Reversible multi-electron reduction of 9,11,20,22-tetraaza-tetrapyridopentacene (tatpp) as axial ligand in the [(bpy)2ru(tatpp)]cl2 complex
The ruthenium complex, [(bpy)2Ru(tatpp)]2+ (12+; bpy is 2,2’-bipyridine where tatpp is 9,11,20,22-tetraaza tetrapyrido[3,2-a:2’3’-c:3”,2”-l:2”’,3”’]-pentacene) is a promising candidate for homogeneous solar photocatalysis, based on the coupling of light absorption by the (bpy)2Ru2+ chromophore moiet...
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| Autores principales: | , , , , |
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| Formato: | Articulo |
| Lenguaje: | Inglés |
| Publicado: |
2009
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| Materias: | |
| Acceso en línea: | http://sedici.unlp.edu.ar/handle/10915/177407 |
| Aporte de: |
| Sumario: | The ruthenium complex, [(bpy)2Ru(tatpp)]2+ (12+; bpy is 2,2’-bipyridine where tatpp is 9,11,20,22-tetraaza tetrapyrido[3,2-a:2’3’-c:3”,2”-l:2”’,3”’]-pentacene) is a promising candidate for homogeneous solar photocatalysis, based on the coupling of light absorption by the (bpy)2Ru2+ chromophore moiety with the tatpp ability to receive and reversible store electrons in aqueous media. In the present communication, a combination of spectroelectrochemistry and voltammetry was applied to compare the electroreduction processes of tatpp in complex 12+ and as a Zn-tatpp adduct. For complex 12+, the radical [(bpy)2Ru(tatpp•-)]+(1•+) is the first electroreduced species that then converts to doubly-reduced, single-protonated [(bpy)2Ru(Htatpp-)]+ (H1+) and doubly-protonated [(bpy)2Ru(H2tatpp)]2+(H212+) by subsequent electron transfer (ET) and proton transfer (PT) reactions. Contrastingly, spectroelectrochemistry of the Zn-tatpp adduct showed negligible amounts of intermediate tatpp•- radical and dominance of double reduced Zn-(Htatpp-) and Zn(H2tatpp) species. Upon further electroreduction, doubly-reduced species form quadruply reduced, protonated species, in both systems. The four electrons uptake in complex 12+ is followed by a rapid homogeneous comproportionation reaction with the initial 12+ reactant leading to the regeneration of intermediate double-reduced species, H212+, while no comporportionation occurs for Zn-tatpp because the reduced species are film-confined, that is, restrained to move to the bulk solution for encounter with the initial reactant. |
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