Salen配体

Zeolite-encapsulated Ru(III)tetrahydro-Schiffbase complex:An efficient heterogeneous catalyst for the hydrogenation of

benzene under mild conditions

Ping Chen,Binbin Fan,Minggang Song,Chun Jin,Jinghong Ma,Ruifeng Li

*

Key Laboratory of Coal Science and Technology,MOE,Institute of Special Chemicals,Taiyuan University of Technology,

79West Yinze Street,Taiyuan 030024,PR China

Received 7January 2006;received in revised form 7April 2006;accepted 7April 2006

Available online 18April 2006

Abstract

A series of Ru(III)tetrahydro-Schiffbase complexes (denoted as Ru[H 4]-Schiffbase with Schiffbase =salen,salpn and salcn,see Scheme 1)were encapsulated in the supercages of zeolite Y by flexible ligand method.The prepared catalysts were characterized by X-ray diffraction,diffuse reflectance UV–Vis spectroscopy,Infrared spectroscopy,elemental analysis,as well as N 2adsorption tech-niques.It was shown that upon encapsulation in zeolite Y,Ru(III)tetrahydro-Schiffbase complexes exhibited higher activity for the hydrogenation of benzene than the corresponding Ru(III)-Schiffbase complexes.This indicates that hydrogenation of the C @N bond of the Schiffbase ligands led to a modification of the coordination environment of the central Ru(III)cations.The stability of the prepared catalysts has also been confirmed against leaching of the complex molecule from the zeolite cavities,as revealed by the result that no loss of catalytic activity was observed within three successive runs with regeneration.Ó2006Elsevier B.V.All rights reserved.

Keywords:Benzene hydrogenation;Ru(III)tetrahydro-Schiffbase complex;Encapsulation;Zeolite Y

1.Introduction

Transition metal complexes have been extensively used for homogeneous hydrogenation of organic substrates such as benzene due to their high selectivity under mild reaction conditions [1,2].However,the difficult recovery and recy-cling of the catalysts limit their reuse.Therefore,increasing demands have been generated for the preparation of effec-tive heterogeneous catalysts.In this context,immobiliza-tion of metal complex is an attractive strategy.Up to date,several methods,such as covalent bonding of ligands with host materials,entrapment or occlusion of complex molecule in polymer matrices or porous inorganic materi-als by steric hindrance,and adsorption of the complexes on the support via ionic interaction,have been examined

for the immobilization of transition metal complexes [3].Among them,the physical encapsulation of transition metal complex molecules into the supercages of zeolites gains incomparable advantages for homogeneous and con-ventional heterogeneous catalysts [4–7].Upon encapsula-tion in the cavities of the zeolites with FAU and EMT topological structures,palladium and rhodium salen com-plexes are highly active for the selective hydrogenation of 1,5-cyclooctadiene to cyclooctene [8],particularly chiral palladium salen complex makes it possible of enantioselec-tive hydrogenation of unsaturated organic compounds such as 3-methyl-2-cyclohexenone [9].In addition,palla-dium and nickel salen complexes grafted on mesostruc-tured silicates and delaminated ITQ zeolites also show good catalytic performance in the hydrogenation of imines [10],while Ru(III)-Schiffbase complex anchored on poly-mer exhibits considerably improved catalytic efficiency for the hydrogenation of styrene [11].The catalytic activity

1566-7367/$-see front matter Ó2006Elsevier B.V.All rights reserved.doi:10.1016/j.catcom.2006.04.003

*

Corresponding author.Tel./fax:+863516010112.E-mail address:rfli@ (R.Li).

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Catalysis Communications 7(2006)

969–973