Sustainable synthesis of cyclic carbonates from CO2 using zinc adeninium bromide as a biorenewable

The design of green catalysts for CO2 utilization purposes is considered a great challenge and a motivation for a sustainable future. In this work, a first-time zinc adeninium bromide (Zn-AHBr) was synthesized and fully characterized using far and mid ATR-FTIR, 1D and 2D NMR spectroscopy, including 1H, 13C and [1H,15N] correlation spectroscopy (HMBC/HSQC), cyclic voltammetry and further supported with theoretical calculations involving energetics using Density functional theory (DFT). The Zn-AHBr was exploited as an unprecedented biorenewable, sustainable catalyst for CO2/epoxide coupling at ambient reaction conditions (1 atm, 80 degrees C over 8 to 16 h) with quantitative conversion of epichlorohydrin, epibromohydrin, glycidol, glycidyl ether, and 1,2epoxy-3-phenoxypropane. Moreover, other Zn-AHX (X: Cl and I) showed excellent up to quantitative conversions toward epichlorohydrin cycloaddition. Furthermore, a plausible mechanism for the cycloaddition reaction was investigated using DFT calculations which indicated a relatively low activation energy (1.1 kcal.mol-1) for the epoxide ring opening, and a much higher value (9.4 kcal.mol- 1) for the cyclic carbonate ring closure as a rate determining step for the reaction.