CO₂ capture by Mn(i) and Re(i) complexes with a deprotonated triethanolamine ligand

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.