Nicotinamide onium halide bidentate hybrid H-bond donor organocatalyst for CO₂fixation

H-bond donor (HBD) and nucleophilic halide cooperating catalysis was well developed in cycloaddition of CO2 with epoxide (CCE) reactions where common strong HBD was prevalent. Here a type of onium halide organocatalyst featured weak C-H and N-H HBD was proposed, designed and evaluated in CCE reactions. Based on biobased nicotinamide, nicotinamidium halide catalyst was prepared by simple alkylation on pyridyl N and/or on amide NH. A mono-alkylated on pyridyl N, 1-octyl nicotinamidium iodide, was screened an optimal catalyst that achieved 96 % yield of carbonate under 1 mol% catalyst loading, 1 atm pressure of CO2, 80 °C, by 24 h. Terminal epoxides were converted successfully into their corresponding cyclic carbonates by 84-99 % yields with 99 % selectivity. Scale-up preparation of styrene carbonate with 100 g of styrene epoxide (by 88 % yield and 98 % selectivity), and preparation of bis(cyclic carbonate) of a commercial diglycidyl ether of bisphenol A (by 79 % yield and 98 % selectivity) showed practical utility. The H-bonding activation between C-H and N-H HBDs with epoxide was validated by 1H NMR titrations. Designed analog catalysts to 1-octyl nicotinamidium iodide with blocked C-H or blocked N-H revealed the bidentate HBDs worked synergistically. The observations of the beneficial outcome of weak pyridium α-C-H and amide N-H H-bond donors proposed a protocol for simple yet efficient biobased H-bond donor organocatalyst development for CCE reactions.