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 L1–3 were coordinated to Ru(III) centers to generate Ru(L1–3)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.