Efficient Reversible Formic Acid/Carbon Dioxide Carbon Neutral Cycle Catalyzed by Biomimetic N-Substituted Azadithiolate Ruthenium Complexes

Yin-Tse Chou (周尹則), Chi-Hsuan Laio, Tung-Kung Wu*

Department of Biological Science & Technology, National Yang Ming Chiao Tung University 

We report here two biomimetic [Ru-Ru] analogs (Ru2ADTX(CO)6, X = Ts or Cbz) containing N-substituted azadithiolate (ADT) moiety of native H-cluster and their evaluation of reversible formic acid/carbon dioxide-hydrogen (FA/CO2-H2) reactivity. The results show that the strongly electron-withdrawing tosyl-substituted Ru2ADTTs(CO)6 1 exhibits a higher preference for CO2 hydrogenation, while the donor-inductive carboxybenzyl-substituted Ru2ADTCbz(CO)6 2 favors FA dehydrogenation, supporting the role of electronic or steric-substituted pendant amine bases in influencing the entry and exit of protons into the Ru-Ru active site and subsequent H2 oxidation and generation. Furthermore, the propensity of TEA in FA dehydrogenation and DBU in CO2 hydrogenation support the role of bases as sacrificial electron donors and co-reagents, respectively. In CO2 hydrogenation reaction, P-ligands with more phosphorus atoms exhibited higher reactivity and final CO2 conversion efficiency, indicating that the number of phosphorus atoms and the different electronic but isosteric substitutions on the P-ligands has significant effect on the reactivity of metal complexes. These results support the combination of the FA dehydrogenation of complex 2 and the CO2 hydrogenation capability of complex 1 to construct an efficient FA/CO2-H2 reversible reaction for sustainable energy supply and environmental CO2 control.