Introducing metal-vinyl ruthenium moieties onto [6]helicene results in a significant enhancement of the chiroptical properties due to strong metal-ligand electronic interactions. The electro-active Ru centers allow the achievement of the first purely helicene-based redox-triggered chiroptical switches. A combination of electrochemical, spectroscopic, and theoretical techniques reveals that the helicene moiety is a noninnocent ligand bearing a significant spin density.

Lowering the boom: 3,4,5‐trinitro‐1H‐pyrazole (TNP, see picture) has been prepared by the unexpected nitration of 3,5‐dinitropyrazole with a super‐electrophile generated from 20–30 % sulfuric oleum mixed with nitric acid. The remarkable stability of TNP results from the preservation of the ring geometry and the specific conformation of the nitro group at C4 which confers low acidity on the material.

Enantiopure mono-cycloplatinated-[8]helicene and bis-cycloplatinated-[6]helicene derivatives were prepared through column chromatography combined with crystallization of diastereomeric complexes using a chiral ancillary sulfoxide ligand. The UV-visible spectra, circular dichroism, molar rotations, and (circularly polarized) luminescence activity of these new helical complexes have been examined in detail and analysed with the help of first-principles quantum-chemical calculations.

Electronic circular dichroism and circularly polarized luminescence acid-base switching activity is demonstrated in helicene-bipyridine proligand (1a) and in its “rollover” cycloplatinated derivative (2a). While proligand 1a displays a strong bathochromic shift (>160 nm) of the non polarized and circularly luminescence upon protonation, complex 2a displays slightly stronger emission. This striking different behavior between singlet emission in the organic helicene and triplet emission in the organometallic one is rationalized using theory. The very large bathochromic shift of the emission observed upon protonation of azahelicene-bipyridine 1a was rationalized by the decrease of aromaticity (promoting a charge transfer-type transition rather than a π–π* one) along with an increase of the HOMO-LUMO character of the transition and stabilization of the LUMO level upon protonation.

International audienceEnantiopure metallahelicenes have been prepared by cyclometalation of 2-pyridyl-substituted benzophenanthrenes followed by resolution using chiral HPLC. They are red phosphors at room temperature and their chiroptical properties can be modulated by oxidation of the metal center to the oxidation state IV

This tutorial review describes the self-disproportionation of enantiomers (SDE) of chiral, non-racemic compounds, subjected to chromatography on an achiral stationary phase using an achiral eluent, which leads to the substantial enantiomeric enrichment and the corresponding depletion in different fractions, as compared to the enantiomeric composition of the starting material. The physicochemical background of SDE is a dynamic formation of homo- or heterochiral dimeric or oligomeric aggregates of different chromatographic behavior. This phenomenon is of a very general nature as the SDE has been reported for different classes of organic compounds bearing various functional groups and possessing diverse elements of chirality (central, axial and helical chirality). The literature data discussed in this review clearly suggest that SDE via achiral chromatography might be expected for any given chiral enantiomerically enriched compound. This presents two very important issues for organic chemists. First, chromatographic purification of reaction products can lead to erroneous determination of the stereochemical outcome of catalytic asymmetric reactions and second, achiral chromatography can be used as a new, nonconventional method for optical purifications. The latter has tremendous practical potential as the currently available techniques are limited to crystallization or chiral chromatography. However, a further systematic study of SDE is needed to develop understanding of this phenomenon and to design practical chromatographic separation techniques for optical purification of non-racemic mixtures by achiral-phase chromatography.

For the first time, enantiomerically enriched atropoisomeric furans have been accessed using a central-to-axial chirality conversion strategy. Hence, oxidation of the enantioenriched dihydrofuran precursors gave rise to axially chiral furans with high enantiopurities accounting from excellent conversion percentages (cp) in most cases.

The incorporation of a rhenium atom within an extended helical π-conjugated bi-pyridine system impacts the chiroptical and photophysical properties of the resulting neutral or cationic complexes, leading to the first examples of rhenium-based phosphors that exhibit circularly polarized luminescence.