[n]Helicene derivatives are ortho-annulated, p-conjugated molecules that are endowed with helical chirality.[1] Enantiopure [n]helicenes with n ! 6 can be isolated at room temperature and, owing to their unique conjugated screw-shaped structure, they exhibit outstanding chiroptical properties, such as extremely large optical rotations; [2a-c, f-h] these properties make them appealing functional materials, particularly in nonlinear optics and as waveguides. [2d,e, 3] One important challenge with regard to further expanding the potential of helicenes is to develop synthetic strategies that provide efficient access to a variety of helical frameworks with tunable chiroptical properties.Herein, we describe a straightforward synthetic procedure that generates the first reported examples of helicene derivatives with a transition metal incorporated into their ortho-annulated p-conjugated backbones.[4] This approach fully exploits the versatility of organometallic chemistry, in that: 1) the construction of the helical backbone is achieved using simple, practical ortho-metalation reactions, and 2) structural engineering of the helicene scaffolds can be performed through either undertaking reactions at the incorporated metal center or by varying the nature of the metal. Furthermore, the presence of the metal center provides these helicene-based systems with unusual photophysical properties. Our initial studies employed the platinum(II) ion, which was selected because of its efficient electronic metalligand interactions, its large associated spin-orbit coupling, and its redox properties. These chiral platinum helicenes exhibit chiroptical properties that can be fine-tuned by chemical oxidation of the metal center. Moreover, replacing platinum(II) with other metal ions, such as iridium(III), provides access to original [n]helicene topologies.Cyclometalated complexes between heavy late-transition metals and 2-phenylpyridine ligands [(N^C)M, e.g. M = platinum(II), iridium(III)] are readily accessible organometallic species that exhibit high phosphorescent efficiency.[5] Therefore to prepare our target metallahelicenes, we investigated the ortho-metalation chemistry of 4-(2-pyridyl)-benzo[g]phenanthrenes 1 a-1 c (Scheme 1), which can be prepared using a Suzuki-coupling/Wittig/photocyclization reaction sequence. An X-ray diffraction study of 1 a (see the Supporting Information) revealed a helical curvature (hc, the angle between the terminal helicene rings) of 33.48, [6] a value typical for [4]helicenes.[7a] All attempts to resolve compounds 1 a-1 c using HPLC failed, showing that 1 a-1 c are not configurationally stable at room temperature; this is usually the case for [4]helicene derivatives.[8] Compounds 1 a-1 c were subjected to a classic two-step metalation reaction [5] (Scheme 1), which afforded air-stable platinum(II) complexes 2 a-2 c (yields > 50 %). These results show that ortho-metalation is a powerful synthetic route to this family of helicene derivatives, and it can be used to synthesize these species in large quan...

The combination of physical properties sensitive to molecular chirality in a single system allows the observation of fascinating phenomena such as magnetochiral dichroism (MChD) and circularly polarized luminescence (CPL) having potential applications for optical data readout and display technology. Homochiral monodimensional coordination polymers of Yb III were designed from a 2,15-bis-ethynyl-hexahelicenic scaffold decorated with two terminal 4-pyridyl units. Thanks to the coordination of the chiral organic chromophore to Yb(hfac) 3 units (hfac À = 1,1,1,5,5,5-hexafluoroacetylaconate), efficient NIR-CPL activity is observed. Moreover, the specific crystal field around the Yb III induces a strong magnetic anisotropy which leads to a singlemolecule magnet (SMM) behaviour and a remarkable room temperature MChD. The MChD-structural correlation is supported by computational investigations.

The combination of physical properties sensitive to molecular chirality in a single system allows the observation of fascinating phenomena such as magnetochiral dichroism (MChD) and circularly polarized luminescence (CPL) having potential applications for optical data readout and display technology. Homochiral monodimensional coordination polymers of Yb III were designed from a 2,15-bis-ethynyl-hexahelicenic scaffold decorated with two terminal 4-pyridyl units. Thanks to the coordination of the chiral organic chromophore to Yb(hfac) 3 units (hfac À = 1,1,1,5,5,5-hexafluoroacetylaconate), efficient NIR-CPL activity is observed. Moreover, the specific crystal field around the Yb III induces a strong magnetic anisotropy which leads to a singlemolecule magnet (SMM) behaviour and a remarkable room temperature MChD. The MChD-structural correlation is supported by computational investigations.

Af used p-helical N-heterocyclic carbene (NHC) system was prepared and examined through its diastereoisomerically pure cycloiridiated complexes.T he latter display light-green phosphorescence with unusually long lifetimes and circular polarization that depends on both the helical NHC P/M stereochemistry and the iridium D/L stereochemistry. These unprecedented features are attributed to extended p conjugation within the helical carbenic ligand and efficient helicene-NHC-Ir interaction.Octahedral cyclometalated iridium(III) complexes [1] have attracted attention due to their applications as phosphors in organic light-emitting devices (OLEDs), [2] as well as their biological activity. [3] To date,s everal classes of enantiopure cycloiridiated systems have been reported. [1b,4] As for Ir III complexes bearing N-heterocyclic carbene (NHC) ligands, while few examples have been shown to display deep-blue phosphorescence (a challenging target in the OLED area), [5,6]

Suitably substituted enantioenriched 4-aryl-1,4dihydro-pyridines prepared by an organocatalytic enantioselective Michael addition were oxidized with MnO 2 into axially chiral 4-arylpyridines with central-to-axial chirality conversion. Moderate to complete percentages (cp) were observed, and amodel for the conversion of chirality is discussed.

Differentiation of enantiomers in chromatography requires specific detectors, based on polarimetry or circular dichroism. Their use is limited to chiral HPLC and SFC. We explain the operating principles of the different chiroptical detectors available and stress the influence of working wavelength and mobile phase on the output signal. Current and relevant applications of chiroptical detectors are absolute configuration assignment, measurement of enantiomeric excesses in complex mixtures and determination of elution order. We focus on the reversals of enantiomeric elution order, an important subject for the understanding of the chiral recognition mechanisms. We review the main parameters which can induce a reversal, show the usefulness of chiroptical detectors to easily identify reversals and emphasize the significance of the isoenantioselective temperature. The aim of this chapter is to highlight the valuable information provided by chiroptical detectors to study unusual behaviour in chiral HPLC and SFC, reversals of enantiomeric elution order and exchange phenomena as dynamic chromatography and self-disproportionation on achiral columns.

Semi-preparative resolution of the atropisomers by chiral liquid chromatography and determination of the barriers to rotation has allowed an unequivocal identification of the regioisomers produced by the reaction between N-(2-methoxyphenyl)-N'-(2-methylphenyl)thiourea and α-chloroacetone. Attention is drawn on the potential use of these optically pure atropisomers as new non-biaryl ligands for enantioselective metal catalysis.

Controlling the properties of supramolecular assemblies requires unveiling the specific interactions between their components. In the present work, the catalytic properties and structure of co‐assemblies composed of a benzene‐1,3,5‐tricarboxamide (BTA) ligand coordinated to copper (the soldier) and seven enantiopure BTAs (the sergeants) have been determined. Whatever the sergeant, the enantioselectivity of the reaction is directly proportional to the optical purity of the supramolecular helices. More strikingly, the role played by the sergeant in the co‐assembly process differs significantly: from almost pure intercalator (when it is incorporated in the stacks of the soldier and generates long homochiral helices) to pure chain capper (when it leads to the formation of partly helically biased and short assemblies). The former situation leads to optimal enantioselectivity for the catalytic system under study (58 % ee) while the latter situation leads to very low selectivity (8 % ee). The successful rationalization of this high and unexpected difference is crucial for the development of more efficient catalysts and more elaborate supramolecular systems.