Design And Preparation Of Inorganic-Organic Hybrid Materials With N-heterocyclic Carbenes And Catalytic Applications

Since much is known about traditional heterogeneous catalysts can provide numerous opportunities for recovering and recycling catalysts from reaction environments. And soluble organic catalysts have a much larger variety of reaction types than traditional solid catalysts but suffer from their inability to be recycled. Recently in the light of organic moiety as the active site and the inorganic supports to provide recovery and recyclability of the organic, organic-inorganic hybrid materials containing metal complexes obtain more attention on catalytic applications.Design and preparation of organic-onorganic hybrid catalysts is an area of extensive research.Especially porous materials with large specific surface areas and uniform pore sizes such as MCM-41, MCM-48, MSU, HMS, FSM-16, and various SBA type materials have superior thermal stability and the preparation of highly dispersed inorganic catalyst from porous materials is now a mature technology. Moreover the these inorganic materials have been widely used as support for the preparation of the hybrid materials . The other support materials such as polymer supports , carbons, biocompatible inorganic materials also are potentially useful for creating a high-performance organic-inorganic hybrid materials catalyst. The immobilization of organic active sites onto the solid supports of the different structure and surface properties to improve catalytic performance can be accomplished. N-Heterocyclic carbenes have show excellent catalytic application in C-C, C-H, C-O, and C-N bond formation and due to the strong abilities both stabilizing and activating metal center . In addition to the similar properties, The NHCs can inform more stable complexs with little tendency of dissociation than organophosphines ligands . A range of homogeneous NHC complexes are widely applied in a variety of organic syntheses reactions such as Suzuki and Heck Coupling reactions, olefin metathesis reactions, etc. But the search for an effective and recyclable NHC complexes catalyst is still a major challenge. Recent there were some reports concerning on the NHC–Pd complex immobilized onto the surface of solid supports and obtain excellent catalytic performances in a lot of reactions such as Suzuki and Heck reactions, etc. It has been known that an imidazolium ionic liquid could act as a ligand or ligand precursor of NHC metal complex .First ,we synthesized organic-inorganic hybrid mesoporous materials (imidazole ionic liquids as a ligand) ,then Pd(OAc)2 was mixed with hybrid materials that has been modified by imidazole ionic liquids to form a immobilized Pd carbene complex. Hereafter using the treatment of H2 reduction to obtain hybrid materials with Pd nanoparticles and organic ligand structure and long-range mesopore ordering of the SBA-15 were not destroyed. The hybrid material was investigated for the alcohol aerobic oxidation and it was found that this material was an active catalyst and showed relatively high stability through the recycling of the catalyst. And congregating and leaching of Pd species did not turn up during the reaction.In addition, by combining different characterization means, the nature of active sites of the catalysts was also discussed. As shown by TEM images, on the surface of mesoporous SBA-15,average size of Pd nanoparticles was 3.5 nm and the size was still kept identical after reused several times, It could be expected that active and stable Pd site might be relative to NHC ligands and the size-restricted mesopores of SBA-15.Beside we synthesized hybrid Mo catalyst by post-grafting. After calcining in different atmosphere,the catalytic performance was investigated in liquid-phase epoxidation of cyclooctene. The immobilized N-heterocyclic carbene-Pd complex was also readily prepared by reaction of HAP-γ-Fe2O3 (hydroxyapatite encapsulated magnetic-γ-Fe2O3 nanocrystallites)-supported imidazolium halide with Pd(OAc)2. It was found that the NHC Pd complex exhibited excellent catalytic activity in the coupling reaction of aryl halides with arylboronic acid. The heterogeneous Pd catalyst was reusable from the reaction mixture by simple magnetic decantation as well as air-stable to allow easy use. The results confirm further that N-heterocyclic carbene is a kind of efficient ligand for stabilizing Pd species.