Efficient Catalysts In situ Generated from Zinc, Amide and Benzyl Bromide for Epoxide/CO₂ Coupling Reaction at Atmospheric Pressure

Abstract

Herein, in situ generated efficient catalysts were designed for fixation of CO2 to cyclic carbonates under mild conditions. Zinc bromide and N,N‐dibenzyl‐N,N‐dimethylammonium bromide, being proved as active catalyst species, were in situ generated from cheap Zn powder, dimethyl formamide and benzyl bromide, and catalyzed the cycloaddition reaction of CO2 and various terminal epoxides in moderate to excellent yields at 80 °C and atmospheric pressure of CO2. The protocol circumvents the preparation of active catalysts, simultaneously possesses good catalytic activity under mild conditions.

Toward a Neutral Single-Component Amidinate Iodide Aluminum Catalyst for the CO2 Fixation into Cyclic Carbonates

“…The reactions were carried out at 80 °C and 1 bar of CO 2 pressure for 24 h employing a combination of 1.5 mol % of complex 2 and 1.5 mol % of tetrabutylammonium iodide (TBAI) as a cocatalyst, while only 1.5 mol % of the single-component catalyst 3 were used under solvent-free conditions. Interestingly, no polycarbonates were obtained under these reaction conditions as expected, since these epoxide substrates generally showed selectivity toward cyclic carbonate formation. − In general, catalyst 2 achieved moderate to excellent yields for the preparation of cyclic carbonates 5a – h (Table , entries 1–8). It is worth noting that the mixed catalytic system ( 2 /TBAI) was reactive toward the formation of a wide variety of cyclic carbonates functionalized with alkyl, aryl, halide, and ether groups, which demonstrates that compound 2 has a broad scope and is selective for cyclic carbonate formation.…”

“…A large number of catalytic systems have been developed for the preparation of cyclic carbonates including organocatalysts − and metal complexes. − These generally act as Lewis acids in the activation of the epoxides for their transformation to cyclic carbonates. The choice of the metal center is essential, and aluminum, an abundant element in the earth’s crust, is one of the most suited metals for cyclic carbonates formation. − Moreover, regarding the use of ligands, Schiff base ligands have been widely investigated, promoting increasing reactivity of the catalysts. , Among the catalytic systems reported in the literature, the bimetallic aluminum­(salen) complex (Figure a) was found to be an excellent catalyst for the preparation of cyclic carbonates under mild reaction conditions .…”

One‐Pot Synthesis of Organic Carbonate from Alcohol and Alkyl Bromide under Low CO2 Pressure

“…When iso-propanol was reacted with bromoethane, 1-bromopropane and 1-bromobutane, the yields of 10-12 were 79 %, 85 % and 84 %, respectively (Table 8, Entries 13-15), which was caused by the steric hindrance. It can be found that steric hindrance had almost no effect on the reaction in the case of iso-butanol, and the yields of the corresponding products 13-15 were higher than 96 % (Table 8, Entries [16][17][18]. The reason for this may be that the branched chain is far away from the hydroxyl group, thus the influence of steric hindrance is weak.…”

“…[14,15] For instance, ethyl methyl carbonate (EMC) as the simplest unsymmetrical carbonate, is widely applied in methylation, ethylation, and methoxycarbonylation reactions. [16] Recently, symmetrical organic carbonates (such as dimethyl carbonate DMC) have been synthesized by transesterification, [17] direct synthesis from CO 2 and alcohols, [18] or one-pot synthesis. [19,20] Compared to symmetrical organic carbonates, unsymmetrical organic carbonates are more difficult to be synthesized.…”

Synthesis of dimethyl carbonate from methanol and CO2 under low pressure

“…12 In this process, thermodynamic limitations and ammonia interferences should be concerned although this method is environmentally friendly. In the rst step of trans-esterication method cyclic carbonate was produced using CO 2 and epoxide as starting materials, 13,14 and then reacted with methanol to produce DMC and the corresponding 1,2-diols. 15 High energy consumption and investment occurred by the separation of intermediate products in two-step transesterication.…”