Nos tutelles

CNRS

Rechercher





Accueil > Les équipes > Architectures Moléculaires (A.R.C) > Thèmes de recherche

1.Chirality : from molecular complexes to coordination assemblies and material networks.

publié le

Chirality in Transition metal Chemistry : Molecules, Supramolecular assemblies & Materials.
H. Amouri & M. Gruselle ; Wiley : Chichester, UK., Novembre 2008.

Chirality is an ever-fascinating topic and is a field, which occurs in various subjects of modern chemistry. Our group has an international expertise in this area and this field represents the cornerstone on which our research activities rely upon. Thus we have prepared variety of chiral structures from mononuclear to coordination assemblies including chiral networks. These compounds exhibit interesting properties see below :

I- Chiral quinone methides

Quinone Methides act as important intermediates in organic syntheses as well as in chemical and biological processes, however examples of isolated species are scarce as a result of their high reactivity. We reported the synthesis and reactivity of the first stable iridium and rhodium o-quinone methide complexes. These compounds undergo interesting C-C bond forming reactions with variety of alkenes and alkynes, further they exhibit planar chirality, hence their differentiation and resolution are stimulating and challenging objectives especially in asymmetric C-C coupling reactions.

Figure. Optically pure metal-stabilized quinone methides. Acc. Chem. Res. 2002, 35, 501. Organometallics 2005, 24, 4240.

II- Bimetallic clusters possessing acetylenic ligands.

Alkyne-dicobalt carbonyl complexes display tetrahedral geometry. They are chiral if the four vertices have different functional groups (Figure). Another method to prepare chiral bimetallic cluster consists of introducing a linker between one of the two metallic centers and carbon vertices. In this example the chirality of the complex can be better described as central chirality (Figure). On the other hand if the two metal centers are linked to the methylene groups of the bridging alkyne, the obtained compound will be chiral with C2-symmetry and should display helical chirality. We prepared a chiral binuclear cobalt complexes of the formula [Co2(CO)4µ,η22-(-H2CC≡CCH2-)(-L-L)2][Δ-Trisphat]2 {L-L = dppm, NH(PPh2)2}, which represent a rare example of an organometallic compound displaying helicoïdal symmetry (Figure 3). The two diastereomers with (Δ, Δ) et (Λ, Δ) were separated through column chromatography.

a)     b)
Enantiomère Λ ou M                Enantiomère Δ ou P                       


Figure. a) Chiral bimetallic cobalt complex with centered chirality. b) Two bladed Chiral bimetallic cobalt complexes with helical chirality (the carbonyl ligands were removed for clarity). Chirality in Transion Metal Chemistry : Molecules, supramolecular assemblies and materials Chichester Wiley 2008.

III-Chiral coordination networks (2-3D)

Oxalate ligands (C2O4)2- have been widely used to construct a variety of coordination networks. In this work we describe an enantioselective method to prepare optically active networks of the formula [cation][M1M2(C2O4)3]n. These chiral networks are obtained upon treatment of the resolved building blocks (Δ)- or (Λ)-[M1(C2O4)3]n- with inorganic brick M2X2 (X= monovalent anion) in presence of a cation. The relative configuration of the connected hexacoordinated centres determines the 2D or 3D architecture of the metal-organic framework. A hetero-chiral arrangement [(Δ)-M1(Λ)-M2)] leads to a 2D network. In contrast, a homo-chiral arrangement [(Δ)-M1(Δ)-M2)] leads to a 3D helical organisation of the connected metallic ions.

Figure. Schematic drawing of (Λ) and (Δ) enantiomers of [M1(C2O4)3]n- metallobricks. Coord. Chem. Rev. 2006, 250, 2491.