Improved methodology for non-covalent immobilization of tert-butyl-azabis(oxazoline)–copper complex on Al-MCM41

Abstract

Please cite this article as: Robert A.Feldman, José M.Fraile, Improved methodology for non-covalent immobilization of tert-butyl-azabis(oxazoline)-copper complex on Al-MCM41, Applied Catalysis A, General http://dx. Highlights-Chiral azabox-copper complex was immobilized on Al-MCM41 in a non-covalent way.-Cu(OTf) 2 was first impregnated by incipient wetness and then treated at 450ºC.-Final modification with azabox leads to stable immobilized complexes.-Better results in enantioselective cyclopropanation are obtained at high temperature. AbstractCopper sites are supported on Al-MCM41 by thermally treating copper(II) triflate that was deposited using the incipient wetness method. The change of the chemical state of the triflate anions following thermal treatment is monitored using TGA and SEM-EDX.Thermal treatment yields copper sites that then can be modified with chiral tert-butylazabis(oxazoline) by adding a solution of this ligand to the support using incipient wetness. The catalyst produced in this way is efficient and stable with good enantioselectivity, and can be used in the cyclopropanation of styrene with ethyl diazoacetate under conditions employing an elevated temperature. The use of thermal treatment in the catalyst preparation method produces catalysts that are superior to the solids prepared by cation exchange or incipient wetness of the pre-formed complex.

Coordinating Ability of Anions, Solvents, Amino Acids, and Gases towards Alkaline and Alkaline‐Earth Elements, Transition Metals, and Lanthanides

“…The choiceo fd ichloromethane as as olvent was based in its reasonable elutropic strength and low coordinating ability. [51]…”

Enhanced Performance of Organic/Inorganic Hybrid Nanomaterials bearing Impregnated [PdL2] Complexes as Counter‐Electrode Catalyst for Dye‐Sensitized Solar Cells

“…Although homogeneous catalysts exhibit very high activity in the catalytic cycle, recovery or re‐use rates can be lower than with heterogeneous catalysts. Based on the understanding of producing the best quality catalyst, the synthesis of heterogeneously immobilized homogeneous catalysts is a current issue which is followed with great interest to the literature . Thus, the catalysts have both high activities and are not quickly degraded.…”

Non-covalent immobilization of chiral copper complexes on Al-MCM41: Effect of the nature of the ligand

“…The Cu-Al-MCM41 catalyst was prepared following the conditions described in our most recent paper [18] The supported chiral catalysts were first tested in the cyclopropanation of styrene (Scheme 1, R = H) with ethyl diazoacetate, using an excess of styrene as solvent at 90ºC, which are the best conditions found in our previous work [18]. At 90ºC in the homogeneous phase, cationic polymerization of styrene rapidly occurs and so the homogeneous reactions were carried out at room temperature.…”

“…Al-MCM41 (Si/Al = 10) was prepared from sodium aluminate and fumed silica in a basic medium with cetyl trimethyl ammonium as the template and 1,3,5trimethylbenzene added to expand the pore size [20]. As previously described [18], Al-MCM41 (500 mg) was added to a solution of copper(II) triflate (42 mg, 0.1 mmol) in 600 µL of methanol and the container was shaken to ensure that the solution was evenly distributed. This material was then calcined (1ÊC/min heating until 450ÊC, maintained for 4 h) under a 100 mL/min flow of air to obtain what we designate "Cu-Al-MCM41".…”

“…In our previous work, we compared different approaches to the electrostatic immobilization of bis(oxazoline)-copper complexes on Al-MCM41, and found that a direct cationic exchange is not easy to accomplish, and that an incipient wetness impregnation method leads to better results in the cyclopropanation reaction of styrene with ethyl diazoacetate [17]. A higher enantioselectivity and recoverability was obtained with a different approach to immobilizing the copper centres on the support, that utilized a three-step immobilization method, consisting of a first impregnation with copper(II) triflate, subsequent thermal treatment of the solid and final modification with the chiral ligand [18]. In this paper we demonstrate how this methodology performs with different bis(oxazoline) and azabis(oxazoline) [19] ligands (Figure 1).…”