Diastereoselective Assembly of Chiral Ru II ‐Coordinated Depsipeptide‐Dendrimers

The synthesis, characterization and chiroptical properties of chiral dendrimers 11 – 14 formed by ruthenium coordination of2,2′‐bipyridine (bpy*) ligands 4 , 7 , 8 and 10 involving two pairs of enantiomerically pure depsipeptide dendrons bound in 4,4′‐position are described. In the case of the first and second generation ligands 4 , 7 and 8 the metallodendrimers 11 , 12 and 13 are formed containing a central [Ru(bpy*) 3 ] 2+ core. After coordination of the third generation dendritic ligand 10 the metallodendrimer 14 with two bpy* ligands, {[Ru(bpy*) 2 Cl 2 ] core} was isolated. The corresponding metallodendrimer 15 with three bpy* ligands was formed in traces only. Dendrimers 11 , 12 and 13 are the first chiral metallodendrimers involving an [Ru(bpy*) 3 ] 2+ core. This chiral coordination motif can have either a Δ or a Λ configuration. To elucidate if there is a preference for a certain configuration 1 H NMR and CD spectroscopy and analytical HPLC were applied. It was found that for the first generation dendrimer 11 the corresponding diastereoisomers with Δ and Λ configuration are formed in equal amounts. On the other hand the Λ diastereoisomers of 12 and 13 are preferably formed upon coordination of the second generation dendrons 7 and 8 with all‐( R , R ) configuration ( 8 ) or mixed ( S , S ) 1 ‐( R , R ) 2 configuration ( 7 ). This demonstrates that the configuration of the outer rather than the inner layer within the depsipeptide dendrons determines which isomer is preferably formed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)