Synthesis of tetradentate N4 Schiff base dioxomolybdenum (VI) complex within MCM-41 as selective catalyst for epoxidation of olefins

Covalent grafting of MCM-41 with 3-chloropropyl trimethoxysilane and subsequent reactions respectively with pypr [N,N′-bis(2-pyrrolmethylidenaminopropyl)amine] and complexation with MoO₂(acac)₂ afforded MoO₂pyprMCM-41. X-ray diffraction and nitrogen sorption analyses revealed the preservation of the textural properties of the support as well as accessibility of the channel system despite sequential reduction in surface area, pore volume and pore size. Elemental analyses showed nearly complete complexation of the supported ligands and the presence of 0.24 mmol molybdenum per gram of the catalyst. Epoxidation of cyclooctene, cyclohexene, 1-hexene and 1-octene in the presence of MoO₂pyprMCM-41 with tert-butyl hydroperoxide (TBHP) were carried out with 21–98% conversion under the mild reaction conditions.     

MCM-41 anchored manganese salen complexes as catalysts for limonene oxidation

This work reports the covalent attachment of three different salen-based complexes on MCM-41, using two different methods. In both methods, a diisocyanate is used as a binder. All the prepared catalysts were tested on the liquid phase limonene oxidation reaction, using diluted t-butyl hydroperoxide as oxidant. Limonene oxide, carveol, carvone and a polymer were the main products obtained. The preservation of the MCM-41 channel system was checked by X-ray diffraction, nitrogen adsorption analysis and transmission electron microscopy (TEM). Catalytic activity seems to increase in the following order: Mn(4-OHsalen) < Mn(4-OHsalhd) < Mn(4-OHsalophen).The most active catalysts were used in four consecutive experiments without any activity loss, confirming the success of the anchoring process and the catalysts stability.     

Activity of Mo(II) allylic complexes supported in MCM-41 as oxidation catalysts precursors

[Mo(η³-C₃H₅)X(CO)₂(NCCH₃)₂] (X = Br, 1a; X = Cl, 1b) complexes reacted with the bidentate ligand RNC(Ph)–C(Ph)NR, R = (CH₂)₂CH₃ (DAB, 2) affording [Mo(η³-C₃H₅)X(CO)₂(DAB)] (X = Br, 4a; X = Cl, 4b), which were characterized by elemental analysis, FTIR and ¹H and ¹³C NMR spectroscopy. The modified silylated ligand RNC(Ph)C(Ph)NR, R = (CH₂)₃Si(OCH₂CH₃)₃ (DAB–Si, 3), was used to immobilize the two complexes in MCM-41 (MCM) mesoporous silica. The new materials were characterized by powder X-ray diffraction, N₂ adsorption analysis, FTIR and ²⁹Si and ¹³C CPMAS solid state NMR spectroscopy. Both the materials and the complexes were tested in the oxidation of cyclooctene and styrene and behaved as active catalyst precursors for cyclooctene and styrene epoxidation with TBHP (t-butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs. Although the homogeneous systems reach 100% conversion of cyclooctene and slightly less for styrene, the loss of catalytic activity in the heterogeneous systems is small, with a 98% conversion of styrene achieved by the chloride containing material.     

Cerium-containing MCM-41 materials as selective acylation and alkylation catalysts

The synthesis of Ce–MCM-41, Al–MCM-41 and Ce–Al–MCM-41-type mesoporous materials was carried out hydrothermally by refluxing the gel with magnetic stirring under atmospheric pressure for 24–36 h. The samples were characterized thoroughly in order to obtain the structural and textural properties, which reveal the presence of well-ordered M41S-type materials. The Ce–MCM-41 samples were used for catalytic acylation of alcohols, thiols, phenols and amines show good activity and selectivity including high chemoselectivity towards selective monofunctional acylation of bifunctional compounds. Quite importantly the acylation of bulky molecules such as cholesterol, ergesterol and β-sitosterol could be achieved using Ce–MCM-41 as solid catalyst. The presence of Ce along with Al in Ce–Al–MCM-41 was found to have synergistic effect as Ce–Al–MCM-41samples were more active catalysts for alkylation of naphthalene compared to either Ce–MCM-41 or Al–MCM-41 with comparable Si/Al or Si/Ce molar ratio.     

Preparation and characterization of a titanium(IV) silsesquioxane epoxidation catalyst anchored into mesoporous MCM-41.

This paper describes the synthesis and spectroscopic study of a titanium(IV) silsesquioxane complex, which is heterogenised in the pores of an MCM-41 host material. Its immobilization is performed via chemical bonding, not by means of physical adsorption. As a linking molecule between the MCM-41 carrier and the silsesquioxane, (3-glycidyloxypropyl)trimethoxysilane is used. Characterization is performed by using nitrogen adsorption techniques, TGA, diffuse reflectance infrared spectroscopy (DRIFT) and ICP-MS. Also its catalytic activity towards the epoxidation of alkenes shows interesting results.     

Chiral manganese(III) Schiff base complexes anchored onto activated carbon as enantioselective heterogeneous catalysts for alkene epoxidation

Two chiral manganese(III) salen catalysts, bearing different chiral diamine bridges, were anchored by direct axial coordination of the metal centre onto the phenolate groups of a modified commercial activated carbon. The modification of the activated carbon was achieved by reaction between sodium hydroxide and surface phenol groups giving rise to phenolate groups (CoxONa), which were characterised by XPS, TG and TG-IR. Characterisation of immobilised manganese(III) salen catalysts onto CoxONa material by XPS, ICP-AES and TG-IR clearly point to reaction between carbon surface phenolate groups and the manganese(III) complexes through axial coordination of the metal centre to these groups.These materials were active and enantioselective in the epoxidation of styrene and α-methylstyrene in dichloromethane at 0 °C using, respectively, m-CPBA/NMO and NaOCl. Only for α-methylstyrene comparable asymmetric inductions were found in the epoxide as the homogeneous phase reactions and catalyst reuse led to no significant loss of catalytic activity and enantioselectivity.     

Synthesis,characterization and sulfide oxidation activity of vanadyl Schiff base complexes anchored on MCM-41

Vanadyl Schiff base complexes covalently attached on the surface of MCM-41 have been synthesized by anchoring Schiff base and subsequent reaction with VO(acac)₂. XRD, nitrogen adsorption and desorption, UV-visible spectroscopy and FT-IR show that vanadyl Schiff base complexes were successfully anchored on the surface of MCM-41 and the mesopore ordering decreased after the anchoring. The so-prepared heterogeneous catalysts have showed high activity for sulfide oxidation.     

Polymer-immobilized manganese(III)-Schiff base complexes for catalytic epoxidation of olefins

Polymer-linked manganese(III)-salen-type Schiff base complexes were prepared by the copolymerization of functionalized Schiff base, styrene, and divinylbenzene at various mixing ratios (1:10:0–1:12:4), followed by introduction of Mn(III) ion. The materials catalyzed epoxidation of cyclohexene with iodosylbenzene in CH₂Cl₂ as rapidly as the monomer complexes. The maximum total turnover reached 170, which is about 13 times higher than that of the monomer. The lifetime of polymer catalysts is discussed in terms of cross-linking and solvent effects.     

Heterogeneous tungsten-based catalysts for the epoxidation of bulky olefins

This paper discusses the design of different W and PW heterogeneous catalysts. The first part focuses on the electrostatic immobilization of those species on organic resins. In the second part, some new silica materials are synthesized as carrier materials for PW species. Both electrostatic immobilization and covalent linking of the species on the modified silica materials are discussed. Besides a thorough spectroscopic study (FT-IR, Raman, NMR, TGA and EPMA), the catalytic properties of the designed catalysts are evaluated for the epoxidation of a variety of bulky olefins.     

Manganese(II) complexes of imidazole based-acetamide as homogeneous and heterogenised catalysts for alkene epoxidation with H2O2

An acetamide derivative which bears two terminal imidazole rings has been synthesized. This biomimetic ligand, N-[2-(1H-imidazol-4-yl)-ethyl]-2-({[2-(1H-imidazol-4-yl)-ethylcarbamoyl]-methyl}-amino)-acetamide, has been also grafted on silica surface via covalent bond. The supported and non-supported biomimetics reacted with manganese(II) ions leading to the formation of the corresponding metal complexes. These have been evaluated as catalysts for alkene epoxidation with H₂O₂ in the presence of ammonium acetate as an additive. Our data showed that the homogeneous and the supported systems are able to overcome the competitive H₂O₂ dismutation, by the use of only two times H₂O₂ with respect to substrate, favouring productive alkene epoxidations to a significant extent.     

Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins

A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios. The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated up to Si/Ti = 50 successfully without forming any extra framework TiO₂. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD, FTIR, UVDRS, ²⁹SiMASNMR, BET surface area and pore size distribution techniques.     

改性中孔分子筛MCM-41催化合成丙酸香叶酯

用H2SO4对中孔分子筛MCM（mobile crystalline material）-41进行改性,得到SO42–修饰的中孔分子筛SO42–/MCM-41。通过X射线衍射、红外光谱、NH3程序升温脱附和N2吸附–脱附等方法对所合成样品进行表征。用SO42–/MCM-41催化合成丙酸香叶酯,考察了催化剂处理方法、催化剂用量、催化剂再生对香叶醇酯化反应结果的影响,并比较了H2SO4、MCM-41和SO42–/MCM-41这3种催化剂对合成丙酸香叶酯的催化性能。结果表明：用浓度为0.50mol/L的硫酸浸泡MCM-41中孔分子筛1h,再于450℃焙烧3.0h,能得到良好长程有序性和结晶度的中孔分子筛SO42–/MCM-41,用其催化合成丙酸香叶酯,香叶醇的转化率最高可达88.82%,丙酸香叶酯的选择性为85.20%;H2SO4改性对MCM-41中孔分子筛结构影响不明显,但可提高其酸性。     

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.     

钼基催化剂在烯烃液相环氧化反应中的应用研究进展

介绍了钼络合物催化剂、固载化的钼络合物催化剂及MoO₃基的固体钼催化剂在烯烃液相环氧化反应中的应用。以有机过氧化物为氧化剂时,不同的钼基催化剂均表现出很好的催化性能,其中络合物中的配体对其催化性能有很大影响,并且可以通过引入手性配体实现对烯烃的不对称环氧化,而固体钼催化剂的性能则与载体上钼物种的种类密切相关。但绝大多数钼催化剂对H₂O₂参与的环氧化反应没有活性,开发对H₂O₂有催化活性的钼基催化剂是一个重要的研究方向。     

Zr (IV)-ninhydrin supported MCM-41 and MCM-48 as novel nanoreactor catalysts for the oxidation of sulfides to sulfoxides and thiols to disulfides

Modification of MCM-41 and MCM-48 mesoporous materials with bonded aminosilane species, Schiff base preparation by ninhydrin and finally complexation with zirconium, has attracted much attention in order to design catalyst with advanced applications in the oxidation of sulfides to sulfoxides and thiols to disulfides in the presence of hydrogen peroxide. In all oxidation of sulfides to sulfoxids 0.4 mL H₂O₂ used as oxidant in the presence of Zr(IV)-ninhydrin supported MCM-41 (0.01 g) or Zr(IV)-ninhydrin supported MCM-48 (0.005 g) at room temperature and solvent-free condition. Also the best conditions for oxidation of thiols to disulfides with 0.4 mL H₂O₂ were 0.005 g Zr(IV)-ninhydrin supported MCM-41 or Zr(IV)-ninhydrin supported MCM-48 at room temperature and in ethanol. These catalysts are characterized by SEM, XRD, TGA, FT-IR, EDS, ICP and BET analysis. Also the Turn over frequency (TOF) and Turn over number (TON) of catalysts are calculated. Obtained results by these heterogeneous catalysts revealed several advantages including short reaction times, simple workup, easy isolation and reusability.     

Diphosphino-functionalized MCM-41 anchored palladium(0) complex as an efficient catalyst for Heck arylation of conjugated alkenes with aryl halides

Diphosphino-functionalized MCM-41 anchored palladium(0) complex (denoted as MCM-41-2P-Pd(0)) was conveniently synthesized from commercially available and cheap γ-aminopropyltriethoxysilane via immobilization on MCM-41, followed by reacting with diphenylphosphinomethanol and palladium chloride and then the reduction with hydrazine hydrate. XRD and XPS spectroscopies were employed to characterize the title palladium complex. It was found that this complex is a highly active and stereoselective catalyst for Heck arylation of conjugated alkenes with aryl halides and can be reused many times without loss of activity.     

CpMo(CO)3Cl as a precatalyst for the epoxidation of olefins

The tricarbonyl complex CpMo(CO)₃C1 was found to act as a precatalyst for the reaction of tert-butyl hydroperoxide and olefins to yield the corresponding epoxides and diols. Under the reaction conditions, oxidative decarbonylation leads to the formation of the dioxo complex CpMoO₂Cl. The catalytic recyclability and the effect of temperature on the catalytic results have been examined, and a reaction mechanism proposed, supported by kinetic modelling.