Mesoporous Silica Supported Unsymmetric Chiral Mn(III) Salen Complex: Synthesis,Characterization and Effect of Pore Size on Catalytic Performance

An unsymmetric chiral Mn(III) salen complex was immobilized onto a series of MCM-41 and MCM-48 mesoporous materials with different pore sizes. The as-synthesized catalysts were characterized by XRD, FT-IR, DR UV-Vis, N₂ sorption and XPS. The results indicated that chiral Mn(III) salen complex was immobilized into the nanopores of supports and the long-range mesoporous ordering of parent supports was maintained after the immobilization. The heterogeneous catalysts were evaluated in the asymmetric epoxidation of styrene, indene, and 1-phenylcyclohexene, and the effect of 3-mercaptopropyltrimethoxysilane dosage and fine-tuning of pore size on the catalytic performance was studied. It was found that the activity and enantioselectivity were closely correlated with the pore sizes of heterogeneous catalysts. The larger pore sizes of supports could lead to higher conversions and ee values.     

Immobilization of new Mn(salen) complex over MCM-41 and its activity in asymmetric epoxidation of styrene

New tetradentate chelates of bis-Schiff bases were synthesized and then these chiral salen ligands were immobilized over mesoporous MCM-41 by using the ion-exchange method. The efficiency of the chiral catalyst was examined in the asymmetric epoxidation of styrene. Chiral Mn(salen) complexes immobilized onto mesoporous MCM-41 were stable during the reaction without any leaching and exhibited relatively high enantioselectivity for epoxidation as compared with homogeneous complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of a siliceous MCM-41 using C22TMACL template and preparation of heterogenized new chiral salen complexes

Purely siliceous MCM-41 has been prepared under both mild and acidic conditions by a solvent evaporation method using C₁₆TMABr and C₂₂TMACl surfactant as templates. A hydrothermal synthesis was also carried out by utilizing a method of adjusting the gel pH to 10. The mesoporous samples synthesized in ethanol solvent by using this evaporation method showed a fully disordered pore system, but those obtained in the hydrothermal synthesis had highly ordered pores. The chiral salen Mn(III) complexes were immobilized on the siliceous MCM-41 by a new grafting method using 3-aminopropyltrimethylsilane and diformylphenols. These ligands on MCM-41 were stable during the reactions. High enantioselectivities were displayed in the epoxidation of styrene by using these heterogenized salen complexes.     

Asymmetric epoxidation of unfunctionalized olefins catalyzed by Mn(III) salen complex immobilized on MCM-48

Chiral Mn(III) salen complexes were supported on mesoporous molecular sieve MCM-48 and employed as catalyst in the asymmetric epoxidation of some unfunctionalized olefins. The as-synthesized catalysts showed excellent enantioselectivity than homogeneous catalysts for α-methylstyrene and the highest ee value (up to >99%) was obtained. Furthermore, these catalysts were also effective for bulkier olefins such as indene and 1-phenylcyclohexene. Compared to homogeneous counterparts, the heterogeneous catalysts are more stable and can be recycled three times without loss of enantioselectivity.     

The catalytic activity of new chiral salen complexes immobilized on MCM-41 in the asymmetric hydrolysis of epoxides to diols

The synthesis of MCM-41 type mesoporous material has been performed by the solvent evaporation method. The chiral salen Co(III)(OAc) complexes are immobilized on a siliceous MCM-41 through the multi-step anchoring and applied as catalysts in the hydrolytic kinetic resolution of racemic epoxides to diols. The incorporation of salen complexes onto the mesoporous material is demonstrated by UV–Vis spectroscopy, and tested with the catalytic hydrolysis reaction. The chiral salen Co(III) complexes catalyze the hydrolysis of epichlorohydine, 1,2-epoxyhexane, epoxystyrene and epoxycyclohexane under very mild conditions. This reaction can proceed in acetonitrile and THF solvents.     

Asymmetric Epoxidation of Styrene on the Heterogenized Chiral Salen Complexes Prepared from Organo-Functionalized Mesoporous Materials

Organosilane-modified mesoporous materials have been prepared under mild and acidic conditions by a solvent evaporation method using C₁₆TMABr surfactant as a template. The mesoporous samples synthesized in ethanol solvent by using this evaporation method showed a fully disordered pore system, but those obtained under hydrothermal conditions had highly ordered pores. The chiral salen Mn(III) complexes were immobilized on these organosilane-functionalized mesoporous silicas by a grafting method. The catalysts used in the asymmetric epoxidation of styrene and cis-stilbene and the effect of different mesoporous structures on the reactivity was investigated. Similar enantioselectivities were observed by using these heterogenized salen complexes as compared with reaction under homogeneous conditions.     

Synthesis of layered crystalline AlSPP and its immobilized chiral salen Mn(III) catalysts applicated in the large scale asymmetric epoxidation of olefins

Chiral salen Mn(III) complex was axially immobilized onto phenoxy-modified organic polymer-inorganic hybrid material layered crystalline aluminium oligo-styrenyl phosphonate-hydrogen phosphate. The prepared catalysts exhibited excellent activities and enantioselectivities for asymmetric epoxidation of unfunctionalized olefins with m-chloroperbenzoic acid as oxidant, especially for the epoxidation of α-methylstyrene (conversion: up to 99 %; ee: exceed 99 %). A point worth emphasizing is that the heterogeneous catalysts afforded remarkable increases of conversions and ee values without adding axial base N-methylmorpholine N-oxide for the asymmetric epoxidation of olefins. The catalyst can be easily recovered and reused with slightly decrease of activity and enantioselectivity after seven cycles. Delightedly, this novel heterogeneous catalyst could also be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which provided the potentiality for application in industry.     

Asymmetric catalysis by chiral salen complexes immobilized on mesoporous materials having modified pore channel system by dimethylcarbonate

The mesoporous materials having bimodal pore structure were synthesized by treatment of dimethylcarbonate (DMC) in the presence of metal salts as a catalyst. The pore system was characterized by BET, TEM analysis and by comparing the catalytic activity under the same conditions. The chiral (salen) Co-MX₃ immobilized on SBA-15 and MCM-48 which were partially desilylated by DMC showed higher activity for the enantioselective kinetic resolution of terminal epoxides with H₂O and phenols, relative to original SBA-15 and MCM-48 having regular pore channels. The heterogeneous catalysts can offer practical advantages of the facile separation from reactants and products, as well as recovery and reuse.     

Chiral Salen Mn(III) Complex Axial Coordination Immobilized on Diamine Modified Alspp and Highly Efficient Large-Scale Epoxidation of Olefins as a Recoverable Catalyst

Aluminium oligo-styrenyl phosphonate-hydrogen phosphate (AlSPP) was used as organic–inorganic hybrid support after chloromethylation, and then with using different diamines as a reactive surface modifier. We realized the homogeneous chiral salen Mn(III) complex axially immobilized on modified AlSPP by a covalent grafting method. The prepared heterogeneous salen Mn(III) complexes were characterized by different techniques such as FT-IR, diffusion reflection UV–Vis, AAS, XPS, N₂ volumetric adsorption, SEM, TEM and TG. The chiral salen Mn(III) complexes were immobilized onto the AlSPP through axial coordination for the first time with m-CPBA/NMO as an oxidant system for asymmetric epoxidation of unfunctionalized olefins. The supported catalyst showed very good performance in the asymmetric epoxidation of α-methylstyrene and indene. The catalyst could be easily recovered and reused without significant loss of activity and enantioselectivity after nine cycles. This novel heterogeneous catalyst could be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which offer great possibilities for application in industry.     

Chiral salen Mn(III) immobilized on sulfoalkyl modified ZSP-IPPA as an effective catalyst for asymmetric epoxidation of unfunctionalized olefins

Sulfoalkyl modified zirconium poly (styrene-isopropenyl phosphonate)-phosphate (ZPS-IPPA), with special structures of new type of organic–inorganic hybrid material were designed and synthesized for immobilization of the chiral salen Mn(III) Jacobsen’s homogenous catalyst by axial coordination. All the heterogeneous chiral salen Mn(III) catalysts with different linkage lengths obtained exhibited great catalytic activity and enantioselectivity in the asymmetric epoxidation of unfunctionalized olefins. The influence of the linkage lengths on the catalytic performance was investigated. What’s more, the catalysts were easily separated from the reaction systems and could be reused for several times without significant loss of catalytic activity.     

介孔材料对乳液聚合稳定性的影响

研究了十二烷基硫酸钠(SDS)在不同介孔材料(MCM-41、MCM-48、SBA-15)存在下的临界胶束浓度(CMC),讨论了介孔材料对间歇乳液聚合的影响。研究表明:孔径最大的介孔材料SBA-15存在下SDS的CMC增加最多;在聚合体系中加入介孔材料对单体转化率没有影响,但增加了乳液聚合时的凝聚率,其中使用小孔径的MCM-41凝聚物较少,而颗粒较大的MCM-48凝聚物较多,同时所得乳液聚合物的分子量下降,分子量分布变宽。     

Indene epoxidation over immobilized methyltrioxorhenium on MCM-41 silica,fumed silica and aluminosilicate materials

The presented report focuses on the testing of heterogenized methyltrioxorhenium (MTO) in indene epoxidation. A range of mesoporous materials with different SiO₂/Al₂O₃ ratios, namely aluminosilicates type Siral and MCM-41 silica and fumed silica, were used as supports for immobilization of MTO. The tested support materials and prepared catalytic systems exhibited high surface area, well-defined regular structure and narrow pore size distribution of mesopores and therefore represent good quality catalysts for various reactions. The immobilized MTO on various supports was tested for the preparation of 1,2-epoxyindane using two forms of hydrogen peroxide as oxidation agents, namely aqueous solution of hydrogen peroxide and its anhydrous form, urea-hydrogen peroxide. The prepared catalysts were successfully used for the preparation of 1,2-epoxyindane with achieved 100 % selectivities to the desired product at high conversions of indene.     

Catalytic study of MCM-41 immobilized RhCl3 for the hydroformylation of styrene

RhCl₃ was chemically immobilized on mesoporous silicate MCM-41 functionalized by amine or phosphorus organosilane to form heterogeneous catalysts: RhCl₃/MCM-41(NH₂) and RhCl₃/MCM-41(PPh₂). XRD and N₂ adsorption–desorption studies illustrated that the functionalized MCM-41 maintained the mesoporous structural ordering, but exhibited reduced pore sizes, total pore volumes and BET surface areas. XPS characterization indicated that chemical interaction between rhodium species of RhCl₃ and the surface ligands occurred, and rhodium (III) species were reduced to lower oxidation states. RhCl₃/MCM-41(NH₂) was tested to be stable for recycling, however a significant rhodium leakage was observed for RhCl₃/MCM-41(PPh₂). The catalytic system formed of the prepared RhCl₃/MCM-41(NH₂) catalyst and additional PPh₃ (PPh₃/Rh = 2.5) showed very good catalytic activity and high selectivity toward the branched aldehydes in the hydroformylation of styrene.     

Layered zinc and lanthanum hydroxide nitrates hosting chiral sulphonato-(salen)manganese(III) complex catalyzed asymmetric epoxidation reactions

Layered zinc and lanthanum hydroxide nitrates were first applied as two ion-exchangeable supports for immobilizing a chiral sulphonato-(salen)manganese(III) complex, and the resulted catalysts were characterized by FT-IR, elemental analysis, ICP-AES, TGA, conductivity, XRD, nitrogen physisorption, along with aqueous particle size and zeta potential. Heterogeneous catalysts showed moderate to good conversions and excellent enantioselectivities in epoxidation of styrene and α-methylstyrene when iodosylbenzene was employed as terminal oxidant. Furthermore, the superiority came from heterogeneity, and only filtration could lead to an effective separation of catalyst from product solution.     

Hoveyda-Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves—The influence of pore size on the catalyst activity

New hybrid olefin metathesis catalysts were prepared by immobilization of Hoveyda-Grubbs type catalyst (commercially available as Zhan catalyst-1B) on the surface of mesoporous molecular sieves differing in pore size and architecture (MCM-41, MCM-48, and SBA-15) and conventional silica for a comparison. The activity of these catalysts was tested in RCM of (−)-β-citronellene, metathesis of 1-decene, ADMET of 1,9-decadiene, and in ROMP of cyclooctene and was found to increase significantly with the increasing pore size of the supports used. In all reactions, the activity of hybrid catalysts based on mesoporous molecular sieves was higher than that of catalyst using conventional silica as a support. In ROMP of cyclooctene, high molecular weight polymer (M_w = 300,000) in high yield (70-80%) was obtained with catalysts based on mesoporous supports, however, only 40% polymer yield was obtained using catalyst based on conventional silica.     

Preparation of MCM-41 Supported Heterogenized Chiral Salen Mn (III) Complex and the Catalytic Activity in the Asymmetric Epoxidation

A chiral Manganese (III) salen complex was immobilized on the walls of MCM-41 (mobile crystalline material) through the multi-grafting method. The immobilized complex was characterized by XRD, FTIR, UV-Vis, ICP and Nitrogen sorption, and was applied to the asymmetric epoxidation of unfuctionalized alkenes including 1,2-dihydronaphthalene, α-methylstyrene, cis-β-methylstyrene, styrene using NaClO and m-chloroperbenzoic acid (m-CPBA) as oxidants respectively. The immobilized complex showed good activity and enantioselectivity in the epoxidation of 1,2-dihydronaphthalene by using NaClO as oxidant. It could also be run for 4 times in the epoxidation of α-methylstyrene without obvious loss of activity or enantiomeric excess.     

Enantioselectivities of Chiral Ti(IV) Salen Complexes Immobilized on MCM-41 in Asymmetric Trimethylsilylcyanation of Benzaldehyde

A new heterogeneous system for catalytic trimethylsilylcyanation of benzaldehyde has been developed by immobilizing Ti(IV) salen onto ordered mesoporous silica (MCM-41). The immobilization was performed according to different methods: (i) direct condensation of silanol on the silica surface with Ti(IV) salen and (ii) multigrafting of salicylaldehyde derivatives and diaminocyclohexane using 3-mercaptopropyl-functionalized MCM-41 as a starting material. The heterogenized salen catalysts showed a high enantioselectivity for the addition of trimethylsilyl cyanide to benzaldehyde.     

Application of new unsymmetrical chiral Mn(III), Co(II,III) and Ti(IV) salen complexes in enantioselective catalytic reactions

New unsymmetrical chiral salen complexes were synthesized and the efficiency of Mn(III), Ti(IV), Co(II) and Co(III) type catalysts were examined in the enantioselective epoxidation of styrene and α‐methylstyrene, the trimethylsilylcyanation of benzaldehyde, the borohydride reduction of aromatic ketones and asymmetric hydrolysis of epoxides to diols, respectively. A very high level of enantioselectivity was attainable over the unsymmetrical chiral salen complexes prepared mainly from salicylaldehyde and 2‐formyl‐4,6‐di‐tert‐butylphenol derivatives. Enantiomeric excess of the corresponding reaction product obtained using unsymmetrical chiral salen catalysts was generally higher than that over conventional symmetric chiral salen catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromium catalysts supported on mesoporous silica for ethylene tetramerization: Effect of the porous structure of the supports

Supported chromium catalysts were prepared by loading Cr(acac)₃ and N-isopropyl bis(diphenylphosphino)amine (PNP) onto methylaluminoxane-modified MCM-41 and SBA-15. The structure of supported catalysts was characterized and the influence of the pore structure of supports on the reactivity for ethylene tetramerization was investigated. The results revealed that the chromium was immobilized on the mesoporous silica in different supported patterns, which was affected by the pore size of the supports and affected catalyst performance. The highest selectivity toward 1-octene was provided by the SBA-15-supported Cr(acac)₃/PNP catalyst, and this value was higher than that of the homogeneous analogs.     

Microporosity in Mesoporous SBA-15 Supports: A Factor Influencing the Catalytic Performance of Immobilized Metalloporphyrin

MnTMPyP cationic metalloporphyrin was immobilized by means of ion exchange on a series of aluminated SBA-15 mesoporous silica supports prepared by different methods. The solids were characterized with XRD, HRTEM, HRSEM, chemical analysis, and nitrogen sorption isotherms. The catalysts were tested in the reaction of cyclohexene oxidation with iodozobenzene. It was found that immobilization significantly enhances catalytic activity as compared to the homogeneous system. In contrast to previously investigated metalloporphyrin catalysts immobilized on aluminated HMS, MCM-41 or FSM-16 type supports, where too narrow pores limited the formation of epoxide and enhanced allylic oxidation, the use of aluminated large pore SBA-15 solids favoured the epoxidation pathway and resulted in yields significantly higher than in the case of homogeneous reaction. The catalysts showed important differences in the level of allylic oxidation. Analysis of various factors potentially influencing the product distribution demonstrates that the key role in determining the contribution of allylic oxidation is the microporosity nature of the support, in particular, the lack or presence of supermicropores capable of accommodating metalloporphyrin species. The MnTMPyP centres confined in supermicropores experience steric limitations, which do not allow for the formation of epoxide and favour allylic oxidation.