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

Synergistic Catalysis in Heterobimetallic Complexes for Homogeneous Carbon Dioxide Hydrogenation

Zeno B G Fickenscher  1 , Peter Lönnecke  1 , Anna K Müller  2 , Oldamur Hollóczki  3 , Barbara Kirchner  2 , Evamarie Hey-Hawkins  1
Affiliations

Synergistic Catalysis in Heterobimetallic Complexes for Homogeneous Carbon Dioxide Hydrogenation

Zeno B G Fickenscher et al. Molecules. .

Abstract

Two heterobimetallic Mo,M' complexes (M' = IrIII, RhIII) 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 IrIII 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.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 3
Scheme 3
Calculated reaction enthalpies for hydride transfer from [MIIIH] to CO2.
Figure 1
Figure 1
Active site of Ni-CODH [6].
Scheme 1
Scheme 1
Synthesis of heterobimetallic complexes C1 and C2 (Cp* = C5Me5).
Figure 2
Figure 2
Cyclic voltammogram of M3 (1 mM), C1 (1 mM) and, C2 (3 mM) in MeCN at room temperature, with 0.10 M [N(nBu)4]PF6 as supporting electrolyte, a glassy carbon electrode (surface area 0.001 cm2), a Ag/AgNO3 (0.01 mol∙l−1) reference electrode, a Pt wire (99.9%) counter electrode, and a voltage sweep rate ν = 100 mV∙s−1.
Figure 3
Figure 3
Molecular structure of a derivative of complex C1 in which the coordinated MeCN has been replaced by N2 during crystallization. The non-coordinating PF6− counterion, all non-coordinating solvent molecules and hydrogen atoms have been omitted for clarity. All non-coordinating carbon atoms and Cp* are drawn as wireframe.
Figure 4
Figure 4
Proposed catalytic scheme for CO2 hydrogenation using a monometallic iridium catalyst (Cp* = C5Me5).
Scheme 2
Scheme 2
Equilibrium between hydrido complex [IrIIIH] and cationic [IrIII(NCCD3)]+ used to determine the thermodynamic hydricity [42].
Figure 5
Figure 5
Hydrido complexes [IrIIIH] and [RhIIIH] (Cp* = C5Me5) with their respective thermodynamic hydricity [42].
Figure 6
Figure 6
Reaction enthalpy profile for the catalyst M1 in MeCN using DBU as a base.
See this image and copyright information in PMC

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