Alkane Oxidation by an Immobilized Nickel Complex Catalyst: Structural and Reactivity Differences Induced by Surface-Ligand Density on Mesoporous Silica

• Published in: Chemistry, an Asian journal an Asian journal, 2013-06, Vol.8 (6), p.1191-1199
• Main Authors: Nakazawa, Jun, Hori, Tomoaki, Stack, T. Daniel P., Hikichi, Shiro
• Format: Article
• Language: English
• Subjects: Catalytic oxidation; Chemistry; heterogeneous catalysis; immobilization; Ligands; mesoporous materials; Nickel; oxidation
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201300165

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 [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 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. Going nowhere fast: An immobilized SBA*‐L‐x/Ni complex was prepared with various ligand loadings and used in the oxidation of cyclohexane. The importance of site‐density control for the development of immobilized catalysts has been demonstrated.