A series of flexible proton-responsive group substituted N^N-bidentate ligand based Mn(I)-complexes have been studied for base free CO2 hydrogenation. We show here that the proton responsive ligand plays a critical role for base free CO2 hydrogenation. Our calculated reaction free energy barrier values for heterolytic H2 cleavage show that such flexible proton-responsive ligands require a very low activation energy (~3 kcal/mol) barrier. Such flexible proton responsive ligands improve the strong dihydrogen (H···H) bonding, which in turn improves the heterolytic H2 cleavage- an important step for base free CO2 hydrogenation. Therefore, we believe that such flexible proton responsive ligand substituted metal complexes can be promising for base free CO2 hydrogenation reactions.