Enantioselective epoxidation of olefins catalyzed by Mn (salen)/MCM-41 synthesized with a new anchoring method

Abstract

New immobilization of the chiral Mn(salen) complex through the complexation of managanese by oxygen atoms of the phenoxyl groups grafted on the surface of MCM-41 leads to a markedly higher ee than for the free complex.

Chiral vanadyl salen catalyst immobilized on mesoporous silica as support for asymmetric oxidation of sulfides to sulfoxides

“…It was shown that the Schiff base ligands are able to coordinate many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations such as asymmetric epoxidation [5][6][7][8], asymmetric sulfide oxidation [9,10], cyclopropanation [11], aziridination [12], Knoevenagel condensation [13], and T. Ben Zid Á I. Khedher (&) Á A. Ghorbel Département de Chimie, Faculté des Sciences de Tunis, Laboratoire de Chimie des Matériaux et Catalyse, 1060 Tunis, Tunisie e-mail: ilyeskhadher@yahoo.com selective hydrogenation reactions under homogenous conditions [14,15]. Due to the advantages of heterogeneous catalysis systems, namely easy catalyst/product separation and simple catalyst recycling, the heterogenization of these homogenous chiral catalysts onto several supports has received great attention in recent years [16][17][18][19][20][21][22]. In spite of this, the use of the chiral vanadium salen Schiff base immobilized on inorganic support as asymmetric oxidation catalysts has been rather scarce and has mainly focused on the asymmetric addition of trimethylsilyl cyanide to aldehydes [23].…”

Enantioselective catalysis with chiral complexes immobilized on nanostructured supports

“…Li and coworkers have been working in the modification of MCM-41 with organic groups, such as phenoxide and benzenesulfonate (Figure 25), to immobilize Jacobsen's (salen)Mn complex through cation exchange. In a first 5 report, 27 the immobilization with a phenoxide group showed to be positive for the epoxidation of α-methylstyrene with aqueous NaClO, as the enantioselectivity increased from 56% ee in solution to 72% ee with the heterogeneous catalyst, and the placement of the catalytic sites inside the mesopores was 10 demonstrated by the lack of activity of the solid to epoxidize the bulkier 1-phenylcyclohexene.…”

Novel Chiral Sulphonato‐Salen‐Manganese(III)‐Pillared Hydrotalcite Catalysts for the Asymmetric Epoxidation of Styrenes and Cyclic Alkenes

“…[32] Salen-Mn(III) complexes supported on amorphous silica or MCM-41 catalysts were less effective in the case of styrene, with an ee and epoxide yield of 30% and 70%, respectively. [32] Chiral salen-Mn(III) catalyst when axially immobilised into MCM-41 via either phenoxy [13] or phenylsulphonic group [14] showed higher ee % than the homogeneous counterparts for the epoxidation of a-methylstyrene.…”

“…Subsequent testing of their catalyst in the epoxidation of nonfunctionalised alkenes using NaOCl as oxidant gave a higher ee for certain alkenes than that found under homogeneous conditions. Recently, Li and co-workers [13,14] demonstrated that chiral salen-Mn(III) catalyst when axially immobilised into MCM-41 through complexation of the manganese via the oxygen atoms of the phenoxy groups [13] produced epoxide with 72% ee, whereas the same complex immobilised via a phenylsulphonic group [14] gave a slightly higher ee value for the epoxidation of a-methylstyrene. These phenoxy or phenylsulphonic group-anchored catalysts showed significantly higher % ee than the homogenous analogues (56% ee) for a-methylstyrene epoxidation.…”

“…These phenoxy or phenylsulphonic group-anchored catalysts showed significantly higher % ee than the homogenous analogues (56% ee) for a-methylstyrene epoxidation. [13,14] Hydrotalcites, due to their high surface area, homogeneous cation site distribution, basicity and anion exchange capacity, find use in many catalytic applications. Examples of these include catalysed reactions such as Knovenagel, [15] Micheal, [16] Claisen-Schmidt, [17] aldolisations, [18] and in hydrogenation of aromatics as well as in selective oxidation reactions [19] and in the BaeyerVilliger oxidation of ketones.…”