Dendrimers containing two metallic layers. Chloride migration from peripheral gold, palladium, or rhodium metals to internal ruthenium atoms

An efficient strategy for the synthesis of carbosilane dendrimers containing double metallic layers has been developed. The method consists of the attachment of the Ru(p-cymene)Cl-2 unit to the branches of a phosphino-terminated dendrimer, followed by abstraction with AgOTf of the chloride ligands from the ruthenium and selective incorporation, through the nitrogen pyridine atom, of the bifunctional 4-pyPPh(2) molecule. Finally, metalation of the resulting species with the complexes [(tht)AuCl], [PdCl(eta(3)-2-MeC3H4)](2), and [RhCl(cod)](2) renders the targeted Ru/Au, Ru/Pd, and Ru/Rh dendrimers. An unexpected migration of the chloride ligand bonded to the peripheral metals to the internal ruthenium atoms was observed and discussed in terms of the results obtained from density functional calculations. In the case of the Ru/Au dendrimers, the different abilities for the ligand transfer process shown by the dendrimers in comparison with a mononuclear Ru/Au model compound are explained in terms of dendritic effects.