Strong Solvent Effects on Catalytic Transfer Hydrogenation of Ketones with [Ir(cod)(NHC)(PR3)] Catalysts in 2-Propanol-Water Mixtures

Abstract

The synthesis and characterization of the new Ir(I)-complexes [IrCl(cod)(Bnmim)], [Ir(cod)(emim)(PPh3)]Cl and [Ir(cod)(Bnmim)(mtppms)] are reported. The zwitterionic complexes [Ir(cod)(NHC)(mtppms)] and Na2[Ir(cod)(NHC)(mtppts)] (NHC = emim, bmim or Bnmim; mtppms-Na and mtppts-Na3 = sodium salts of mono- and trisulfonated triphenylphosphine, respectively) were found to be effective precatalysts for transfer hydrogenation of aromatic and aliphatic ketones in basic 2-propanol-water mixtures with initial turnover frequencies up to 510 h−1 at 80 °C, and their catalytic performances were compared to those of [IrCl(cod)(NHC)] complexes (NHC = emim, bmim, Bnmim, IMes) and [Ir(cod)(emim)(PPh3)]Cl. Three of the catalysts were characterized by single-crystal X-ray diffraction. The reaction rates of the transfer hydrogenation of acetophenone and benzophenone showed strong dependence on the water concentration of the solvent, indicating preferential solvation of the catalytically active metal complexes.

Selective Hydration of Nitriles to Corresponding Amides in Air with Rh(I)-N-Heterocyclic Complex Catalysts

“…It was found that complexes 1-4 efficiently catalyzed the hydration of benzonitrile to benzamide in a water/2-propanol = 1/1 mixture in air and under mild conditions (≤80 • C). The choice of 2-propanol as the organic component of the solvent was based on its unique favourable effects on certain reactions, e.g., hydrogenation and transfer hydrogenation of ketones [58]. The reactions did not display an induction period ( Figure S1) and they proved completely selective; no products other than benzamide were detected by GC-MS or 1 H NMR spectroscopy.…”

Reaction and separation system for CO2 hydrogenation to formic acid catalyzed by iridium immobilized on solid phosphines under base-free condition

“…And the spectra were consistent with those of similar structure reported in the literature. 71 XPS analysis was also carried out to detect the oxidation state of Ir (see Figure S2 ).…”

Immobilization of an Iridium(I)-NHC-Phosphine Catalyst for Hydrogenation Reactions under Batch and Flow Conditions

“…Previously, we have observed that water had a very peculiar effect on the rate of transfer hydrogenation reactions catalyzed by Na 2 [Ir(cod)(emim)(mtppts)] [49]. Namely, the rate of hydrogen transfer reduction of acetophenone in aqueous 2-propanol mixtures showed a significant increase with increasing water concentrations (sometimes upon passing through a minimum at around x = 0.7 concentration of 2-propanol; x = mole fraction).…”