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  • Title: Iridium Complexes with Proton-Responsive Azole-Type Ligands as Effective Catalysts for CO2 Hydrogenation.
    Author: Suna Y, Himeda Y, Fujita E, Muckerman JT, Ertem MZ.
    Journal: ChemSusChem; 2017 Nov 23; 10(22):4535-4543. PubMed ID: 28985455.
    Abstract:
    Pentamethylcyclopentadienyl iridium (Cp*Ir) complexes with bidentate ligands consisting of a pyridine ring and an electron-rich diazole ring were prepared. Their catalytic activity toward CO2 hydrogenation in 2.0 m KHCO3 aqueous solutions (pH 8.5) at 50 °C, under 1.0 MPa CO2 /H2 (1:1) have been reported as an alternative to photo- and electrochemical CO2 reduction. Bidentate ligands incorporating an electron-rich diazole ring improved the catalytic performance of the Ir complexes compared to the bipyridine ligand. Complexes 2, 4, and 6, possessing both a hydroxy group and an uncoordinated NH group, which are proton-responsive and capable of generating pendent bases in basic media, recorded high initial turnover frequency values of 1300, 1550, and 2000 h-1 , respectively. Spectroscopic and computational investigations revealed that the reversible deprotonation changes the electronic properties of the complexes and causes interactions between pendent base and substrate and/or solvent water molecules, resulting in high catalytic performance in basic media.
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