Selective monosulfoxidation of tetrathiafulvalenes into chiral TTF‐sulfoxides

Abstract

Four inner tetrathiafulvalene-sulfoxides have been synthesized upon reaction of tetrathiafulvalene (TTF), tetramethyl-tetrathiafulvalene (TMTTF), tetrakis (thiomethyl)-tetrathiafulvalene (TMT-TTF), and bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) with enantiopure (+) or (-)-(8,8-dichlorocamphorylsulfonyl)-oxaziridine as oxidizing agent. Chiral HPLC studies indicate very weak enantioselectivities for TTF-SO 3 and TMTTF-SO 4, formation of racemic mixture in the case of TMT-TTF-SO 5, and a rather good selectivity, up to 44% ee, in the case of BEDT-TTF-SO 1. The solid state structures of TMTTF-SO 4 and TMT-TTF-SO 5 have been determined by single crystal X-ray diffraction. Both compounds crystallize as racemates in the centrosymmetric triclinic space group P-1. Theoretical calculations at DFT/B3LYP/6-31+G* level afford optimized geometries in good accordance with the experimental structures and emphasize the participation of the chiral sulfoxide group in HOMO and LUMO. Time-dependent DFT calculations corroborated with electronic circular dichroism spectra allow the assignment of the absolute configuration (R) for the major enantiomer of 1 when the (+)-sulfonyl-oxaziridine is used as oxygen transfer reagent. Preliminary semipreparative HPLC separation provided enantioenriched fractions up to 63% ee.

Regioselective synthesis of chiral dimethyl-bis(ethylenedithio)tetrathiafulvalene sulfones

“…The S=O bond lengths have values of 1.396(5) Å for S2=O1 and 1.380(5) Å for S2=O2, which are somewhat shorter than the usual values of 1.43–1.44 Å reported in the literature [ 30 – 32 ] ( Table 1 ). Moreover, these S=O bonds are shorter when compared to those in inner TTF sulfoxides [ 27 – 28 ], yet the same feature was already observed in other sulfoxide/sulfone series [ 30 – 31 ]. The central C7=C8 bond measures 1.346(6) Å, which is a typical value for a neutral donor.…”

“…In our previous studies dealing with the sulfoxidation of the BEDT-TTF donor we could selectively obtain the inner BEDT-TTF sulfoxide ( Scheme 1 ) by using chiral sulfonyl-oxaziridines as oxidizing agent [ 27 – 28 ]. However, the inner BEDT-TTF sulfoxide was shown to be of only limited interest as precursor for molecular conductors, since it does not reversibly oxidize into a radical cation.…”

“…One of the possibilities hardly addressed so far in TTF chemistry is the oxidation of the sulfur atoms into sulfoxides or sulfones. Indeed, only two reports deal with the oxidation of BEDT-TTF into BEDT-TTF monosulfoxides ( Scheme 1 ), along with enantioselectivity issues [ 27 – 28 ]. We describe herein the synthesis, characterization and solid-state structures of the ( S , S ) and ( R , R ) enantiomers of DM-BEDT-TTF monosulfones 1 ( Scheme 1 ).…”

Tetramethyl‐Bis(ethylenedithio)‐Tetrathiafulvalene (TM‐BEDT‐TTF) Revisited: Crystal Structures, Chiroptical Properties, Theoretical Calculations, and a Complete Series of Conducting Radical Cation Salts

“…4 The access to a large library of chiral precursors is thus of paramount importance, and, accordingly, several families of TTFs, in which the chiral information has been addressed in different ways, have been described. 1 For example, derivatives with stereogenic carbon atoms such as bis(ethylenedithio)-tetrathiafulvalenes (BEDT-TTF), 5,6 TTF-oxazolines [7][8][9][10][11][12] and bis(oxazolines), 13,14 bis(pyrrolo)-TTFs, 15 C 3 symmetric tris(TTF) affording supramolecular helical aggregates, 16,17 or with stereogenic sulfur atoms in TTF-sulfoxides 18,19 have been reported. Complete series of conducting salts, comprising both enantiomeric and racemic forms, have been prepared by electrocrystallization of EDT-TTF-oxazolines (EDT = ethylenedithio).…”

Order Versus Disorder in Chiral Tetrathiafulvalene‐Oxazoline Radical‐Cation Salts: Structural and Theoretical Investigations and Physical Properties

“…Because the large majority of molecular conductors and superconductors are based on tetrathiafulvalene (TTF) derivatives, [8] a most useful family of organic redox-active molecules, [9] much effort is currently being directed towards the synthesis of enantiopure TTFs [2] with the ultimate goal to produce chiral-conducting materials. Accordingly, several families of chiral TTFs, for example, bis(ethA C H T U N G T R E N N U N G ylA C H T U N G T R E N N U N G enedithio)-tetrathiafulvalene (BEDT-TTF) derivatives, [10] EDT-TTF-oxazolines (EDT = ethylenedithio), [11] EDT-TTF-bis(oxazolines), [12] TTFs with chiral side chains, [13] bisA C H T U N G T R E N N U N G (pyrrolo)-TTFs, [14] and TTF-sulfoxides, [15] have been described (Figure 1). …”