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

Abstract

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.