H. Amouri & M. Gruselle ; Wiley : Chichester, UK., 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, stabilization and reactivity of the first 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. Synlett 2011, 1357. Chirality 2013, 25, 449.
II- Resolution of metal complexes via chiral anion recognition.
Resolution of a rare binuclear ruthenium compounds via chiral anion recognition
The binuclear ruthenium trans-[bis(Cp*Ru)-carbazolyl][PF6] has a C2 symmetry and belongs to compounds with planar chirality (Figure 1).
Figure. a) Binuclear ruthenium complex trans-[bis(Cp*Ru)-carbazolyl][PF6]. b) Structure of trans-[(Sp,Sp)-bis(Cp*Ru)-carbazolyl][Δ-TRISPHAT] showing chiral anion recognition [Δ-TRISPHAT]. Organometallics 2004, 23, 4338.
The PF6- anion of the racemic dinuclear ruthenium compound can be replaced by Δ-Trisphat through anion metathesis to give two pair of diastereomers. These diastereomers trans-[(Sp,Sp)-bis(Cp*Ru)-carbazolyle][Δ-TRISPHAT] can be separated by fractional crystallization. X-ray molecular structure of the trans-[(Sp,Sp)-bis(Cp*Ru)-carbazolyle][Δ-TRISPHAT] was ascertained by single crystal X-ray diffraction study. The complex crystallizes in the chiral space group P21. The absolute configuration was determined by using the Flack’s parameter (x = 0.07). The CD curve of the crystal was recorded and confirmed the configuration obtained from the X-ray study.
Our future objectives are devoted to the use of such chiral complexes as ligands to promote enantioselective catalytic C-C bond formation.
III- 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,η2,η2-(-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 ). The two diastereomers with (Δ, Δ) et (Λ, Δ) were separated through column chromatography.
b)
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.
IV- Chiral Luminescent compounds
In this work we designed a novel class of luminescent square planar platinum complexes displaying a π-bonded chiral thioquinonoid ligand. Remarkably, the presence of the chiral organometallic ligand controls the aggregation of this square planar luminophores and imposes a homo- or a hetero-chiral arrangement at the supramolecular level, displaying non-covalent Pt---Pt et π-π interactions. Interestingly these complexes are deep red emitters in the crystalline state, and their photophysical properties can be traced to their aggregation in the solid state.
Figure. CD curves of (pR, R) and (pS, S) enantiomers of luminescent square planar platinum complexes. Chem. Eur. J. 2016, 22, 8032. (Hot paper - couverture). Affiché sur le site web du CNRS en octobre 2016.