Polyfunctional ligands and polymetallic complexes were synthesized and characterized to study the cooperative effects in catalysis
The aromatic rings present in the ligands based on 9,10-dihydroanthracene allow to envisage a π coordination to the metal centers and the modularity of the succinic anhydride heterocycle causes a dative coordination.
New diphosphites chiral ligands have been synthesized, and the corresponding catalytic systems with rhodium (I) and palladium (II) give rise to high enantiomeric excess in the hydroformylation process and allylic alkylation, respectively (Tetrahedron: Asymmetry 2009, 20, 1009). This same type of ligands can both be an organometallic precursor but also be used as organocatalyst having excellent chemoselectivity in the formation of C-C bonds and in the Michael addition of a,b-unsaturated ketones (Eur. J. Org. Chem. 2014, 2160).
Also, the formation of mono, bis-and tris-complexes via metal-ligand π-interactions was performed. The organometallic precursor [RuCp(CH3CN)3]PF6 is used as a source of electrophilic group « RuCp+ ». Selective coordination could be observed according to the electronic and steric effects of the ligands. Structures by X-ray diffraction were obtained and the theoretical modeling studies at DFT level have allowed us to justify the selectivity observed for the coordination of the different aromatic rings (Dalton Trans. 2013, 42, 1136).
Hetero-polymetallic Pd(II)/Ru(II) complexes (bis-and tris-heteropolymetallic) show the electronic communication between the two metals (Organometallics 2014, 33, 1812). The presence of the fragment « RuCp+ » influences the reactivity of the palladium in the Suzuki-Miyaura cross-coupling reaction by a stability of Pd(II) and therefore a difficult reduction in Pd(0), which is the catalytically active species, and highlighted by electrochemical analysis.
The collaboration with LBPB team of LHFA has allowed the development of a new form of coordination of phosphine-arylboranes, involving a secondary π interaction between a mesityl group of borane moiety and the metallic center of palladium (Chem. Commun. 2011, 47, 8163). These preliminary results have encouraged us to apply these ambiphilic ligands in Suzuki-Miyaura couplings, observing an excellent regioselectivity in the formation of unsymmetrical 2,6-diarylpyridines by way of a dual sequential process (Adv. Synth. Catal. 2013, 355, 2274).