Organio-inorgaic Hybrid Materials With Transition Metal Complesxes:Synthesis And Catalytic Properties In Alkene Epoxidation

Synthesis and Catalytic Properties in Alkene EpoxidationEpoxides are a class of highly versatile intermediates in organic synthesis, which can be converted to other valuable compounds by selective ring opening or functional groups transformation, it is very important in medicine, pesticides, fragrances and other fine chemicals synthesis. The current industry methods for the synthesis of epoxides are Ag/Al2O3/O2 (Ethylene oxide). Halcon (Propylene oxide) and halogenohydrin (Propylene oxide). However, Ag/Al2O3/O2 (EO) systems showed lower efficiency for other alkenes. For the halogenohydrin process, the production of large amounts of chlorine-containing waste water leads to severely environmental pollution. In Halcon process, many side-products are produced, which suffers from the costly material consumption and equipment cauterization. Therefore, the development of high efficiency and low pollution epoxidation process is very meaningful work.Some biomimetic catalysts (such as chiral metalloporphyrin, chiral Schiff base metal complexes, metal peptide eye, phenanthroline metal complexes, bipyridyl metal complexes and other multi-nitrogen, nitrogen-oxygen organic metal complexes and so on) were found as efficient homogeneous catalysts for the epoxidation of alkenes. However, it is difficult to recover and reuse those homogeneous metal complexes, and the catalytic activity of these homogeneous catalysts decreases due to the formation of inactive dimericμ-oxo species, which has restricted their wide applications in industrial and laboratory synthesis. One way to overcome this problem is to immobilize them on solid supports to synhesis organic-inorganic hybrid materials. In comparison with the homogeneous counterparts, heterogeneous systems show many advantages such as easy separation and recovery of the catalyst from reaction media, higher stability of catalytic species and catalyst protection against destruction. For olefin epoxidation. many good performance of the organic-inorganic hybrid materials have been reported. In this area, it is still an interesting and significant subject to develop more excellent performance and environmentally friendly organic-inorganic hybrid heterogeneous epoxidation catalyst systems.Based on the above, in this thesis, we try to prepare and characterization novel transition metal complexes functionalized organic-inorganic hybrid materials, and study their catalytic properties in alkene epoxidation. By selecting appropriate metal ions and organic ligands, combined with the use of certain inorganic supports, we synthesis a variety of new highly efficient hetergeneous epoxidation catalysts. In the epoxidation reaction text, the influence of different reaction parameters-such as the alkenes. oxidants and solvents-on the catalytic performance of the hybrid materials has been studied and discussed, and combined with a variety of characterization of the catalyst structure and surface properties to study the nature of catalyst active center and catalytic mechanism. The main contents and results are summarized as follows:1. Mesoporous SBA-15 Modified with Manganese Pyrazolylpyridine Complexes: preparation and catalytic propertiesA manganese-based hybrid mesoporous material was synthesized by covalent grafting of [MnⅡ(1)2](OAc)2 (1=[3-(2-pyridyl) pyrazol-1-yl]aceticacid amide) onto the surface of SBA-15. Catalytic tests showed that the hybrid material could act as an efficient heterogeneous catalyst for the epoxidation of a wide range of alkenes (including terminal ones) under mild reaction conditions when peracids (e.g.. meta-chloroperbenzoic acid) are used as oxidants. Moreover, the catalytic performance of the hybrid materal is oxidant-dependent, these contrasting mechanistic behaviors can be rationalized on the basis of the physical parameters of the substitutes on O-O bond in these two oxidants (t-BuOOH and m-CPBA). The chlorophenyl group of m-CPBA has a stronger ability to withdraw electron density from the peroxo unit alkyl group in t-BuOOH. This feature may result in an easy homolytic cleavage of the O-O bond (radical pathway) after the formation of a t-BuOO-MnⅡfragment, while a heterolytic cleavage of the O-O bond is dominant in the m-CPBA case. It exhibits higher catalytic activity and selectivity towards epoxides in the presence of an aprotic solvent (e.g.. CH3CN). UV-vis measurements revealed that high-valent O=MnⅣ-species are easily formed during the reaction course, when meta-chloroperbenzoic acid is used as oxidant and CH3CN is used as solvent, being probably the reason for the high activity of the hybrid material and its selectivity towards epoxide formation.2. Mesoporous materials modified with oxodiperoxo tungsten complexes: preparation and catalytic propertiesA hybrid mesoporous SBA-15 material containing an oxodiperoxo tungsten complex of the type [WO(O2)21] (1=[3-(2-pyridyl) pyrazol-1-yl] aceticacid amide) was synthesized by a post-grafting route (WO5(I)-SBA-15). The catalytic property of the heterogeneous oxodiperoxo tungsten complex catalyst in the epoxidation of cyclooctene with H2O2 as the oxidant was investigated in comparison with other three kinds of hybrid tungsten containing SBA-15 materials bearing ethylenediamine (2), imidazole (3) or 4,4'-bipyridine (4) ligands. It was found that all oxodiperoxo tungsten catalysts were active at the reaction temperature of 55℃with CH3CN as solvent. However, only the catalyst with the pyrazolylpyridine ligand showed good recoverability and relatively high stability against leaching of active tungsten species. Moreover, this catalyst showed very high efficiency for H2O2 utilization (>99.5%). The high stability of WO5(1)-SBA-15 can be attributed to two factors:First, there is strong covalent grafting between the organic ligand system and the inorganic mesoporous material; second, the nitrogen-containing bidentate ligand has strong coordination ability, can form strong binding between the WO(O2)2 unit and the chelating ligand. In addition, by comparing with different types of inorganic supports it was found that the presence of large the pores on the support are favoring the increase of catalytic activity, and the existence of appropriate Lewis acid in supports can also increase the catalytic activity.3. Carbon-supported oxodiperoxo tungsten Pyrazolylpyridine Complexes: preparation and catalytic propertiesCarbon materials SC and NC-2 supported oxodiperoxo tungsten complex of the type [WO(O2)21] (1=[3-(2-pyridyl) pyrazol-1-yl] aceticacid amide) was synthesized by a post-grafting route (WO5(1)-SC and WO5(1)-NC-2). The catalytic property of the two catalysts in the epoxidation of allylic alcohols with H2O2 as the oxidant was investigated. The catalytic performance of the catalysts are solvent-dependent. When using common organic solvents (such as acetonitrile) as reaction medium, the two catalysts showed very low reactivity, when water was used as the reaction medium, the activity of the catalysts can be significantly improved. Combined with some characterization results, the oxygen groups presence on the surface of the carbon supports making the catalysts show high catalytic activity in the water system. In contrast. WO5(1)-NC-2 catalytic activity is higher than WO5(1)-SC. on the one hand, it may be due to the differences of surface properties (polar) of the two carbon supports; On the other hand. NC-2 has higher surface (>800m2/g) and active species can be uniform, highly dispersed on the support surface. These catalysts can efficiently catalyze allylic alcohols with high yields under mild solvent-free conditions without any additives. Of significant practical importance. WO5(1)-NC-2 shows excellent activity (TOF up to 10125 h-1 per W site). Furthermore. WO5(1)-SC and WO5(1)-NC-2 can be easily separated by simple filtration and reused for at least six times with no apparent loss of activity.4. Chiral MnⅢ(salen) complex Modified mesoporous aluminum phosphate: preparation and catalytic properties of asymmetric epoxidation of alkenes.Through the method of grafting, the aminopropyl axial chiral MnⅢ(salen) complexes was immobilized on the mesoporous aluminum phosphate, hetergeneous chiral MnⅢ(salen) catalyst with different pore structure (Salen-Mn-AP-AlP0.9O, Salen-Mn-AP-AlP1.0O and Salen-Mn-AP-AlP1.1O) can be obtained through the modulation of P/Al ratio. Catalytic tests showed that the hybrid materials could act as efficient heterogeneous catalysts for the asymmetric epoxidation olefins (such as: styrene andα-methyl styrene. trans-1.2-styrene) with NaClO/PPNO (or m-CPBA/NMO). Moreover, the catalyst with large pore size favoring the improved selectivity of the chiral catalyst (ee%). Salen-Mn-AP-AlP1.1O catalyst can give similar ee value with the homogeneous catalysts for asymmetric epoxidation of styrene (orα-methyl styrene).