Alkane Oxidation by an Immobilized Nickel Complex Catalyst: Structural and Reactivity Differences Induced by Surface‐Ligand Density on Mesoporous Silica |
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| Authors: | Dr Jun Nakazawa Tomoaki Hori Prof?Dr T Daniel P Stack Prof?Dr Shiro Hikichi |
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| Institution: | 1. Department of Material and Life Chemistry, Kanagawa University, Yokohama, Kanagawa 221‐8686 (Japan), Fax: (+81)?45‐413‐9770;2. Department of Chemistry, Stanford University, Stanford, CA, 94305‐5080 (USA) |
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| Abstract: | Immobilized nickel catalysts SBA*‐ L ‐x/Ni ( L =bis(2‐pyridylmethyl)(1H‐1,2,3‐triazol‐4‐ylmethyl)amine) with various ligand densities ( L content (x)=0.5, 1, 2, 4 mol % Si) have been prepared from azidopropyl‐functionalized mesoporous silicas SBA‐N3‐x. Related homogeneous ligand LtBu and its NiII complexes, Ni( LtBu )(OAc)2(H2O)] ( LtBu /Ni) and Ni( LtBu )2]BF4 (2 LtBu /Ni), have been synthesized. The L /Ni ratio (0.9–1.7:1) in SBA*‐ L ‐x/Ni suggests the formation of an inert Ni L 2] site on the surface at higher ligand loadings. SBA*‐ L ‐x/Ni has been applied to the catalytic oxidation of cyclohexane with m‐chloroperbenzoic acid (mCPBA). The catalyst with the lowest loading shows high activity in its initial use as the homogeneous LtBu /Ni catalyst, with some metal leaching. As the ligand loading increases, the activity and Ni leaching are suppressed. The importance of site‐density control for the development of immobilized catalysts has been demonstrated. |
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| Keywords: | heterogeneous catalysis immobilization mesoporous materials nickel oxidation |
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