Cooperative Effects of Heterodinuclear Ir^III–M^II Complexes on Catalytic H₂ Evolution from Formic Acid Dehydrogenation in Water

Abstract

Novel heterodinuclear IrIII–MII complexes (M = Co, Ni, or Cu) with two adjacent reaction sites were synthesized by using 3,5-bis­(2-pyridyl)-pyrazole (Hbpp) as a structure-directing ligand and employed as catalysts for H2 evolution through formic acid dehydrogenation in water. A cooperative effect of the hetero-metal centers was observed in the H2 evolution in comparison with the corresponding mononuclear IrIII and MII complexes as the components of the IrIII–MII complexes. The H2 evolution rate for the IrIII–MII complexes was at most 350-fold higher than that of the mononuclear IrIII complex. The catalytic activity increased in the following order: IrIII–CuII complex < IrIII–CoII complex < IrIII–NiII complex . The IrIII–H intermediates of the IrIII–MII complexes were successfully detected by ultraviolet–visible, 1H nuclear magnetic resonance, and ESI-TOF-MS spectra. The catalytic enhancement of H2 evolution by the IrIII–MII complexes indicates that the IrIII–H species formed in the IrIII moiety act as reactive species and the MII moieties act as acceleration sites by the electronic effect from the MII center to the IrIII center through the bridging bpp– ligand. The IrIII–MII complexes may also activate H2O at the 3d MII centers as a proton source to facilitate H2 evolution. In addition, the affinity of formate for the IrIII–MII complexes was investigated on the basis of Michaelis–Menten plots; the IrIII–CoII and IrIII–NiII complexes exhibited affinities that were relatively higher than that of the IrIII–CuII complex. The catalytic mechanism of H2 evolution by the IrIII–MII complexes was revealed on the basis of spectroscopic detection of reaction intermediates, kinetic analysis, and isotope labeling experiments.

Multiwavelets applied to metal–ligand interactions: Energies free from basis set errors

“…We have build our test set to include ligands of various size, many of which are common incoming ligands in metal-catalyzed reactions (such as H2, CO, alkenes, methanol). 3,4,5,6,7,8,9,10 Several features are observed from our computed results (Figure 2, see also SI, Figure S1 to S4). Firstly, the magnitude of the BSSE is largest for DZ basis sets, with an average value of 9.92 kcal/mol for the 26 kcal/mol).…”

“…1,2 Many of the studied reactions involve metal complexes that throughout the course of the reaction bind or lose a ligand, for example, there may be incoming substrates such as alkenes or hydrogen (H2), or leaving ligands such as solvent or product molecules (Scheme 1). 3,4,5,6,7,8,9,10 The difficulty of contemporary DFT functionals to accurately compute metal-ligand interactions has been highlighted in the literature. 11,12,13,14,15,16,17,18,19,20,21,22 Many of the reported studies focus on the performance of different DFT functionals and the importance of including dispersion corrections in the computed energies.…”

Formate-driven catalysis and mechanism of an iridium–copper complex for selective aerobic oxidation of aromatic olefins in water

“…1a , were synthesized and characterized according to literature procedures. 37 The aerobic oxidation reactions afforded by 1–4 were conducted using p -styrenesulfonate (StyreneS) as a water-soluble model substrate ( Fig. 1b ).…”

“…Mechanistic insights into selective aerobic oxidations performed by M–H species in water have yet to be gained. Herein, we report that an Ir III –Cu II hetero-dinuclear complex 37 successfully catalyses Wacker-type oxidation of aromatic olefins driven by formate to produce corresponding methyl ketones in water. We found that a hydrophobic interaction between an Ir–H intermediate and the substrate aromatic ring in water promoted the selective aerobic oxidation of aromatic olefins.…”

Multiwavelets Applied to Metal-Ligand Interactions: Energies Free from Basis Set Errors

“…1,2 Many of the studied reactions involve metal complexes that throughout the course of the reaction bind or lose a ligand, for example, there may be incoming substrates such as alkenes or hydrogen (H2), or leaving ligands such as solvent or product molecules (Scheme 1). 3,4,5,6,7,8,9,10 The difficulty of contemporary DFT functionals to accurately compute metal-ligand interactions has been highlighted in the literature. 11,12,13,14,15,16,17,18,19,20,21,22 Many of the reported studies focus on the performance of different DFT functionals and the importance of including dispersion corrections in the computed energies.…”