Facile synthesis of crystalline viologen-based porous ionic polymers with hydrogen-bonded water for efficient catalytic CO₂ fixation under ambient conditions

Abstract

In this work, we report a series of crystalline viologen-based porous ionic polymers (denoted VIP-X, X ¼ Cl or Br), that have in situ formed dicationic viologens paired with halogen anions and intrinsic hydrogenbonded water molecules, towards metal-free heterogeneous catalytic conversion of carbon dioxide (CO 2 ) under mild conditions. The targeted VIP-X materials were facilely constructed via the Menshutkin reaction of 4,4 0 -bipyridine with 4,4 0 -bis(bromomethyl)biphenyl (BCBMP) or 4,4 0 -bis(chloromethyl) biphenyl (BBMBP) monomers. Their crystalline and porous structures, morphological features and chemical structures and compositions were fully characterized by various advanced techniques. The optimal catalyst VIP-Br afforded a high yield of 99% in the synthesis of cyclic carbonate by CO 2 cycloaddition with epichlorohydrin under atmospheric pressure (1 bar) and a low temperature (40 C), while other various epoxides could be also converted into cyclic carbonates under mild conditions. Moreover, the catalyst VIP-Br could be separated easily and reused with good stability. The remarkable catalytic performance could be attributed to the synergistic effect of the enriched Br À anions and available hydrogen bond donors -OH groups coming from H-bonded water molecules.Scheme 1 Synthetic route to crystalline viologen-based porous ionic polymers VIP-X (X ¼ Cl or Br) with intrinsic H-bonded water molecules via the Menschutkin reaction of 4,4 0 -bipyridine with (a) BCMBP and (b) BBMBP under solvothermal conditions (i.e., CH 3 CN, 100 C, 48 h). This journal isScheme 2 A proposed catalytic reaction mechanism for the cycloaddition of CO 2 with epoxides over the catalyst VIP-Br with Br À anions and H-bonded water molecules.This journal is

Recent developments in organocatalysed transformations of epoxides and carbon dioxide into cyclic carbonates

“…Chen et al used the Menschutkin reaction to synthesise pyridinium-based porous ionic polymers from bipyridine and 4,4'-bis(bromomethyl/chloromethyl)biphenyl monomers. 167 The conversion of various epoxides into cyclic carbonates could be achieved at 1 bar of carbon dioxide and 60-120 o C, but required a reaction time of 48-72 h. When the bromide containing polymer was used to catalyse the reaction of epichlorohydrin with carbon dioxide, the yield of cyclic carbonate slightly decreased from 99% to 94% after five uses.…”

Emerging Ionic Polymers for CO

“…[14] Porous ionic polymers (PIPs) are a class of POPs that have controllable porous structures, abundant ionic sites, good ion exchange properties, and tuneable chemical functionalities. [50] In particular, halogen-based PIPs have better CO 2 capture ability due to the strong dipole-quadrupole interactions of their ionic moieties with CO 2 . As discussed previously, the halogen anion plays the role of an active nucleophile for the CO 2 cycloaddition reaction.…”

“…As discussed previously, the halogen anion plays the role of an active nucleophile for the CO 2 cycloaddition reaction. [50] Moreover, IL moieties in the polymer backbone have an intrinsic hydrophilicity that can chemically absorb nearby water molecules via H-bonding. A sufficient amount of water can enhance the coupling of CO 2 with epoxide by forming H-bonds with the oxygen atom on the epoxide.…”

Elucidating the role of non-covalent interactions in unexpectedly high and selective CO2 uptake and catalytic conversion of porphyrin-based ionic organic polymers

“…35,[39][40][41][42] Consequently, the CO2 uptake capacity of viologen linked ICOPs is found to be significantly higher compared to their neutral counterparts. 34,43,44 Moreover, unlike other porous materials, selective recognition of viologen linked ICOPs can be manipulated by simply controlling the redox state of viologen or the nature of counter-ions for the desired application. 39,41 In recent years, several cationic viologen linked ICOPs with good surface areas has been reported for CCU.…”

“…39,41 In recent years, several cationic viologen linked ICOPs with good surface areas has been reported for CCU. 34,39,[43][44][45][46][47][48][49] The general understanding of these studies is that the high CO2 capture capacity of viologen linked ICOPs is credited mostly to tetrel bonding interaction between counter anions and CO2. 50 Commonly, nitrogen-based groups in CCU applications are preferred for their Lewis basic characters to form non-covalent interactions with electron-deficient central carbon (Lewis acid) of CO2.…”