Fixation of CO2 into cyclic carbonates by halogen bonding catalysis.

Halogen bonding, parallel to hydrogen bonding, was introduced into the catalytic cycloaddition of carbon dioxide into epoxide (CCE) reactions. A series of halogen bond donor (XBD) catalysts of N -iodopyridinium halide featured with N-I bond were synthesized and evaluated in CCE reactions. The optimal XBD catalyst, 4-(dimethylamino)- N -iodopyridinium bromide ([DMAPI]Br), under screened conditions at 100 °C, ambient pressure, and 1 mol % catalyst loading, realized 93% conversion of styrene oxide into cyclic carbonate in 6 h. The substrate scope was successfully extended with excellent yields (mostly 93% up) and quantitative selectivity (more than 99%). 1 H NMR titrations of the catalyst [DMAPI]Br on substrate epoxide certified that N-I bond directly coordinated with the epoxide oxygen. Plausible mechanism of halogen bonding catalysis was proposed, in which DMAPI cation functioned as halogen bond donor activated the epoxide and the counter anion bromide attacked the methylene carbon to initiate the ring-opening of the epoxide. CCE reactions promoted by N -iodopyridinium halide exemplified a first case of halogen-bonding catalysis in epoxide activation and CO 2 transformation.