Jeanne Crassous

Chiral transfer in coordination complexes: towards molecular materials

In this critical review we present examples of coordination complexes with efficient chiral transfer determining stereochemistry at the metal centre and throughout the overall molecular assembly. The general features controlling the transmission of chirality are presented. The transfer of chirality are considered here with the special purpose of obtaining a molecular material displaying a particular property or function. Coordination complexes in fields as diverse as chiral luminescent materials, homochiral MOFs, chiral liquid crystals, enantioselective sensors, chiroptical switches, and magnetochiral compounds are presented (162 references).

Metal−Bis(helicene) Assemblies Incorporating π-Conjugated Phosphole-Azahelicene Ligands: Impacting Chiroptical Properties by Metal Variation

The synthesis of phosphole-modified aza[6]helicenes and the complexation of these pi-conjugated ditopic ligands with metallic ions are described. The chiroptical properties of these metal-bis(helicene) assemblies were experimentally evaluated and studied by first-principles theoretical calculations. The results show that the metal impacts the chiroptical properties of these complexes through electronic interactions with the chiral pi-conjugated ligands.

Metallahelicenes: Easily Accessible Helicene Derivatives with Large and Tunable Chiroptical Properties†

Enantiopure 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.

Helicene-based transition metal complexes: synthesis, properties and applications

The coordination and/or organometallic chemistry of π-helicenic ligands is a powerful tool to generate multifunctional molecules displaying optimized chiroptical properties combined with new properties furnished by the metallic center. In this review, we relate the different examples that have been described in this field of research to date.

Progress toward the first observation of parity violation in chiral molecules by high-resolution laser spectroscopy†

Parity violation (PV) effects in chiral molecules have so far never been experimentally observed. To take up this challenge, a consortium of physicists, chemists, theoreticians, and spectroscopists has been established and aims at measuring PV energy differences between two enantiomers by using high-resolution laser spectroscopy. In this article, we present our common strategy to reach this goal, the progress accomplished in the diverse areas, and point out directions for future PV observations. The work of André Collet on bromochlorofluoromethane (1) enantiomers, their synthesis, and their chiral recognition by cryptophanes made feasible the first generation of experiments presented in this article.

Preparation of enantiomerically pure C76 with a general electrochemical method for the removal of Di(alkoxycarbonyl)methano bridges from methanofullerenes: The retro-bingel reaction

Serendipitously discovered during electrochemical investigations on the stability of anion 1, a preparatively useful electrochemical procedure, the retro-Bingel reaction, has been identified as a method for removing di(alkoxycarbonyl)methano bridges from methanofullerenes. This procedure was applied to prepare the first samples of enantiomerically pure D2-C76 with unambiguous optical purity.

Assembly of π‐Conjugated Phosphole Azahelicene Derivatives into Chiral Coordination Complexes: An Experimental and Theoretical Study

Aza[n]helicene phosphole derivatives have been prepared from aza[n]helicene diynes by the Fagan-Nugent route. Their photophysical properties (UV/Vis absorption and emission behavior) have been evaluated. Their behavior as P,N chelates towards coordination to Pd(II) and Cu(I) has been investigated: metal-bis(aza[n]helicene phosphole) assemblies are formed by a highly stereoselective coordination process, as demonstrated by X-ray crystallography. An aza[6]helicene phosphole bearing an enantiopure helicene part has been obtained, which allows the preparation of enantiopure Pd(II) and Cu(I) complexes with original topologies and high molar rotation (MR) and circular dichroism (CD). The structure-property relationship established from the experimental data has been studied in detail by theoretical studies (TDDFT calculations of UV/Vis, CD, and MR). Aza[n]helicene phosphole derivatives show pi conjugation extended over the entire molecule, and its influence on the MR of aza[6]helicene phosphole 5 c has been demonstrated. Finally, it has been shown that the nature of the metal (coordination geometry and electronic interaction) can have a great impact on the amplitude of the chiroptical properties in metal-bis(aza[n]helicene phosphole) assemblies.

Chemistry of C84: Separation of Three Constitutional Isomers and Optical Resolution of D2‐C84 by Using the “Bingel–Retro‐Bingel” Strategy

The pure enantiomers of D2 -C84 as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C84 (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C84 , separated, and unambiguously structurally characterized.

From Hetero- to Homochiral Bis(metallahelicene)s Based on a PtIII−PtIII Bonded Scaffold: Isomerization, Structure, and Chiroptical Properties

Hetero- and homochiral diastereomeric bis(metallahelicene)s have been synthesized. They possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands. It is shown that heterochiral (P,M)-bis(Pt(III)-[6]helicene) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene). A theoretical study shows a unique σ-π conjugation between the two π-helices and the σ-Pt(III)-Pt(III) scaffold that impacts the strong chiroptical properties.

Helicene Quinones: Redox-Triggered Chiroptical Switching and Chiral Recognition of the Semiquinone Radical Anion Lithium Salt by Electron Nuclear Double Resonance Spectroscopy

We present the synthesis and characterization of enantiomerically pure [6]helicene o-quinones (P)-(+)-1 and (M)-(-)-1 and their application to chiroptical switching and chiral recognition. (P)-(+)-1 and (M)-(-)-1 each show a reversible one-electron reduction process in their cyclic voltammogram, which leads to the formation of the semiquinone radical anions (P)-(+)-1(•-) and (M)-(-)-1(•-), respectively. Spectroelectrochemical ECD measurements give evidence of the reversible switching between the two redox states, which is associated with large differences of the Cotton effects [Δ(Δε)] in the UV and visible regions. The reduction of (±)-1 by lithium metal provides [Li(+){(±)-1(•-)}], which was studied by EPR and ENDOR spectroscopy to reveal substantial delocalization of the spin density over the helicene backbone. DFT calculations demonstrate that the lithium hyperfine coupling A((7)Li) in [Li(+){(±)-1(•-)}] is very sensitive to the position of the lithium cation. On the basis of this observation, chiral recognition by ENDOR spectroscopy was achieved by complexation of [Li(+){(P)-(+)-1(•-)}] and [Li(+){(M)-(-)-1(•-)}] with an enantiomerically pure phosphine oxide ligand.