Christophe Lescop

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.

Dibenzophosphapentaphenes: Exploiting P Chemistry for Gap Fine-Tuning and Coordination-Driven Assembly of Planar Polycyclic Aromatic Hydrocarbons

A synthetic route to planar P-modified polycylic aromatic hydrocarbons (PAHs) is described. The presence of a reactive σ(3),λ(3)-P moiety within the sp(2)-carbon scaffold allows the preparation of a new family of PAHs displaying tunable optical and redox properties. Their frontier molecular orbitals (MOs) are derived from the corresponding phosphole MOs and show extended conjugation with the entire π framework. The coordination ability of the P center allows the coordination-driven assembly of two molecular PAHs onto a Au(I) ion.

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.

Engineering New Metal-Organic Frameworks Built from Flexible Tetrapyridines Coordinated to Cu(II) and Cu(I)

A series of new metal-organic frameworks have been constructed by the coordination of Cu(II) and Cu(I) with pentaerythrityl tetrakis(4-pyridyl) ether (1 = PETPE), a flexible tetradentate ligand. Networks derived from Cu(OOCCH(3))(2), Cu(NO(3))(2), and CuBF(4) proved to have different topologies (diamondoid, PtS, and SrAl(2), respectively). This reflects (1) the ability of PETPE (1) to adopt diverse conformations and (2) the varied geometries of complexes of Cu(II) and Cu(I). Extended PETPE (2), a tetrapyridine with phenyl spacers inserted into the pentaerythrityl core of PETPE (1), yielded an expanded version of the PtS network derived from simple PETPE (1) and Cu(NO(3))(2). However, increases in the ability of the network to accommodate guests were largely offset by interpenetration of independent networks. Attempts to thwart interpenetration by converting ligand 2 into methyl-substituted derivative 3 led to the construction of networks with alternative topologies. In particular, the reactions of ligand 3 with both Cu(II) and Cu(I) yielded isostructural Pt(3)O(4) networks, despite the preference of the two oxidation states for coordination spheres with different geometries. Together, these observations demonstrate that PETPE (1) and related compounds are useful ligands for constructing metal-organic frameworks, with a distinctive ability to accommodate a single metal in different oxidation states, as well as to adapt to a metal in a single oxidation state but with different counterions or secondary ligands.

BISPENTAMETHYLCYCLOPENTADIENYL URANIUM(IV) THIOLATE COMPOUNDS. SYNTHESIS AND REACTIONS WITH CO2 AND CS2

Abstract The bisthiolate uranium complexes [U(Cp*)2(SR)2] (R=Me, iPr, tBu, Ph) were synthesized by treatment of [U(Cp*)2(Cl)2] with NaSR; the crystal structure of [U(Cp*)2(SMe)2] was determined. Their reactions with CO2 or CS2 gave the insertion derivatives [U(Cp*)2(SR)(E2CSR)] (E=O and R=tBu; E=S and R=Me, iPr or tBu) and [U(Cp*)2(E2CSR)2] (E=O and R=tBu; E=S and R=Me or tBu); [U(Cp*)2(StBu)(S2CStBu)] was characterized by its crystal structure. Treatment of this latter with CO2 gave the mixed insertion complex [U(Cp*)2(O2CStBu)(S2CStBu)]. Thermolysis of the insertion compounds led to the reverse elimination reaction of CO2 and CS2. Reduction of [U(Cp*)2(O2CStBu)2] with Na(Hg) afforded the corresponding U(III) anionic complex.

2,2′‐Biphospholes: Building Blocks for Tuning the HOMO–LUMO Gap of π‐Systems Using Covalent Bonding and Metal Coordination

new angle: The insertion of a 2,2′-biphosphole subunit into π-conjugated systems offers a new way to control the HOMO-LUMO gap. Tuning of the dihedral angle (θ) between the two phosphorous heterocycles, either by metal coordination or covalent bonding through the P substitution can lead to control of the band gap. These new π-conjugated systems can be used as emitting materials in white organic light-emitting devices (WOLEDs).

An aromatic-antiaromatic switch in P-heteroles. A small change in delocalisation makes a big reactivity difference.

The low aromaticity of phosphole can be switched to low antiaromaticity by oxidizing the phosphorus atom. This subtle change in the mode of delocalisation alters substantially the chemical behaviour of these heteroles.

Coordination-Driven Hierarchical Organization of π-Conjugated Systems: From Molecular to Supramolecular π-Stacked Assemblies

The reaction of U-shaped, bimetallic, Cu(I) complexes, assembled from a heteroditopic pincer, with cyano-capped pi-conjugated linkers gives a straightforward access to pi-stacked metallocyclophanes in good yields. In these assemblies, the pi-walls have an almost face-to-face arrangement. The versatility of this rational supramolecular synthesis is demonstrated with the use of linkers that have nanoscale lengths (up to 27.7 A), different chemical compositions (oligo(para-phenylenevinylene)s OPVs, oligo(phenylene)s, oligo(phenylethynylene)s), and alternative geometries (linear, angular). Linkers that incorporate an internal pyridyne moiety can also be employed. X-ray diffraction studies revealed that the metallocyclophanes based on linear linkers self-organize into infinite pi-stacked columns in the solid state with intermolecular distances of about 3.6 A. This approach, based on coordination-driven self-assembly, provides a novel and rational strategy for the stacking of extended pi-systems in the solid state.

Assembly of Helicene‐Capped N,P,N,P,N‐Helicands within CuI Helicates: Impacting Chiroptical Properties by Ligand–Ligand Charge Transfer

Helicat- und Helicenchemie treffen sich, wenn funfzahnige Phosphol-Pyridin-Helicanden an CuI- oder AgI-Zentren koordinieren. Bei diesem Prozess entstehen konfigurationsstabile Doppelstranghelicate mit verbruckenden Phosphanen in mehreren Koordinationsmodi. Mit enantiomerenreinen Helicenen versehene Helicanden ergaben enantiomerenreine Helicate.

Functional phosphorus-based π-conjugated systems: Structural diversity without multistep synthesis

The synthesis and properties of linear π-conjugated systems incorporating phosphole rings are described. Their supramolecular organization in the solid state can be controlled either by chemical modifications or coordination to transition metals of the phosphorus atom. Furthermore, chemical transformations of the phosphole ring allow organizing these P-chromophores in 3D assemblies exhibiting σ-π conjugation or in organometallic ferrocene-like derivatives. Phosphole-pyridine-containing π-conjugated chromophores act as P,N-chelates toward transition-metal ions, giving rise to mono- and di-nuclear complexes. The specific properties of these complexes make them valuable materials for organic light-emitting diodes (OLEDs) and interesting building blocks for the tailoring of π-conjugated systems.