Asymmetric Catalysis in Confined Space Provided by l-Proline Functionalized Mesoporous Silica with Plugs in the Pore

Abstract

Mesoporous silica having L-proline functionality and plugged pore structure was synthesized by direct microwave synthesis under acidic condition using Pluronic P123 as template and sodium metasilicate nonahydrate as silica source. The direct synthesis resulted in the prismatic or disk types with short channels and plugs in the pore structure. Due to the presence of plugs, dual mesoporosities with 7 and 3 nm pore diameter were generated leading to an existence of cavitation. Tri-functionality of this materials i.e. chiral organofunctional group, plugs, and short channel, would be useful for the asymmetric diethyl malonate addition reaction and asymmetric epoxidation reaction of a,b-unsaturated aldehydes. We proved that the formation of plugs in the mesoporous silica governs the formation of dual mesoporosities providing an enhancement of enantiomeric excess in the asymmetric catalysis.This finding might open an important application of the amino-acid organo multifunctionalized mesoporous silica for asymmetric reactions.

Recyclable organocatalysts based on hybrid silicas

“…Some silica-supported organocatalysts (M87-M96) for asymmetric Michael addition following the enamine pathway have been described in the literature and they are summarized in Figure 10. 50,193 The suggested mechanism for this epoxidation reaction involves the formation of an enamine intermediate. Following a similar methodology the same group prepared plugged trans-(1R,2R)-diaminocyclohexane functionalized mesoporous silicas M91a-d for asymmetric 1,4-addition reactions, by varying the amount of organosilane and the heating method (microwave for M91a,c or hydrothermal for M91b,d).…”

“…Chiral enhancement in the diethyl malonate conjugate addition to cyclohex-2-en-1-one has also been observed in Lproline derived materials possessing short channels and plugs in the pore structure (compare M90a-c and M90d in Scheme 13). 50,193 Zaera has also described the conjugate addition of p-tert-butylbenzenethiol to 2-cyclohexen-1-one catalyzed by cinchonidines M102a,b and M103a,b. 91 Although full conversions were achieved after one day in benzene at room temperature with the supported catalysts, a loss of enantioselectivity was observed upon tethering, which was attributed to the interference of the surface of the solid on the catalytic performance.…”

A novel and facile strategy for synthesis plugged SBA-15

“…However, as-synthesized materials show different type hysteresis loops due to different pore types. The adsorption-desorption isotherms of PHTS-1 and PHTS-2 samples exhibit an H2-type hysteresis loop and a slow N 2 capillary condensation in the 0.40-0.74 P/P 0 , which can be indicated to the presence of the inkbottle-type pore structure [5][6][7][8][9][10][11][12][13][14][15], thereinto, the sample PHTS-1 is completed plugged pores material, and that PHTS-2 is partially plugged pores material [11]. From Figure 2a, the desorption branch of sample PHTS-3 shows two major capillary condensation steps in the relative pressure ranges from 0.40-0.50 P/P 0 and 0.55-0.65 P/P 0 , implying the pore blocking effect [5][6][7]10], and leading to the pore size distributions focus on about 3.9 nm and 5.4 nm, as can be identified from the corresponding pore size distribution curves ( Figure 2b).…”

“…Oliveira [12]. Plugged structure materials were an advantageous catalyst support and adsorbent, and had played an important role in the asymmetric addition and epoxidation reaction [13,14], isopropylation [15], decomposition [16], hydrodechlorination [17], oligomarization reaction [18] and hydrocarbons adsorption [19], and so forth.…”

Styrene Epoxidation in Aqueous over Triazine-Based Microporous Polymeric Network as a Metal-Free Catalyst

“…However the use of these nitrogenous material as an organocatalysts have a number of formidable problems such as corrosion, deposition on reactor walls and moreover tedious product/catalyst separation procedure due to their homogenous modus operandi. To overcome these problems efforts have been made towards immobilization of nitrogenous materials onto organic, polymeric, or inorganic nanoporous supports [12]. Although immobilization of the homogenous catalyst reduces several drawback but are prone to problems like less number of active sites, high loading and leaching of anchored organocatalyst during reaction.…”