CO2 capture at low concentration by catalysts is potentially useful for developing photocatalytic and electrocatalytic CO2 reduction systems. We investigated the CO2-capturing abilities of two complexes, fac-Mn(X2bpy)(CO)3(OCH2CH2NR2) and fac-Re(X2bpy)(CO)3(OCH2CH2NR2) (X2bpy = 4,4'-X2-2,2-bipyridine and R = -CH2CH2OH), which work as efficient catalysts for CO2 reduction. Both complexes could efficiently capture CO2 even from Ar gas containing only low concentration of CO2 such as 1% to be converted into fac-M(X2bpy)(CO)3(OC(O)OCH2CH2NR2) (M = Mn and Re). These CO2-capturing reactions proceeded reversibly and their equilibrium constants were >1000. The substituents of X2bpy strongly affected the CO2-capturing abilities of both Mn and Re complexes. The density functional theory (DFT) calculation could be used to estimate the CO2-capturing abilities of the metal complexes in the presence of triethanolamine.