A rhenium(I) tricarbonyl diimine complex with a N,N-dimethylformamide ligand captures one CO2 molecule in the presence of triethanolamine (TEOA), giving fac-[Re-I(bpy)(CO)(3){R2N-CH2CH2O-COO}] (bpy = 2,2'-bipyridine, R = CH2CH2OH). This could be a predominant complex in various photocatalytic CO2 reduction reactions using [Re-I(NAN)(CO)(3)X](n+) (N<^>N = diimine ligand; X = monodentate ligand; n = 0, 1) type complexes in the presence of TEOA.