First-Generation Chiral Metallodendrimers: Stereoselective Synthesis of RigidD3-Symmetric Tetranuclear Ruthenium Complexes

Condensation reactions between the enantiopure, substitutionally inert building blocks Δ-[Ru(1,10-phenanthroline-5,6-dione) 3 ][PF 6 ] 2 ( 2 ) and Δ-[Ru(phen) 2 (1,10-phenanthroline-5,6-diamine)][PF 6 ] 2 ( 3 ) gave the D 3 -symmetric tetramer [(Δ-(phen) 2 Ru(tpphz)) 3 -Δ-Ru] 8+ (ΔΔ 3 - 1 ) in 68% isolated yield as the PF 6 - salt (where tpphz is tetrapyrido[3,2- a:2‘,3‘- c:3‘‘,2‘‘- h:2‘‘,3‘‘- j ]phenazine). Reactions between appropriate enantiomers of 2 and 3 also yielded the remaining D 3 isomers ΛΔ 3 - 1, ΔΛ 3 - 1, and ΛΛ 3 - 1 which collectively represent the highest nuclearity Ru oligomers based on bidentate type ligands prepared in a stereospecific fashion to give diasteromerically and enantiomerically pure products. The complexes were purified via cation-exchange HPLC. 1 H and 13 C NMR, COSY and HMQC NMR, and UV−visible spectroscopy were employed to characterize these supramolecular assemblies. MALDI-TOF mass spectrometry gave parent molecular ion peaks corresponding to the species m/z 2638 [ 1 − 8PF 6 ] +, 2783 [ 1 − 7PF 6 ] +, 2928 [ 1 − 6PF 6 ] +, 3073 [ 1 − 5PF 6 ] +, 3218 [ 1 − 4PF 6 ] +, and 3363 [M − 3PF 6 ] +, proving the macromolecular structure. Circular dichroism spectroscopy was used to determine the absolute stereochemistry and optical purity of each of these stereoisomers.