Bimetallic η6,η1 SCS- and PCP-Pincer Ruthenium Palladium Complexes: Synthesis, Structure, and Catalytic Activity

The synthesis of eta(6),eta(1) SCS- and PCP-pincer ruthenium palladium complexes [3](+)-[6](+) by direct eta(6)-coordination of [Ru(C5R5)](+) (R = H or Me) to the arene ring of eta(1)-palladated ECE-pincer ligands (E = S or P) is described. In the resulting hetero bis-organometallic complexes, the pi- and sigma-electrons of the ECE-pincer phenyl anion are involved in eta(6)- and eta(1)-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](+) and [4](+), replacement of the cyclopentadienyl ligand (complex [3](+)) by the more hindered pentamethylcyclopentadienyl ligand (complex [4](+)) 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](+) in solution is frozen for the more hindered complex [4](+). Finally, preliminary catalytic studies in the cross-coupling reaction between trans-phenylvinylboronic acid and vinylepoxide show that, for SCS-pincer palladium complexes, eta(6)-coordination of [Ru(C5R5)](+) has a positive influence on the catalytic activity of the palladium center.