Catechol‐Bearing Dipyrazinylpyridine Complexes of Ruthenium(II)

The new tridentate ligand 4‐(3,4‐methylenedioxyphenyl)‐2,6‐dipyrazinylpyridine ( 2 ) was prepared in good yield in a one‐pot reaction. The Ru II complexes [Ru( 2 ) 2 ](PF 6 ) 2 and [Ru( 1 )( 2 )](PF 6 ) 2 [ 1 is 2,6‐dipyrazinyl‐4‐(4‐tolyl)pyridine] were prepared in good yields and tested as photosensitizers against [Ru( 1 ) 2 ](PF 6 ) 2 and [Ru(ttpy) 2 ](PF 6 ) 2 [ttpy is 4′‐(4‐tolyl)‐2,2′:6′,2″‐terpyridine]. The photosensitization ability follows the order [Ru( 1 ) 2 ](PF 6 ) 2 > [Ru( 1 )( 2 )](PF 6 ) 2 > [Ru( 2 ) 2 ](PF 6 ) 2 >> [Ru(ttpy) 2 ](PF 6 ) 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 ](PF 6 ) 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, 69451 Weinheim, Germany, 2007)