Low Potential CO₂ Reduction by Inert Fe(II)-Macrobicyclic Complex: A New Concept of Cavity Assisted CO₂ Activation

The advantage of a pre-organized pi-cavity of Fe(II) complex of a newly developed macrobicycle cryptand is explored for CO2 reduction by overcoming the problem of high overpotential associated with the inert nature of the cryptate. Thus, a bipyridine-centered tritopic macrobicycle having a molecular pi-cavity capable of forming Fe(II) complex as well as potential for CO2 encapsulation is synthesized. The inert Fe(II)-cryptate shows much lower potential in cyclic voltammetry than the Fe(II)-tris-dimethylbipyridine (Fe-MBP) core. Interestingly, this cryptate shows electrochemical CO2 reduction at a considerably lower potential than the Fe-MBP inert core. Therefore, this study represents that a well-structured pi-cavity may generate a new series of molecular catalysts for the CO2 reduction reaction (CO2RR), even with the inert metal complexes.