Dendritic systems based on dinuclear ruthenium or rhodium units generating peripheral catalytic sites

A series of dendritic cations 1-4 containing Ru(2)S(3) or Rh(2)S(3) units, either in the core or in the dendrons, has been synthesized and characterized. The X-ray crystal structure analysis of 2-Cl shows a trigonal bipyramidal Rh(2)S(3) core with propeller-like para-hydroxyphenyl substituents at the sulfur atoms. Reaction of the peripheral OH groups with diphenylphosphino benzoic acid results in the formation of phosphine-functionalized dendritic cations 5-8. The ruthenium-containing cation 5, with three PPh(2) functions at the periphery, acts as ligand for rhodium(I) and enhances significantly the catalytic activity of [[Rh(CO)(2)Cl](2)] for the carbonylation of methanol.