The chemical fixation of CO2 under mild reaction conditions is of significance from a sustainable chemistry viewpoint. Herein a CO2-reactive protic ionic liquid (PIL), [HDBU(+)][TFE(-)], was designed by neutralization of the superbase 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with a weak proton donor trifluoroethanol (TFE). As a bifunctional catalyst for simultaneously activating CO2 and the substrate, this PIL displayed excellent performance in catalyzing the reactions of CO2 with 2-aminobenzonitriles at atmospheric pressure and room temperature, thus producing a series of quinazoline-2,4(1H,3H)-diones in excellent yields.
The CO 2 -involved synthesis of chemicals is of significance. In this work, we found that 1-alkyl-3-methylimidazolium ionic liquids (ILs) had high efficiency for catalyzing the formylation of amines using CO 2 and phenylsilane at room temperature, producing the corresponding formylated products in excellent yields under the metal-free condition. The ILs acted as bifunctional catalysts, which activated the Si−H bond of phenylsilane to react with CO 2 to form the formoxysilane intermediate and simultaneously activated the amine substrate through the hydrogen bond. Moreover, the imidazolium cation and the anions of the ILs showed an excellent synergistic effect on catalyzing the formylation of amines.T he metal-free catalytic process can reduce cost and avoid the pollution caused by metals and is thus regarded as a green process, which has been paid much attention in chemical synthesis. 1 The CO 2 -involved chemical synthesis has been widely investigated in the past decades because CO 2 is a cheap, renewable, abundant, and green C1 resource. 2 However, due to the inherent thermodynamic and kinetic stability of CO 2 , it is challenging to activate CO 2 and achieve its transformation under mild conditions, especially at room temperature. So far, much work has focused on exploring efficient catalysts or catalytic systems for CO 2 conversion. 3 Metal-based catalysts have been widely applied in the CO 2 -involved chemical synthesis. 4 Recently, metal-free catalytic systems have been reported, showing promising potential for the CO 2 transformation. 5 For example, N-heterocyclic carbenes (NHCs) can activate CO 2 and catalyze CO 2 conversion at room temperature and atmospheric pressure. 5a However, compared with the metal catalysis, the nonmetal-catalyzed CO 2 conversion is still in an early stage.Ionic liquids (ILs), composed of organic cations and organic/inorganic anions, possess unique features such as high thermal and chemical stability, negligible vapor pressure, easy separation and tunable properties. Notably, most of the ILs are nonmetallic salts, which have displayed promising applications in many areas, especially in catalysis. 6 For example, task-specific ILs have realized the CO 2 capture and conversion under mild and metal-free conditions. Protic IL (e.g., [DBUH][TFE]) served as a bifunctional catalyst and achieved the CO 2 conversion at atmospheric pressure and room temperature in the synthesis of quinazoline-2,4(1H,3H)-diones from CO 2 and 2-aminobenzonitriles. 6d ILs are designable via selecting cations and anions and thus can provide the ILs specific functions as a result of the cooperative or synergistic effects between the ions. 7 As nonmetal catalysts, ILs are promising due to their advantages such as easy separation, recyclability, stability to air and water, and so on.Formamides are versatile chemicals and important building blocks, which are generally produced via the formylation of amines. Using CO 2 instead of toxic CO for the N-formylation reaction is an attractive and green alternative for the pr...
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