Bimetallic η6,η1-and PCP-pincer ruthenium palladium complexes: synthesis, structure, and catalytic activity

Abstract

The synthesis of η6,η1 SCS- and PCP-pincer ruthenium palladium complexes [3] þ-[6] þ by direct η6-coordination of [Ru(C5R5)] þ (R = H or Me) to the arene ring of η1-palladated ECE-pincer ligands (E = S or P) is described. In the resulting hetero bis-organometallic complexes, the π- and σ-electrons of the ECE-pincer phenyl anion are involved in η6- and η1-coordination to ruthenium(II) and palladium(II), respectively. In addition to electrochemical data, which show that both metal centers are electron poor, steric effects are clearly observed by X-ray crystallography and solution NMR spectroscopy. With SCS-pincer derivatives [3] þ and [4] þ , replacement of the cyclopentadienyl ligand (complex [3] þ ) by the more hindered pentamethylcyclopentadienyl ligand (complex [4] þ ) induces an inversion of the configuration of one sulfur atom in the solid state. In parallel, the dynamic inversion of configuration of the sulfur ligand observed for [3] þ in solution is frozen for the more hindered complex [4] þ . Finally, preliminary catalytic studies in the cross-coupling reaction between trans-phenylvinylboronic acid and vinylepoxide show that, for SCS-pincer palladium complexes, η6-coordination of [Ru(C5R5)] þ has a positive influence on the catalytic activity of the palladium center.