Synergistic Catalysis in Heterobimetallic Complexes for Homogeneous Carbon Dioxide Hydrogenation

Zeno B G Fickenscher; Peter Lönnecke; Anna K Müller; Oldamur Hollóczki; Barbara Kirchner; Evamarie Hey-Hawkins

doi:10.3390/molecules28062574

Synergistic Catalysis in Heterobimetallic Complexes for Homogeneous Carbon Dioxide Hydrogenation

Molecules. 2023 Mar 12;28(6):2574. doi: 10.3390/molecules28062574.

Authors

Zeno B G Fickenscher¹, Peter Lönnecke¹, Anna K Müller², Oldamur Hollóczki³, Barbara Kirchner², Evamarie Hey-Hawkins¹

Affiliations

¹ Institute of Inorganic Chemistry, Universität Leipzig, Johannisallee 29, 04103 Leipzig, Germany.
² Mulliken Center for Theoretical Chemistry, Institute for Physical and Theoretical Chemistry, Beringstr. 4, 53115 Bonn, Germany.
³ Department of Physical Chemistry, Faculty of Science and Technology, University of Debrecen, Egyetem ter 1, H-4010 Debrecen, Hungary.

Abstract

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.

Keywords: bimetallic complex; carbon dioxide; hydrogenation; synergistic catalysis.

Grants and funding

Financial support from the Studienstiftung des deutschen Volkes (doctoral fellowships for Z.B.G.F) and the Graduate School BuildMoNa is gratefully acknowledged. O.H. acknowledges the financial support from the National Research, Development and Innovation Office through the project OTKA-FK 138823, the János Bolyai Research Scholarship of the Hungarian Academy of Sciences, and the ÚNKP-22-5 New National Excellence Program from the National Research, Development and Innovation Fund.