structure of P1H 38 S benzene Cl Cl EtOH N 39 HO OH Cl Cl 41% is depicted in Figure 2. The whole fused heteroaromatic 54% 40 system is nearly planar except ethoxycarbonyl. The dihedral Scheme S1. The synthesis of compound P1H 41 angle between the pyrimidine ring and ethoxycarbonyl arm is 42 76.63°. Unexpectedly, the chemical shifts （ δ ） of the H 2.2 Synthesis of 3,4-Dichlorocyclobutene-1,2-dione 43 atom(C8-H) of pyrimidine ring is 10.08 ppm and 9.72ppm in 44 A mixture of squaric acid (1.14 g, 10 mmol), thionyl dichloride DMSO-d6 and CD 3CN-d3, which mean that C8-H 45 (1.8 ml, 20 mmol) and DMF (200ul) in dry benzene (10 ml) was possesses relative acidity and easily forms a vinyl carbanion Analyst 46 refluxed for 6 h at 60 ℃.