Catechol-bearing dipyrazinylpyridine complexes of ruthenium(II)

Abstract

The new tridentate ligand 4-(3,4-methylenedioxyphenyl)-2,6- dipyrazinylpyridine (2) was prepared in good yield in a one-pot reaction. The RuII complexes [Ru(2)2](PF6)2 and [Ru(1)(2)](PF6)2 [1 is 2,6-dipyrazinyl-4-(4-tolyl) pyridine] were prepared in good yields and tested as photosensitizers against [Ru(1)2](PF6)2 and [Ru(ttpy) 2](PF6)2 [ttpy is 4′-(4-tolyl)-2, 2′:6′,2″-terpyridine]. The photosensitization ability follows the order [Ru(1)2](PF6)2 > [Ru(1)(2)](PF6)2 > [Ru(2)2]-(PF 6)2 ≫ [Ru(ttpy)2](PF6) 2, which is explainable in terms of mechanism and driving force. Hydrolysis of the methylene acetal function affords the catechol-appended complexes [Ru(3)2](PF6)2 and [Ru(1)(3)](PF 6)2 [3 is 4-(3,4-dihydroxyphenyl)-2,6-dipyrazinylpyridine] in excellent yields. These insoluble, paramagnetic precipitates when tested as photosensitizers in homogeneous solution and in one case adsorbed on titania are able to generate photocurrents in a photovoltaic cell, albeit more weakly compared to the so-called N719 dye. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007.