A new C2-symmetric atropisomeric thiophene-based monomer for inherently chiral electroactive materials: synthesis, HPLC resolution, and absolute configuration assignment

Herein, we report on the synthesis and high-performance liquid chromatography (HPLC) resolution of a new atropisomeric C2-symmetry chiral monomer based on the 3,3′-bithiophene core, which was developed to produce novel, inherently oligomeric chiral electroactive materials. The analytical enantioseparation was optimized using the cellulose-type Chiralpak IB-3 column and a mixture of n-hexane–methanol–dichloromethane 90:5:5 (v/v/v) as the mobile phase. During the scale-up of the enantioseparation analytical conditions to a semipreparative level, remarkable deformations in the HPLC profile, such as peak splitting and plateau zones between enantiomeric peaks, were observed. We demonstrate the effects of sample diluent as they relate to distorted peak profiles, as well as provide experimental solutions to prevent the disturbing phenomenon. The optimized chromatographic conditions were exploited to collect milligram amounts of the enantiopure sample, which was submitted to chiroptical and stereochemical characterization studies

TetraPh-Tol-BITIOPO: a new atropisomeric 3,3’-bithiophene based phosphine oxide as organocatalyst in Lewis Base-catalyzed Lewis Acid mediated reactions

A new chiral phosphine oxide based on 3,3’-bithiophene scaffold (tetraPh-Tol-BITIOPO) was synthesized, fully characterized and separated into antipodes through chiral HPLC. This new compound was successfully employed as organocatalyst in Lewis base-catalyzed Lewis acid mediated reactions involving trichlorosilyl compounds. The new atropisomeric catalyst was able to promote the allylation of aldehydes with allyltrichlorosilane in up to 98% yield and up to 96% enantiomeric excess (ee), and the direct aldol reaction to afford β-hydroxy ketones and β-hydroxy thioesters, with good chemical yields and modest stereochemical efficiency. Computational studies helped to elucidate and to rationalize the stereochemical outcome of the reactions catalyzed by TetraPh-Tol-BITIOPO, that was found to favour the formation of the isomer with the opposite absolute configuration in comparison with the products obtained with the previously reported 3,3’-bithiophene-based catalyst

Miniaturized enantioselective tubular devices for the electromechanical wireless separation of chiral analytes

Chirality plays a crucial role in different research fields, ranging from fundamental physico-chemistry to applied aspects in materials science and medicine. In this context, enantioselective loading and pumping of chiral analytes for analysis, separation, and cargo delivery applications is an interesting scientific challenge. Herein, we introduce artificial chiral soft electromechanical pumps based on a bi-layer film built up by electrodepositing polypyrrole and an inherently chiral conducting oligomer at its internal surface. The enantioselective device can be driven by bipolar electrochemistry to act as a pump, allowing the selective loading and separation of different chiral analytes injected as pure enantiomers and in racemic form (i.e., doxorubicin, a chemotherapy drug, limonene, carvone, and a chiral ferrocene). The synergy between wireless electromechanical actuation and inherent enantiodiscrimination features makes these actuators excellent candidates for the controlled handling of chiral molecules in the frame of potential applications ranging from analysis to drug delivery

In Situ Electrochemical Investigations of Inherently Chiral 2,2′-Biindole Architectures with Oligothiophene Terminals

AbstractThe synthesis and characterization of three new inherently chiral N,N′‐dipropyl‐3,3′‐diheteroaryl‐2,2′‐biindole monomers, nicknamed Ind2T4, Ind2T6 and Ind2Ph2T4, which differ in the number of thiophenes as terminals, are reported. In addition to a full monomer characterization, stable electroactive oligomeric films were obtained by electro‐oxidation upon cycling to potentials which activate the thiophene terminals. Cyclic voltammetry, UV‐Vis‐NIR spectroelectrochemistry and in situ conductance measurements show that oligomeric films of Ind2T6 present the best stability and electrochromic switching performance. Enantioselective tests with a chiral ferrocene amine clearly show the potential as chiral selectors for analytical and sensing purposes

Electrocatalytic reduction of bromothiophenes on gold and silver electrodes: An example of synergy in electrocatalysis

The electroreduction of bromothiophenes on Au and Ag provides a striking model of synergy in electrocatalysis, when a second group specifically interacting with the catalytic surface is present besides the reacting one, providing an auxiliary anchoring effect. The high catalytic activity of Ag for bromobenzene reduction is enhanced in the bromothiophene case. Moreover, Au, having for bromobenzene a much lower and less reproducible catalytic effect than Ag on account of the repulsive effect of its very negative surface charge in the working potential range, approaches Ag activity in the case of 2-bromothiophene, where the anchoring S group is adjacent to the Br group to be cleaved. The beneficial anchoring effect is lower when it has to be shared between two Br leaving groups adjacent to the S group, and becomes negligible in the case of a bromide leaving group in 3-position. Keywords: Molecular electrocatalysis, Dissociative electron transfer, Anchoring groups, Bromothiophenes, Gold electrodes, Silver electrode

Chiral Recognition: A Spin‐Driven Process in Chiral Oligothiophene. A Chiral‐Induced Spin Selectivity (CISS) Effect Manifestation

In this paper it is experimentally demonstrated that the electron-spin/molecular-handedness interaction plays a fundamental role in the chiral recognition process. This conclusion is inferred comparing current versus potential (I-V) curves recorded using chiral electrode surfaces, which are obtained via chemisorption of an enantiopure thiophene derivative: 3,3 & PRIME;-bibenzothiophene core functionalized with 2,2 & PRIME;-bithiophene wings (BT2T4). The chiral recognition capability of these chiral-electrodes is probed via cyclic voltammetry measurements, where, Ag nanoparticles (AgNPs) capped with enantiopure BT2T4 (BT2T4@AgNP) are used as the chiral redox probe. Then, the interface handedness is explored by recording spin-polarized I-V curves in spin-dependent electrochemistry (SDE) and magnetic-conductive atomic force microscopy (mc-AFM) experiments. The quality of the interfaces is thoroughly cross-checked using X-ray photoemission spectroscopy, Raman, electrodesorption measurements, which further substantiate the metal(electrode)-sulfur(thiophene) central role in the chemisorption process. Spin-polarization values of about 15% and 30% are obtained in the case of SDE and mc-AFM experiments, respectively

Theoretical insights into the Electronic and Structural Properties of New, Low-band Gap Inherently Chiral Ethylendioxythiophene-based Oligothiophene

In the last years, conjugated oligothiophene macrocycles have attracted increasing scientific interest due to some peculiar properties related to their cyclic structure [1-3]. T. Benincori et al. synthesized the 2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene nicknamed BT2T4 (Figure 1) that represents the first member of a new class of chiral oligothiophenes in which chirality results from a tailored torsion produced in the polyconjugated backbone and not from the presence of stereogenic centres, external to it. Interestingly, the FeCl3 oxidation of the enantiopure BT2T4 produce a mixture of chiral macrocycles, like dimers and trimers. [4] Recently, also thanks to DFT and TD-DFT calculations, we have studied the new monomer BT2E4 in order to investigate the role of the insertion of 3,4-ethylenedioxythiophene (EDOT) units on the electronic and molecular properties of neutral and charged monomer and oligomer species. Furthermore, the electroactive films were evaluated by cyclic voltammetry (CV), UV/vis spectroelectrochemistry and CV coupled with in-situ conductance measurements. [5]Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

3,3\u2032-Bithiophene-Based Chiral Bisphosphine Oxides as Organocatalysts in Silicon-Derived Lewis Acid Mediated Reactions

This account summarizes the development of new biheteroaromatic chiral bisphosphine oxides. 3,3\u2032-Bithiophene-based phosphine oxides (BITIOPOs) have been successfully used as organocatalysts to promote Lewis base catalyzed, Lewis acid mediated stereoselective transformations. These highly electron-rich compounds, in combination with trichorosilyl derivatives (allyltrichlorosilane and silicon tetrachloride), generate hypervalent silicon species that act as chiral Lewis acids in highly diastereo- and enantioselective organic reactions. Several relevant examples related to these applications are discussed in detail. 1 Introduction 2 The BITIOPO Family 3 Enantioselective Opening of Epoxides 4 Enantioselective Allylation of Aldehydes 5 Stereoselective Direct (Double) Aldol-Type Reaction with Ketones 6 Stereoselective Direct Aldol-Type Reaction with Ester Derivatives 7 Conclusions