Autonomous Chiral Microswimmers with Self‐mixing Capabilities for Highly Efficient Enantioselective Synthesis

Abstract

The development of chiral catalysts plays a very important role in various areas of chemical science. Heterogeneous catalysts have the general advantage of allowing a more straightforward separation from the products. One specific case of heterogeneous catalysis is electrocatalysis, being potentially a green chemistry approach. However, a typical drawback is that the redox conversion of molecules occurs only at the electrode/ electrolyte interface, and not in the bulk of the electrolyte. The second limitation is that the electrodes have to be physically connected to a power supply to induce the desired reactions. To circumvent these problems, we propose here a complementary approach by replacing macroscopic electrodes with an ensemble of self-propelled redox active microswimmers. They move autonomously in solution while transforming simultaneously a prochiral starting compound into a specific enantiomer with a very high enantiomeric excess, accompanied by a significantly increased production rate of the favorite enantiomer.

Magnetic field-enhanced redox chemistry on-the-fly for enantioselective synthesis

“…In the transition state the intermediate species is more likely to evolve towards a final enantiomer with the energetically more favorable stereochemistry, as we have already demonstrated in one of our previous studies. 22 The magnetic field enhancement of the redox conversion has been evaluated by comparing the yield of an asymmetric model reaction, the reduction of acetophenone into the enantiomers of phenylethanol, in the absence and in the presence of an orthogonal magnetic field. In the presence of a magnet, the Janus swimmers exhibit well-defined clockwise or anticlockwise motion, with an up to one order of magnitude higher speed.…”

“…[14][15][16] In particular the latter approach presents outstanding enantioselectivity, related to diastereomeric interactions between the chiral oligomer surface and the analyte antipodes in solution, resulting in thermodynamic differences in terms of redox potentials, which allow the preferential conversion of only one of the analyte enantiomers.17,18 This energetic differentiation has been exploited to design unconventional approaches for the electrochemical recognition of chiral probes.19-21 Furthermore, these oligomeric systems were used for the enantioselective conversion of molecules with a prostereogenic carbon-oxygen double bond into the corresponding chiral hydroxyl derivatives via chemistry-on-the-fly. 22 In particular, selfpropelled Zn particles, functionalized with oligomers of 2,2-bis[2-(5,2-bithienyl)]-3,3-bithianaphthene (BT2T4), were employed as mobile microreactors for the enantioselective synthesis of the antipodes of phenyl ethanol and mandelic acid. This approach is based on the coupling of the spontaneous oxidation of Zn in acid media, acting as a source of electrons, and the enantioselective reduction of the prochiral starting compound on the surface of the inherently chiral oligomer.…”

“…[19][20][21] Furthermore, these oligomeric systems were used for the enantioselective conversion of molecules with a prostereogenic carbon-oxygen double bond into the corresponding chiral hydroxyl derivatives via chemistry-onthe-y. 22 In particular, self-propelled Zn particles, functionalized with oligomers of 2,2-bis[2-(5,2-bithienyl)]-3,3-bithianaphthene (BT 2 T 4 ), were employed as mobile microreactors for the enantioselective synthesis of the antipodes of phenylethanol and mandelic acid. This approach is based on the coupling of the spontaneous oxidation of Zn in acidic media, acting as a source of electrons, and the enantioselective reduction of the prochiral starting compound on the surface of the inherently chiral oligomer.…”

Mixed-Linker Chiral 2D Covalent Organic Frameworks with Controlled Layer Stacking for Electrochemical Asymmetric Catalysis

“…Organic electrosynthesis utilizes electrons as reagents and eliminates the need for stoichiometric quantities of chemical oxidants or reductants, which makes it a sustainable synthetic platform for redox reactions. − Asymmetric catalysis, which focuses on manipulating the stereochemistry of organic reactions, has been extensively investigated and is widely acknowledged as one of the most critical research domains in synthetic chemistry. − Therefore, the combination of organic electrosynthesis and asymmetric catalysis holds immense importance. − After Grimshaw and co-workers reported the base-mediated electrochemical reduction of coumarin in 1967, numerous methodologies and strategies, including chiral auxiliaries, solvents, supporting electrolytes, and catalysts, have been employed to carry out enantioselective electrochemical reactions. Nevertheless, the resulting solid electrocatalysts typically suffer unsatisfactory enantioselectivity and/or narrow substrate scopes. − Here, we illustrate that covalent organic frameworks (COFs) containing both redox-active moieties and chiral organocatalysts can be efficient sustainable electrocatalysts for highly enantioselective catalysis.…”

“…4−6 Therefore, the combination of organic electrosynthesis and asymmetric catalysis holds immense importance. 7−9 After Grimshaw and co-workers reported the base-mediated electrochemical reduction of coumarin in 1967, 10 numerous methodologies and strategies, including chiral auxiliaries, 11 solvents, 12 supporting electrolytes, 13 and catalysts, 14 have been employed to carry out enantioselective electrochemical reactions. Nevertheless, the resulting solid electrocatalysts typically suffer unsatisfactory enantioselectivity and/or narrow substrate scopes.…”