The critical ligand effects in copper-catalyzed boracarboxylation of styrene were investigated using density functional theory (DFT) calculations. Based on the rate-determining CO₂ insertion step, the computations reveal that the reactivity of the catalysts ligated by monophosphine ligands is controlled by the ligand's electronic properties. This is consistent with the nature of nucleophilic attack on CO₂ by the benzylcopper intermediate. In contrast, the NHC ligands exert significant steric effects on the reactivity. The ineffectiveness of bidentate phosphine ligands originated from the large distortion of the catalyst and CO₂ that is caused by the sterically congested transition state of CO₂ insertion.