Cyclic carbonate synthesis from CO2 and epoxides over diamine-functionalized porous organic frameworks

Abstract

Porous aromatic polymers functionalized with ethylenediamine (CBAP-1(EDA)) and then complexed with Zn2+ or Co2+ ions (CBAP-1(EDA-Zn)) and (CBAP-1(EDA-Co) were synthesized and applied as a catalyst for the solventless synthesis of cyclic carbonates from CO2 and epoxides. The properties of the catalysts were examined by various analytical techniques. CBAP-1(EDA) alone enabled the high catalytic conversion of epoxides (>98%) to five-membered cyclic carbonates at 130°C under solvent-, metal-, and co-catalyst-free conditions with high selectivity. The catalytic activity of CBAP-1(EDA) was enhanced in the presence of a nucleophile and Lewis acidic metal ion sites. Thus, CBAP-1(EDA) with tetrabutylammonium bromide (TBAB) had shown 98% conversion of epoxide at 80°C and 1MPa CO2 in 8h, whereas CBAP-1(EDA-Zn) and CBAP-1(EDA-Co) with TBAB achieved 96% epoxide conversion in 36h at room temperature (RT). The stability of the catalysts was confirmed by hot-filtering and reusability tests, which demonstrated that the catalysts could be reused for up to five consecutive runs without any noticeable decline in catalytic activity. The synergism between the basic catalytic sites in CBAP-1(EDA) and TBAB and the Lewis metallic sites was explained by the proposed reaction mechanistic pathway covering both high temperature (metal- and halogen-free) and RT conditions (with metal and halogen).