Next Article in Journal
Investigation of Iron Vanadates for Simultaneous Carbon Soot Abatement and NH3-SCR
Next Article in Special Issue
Isolation, Characterization, and Environmental Application of Bio-Based Materials as Auxiliaries in Photocatalytic Processes
Previous Article in Journal
Investigation of Catalytic Ozonation of Recalcitrant Organic Chemicals in Aqueous Solution over Various ZSM-5 Zeolites
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Communication

A New Mn–Salen Micellar Nanoreactor for Enantioselective Epoxidation of Alkenes in Water

1
Department of Chemical Sciences, University of Catania, Viale Andrea Doria 6, 95125 Catania, Italy
2
University of Catania Research Unit (I.N.S.T.M.) UdR of Catania, Viale A. Doria 6, 95125 Catania, Italy
*
Author to whom correspondence should be addressed.
Catalysts 2018, 8(4), 129; https://doi.org/10.3390/catal8040129
Submission received: 28 February 2018 / Revised: 21 March 2018 / Accepted: 22 March 2018 / Published: 25 March 2018
(This article belongs to the Special Issue Reactions in Water and in Micelles)

Abstract

:
A new chiral Mn–salen catalyst, functionalized with a long aliphatic chain and a choline group, able to act as surfactant catalyst for green epoxidation in water, is here described. This catalyst was employed with a commercial surfactant (CTABr) leading to a nanoreactor for the enantioselective epoxidation of some selected alkenes in water, using NaClO as oxidant. This is the first example of a nanoreactor for enantioselective epoxidation of non-functionalized alkenes in water.

Graphical Abstract

1. Introduction

Water is an abundant molecule in nature and, due to its diffusion, cost, non-toxicity, and environmental compatibility, is probably one of the most desirable solvents for reactions. In fact, organic solvents are commonly used in the pharmaceutical and chemical industries as reaction media; however, for toxicological and environmental pollution reasons [1], industries aspire to reduce the number and amount of solvents applied in a drug or chemical production. However, the use of water as solvent for organic synthesis is limited by the low solubility of organic compounds and the facile decomposition of many active species in water. These drawbacks have recently been resolved by the use of nanocapsular systems [2] and micelles [3], which dissolve and stabilize organic substrates in water and, in some examples, act as molecular reactors for organic synthesis [4,5,6,7,8].
Olefin epoxidation is an important and useful reaction because it leads to a wide range of organic compounds with significant applications in several technological fields [9]. In particular, chiral Mn(III)-salen complexes have been used as catalysts to obtain chiral epoxides, which represent an essential target due to the importance of enantiomerically pure compounds in industry and pharmaceuticals [10,11,12]. In this context, many efforts have been addressed to leave behind the “poor eco-friendly conditions” (e.g., the use of organic solvent and reaction with strong conditions) and move toward more efficient and eco-compatible reactions, by using efficient heterogeneous catalysts [13,14,15,16] and/or reactions in aqueous media [3]. However, few examples of enantioselective epoxidation in water are reported in the literature [17,18,19,20,21,22]. A possible solution can be found by using a self-assembly process to obtain amphiphilic or self-assembled nanostructures [23,24,25], able to solubilize organic substrates in water.
Recently, our research group has developed new protocols to obtain epoxides with high enantioselectivity in water exploiting micelles, in which the surfactant act as co-ligand for a chiral Mn(III)-salen catalyst [17,18]. In these systems, the micellar catalyst acts as a nanoreactor for the epoxidation reaction.
Here we present the design, synthesis, and catalytic application of a new nanoreactor, in which chiral Mn(III)-salen catalyst 1-Mn is itself a surfactant. Micellar nanoreactor consists in catalyst 1-Mn and cetyltrimethylammonium bromide (CTABr), mixed in an appropriate ratio (see Figure 1). Epoxidation results obtained with selected alkenes confirm the ability of our system to act as enantioselective catalyst in water. To the best of our knowledge, this is the first example of chiral nanoreactor able to efficiently catalyze enantioselective epoxidation in pure water.

2. Results and Discussion

Surfactant catalyst 1-Mn was synthesized according the multi-step pathway shown in Scheme 1.
In the first step, 3-(tert-butyl)-2-hydroxybenzaldehyde was reacted with aqueous paraformaldehyde and HCl, leading to the 5-chloromethylated Compound 2 in high yield (95%) [26]. The reaction of 2 with a stoichiometric amount of tetradecanol in the presence of sodium hydroxide allowed for the selective introduction of the long aliphatic chain in 5-position, fundamental for the surfactant activity, (Compound 3, yield 32%). Ethanolamine was hypermethylated by reaction with an excess of methyl iodide, in the presence of potassium carbonate, thus obtaining choline iodide 4 in almost quantitative yield. The choline derivative 4 was covalently bound to the aldehyde 2 following the same procedure used to prepare the aliphatic aldehyde 3. Thus, using an equimolar ratio of 2 and 4 in basic conditions, the water-soluble choline-aldehyde 5 was synthesized in 31% yield. The salen moiety was assembled using the (1R,2R)-diphenyl-ethylendiamino-monochloride 6 [27,28], which, in the presence of the aldehyde 3, afforded the mono-imino-amine-monochloride 7 in quantitative yield. Finally, surfactant chiral salen ligand 1 was obtained by condensation of 5 and 7, in the presence of triethylamine (yield 67%). This strategy is the most viable way to obtain a “non-symmetrical salen ligand” in high yield [29,30,31]. The water-soluble manganese catalyst 1-Mn was obtained in quantitative yield by addition of manganese acetate to the corresponding chiral ligand 1. Compounds were fully characterized by NMR and ESI-MS (see Supplementary Materials).
The micellar nanoreactor was assembled using 1-Mn and cetyltrimethylammonium bromide (CTABr) as co-surfactant in a different molar ratio (see Table 1). We selected a cationic surfactant to obtain a micellar surface fully covered by the same positive charges. In addition, catalyst was designed in order to confine the catalytic metal center inside the hydrophobic region of the nanoreactor (see Figure 1), in contrast with our previous works where it was located on the Stern layer [17,18]. We think the catalytic site sequestered in the interior of micelles should lead to higher reaction rates, due to a proximity effect with the alkene inside the core of a micelle.
Micellar nanoreactor was characterized by DOSY measurements. In particular, diffusion coefficient data allowed us to calculate the hydrodynamic radius of the micelle [32,33,34,35,36]. The diffusion coefficient of a 0.03 M solution of CTABr in D2O (the same concentration used in the epoxidation reaction) is 1.20 × 10−10 m2 s−1, corresponding to a hydrodynamic radius of ca. 2.15 nm (see Section 3) and thus in accordance with the formation of a micelle (the c.m.c. of CTABr is 8.6 × 10−4 M). The same measurements were performed with a 0.03 M solution of CTABr and 1 mM 1-Mn in D2O, and a diffusion coefficient of 1.17 × 10−10 m2 s−1 was found (hydrodynamic radius of ca. 2.21 nm, see Section 3), thus confirming that the presence of our catalyst does not modify the dimension of the micelle.
Once the presence of micellar systems, with and without the addition of 1-Mn, was confirmed, we tested our system as nanoreactor in the enantioselective epoxidation of some selected aromatic alkenes, in particular 6-cyano-2,2-dimethylchromene, 1,2-dihydronaphthalene, and cis-β-ethylstyrene in water, using NaClO as the oxidant. Results are summarized in Table 1. In fact, as reported by Corey et al., alkenes that are conjugated with a π-system are ideal substrates for enantioselective epoxidation by using a Jacobsen catalytic system [37].
Due to the high reactivity of 6-cyano-2,2-dimethylchromene in the oxidation reactions [38], using 0.03 M CTABr and 5% catalyst, total conversion in epoxide is complete in 3 h, with an enantiomeric excess of ca. 83% (Entries 1–2). The increase in concentration of CTABr from 0.03 to 0.06 M does not affect enantioselectivity and conversion values (Entries 3–4). Enantiomeric excess values with 1,2-dihydronaphthalene were also in the range of 80–84%, confirming the ability of the nanoreactor to achieve enantioselectivity. As shown in our previous works [17,18], 1,2-dihydronaphthalene presents lower reaction rates compared to 6-cyano-2,2-dimethylchromene.
In fact, under the same conditions, after 1 h of reaction, only a 17% conversion was obtained (Entry 1 vs. Entry 5). After 8 h of reaction, a 46% conversion value was observed (Entry 6). The increase in concentration of the catalyst 1-Mn (10% respect to the substrate) was not sufficient to reach full conversion, affording a conversion of 64% (Entry 7). With 0.06 M CTABr, conversions increased to 76% after 1 h and 100% after 3 h (Entries 8 and 9, respectively). These results suggest strong contribution from the nature of the substrate to the reaction rate.
This hypothesis was confirmed considering cis-β-ethylstyrene: using 0.03 M CTABr and 5% catalyst, conversion reached 73% in 1 h and 100% after 2 h. However, the enantioselectivity value observed was 51% (Entries 10–11).
In order to increase enantioselectivity with this alkene, we evaluated the effect of CTABr surfactant concentration, performing epoxidation reactions at 0.015, 0.03, and 0.06 M CTABr, using 10% catalyst (Entries 12–17). We noted that the 10% catalyst amount led to a slight improvement in enantioselectivity (56–58%), while the reaction rates remained quite similar.
Noteworthy, the simple CTABr micelle containing selected alkenes in water, after the addition of NaClO, leads to a racemic mixture of epoxides; in the classic biphasic system (CH2Cl2/H2O), this reaction has never been observed [10,11,12,40]. Thus, the presence of the chiral catalyst is essential to catalyze the enantioselective epoxidation of alkenes.
The recovery of the catalyst was also evaluated. In particular, after complete conversion of the starting alkene (we tested recovery using 1,2-dihydronaphthalene as substrate), 1-Mn was extracted by an addition of dichlorometane. The organic phase was dried, and the resulting catalyst was reused in a new epoxidation, using the same conditions reported in Entry 9 of Table 1. Conversions and enantiomeric excess are reported in Figure 2. After five cycles, enantiomeric excess was constant, demonstrating the robustness of the catalyst.
Finally, we tested the sustainability of our protocol measuring the EcoScale of our process [41,42]. This scale takes into consideration the yield of the reaction, combined to several parameters, such as the price of reaction components, the safety of reagents, the technical setup, the temperature/time, the workup, and the purification. These parameters influence the quality of reaction conditions. After calculation of the appropriate “penalty points,” the EcoScale value can be obtained. An ideal “green” reaction has an EcoScale of 100. In our case, an EcoScale value of 93 was calculated, thus confirming an excellent protocol.

3. Materials and Methods

3.1. General

The NMR experiments were carried out at 27 °C on a Varian UNITY Inova 500 MHz spectrometer (1H at 499.88 MHz, 13C-NMR at 125.7 MHz, Varian-Agilent, Santa Clara, CA, USA) equipped with pulse field gradient module (Z axis) and a tunable 5 mm Varian inverse detection probe (ID-PFG). ESI mass spectra were acquired on a API 2000™ AB Sciex (Milano, Italy) using MeOH (positive ion mode). All chemicals were reagent grade and were used without further purification. Enantiomeric excesses were determined by GC analysis with a Perkin Elmer Capillary (Perkin Elmer, Waltham, MA, USA) using a dimethylpentyl-beta (DIMEPEBETA-086) chiral column (25 m × 0.25 mm ID, 0.25 μm film) for 6-cyano-2,2-dimethylchromene; DiAcTBuSiliBETA-ov-1701 chiral column (25 m × 0.25 mm ID, 0.25 μm film) for cis-β-ethylstyrene and dimethyl-pentyl-beta (DMePeBETACDX) chiral column (25 m × 0.25 mm ID, 0.25 μm film) for 1,2-dihydronaphthalene. The absolute configuration of the obtained epoxides were determined by measuring the optical rotation with a polarimeter. Absolute configurations were assigned by comparison of the measured [α]D20 values with those reported in the literature [43]. 1H-NMR characterizations of Compounds 2 and 4 are according to those reported in the literature [15].

3.2. DOSY Measurements

The DOSY technique provides information about the size of the molecular aggregate in solution. In fact, by means of the Stokes–Einstein equation, the diffusion coefficient of the CTABr can be converted into its hydrodynamic radius Rh, and this value can be compared with the calculated radius obtained by the Hyperchem-minimized structure of the surfactant (in the maximum extension, CTABr is ca. 2 nm, leading a micellar aggregates of ca. 4 nm of diameter). Thus, combining the diffusion coefficient of the CTABr (D = 1.20 × 10−10 m2 s−1) with the viscosity of D2O at 298 K in the Stokes–Einstein equation (R = kBT/6πηD, where kB is the Boltzmann constant, T is the absolute temperature, and η is the viscosity of D2O at 298 K (0.85 cP)), a hydrodynamic radius Rh(exp) = 2.15 nm was obtained. The same treatment for the nanoreactor containing CTABr and 1-Mn give a Rh(exp) = 2.21 nm.

3.3. Synthesis and Characterization

Synthesis of the aldehyde 2. An amount of 0.720 mL (8.6 mmol) of aqueous formaldehyde and 9 mL of HCl conc. were added to 1 g (5.61 mmol) of the 3-tBut-salicylaldehyde. The mixture was stirred at 90 °C for 16 h. The reaction was cooled to room temperature, obtaining a precipitate. Diethyl ether was added to the aqueous solution, extracted, and dried with Na2SO4. Evaporation of the solvent afforded Compound 2 (yield 95%). 1H-NMR (500 MHz, CDCl3) δ 11.85 (s, 1H, OH), 9.87 (s, 1H, CHO), 7.53 (d, J = 2.5 Hz, 1H, ArH), 7.44 (d, J = 2.5 Hz, 1H, ArH), 4.59 (s, 2H, –CH2Cl), 1.43 (s, 9H, Ar–CH3). Anal. Calcd. For C12H15ClO2: C, 63.58; H, 6.67; Cl, 15.64. Found C, 63.51; H, 6.62; Cl, 15.58.
Synthesis of the aldehyde 3. Tetradecanol (629 mg, 2.95 mmol) was dissolved in 25 mL of acetonitrile dry, and 118 mg (2.95 mmol) of NaOH was added. The mixture was heated at 70 °C for 4 h, and 700 mg (3.10 mmol) of the aldehyde 2, dissolved in 15 mL of acetonitrile dry, were then added dropwise in 1 h. The reaction was stirred at 70 °C overnight under nitrogen. Then, the solvent was removed under reduced pressure, and the crude product was dissolved in CH2Cl2 and washed with water. The organic phase was dried with Na2SO4 and purified by column chromatography (n-hexane/EtOAc 98/2) affording the pure Compound 3 as oil (yield 32%). 1H-NMR (500 MHz, CDCl3) δ 11.76 (s, 1H, OH), 9.87 (s, 1H, CHO), 7.49 (d, J = 2.0 Hz, 1H, ArH), 7.37 (d, J = 2.0 Hz, 1H, ArH), 4.44 (s, 2H, Ar–CH2–O), 3.48 (t, J = 6.5 Hz, 2H, O–CH2–CH2–), 1.62 (m, 2H, O–CH2CH2–), 1.42 (s, 9H, Ar–CH3), 1.25–1.30 (m, 22H, O–CH2–CH2(CH2)11–CH3), 0.88 (t, J = 7.5 Hz, 3H, O–CH2–CH2–(CH2)11CH3). 13C-NMR (125 MHz, CDCl3) δ 197.0, 160.7, 138.3, 133.9, 130.9, 129.3, 120.3, 72.2, 70.7, 34.8, 31.9, 29.7, 29.66, 29.61, 29.47, 26.34, 29.2. ESI-MS m/z 405.3 [M + H]+. Anal. Calcd. For C26H44O3: C, 77.18; H, 10.96. Found C, 77.09; H, 10.89.
Synthesis of the choline iodide 4. A suspension containing 2 g (32.7 mmol) of ethanolamine, 9 g (65.4 mmol) of K2CO3 anhydrous, and 23.11 g (163 mmol) of CH3I in 25 mL of acetonitrile dry was stirred vigorously overnight at 65 °C under nitrogen. Then, reaction was filtered to remove the base, and solvent was removed under reduced pressure to yield pure hypermethylated Compound 4 (yield 98%).1H-NMR (500 MHz, D2O) δ 4.10 (m, 2H, OH–CH2–), 3.56 (t, J = 5.0 Hz, 2H, –CH2–N), 3.25 (s, 9H, N(CH3)3). Anal. Calcd. For C5H14INO: C, 25.99; H, 6.11; N, 6.06. Found C, 25.91; H, 6.03; N, 6.01.
Synthesis of the choline-aldehyde 5. Choline iodide 4 (459 mg, 1.98 mmol) was dissolved under nitrogen in 40 mL of acetonitrile dry. Then, 79 mg (1.98 mmol) of NaOH was added, and the mixture was stirred at 70 °C for 3 h. Then, a solution of the aldehyde 2 (463 mg, 2.05 mmol, in 25 mL of acetonitrile dry) was added dropwise in 1 h. The reaction was stirred under nitrogen overnight at 70 °C. The reaction was monitored by TLC following the disappearance of the starting aldehyde 2. The reaction was cooled to room temperature, the solvent was removed under reduced pressure, and Compound 5 (yield 31%) was purified by alumina column (from CH2Cl2 100% to CH2Cl2/CH3OH 95/5). 1H-NMR (500 MHz, CDCl3) δ 11.87 (s, 1H, OH), 9.91 (s, 1H, CHO), 7.45 (d, J = 2.0 Hz, 1H, ArH), 7.43 (d, J = 2.0 Hz, 1H, ArH), 4.56 (m, 2H, –CH2–N(CH3)3), 4.00 (m, 4H, Ar–CH2–O and O–CH2–CH2–), 3.44 (s, 9H, N(CH3)3), 1.42 (s, 9H, Ar-CH3). 13C-NMR (125 MHz, DMSO-d6) 109.81, 160.71, 136.95, 129.17, 128.80, 122.16, 117.74, 66.94, 55.14, 53.20, 45.71, 22.52, 14.39. ESI-MS m/z 294.2 [M]+. Anal. Calcd. For C17H28INO3: C, 48.46; H, 6.70; N, 3.32. Found C, 48.41; H, 6.62; N, 3.28.
Synthesis of the aldehyde 7. To a solution of 190 mg (0.766 mmol) of (1R,2R)-diphenyl-ethylendiamino-monochloride 6 [27,28] dissolved in 20 mL of a mixture 50/50 of methanol/ethanol was added dropwise 299 mg (0.740 mmol) of aldehyde 3, dissolved in 10 mL of the same solvent mixture. The reaction was stirred at room temperature for 24 h. Then, the solvent was removed under reduced pressure, and the crude product was washed with a few milliliters of water to remove the starting reagent 6 and filtered, yielding Compound 7 (yield 98%). 1H-NMR (500 MHz, DMSO-d6) δ 13.36 (s, 1H, OH), 8.74 (s, 1H, CHN), 8.55 (s br, 3H, NH3), 7.36 (m, 2H, ArH), 7.19–7.29 (m, 10H, ArH), 5.03 (d, J = 10 Hz, 1H, CH methine), 4.88 (d, J = 10.0 Hz, 1H, CH methine), 4.35 (s, 2H, Ar–CH2–O), 3.36 (t, J = 6.0 Hz, 2H, O–CH2–CH2–), 1.48 (m, 2H, O–CH2CH2–), 1.38 (s, 9H, ArCH3), 1.19–1.26 (m, 22H, O–CH2–CH2(CH2)11–CH3), 0.82 (t, J = 6.5 Hz, 3H, O–CH2–CH2–(CH2)11CH3). 13C-NMR (125 MHz, DMSO-d6) 156.83, 138.65, 133.68, 129.185, 128.98, 128.54, 128.48, 128.02, 126.74, 68.29, 60.73, 57.19, 36.55, 32.55, 31.29, 29.82, 29.01, 28.70, 25.71, 25.51, 22.10, 13.96. ESI-MS m/z 599.7 [M]+. Anal. Calcd. For C40H59ClN2O2: C, 75.62; H, 9.36; N, 4.41. Found: C, 75.54; H, 9.27; N, 4.32.
Synthesis of 1. To a solution of ethanol (30 mL) containing 270 mg (0.641 mmol) of 5 and 406 mg (0.641 mmol) of 7, 190 µL of triethylamine were added slowly. The mixture was stirred at room temperature overnight. The solvent was then removed under reduced pressure. The salen (1) (yield 67%) was purified by a neutral alumina column (CH2Cl2 containing 5% CH3OH). 1H-NMR (500 MHz, CDCl3) δ 13.93 (s, 1H, OH), 13.75 (s, 1H, OH), 8.38 (s, 1H, CHN), 8.34 (s, 1H, CHN), 7.14–7.24 (m, 12H, ArH), 6.97 (m, 2H, ArH), 4.75 (m, 2H, CH methine), 4.39 (s, 2H, Ar–CH2–O), 4.31 (s, 2H, Ar–CH2–O), 3.93 (m, 2H, –CH2–N(CH3)3, 3.86 (m, 2H, O–CH2–CH2–N(CH3)3), 3.43 (t, J = 6.5 Hz, 2H, O–CH2–CH2–), 3.38 (s, 9H, N(CH3)3), 1.60 (m, 2H, O–CH2CH2–), 1.42 (s, 18H, Ar–CH3), 1.25–1.30 (m, 22H, O–CH2–CH2(CH2)11–CH3), 0.88 (t, J = 7.5 Hz, 3H, O–CH2–CH2–(CH2)11CH3). 13C-NMR (125 MHz, CDCl3) δ 166.73, 166.36, 139.30, 130.00, 129.81, 129.73, 129.62, 128.38, 127.96, 127.63, 79.99, 73.60, 72.69, 70.50, 63.50, 54.92, 45.87, 31.91, 29.67, 29.29, 26.21, 22.68, 15.49, 14.11, 8.60. ESI-MS m/z 874.7 [M]+. Anal. Calcd. For C57H84IN3O4: C, 68.31; H, 8.45; N, 4.19. Found: C, 68.22; H, 8.36; N, 4.10.
Synthesis of 1-Mn. In a round bottom flask containing 430 mg (0.430 mmol) of the salen 1 dissolved in 15 mL of absolute ethanol, 171 mg (0.643 mmol) of manganese (III) acetate dehydrate were added. The mixture was stirred at room temperature overnight. The solvent was then removed under reduced pressure, and the crude product was dissolved in CH2Cl2 and filtered to remove the excess of manganese (III) acetate. Evaporation of the solvent afforded 1-Mn as a brown precipitate (yield 98%). ESI-MS m/z 927.5 [M]+. Anal. Calcd. For C59H72IMnN3O6: C, 64.36; H, 6.59; N, 3.82. Found: C, 64.30 H, 6.51; N, 3.75.
Enantioselective epoxidation in the nanoreactor. In a typical run, alkene and n-dodecane (internal standard) were added to a stirred solution of surfactant and the catalyst 1-Mn in distilled water (1 mL) and phosphate buffer (1 mL, 0.05 M Na2HPO4 at pH 11.2); after the complete solubilization, NaClO was added dropwise (5 µL/10 min) to the mixture and the reaction was kept in a round-bottom flask at 25 °C in a thermostatic bath. After a certain reaction time, the aqueous solution was extracted with 1 mL of CH2Cl2. Combined organic extracts were dried over anhydrous MgSO4, reduced to a small volume, and analyzed by GC as described above.

4. Conclusions

A new surfactant catalyst, containing a chiral Mn–salen framework, able to catalyze in water enantioselective epoxidation of non-functionalized alkenes, is here presented. Epoxidation reactions were carried out into micellar systems, containing also a commercial surfactant (CTABr), thus forming the first nanoreactor able to achieve enantioselectivity in water. The epoxidation reactions with 6-CN-2,2-dimethylchromene and 1,2-dihydronaphthalene exhibited excellent results, with high conversions and enantioselectivity values. The structure of the surfactant catalyst likely plays a crucial role: in particular, the position of the catalytic metal center with respect to the micellar aggregate leads to different reactivities toward different alkenes. We are working on optimizing the nanoreactor structure: in particular, we believe that the length of the aliphatic moiety of the catalyst is crucial for improving the reactivity of aliphatic alkenes (e.g., cis-β-ethylstyrene).

Supplementary Materials

The following are available online at https://www.mdpi.com/2073-4344/8/4/129/s1: NMR, gCOSY, and ESI-MS spectra.

Acknowledgments

Dedicated to Prof. Gaetano A. Tomaselli in occasion of his retirement. This work was supported by the University of Catania—Department of Chemical Science (Piano per la Ricerca—Linea Intervento 2).

Author Contributions

F.P.B. and G.T.S. conceived and designed the experiments; G.T.S. and S.S. performed the synthesis; C.M.A.G., R.M.T., and R.P. performed the epoxidation experiments; A.P. and M.E.A. analyzed the data; G.T.S. wrote the paper.

Conflicts of Interest

The authors declare no conflict of interest.

References and Notes

  1. Welton, T. Solvents and sustainable chemistry. Proc. Math. Phys. Eng. Sci. 2015, 471, 20150502. [Google Scholar] [CrossRef] [PubMed]
  2. Gangemi, C.M.A.; Pappalardo, A.; Trusso Sfrazzetto, G. Applications of supramolecular capsules derived from resorcin[4]arenes, calix[n]arenes and metalloligands: From biology to catalysis. RSC Adv. 2015, 5, 51919–51933. [Google Scholar] [CrossRef]
  3. Kitanosono, T.; Masuda, K.; Xu, P.; Kobayashi, S. Catalytic Organic Reactions in Water toward Sustainable Society. Chem. Rev. 2018, 118, 679–746. [Google Scholar] [CrossRef] [PubMed]
  4. Cotanda, P.; Lu, A.; Patterson, J.P.; Petzetakis, N.; O’Reilly, R.K. Functionalized Organocatalytic Nanoreactors: Hydrophobic Pockets for Acylation Reactions in Water. Macromolecules 2012, 45, 2377–2384. [Google Scholar] [CrossRef]
  5. Scarso, A. Micellar Nanoreactor. In Encyclopedia of Inorganic and Bioinorganic Chemistry; John Wiley & Sons Ltd.: Chichester, UK, 2016; pp. 1–16. [Google Scholar] [CrossRef]
  6. Hou, S.; Xie, C.; Yu, F.; Yuan, B.; Yu, S. Selective hydrogenation of α-pinene to cis-pinane over Ru nanocatalysts in aqueous micellar nanoreactors. RSC Adv. 2016, 6, 54806–54811. [Google Scholar] [CrossRef]
  7. Lee, L.-C.; Lu, J.; Weck, M.; Jones, C.W. Acid−Base Bifunctional Shell Cross-Linked Micelle Nanoreactor for One-Pot Tandem Reaction. ACS Catal. 2016, 6, 784–787. [Google Scholar] [CrossRef]
  8. Vriezema, D.M.; Aragones, M.C.; Elemans, J.A.A.W.; Cornelissen, J.J.L.M.; Rowan, A.E.; Nolte, R.J.M. Self-Assembled Nanoreactors. Chem. Rev. 2005, 105, 1445–1489. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  9. Baleizão, C.; Garcia, H. Chiral Salen Complexes:  An Overview to Recoverable and Reusable Homogeneous and Heterogeneous Catalysts. Chem. Rev. 2006, 106, 3987–4043. [Google Scholar] [CrossRef] [PubMed]
  10. Jacobsen, E.N. Catalytic Asymmetric Synthesis; Ojima, I., Ed.; VCH: Weinheim, Germany, 1993; Chapter 4.2; pp. 159–202. [Google Scholar]
  11. Yoon, T.P.; Jacobsen, E.N. Privileged Chiral Catalysts. Science 2003, 299, 1691–1693. [Google Scholar] [CrossRef] [PubMed]
  12. Arends, I.W.E.E. Metal-Catalyzed Asymmetric Epoxidations of Terminal Olefins Using Hydrogen Peroxide as the Oxidant. Angew. Chem. Int. Ed. 2006, 45, 6250–6252. [Google Scholar] [CrossRef] [PubMed]
  13. McMorn, P.; Hutchings, G.J. Heterogeneous enantioselective catalysts: Strategies for the immobilisation of homogeneous catalysts. Chem. Soc. Rev. 2004, 33, 108–122. [Google Scholar] [CrossRef] [PubMed]
  14. Shi, Z.-H.; Li, N.-G.; Shi, Q.-P.; Tang, Y.-P.; Tang, H.; Shen, M.-Z.; Duan, J.-A. Immobilization of Chiral Manganese(III)-salen Complexes for Enantioselective Epoxidation of Unfunctionalised Olefins. Curr. Org. Synth. 2014, 11, 204–243. [Google Scholar] [CrossRef]
  15. La Paglia Fragola, V.; Lupo, F.; Pappalardo, A.; Trusso Sfrazzetto, G.; Toscano, R.M.; Ballistreri, F.P.; Tomaselli, G.A.; Gulino, A. A surface-confined O=MnV(salen) oxene catalyst and high turnover values in asymmetric epoxidation of unfunctionalized olefins. J. Mater. Chem. 2012, 22, 20561–20565. [Google Scholar] [CrossRef]
  16. Trusso Sfrazzetto, G.; Millesi, S.; Pappalardo, A.; Toscano, R.M.; Ballistreri, F.P.; Tomaselli, G.A.; Gulino, A. Olefin epoxidation by a (salen)Mn(III) catalyst covalently grafted on glass beads. Catal. Sci. Technol. 2015, 5, 673–679. [Google Scholar] [CrossRef]
  17. Ballistreri, F.P.; Brinchi, L.; Germani, R.; Savelli, G.; Tomaselli, G.A.; Toscano, R.M. Enantioselective epoxidations of alkenes catalyzed by (salen)Mn(III) in aqueous surfactant systems. Tetrahedron 2008, 64, 10239–10243. [Google Scholar] [CrossRef]
  18. Ballistreri, F.P.; Gangemi, C.M.A.; Pappalardo, A.; Tomaselli, G.A.; Toscano, R.M.; Trusso Sfrazzetto, G. (Salen)Mn(III) Catalyzed Asymmetric Epoxidation Reactions by Hydrogen Peroxide in Water: A Green Protocol. Int. J. Mol. Sci. 2016, 17, 1112–11121. [Google Scholar] [CrossRef] [PubMed]
  19. Bérubé, C.; Barbeau, X.; Lagüe, P.; Voyer, N. Revisiting the Juliá-Colonna Enantioselective Epoxidation: Supramolecular Catalysis in Water. Chem. Commun. 2017, 53, 5099–5102. [Google Scholar] [CrossRef] [PubMed]
  20. Malkov, A.V.; Czemerys, L.; Malyshev, D.A. Vanadium-Catalyzed Asymmetric Epoxidation of Allylic Alcohols in Water. J. Org. Chem. 2009, 74, 3350–3355. [Google Scholar] [CrossRef] [PubMed]
  21. Colladon, M.; Scarso, A.; Strukul, G. Towards a Greener Epoxidation Method: Use of Water-Surfactant Media and Catalyst Recycling in the Platinum-Catalyzed Asymmetric Epoxidation of Terminal Alkenes with Hydrogen Peroxide. Adv. Synth. Catal. 2007, 349, 797–801. [Google Scholar] [CrossRef]
  22. Li, J.; Hu, F.; Xie, X.-K.; Liu, F.; Huang, Z.-Z. Synthesis of new functionalized chiral ionic liquid and its organocatalytic asymmetric epoxidation in water. Catal. Commun. 2009, 11, 276–279. [Google Scholar] [CrossRef]
  23. Prasad, S.; Achazi, K.; Bottcher, C.; Haag, R.; Sharma, S.K. Fabrication of nanostructures through self-assembly of non-ionic amphiphiles for biomedical applications. RSC Adv. 2017, 7, 22121–22132. [Google Scholar] [CrossRef]
  24. Morotti, T.; Calabrese, V.; Cavazzini, M.; Pedron, D.; Cozzuol, M.; Licciardello, A.; Tuccitto, N.; Quici, S. Zirconium phosphate/phosphonate multilayered films based on push–pull stilbazolium salt: Synthesis, characterization and second harmonic generation. Dalton Trans. 2008, 2974–2982. [Google Scholar] [CrossRef] [PubMed]
  25. Tuccitto, N.; Giamblanco, N.; Licciardello, A.; Marletta, G. Patterning of lactoferrin using functional SAMs of iron complexes. Chem. Commun. 2007, 2621–2623. [Google Scholar] [CrossRef] [PubMed]
  26. Gulino, A.; Trusso Sfrazzetto, G.; Millesi, S.; Pappalardo, A.; Tomaselli, G.A.; Ballistreri, F.P.; Toscano, R.M.; Fragalà, L. Nerve Gas Simulant Sensing by an Uranyl–Salen Monolayer Covalently Anchored on Quartz Substrates. Chem. Eur. J. 2017, 23, 1576–1583. [Google Scholar] [CrossRef]
  27. Ballistreri, F.P.; Condorelli, G.G.; Fragalà, I.; Motta, A.; Pappalardo, A.; Tomaselli, G.A.; Tudisco, C.; Trusso Sfrazzetto, G. Covalent functionalization of silicon surfaces with cavitand-modified salen. Eur. J. Inorg. Chem. 2011, 2124–2131. [Google Scholar] [CrossRef]
  28. Amato, M.E.; Ballistreri, F.P.; D’Agata, S.; Pappalardo, A.; Tomaselli, G.A.; Toscano, R.M.; Trusso Sfrazzetto, G. Enantioselective Molecular Recognition of Chiral Organic Ammonium Ions and Amino Acids Using Cavitand–Salen Based Receptors. Eur. J. Org. Chem. 2011, 5674–5680. [Google Scholar] [CrossRef]
  29. Kleij, A.W. Nonsymmetrical Salen Ligands and Their Complexes: Synthesis and Applications. Eur. J. Inorg. Chem. 2009, 193–205. [Google Scholar] [CrossRef]
  30. Pappalardo, A.; Amato, M.E.; Ballistreri, F.P.; Tomaselli, G.A.; Toscano, R.M.; Trusso Sfrazzetto, G. Pair of Diastereomeric Uranyl Salen Cavitands Displaying Opposite Enantiodiscrimination of α-Amino Acid Ammonium Salts. J. Org. Chem. 2012, 77, 7684–7687. [Google Scholar] [CrossRef] [PubMed]
  31. D’Urso, A.; Tudisco, C.; Ballistreri, F.P.; Condorelli, G.G.; Randazzo, R.; Tomaselli, G.A.; Toscano, R.M.; Trusso Sfrazzetto, G.; Pappalardo, A. Enantioselective extraction mediated by a chiral cavitand–salen covalently assembled on a porous silicon surface. Chem. Commun. 2014, 50, 4993–4996. [Google Scholar] [CrossRef] [PubMed]
  32. Ballistreri, F.P.; Pappalardo, A.; Toscano, R.M.; Tomaselli, G.A.; Trusso Sfrazzetto, G. A New Heteroditopic Chiral Uranyl–Salen Receptor for Molecular Recognition of Amino Acid Ammonium Salts. Eur. J. Org. Chem. 2010, 20, 3806–3810. [Google Scholar] [CrossRef]
  33. Pappalardo, A.; Ballistreri, F.P.; Li Destri, G.; Mineo, P.G.; Tomaselli, G.A.; Toscano, R.M.; Trusso Sfrazzetto, G. Supramolecular Polymer Networks Based on Calix[5]arene Tethered Poly(p-phenyleneethynylene). Macromolecules 2012, 45, 7549–7556. [Google Scholar] [CrossRef]
  34. Giuffrida, M.L.; Rizzarelli, E.; Tomaselli, G.A.; Satriano, C.; Trusso Sfrazzetto, G. A novel fully water-soluble Cu(I) probe for fluorescence live cell imaging. Chem. Commun. 2014, 50, 9835–9838. [Google Scholar] [CrossRef] [PubMed]
  35. Tuccitto, N.; Trusso Sfrazzetto, G.; Gangemi, C.M.A.; Ballistreri, F.P.; Toscano, R.M.; Tomaselli, G.A.; Pappalardo, A.; Marletta, G. Memory-Driven Order-Disorder Transition of 3D-Supramolecular Architecture Based on Calix[5]arene and Porphyrin Derivatives. Chem. Commun. 2016, 52, 11681–11684. [Google Scholar] [CrossRef] [PubMed]
  36. Puglisi, R.; Ballistreri, F.P.; Gangemi, C.M.A.; Toscano, R.M.; Tomaselli, G.A.; Pappalardo, A.; Trusso Sfrazzetto, G. Chiral Zn–salen complexes: A new class of fluorescent receptors for enantiodiscrimination of chiral amines. New J. Chem. 2017, 41, 911–915. [Google Scholar] [CrossRef]
  37. Kurti, L.; Blewett, M.M.; Corey, E.J. Origin of Enantioselectivity in the Jacobsen Epoxidation of Olefins. Org. Lett. 2009, 11, 4592–4595. [Google Scholar] [CrossRef] [PubMed]
  38. Bulman Page, P.C.; Chan, Y.; Armylisas, A.H.N.; Alahmdi, M. Asymmetric epoxidation of chromenes mediated by iminium salts: Synthesis of mollugin and (3S,4R)-trans-3,4-dihydroxy-3,4-dihydromollugin. Tetrahedron 2016, 72, 8406–8416. [Google Scholar] [CrossRef]
  39. Epoxidation reactions with 6-CN-2,2-dimethylchromene, 1,2-dihydronaphthalene and cis-β-ethylstyrene were carried out also without phosphate buffer (in the same condition of entry 4, 9 and 17 reported in Table 1), obtaining the same results of conversion and enantiomeric excess measured in the presence of phosphate buffer.
  40. We performed epoxidation of 6-CN-2,2-dimethylchromene without 1-Mn, with CTABr = [0.06], [alkene] = [NaClO] = 1.17 × 10−2 M, 0.05 M Na2HPO4 at pH 11.2, obtaining a conversion of 52% after 1 h, and 100% after 6 h; with 1,2-dihydronaphthalene, with the same conditions, conversion value was 38% after 1 h and 100% after 12 h while with cis-β-ethylstyrene we observed 47% of conversion after 1 h and 100 after 8 h.
  41. Van Aken, K.; Strekowski, L.; Patiny, L. EcoScale, a semi-quantitative tool to select an organic preparation based on economical and ecological parameters. Beilstein J. Org. Chem. 2006. [Google Scholar] [CrossRef] [PubMed]
  42. Gałuszka, A.; Konieczka, P.; Migaszewski, Z.M.; Namiesnik, J. Analytical Eco-Scale for assessing the greenness of analytical procedures. Trends Anal. Chem. 2012, 37, 61–72. [Google Scholar] [CrossRef]
  43. Scheurer, A.; Mosset, P.; Spiegel, M.; Saalfrank, R.W. Reverse asymmetric catalytic epoxidation of unfunctionalized alkenes. Tetrahedron 1999, 55, 1063–1078. [Google Scholar] [CrossRef]
Figure 1. Schematic representation of the micellar nanoreactor and chemical structure of the catalyst 1-Mn and CTABr.
Figure 1. Schematic representation of the micellar nanoreactor and chemical structure of the catalyst 1-Mn and CTABr.
Catalysts 08 00129 g001
Scheme 1. Synthesis of catalyst 1-Mn.
Scheme 1. Synthesis of catalyst 1-Mn.
Catalysts 08 00129 sch001
Figure 2. Enantiomeric excess (E.E.) variations and conversion values measured after 3 h by recycling 1-Mn in the epoxidation of 1,2-dihydronaphthalene. Reaction conditions are reported in Entry 9 of Table 1.
Figure 2. Enantiomeric excess (E.E.) variations and conversion values measured after 3 h by recycling 1-Mn in the epoxidation of 1,2-dihydronaphthalene. Reaction conditions are reported in Entry 9 of Table 1.
Catalysts 08 00129 g002
Table 1. Enantioselective epoxidation of 6-CN-2,2-dimethylchromene, 1,2-dihydronaphthalene, and cis-β-ethylstyrene with NaClO catalyzed by micellar nanoreactor containing 1-Mn and CTABr in H2O at 25 °C a.
Table 1. Enantioselective epoxidation of 6-CN-2,2-dimethylchromene, 1,2-dihydronaphthalene, and cis-β-ethylstyrene with NaClO catalyzed by micellar nanoreactor containing 1-Mn and CTABr in H2O at 25 °C a.
AlkeneEntry[CTABr] (M)1-Mn (%) bTime (h)e.e. (%) cConv. (%) c
Catalysts 08 00129 i00110.035183 e85
20.035382 e100
30.065183 e87
40.065383 e100
Catalysts 08 00129 i00250.035183 f17
60.035882 f46
70.0310884 f64
80.0610180 f76
90.0610383 f100
Catalysts 08 00129 i003100.035150 g73
110.035251g100
12 d0.01510156 g88
13 d0.01510457 g100
14 d0.0310156 g86
15 d0.0310458 g100
16 d0.0610158 g85
17 d0.0610457 g100
a In all experiments [alkene] = [NaClO] =1.17 × 10−2 M, buffered with 1 mL of 0.05 M Na2HPO4 at pH 11.2 in a total volume of 2 mL [39]. b referred to the alkene concentration. c Enantiomeric Excess (e.e.) and Conversion values (Conv.) were determined by Gas chromatographic (GC) analysis using a chiral column (see Section 3) and n-dodecane as internal standard. d NaClO was added dropwise in 1 h. e config. (3R,4S) determined by measuring the optical rotation. f config. (1R,2S) determined by measuring the optical rotation. g Enantiomeric excess (e.e.) value is referred to the to the major cis epoxide (cis/trans = 4).

Share and Cite

MDPI and ACS Style

Ballistreri, F.P.; Toscano, R.M.; Amato, M.E.; Pappalardo, A.; Gangemi, C.M.A.; Spidalieri, S.; Puglisi, R.; Trusso Sfrazzetto, G. A New Mn–Salen Micellar Nanoreactor for Enantioselective Epoxidation of Alkenes in Water. Catalysts 2018, 8, 129. https://doi.org/10.3390/catal8040129

AMA Style

Ballistreri FP, Toscano RM, Amato ME, Pappalardo A, Gangemi CMA, Spidalieri S, Puglisi R, Trusso Sfrazzetto G. A New Mn–Salen Micellar Nanoreactor for Enantioselective Epoxidation of Alkenes in Water. Catalysts. 2018; 8(4):129. https://doi.org/10.3390/catal8040129

Chicago/Turabian Style

Ballistreri, Francesco P., Rosa Maria Toscano, Maria Emanuela Amato, Andrea Pappalardo, Chiara M. A. Gangemi, Sofia Spidalieri, Roberta Puglisi, and Giuseppe Trusso Sfrazzetto. 2018. "A New Mn–Salen Micellar Nanoreactor for Enantioselective Epoxidation of Alkenes in Water" Catalysts 8, no. 4: 129. https://doi.org/10.3390/catal8040129

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop