title: Alkane oxidation by an immobilized nickel complex catalyst: structural and reactivity differences induced by surface-ligand density on mesoporous silica.
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 L(tBu) and its Ni(II) complexes, [Ni(L(tBu))(OAc)2(H2O)] (L(tBu)/Ni) and [Ni(L(tBu))2]BF4 (2 L(tBu)/Ni), have been synthesized. The L/Ni ratio (0.9-1.7:1) in SBA*-L-x/Ni suggests the formation of an inert [NiL2] 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 L(tBu)/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.
authors.affiliation: Department of Material and Life Chemistry, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan. jnaka@kanagawa-u.ac.jp
authors.forename: Jun
authors.initials: J
authors.lastname: Nakazawa
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Hori
authors.forename: T Daniel P
authors.initials: TD
authors.lastname: Stack
authors.forename: Shiro
authors.initials: S
authors.lastname: Hikichi