Carbon dioxide (CO2) is an intrinsically stable molecule. However, its reactivity toward nucleophilic bases has constituted an appealing characteristic for applications such as CO2 capture and functionalization. To shed light on the role of nucleophilic bases in CO2 functionalization, we performed some mechanistic studies using nitrogen-containing bases as an additive—in catalytic amounts—for carboxylation reactions of Grignard reagents. Our kinetic analysis and in situ infrared spectroscopy revealed the role of nucleophilic bases, particularly that of DBU (1,8-diazabicycloundec-7-ene), in CO2 (de)activation for carboxylation reactions.