Efficient carbon-neutral cycle reactions catalyzed by N-substituted biomimetic [Ru–Ru]-Based H-clusters

Herein, we report two biomimetic [Ru–Ru] analogs (Ru₂ADTX(CO)₆, X = Ts or Cbz), which contain the N-substituted azadithiolate (ADT) moiety of the native H-cluster, and their differential reactivity to the formic acid/carbon dioxide-hydrogen (FA/CO₂–H₂) “carbon-neutral cycle” reaction. 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 electronically- or sterically-substituted pendant amine bases in influencing the entry and exit of protons from 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 the CO₂ hydrogenation reaction, the 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 have significant effects 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 a sustainable supply of energy and environmental CO₂ control.