Chiral ruthenium-terpyridine based metallodendrimers: Facile synthesis, characterization, and photophysical studies

The new chiral ligand 4′-[6-(2,2′-diethoxy-1,1′-binaphthyl)]-2,2′: 6′,2″-terpyridine (L₁) was synthesized in three steps in 47% overall yield starting from 6,6′-dibromo-2,2′-diethoxy-1,1′-binaphthalene. L₁ was quantitatively converted to 4′-[6-(2,2′-dihydroxy-1,1′-binaphthyl)]-2,2′: 6′,2″-terpyridine (L₂) by treatment with BBr₃, while L₂ was treated with tert-butyldimethylsilyl chloride to give to 4′-{6-[2,2′-bis(tert-butyldimethylsiloxy)-1,1′- binaphthyl]}-2,2′:6′,2″-terpyridine (L₃) in high yields. These new chiral terpyridine ligands L_1-3 were coordinated to Ru(III) centers to generate Ru(L_1-3)Cl₃ which were then treated with the tetrakis(terpyridine) core in the presence of 4-ethylmorpholine to afford chiral Ru(terpy)₂²⁺ based metallodendrimers containing enantiopure 1,1′-bi-2-naphthyl units in their peripheries. These chiral metallodendrimers were characterized by NMR, ESI-MS, and cyclic voltammetry, while their photophysical properties were studied using UV-Vis, luminescence, and circular dichroism spectroscopies.