Synthesis and Resolution of Planar-Chiral Ruthenium-Palladium Complexes with ECE′ Pincer Ligands

The synthesis and chiral resolution of the first planar-chiral ECE'-metal complexes of type e was reported. n1-coordination of the metal (M) was carried out first, followed by n6 of a second metal fragment (M'). The ECE'-palladium complexes have to carry N, S, and P substituents with aliphatic groups to selectively address the pincer arene ring with the arenophile. Complexes 3-[BF4], 4-[PF6], and 5-[BF 4] were obtained as brown (3+) or white (4+ or 5+) powders upon completion of the reaction and after purification by chromatography on silica gels. The P NMR spectra of pure enantiomeric chiral counterion in dichloromethane show two well-resolved singlets in a 1:1 ratio for the coordinated P ligand, whereas, in the same condition 4-[Cl] and 5-[Cl] give a singlet. The new approach towards planar-chiral ECE'-ruthenium-palladium complexes might lead to new and efficient asymmetric catalysts.