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.
Highlights
Hydrogenation of ketones is an important synthetic transformation leading to alcohols which themselves are valuable products or intermediates for the synthesis of pharmaceuticals, flavours and fragrances, crop protection agents, etc
[Ir(cod)(emim)(mtppms)] catalysed with outstanding activity the well as the dehydrogenation of formate resulting in a reversible H2 storage/delivery process based on hydrogenation of bicarbonate, as well as the dehydrogenation of formate resulting in a reversible H2 aqueous solution of NaHCO3 /NaHCO2 [32,33]
Catalysts Used for Transfer Hydrogenation of Ketones from Basic 2-Propanol and Solid-State Structural
Summary
Hydrogenation of ketones is an important synthetic transformation leading to alcohols which themselves are valuable products or intermediates for the synthesis of pharmaceuticals, flavours and fragrances, crop protection agents, etc. The most abundant homogeneous catalysts of transfer hydrogenations contain tertiary phosphine ligands, complexes with N-heterocyclic carbene (NHC) ligands are studied in increasing numbers by several research groups [36,37,38,39,40,41]. Ir(III)-bis-NHC complexes complexes were were synthesized and applied as catalysts for transfer hydrogenation of ketones [18,19]. )}]BF4 4(bis(NHC (bis(NHCMeMe methylene-bis(N-methyl)imidazole-2-ylidene) was used as catalyst in transfer hydrogenation of acetophenone and afforded 98% conversion in 5 h.
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