Efficient Synthesis of Cyclic Carbonates by Mg^II/Phosphine‐Catalyzed Coupling Reactions of Carbon Dioxide and Epoxides

Abstract

Carbon dioxide (CO 2 ) is an abundant, cheap, and green solvent, and it is also a renewable C 1 source for chemical syntheses. [1] Nevertheless, the activation and fixation of CO 2 remains a challenging task for researchers in organic and organometallic chemistry because of its thermodynamic stability and low reactivity. [2] With regard to the depletion of petroleum reserves and the greenhouse effect from the increase in CO 2 emissions, catalytic processes that employ CO 2 as a feedstock have been investigated intensively over the last two decades. [3] Promising methodology in this area is the coupling reactions of CO 2 with epoxides to produce cyclic carbonates, [4] which are useful as synthetic intermediates, [5] aprotic polar solvents, and feedstock for engineering plastics. [6] Numerous catalysts have been developed for this reaction system. [7] Although the advances have been significant, there are drawbacks, such as low catalytic stability and reactivity, air sensitivity, and the need for a co-solvent, high pressures, or high temperatures.Continuous efforts have been made to improve existing techniques and to discover new methods for CO 2 activation, [2c, 8] which generally requires organometallic reagents, organic halides, [9] or other preactivated/in situ generated carboxyl zwitterionic complexes, such as compound 1, obtained from phosphines, [8a, 10] compound 2, obtained from tertiary amines or tetralkylammonium salts, [2a, 8b, 11] compound 3, obtained from N-heterocyclic carbenes (NHCs), [12] compound 4, obtained from 4-(dimethylamino)pyridine (DMAP), [2c, 13] and compound 5, obtained from 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) [8c, 14] (Scheme 1). Tetrabutylammonium bromide (TBAB), DMAP, and NHC-based catalyst systems have been studied extensively because of their ease of preparation and commercial availability. High temperatures are required in most cases, [2a, 6b] despite the heat that is released from the coupling reaction of epoxides with CO 2 . [15] Phosphine-based catalyst systems have attracted only a little attention. [16] Therefore, this study evaluated phosphines as potential co-catalysts for the activation of CO 2 at room temperature to reduce energy costs during the reaction.The synthesis of vinyl ethylene carbonate (VEC, 7 a), which is an effective electrolyte additive for high-performance Li ion battery applications and an important intermediate for fine chemicals, [6b, 17] was initially chosen as a model for investigating the reaction parameters (Table 1). Mg II complexes are used widely because they are relatively less expensive than other complexes, and they are efficient catalysts in organic syntheses. [18] Magnesium is the central ion of the porphyrin in the green pigment of plants, chlorophyll, which is widely distributed in natural metabolism systems, and it is essential for the photosynthesis of glucose from CO 2 . [19] A few studies have reported that Mg II -based catalysts for the coupling of epoxides with CO 2 still require further improvements. [20] Some of ...

Metalated porous porphyrin polymers as efficient heterogeneous catalysts for cycloaddition of epoxides with CO2 under ambient conditions

“…For this reaction, a number of homogeneous catalysts such as ionic liquids [5,6], alkali metal halides [7], metal salen complexes [8][9][10][11][12][13], and metalloporphyrins [14][15][16][17][18], and heterogeneous catalysts such as metal oxides [19][20][21], zeolites [22,23], ion-exchanged resins [24], mesoporous materials [25][26][27], nanoporous polymers [28,29], and metalorganic frameworks (MOFs) [30,31] have been employed. Notably, most of these catalysts normally require harsh conditions such as relatively high temperature, high CO 2 pressure, and high catalyst loadings.…”

Docking Site Modulation of Isostructural Covalent Organic Frameworks for CO2 Fixation

“…For example,t he product of cyclic carbonates serve as the raw materials for polycarbonates which were widely used as green electrolytesi nb atteries. [4] Av ariety of homogeneous catalysts involvingt ransition metal complexes, [5][6][7] and alkali metals alts [8] have been welli nvestigated and exhibit appreciable performance on reactions of CO 2 and epoxides with high conversion yields. Although homogeneous catalysts are efficient, the difficultiesi ns eparation andr ecycling have limited their real application.I nc ontrast, heterogeneous catalysts have been widely applied in industryb ecause of easy separation, good recyclability,l ess catalyst contamination in the products and low cost.…”

Frustrated Lewis Pair Chemistry with Magnesium Lewis Acids

“…This interac- These findings represent a rare example of a magnesium/ phosphorus FLP and demonstrate the possibilities of this research area. It is highly likely that the recently reported conversion of epoxide/CO 2 mixtures to cyclic carbonates by an MgBr 2 / PPh 3 catalyst [46] also proceeds through an FLP mechanism in which Mg activates the epoxide, and PPh 3 (instead of Bras proposed by the authors) is responsible for nucleophilic ring opening. The introduction of metal centers such as Mg in FLP chemistry seems attractive.…”