Dendrimers Containing Two Metallic Layers. Chloride Migration from Peripheral Gold, Palladium, or Rhodium Metals to Internal Ruthenium Atoms

Abstract

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)Cl2 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-pyPPh2 molecule. Finally, metalation of the resulting species with the complexes [(tht)AuCl], [PdCl(η3-2-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.

Synthesis of Carbosilane Dendrimers Containing up to Four Metal Layers

“…The strategy that we first designed consisted of the progressive growing of the ruthenium dendrimer 1 by successive reactions with some of the units prepared above. Our first attempts were addressed to introduce the ditopic ligand 3 to 1; unexpectedly, the coordination of 3 was not selective, in contrast to our earlier results carried out with 4-pyPPh 2 , [13] and a mixture of products resulting from the coordination of the ligand to 1 by nitrogen or phosphorus atoms was obtained. We reasoned that the use of metal complexes, such as 5, instead of free ligand 3, could overcome this problem since in such derivatives the phosphorus donor centers are blocked.…”

“…This behaviour had been previously observed for dendrimer 8. [13] In contrast, the results obtained by addition of (PPh 4 )I were different. In this case, the reaction of an equimolar amount of the iodide salt (PPh 4 )I to a solution of 9 promoted a selective attack on the AuÀN bond resulting in the release of the cationic palladium complex 6.…”

“…The notation used in the ESI mass spectral assignments is shown in Figure 6. [17] [AuClA C H T U N G T R E N N U N G (tht)], [18] [RuCl 2 A C H T U N G T R E N N U N G (p-cymene)] 2 , [19] 4-pyPPh 2 , [20] [ [13] and dendrimers 1,…”

“…It is evident that steric effects play an important role here. We therefore decided to start the process of growing multimetallic dendrimers with the ruthenium dendrimer 8, which had been prepared earlier from 2 and [AuClA C H T U N G T R E N N U N G (tht)] [13] ( Figure 2). Thus, 8 would be the core dendrimer from and around which we would try to construct the new three-or four-metal-layer dendrimers.…”

“…Recently, we published a method for the construction of carbosilane dendrimers containing two metal layers: an internal one composed of ruthenium moieties and another, on the periphery of the molecule, composed of gold, palladium or rhodium fragments. [13] The crucial step in our process is the selective binding of the 4-pyridyldiphenylphosphine (4-pyPPh 2 ) ligand to the [RuA C H T U N G T R E N N U N G (pcymene)] 2 + unit through the nitrogen atom donor (Scheme 1).…”