A New Application Area for Ag‐NHCs: CO₂ Fixation Catalyst

Abstract

Abstract The first example of the silver‐NHC catalyzed cycloaddition of CO 2 to terminal epoxides is reported. The choice of NHC substituents, halides and the nature of additives were determined to be important. Ionic [(C n mim) 2 Ag] 2 [Ag 2 Br 4 ] (C n mim=1‐(C n H 2 n +1 )‐3‐methylimidazol‐2‐ylidene; n =4–18) catalysts exhibited a high yield of styrene carbonate (77–92 %) in the presence of 4‐dimethylaminopyridine (DMAP) as a cocatalyst without needing any solvent. The catalytic activity improved as the length of the alkyl groups ( n ) increased, although substituents longer than C 14 did not produce any further beneficial effect. For the protocol performed at 1.5 M Pa pressure and 100 °C the TOF was calculated to be 440 h −1 . A prolonged reaction time and increased pressure of CO 2 increased the yield. Used without any additive, compound C 14 was able to fix CO 2 with PO (propylene oxide) quantitatively at 120 °C, 2.0 M Pa and could be used at least seven times without loss of activity and selectivity. The nucleophilic nature of the anion is decisive for the formation of the product.