A nucleophile attacks the coordinated epoxide to activate the reaction. A co-catalyst e.g., tetrabutylammonium bromide, (TBAB) forms a Bromo-alkoxy intermediate . The authors suggested the Zn-N bond dissociation and creation of active sites of Zn-OH species (lowcoordinated Zn species) that act as Lewis acid/base for CO2 cycloaddition. They also claimed that the dissociated N-species (pyrrolic or pyridinic) were inactive sites for the reaction (Figure ) .