Synthesis and catalytic properties of neutral and cationic rhodium- and iridium-containing carbosilane dendrimers

The reaction of phosphanyl-terminated carbosilane dendrimers containing only one phosphorus ligand per arm with [MCl(cod)]2(M = Rh, Ir; cod = cycloocta-1,5-diene) resulted in the grafting of MCl(cod) moieties on the surface of the dendrimer. However, dendrimers displaying two phosphorus ligands per arm gave very unstable species which were not isolated. On the other hand, the last group of dendrimers reacted with [MCl(cod)]2, in the presence of silver salts, to afford cationic dendrimers in which a metal fragment is attached simultaneously to both phosphorus atoms of the same arm. The substitution of cod with 1,1-bis(diphenylphosphino)ferrocene (dppf) in one example of the latter group yielded a bimetallic Rh/Fe layer-containing dendrimer. The new metallodendrimers were tested as catalysts in the hydrogenation of 1-hexene.