Quinoline-functionalized N-heterocyclic carbene complexes of iridium: Synthesis, structures and catalytic activities in transfer hydrogenation |
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Authors: | Jia-Feng Sun Brenda A. Dougan Yong Cheng Xue-Tai Chen Zi-Ling Xue |
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Affiliation: | a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China b Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA |
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Abstract: | Iridium complexes containing quinoline-functionalized N-heterocyclic carbene (NHC) ligands have been synthesized by the transmetalation route from silver carbene precursors. The silver complexes undergo a facile reaction with [Ir(COD)Cl]2 (COD = 1,5-cyclooctadiene) to yield a series of carbene complexes [(NHC)Ir(COD)Cl] (NHC = 3-methyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2a); 3-n-butyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2b); 3-benzyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2c); 1,3-di(8-quinolylmethyl)imidazole-2-ylidene (2d). The coordinated COD was replaced by carbon monoxide to yield the corresponding carbonyl species [(NHC)Ir(CO)2Cl] (3). Complexes 2 and 3 have been characterized by IR, ESI-MS, 1H and 13C NMR and elemental analyses. The molecular structures of complexes 2b and 2c have been confirmed by single-crystal X-ray diffraction. Two analogous Ir(I) complexes 5 and 6 with naphthalene-containing NHC have also been synthesized and characterized. These Ir(I) complexes in the current work have been proved to be active catalysts in the transfer hydrogenation of ketones to alcohols using 2-propanol as the hydrogen source. |
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Keywords: | N-heterocyclic carbene Iridium Transfer hydrogenation Catalysis |
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