Synergistic Catalysis in Heterobimetallic Complexes for Homogeneous Carbon Dioxide Hydrogenation

Two heterobimetallic Mo,M' complexes (M' = Ir-III, Rh-III) were synthesized and fully characterized. Their catalytic activity in homogeneous carbon dioxide hydrogenation to formate was studied. A pronounced synergistic effect between the two metals was found, most notably between Mo and Ir, leading to a fourfold increase in activity compared with a binary mixture of the two monometallic counterparts. This synergism can be attributed to spatial proximity of the two metals rather than electronic interactions. To further understand the nature of this interaction, the mechanism of the CO2 hydrogenation to formate by a monometallic Ir-III catalyst was studied using computational and spectroscopic methods. The resting state of the reaction was found to be the metal-base adduct, whereas the rate-determining step is the inner-sphere hydride transfer to CO2. Based on these findings, the synergism in the heterobimetallic complex is beneficial in this key step, most likely by further activating the CO2.

Automated summary

Two heterometallic Mo,M' complexes (M' = Ir-III, Rh-III) were synthesized and characterized. They showed a significant synergistic effect, especially Mo and Ir, leading to a fourfold increase in catalytic activity compared to a binary mixture of the monometallic counterparts. The mechanism of CO2 hydrogenation to formate by a monometallic Ir-III catalyst was studied, revealing the importance of the metal-base adduct and inner-sphere hydride transfer.