Stronger Together! Mechanistic Investigation into Synergistic Effects during Homogeneous Carbon Dioxide Hydrogenation Using a Heterobimetallic Catalyst

Abstract

A series of group 6 heterobimetallic complexes [M0;IrIII] (M = Cr, Mo, W) were synthesized and fully characterized, and the catalytic behavior was studied. The heterobimetallic complex [Mo0;IrIII] (C1) was by far the most active and has shown a considerable synergistic effect, with both metals actively participating in homogeneous carbon dioxide hydrogenation, leading to formate salts. Based on theoretical calculations, the synergistic interaction is due to Pauli repulsion, lowering the transition state and thus enabling higher catalytic activity. The mechanism of both the hydrogenation itself and the synergistic interaction was studied by NMR spectroscopy, kinetic measurements, and theoretical calculations. The homogeneous nature of the reaction was proven using in situ high-pressure (HP) NMR experiments. The same experiments also showed that the octahedral Mo(CO)3P3 moiety of the complex is stable under the reaction conditions. The hydride complex is the resting state because the hydride transfer is the rate-determining step. This is supported by kinetic measurements, in situ HP NMR experiments, and theoretical calculations and is in contrast to the monometallic IrIII counterpart of C1.

Molybdenum-catalyzed hydrogenation of carbon dioxide, bicarbonate, and inorganic carbonates to formates

“…27 Lately, Hawkins and co-workers reported the heterobimetallic Mo/Ir-catalyzed hydrogenation of CO 2 to formate with a TON of 128. 28 In 2020, computational studies by Liu and Ke 29 on group VI NHC-supported complexes revealed that these low electronegativity and low oxidation state complexes could be effective catalysts for CO 2 hydrogenation. Prompted by this study, we delve into the CO 2 hydrogenation using Mo catalysts bearing bidentate phosphine ligands with varied bite angles.…”

Heterobimetallic Complexes of Bi- or Polydentate N-Heterocyclic Carbene Ligands and Their Catalytic Properties

“…Although several examples of synergism in catalysis by such mixed-metal clusters were discovered, the widespread application of such catalysts was hampered by their instability, resulting in the formation of several catalytically active fragments [5]. The application of catalysts in which the two different metal ions were bridged by heterodifunctional ligands proved more successful [6][7][8][9], especially with early/late heterobimetallic complexes [10]. It was recognized from the beginning of such studies that in bimetallic dinuclear complexes, the two metal ions may not only cooperate in the catalysis of a given reaction but also act independently, allowing consecutive catalytic transformations.…”