The 1,6,7,12-Tetraazaperylene Bridging Ligand as an Electron Reservoir and Its Disulfonato Derivative as Redox Mediator in an Enzyme-Electrode Process.

The homodinuclear ruthenium(II) complex [{Ru(l-N ₄ Me ₂ )} ₂ (μ-tape)](PF ₆ ) ₄ {[1](PF ₆ ) ₄ } (l-N ₄ Me ₂ =N,N'-dimethyl-2,11-diaza[3.3](2,6)-pyridinophane, tape=1,6,7,12-tetraazaperylene) can store one or two electrons in the energetically low-lying π* orbital of the bridging ligand tape. The corresponding singly and doubly reduced complexes [{Ru(l-N ₄ Me ₂ )} ₂ (μ-tape ^.- )](PF ₆ ) ₃ {[2](PF ₆ ) ₃ } and [{Ru(l-N ₄ Me ₂ )} ₂ (μ-tape ^2- )](PF ₆ ) ₂ {[3](PF ₆ ) ₂ }, respectively, were electrochemically generated, successfully isolated and fully characterized by single-crystal X-ray crystallography, spectroscopic methods and magnetic susceptibility measurements. The singly reduced complex [2](PF ₆ ) ₃ contains the π-radical tape ^.- and the doubly reduced [3](PF ₆ ) ₂ the diamagnetic dianion tape ^2- as bridging ligand, respectively. Nucleophilic aromatic substitution at the bridging tape in [1] ⁴⁺ by two sulfite units gave the complex [{Ru(l-N ₄ Me ₂ )} ₂ {μ-tape-(SO ₃ ) ₂ }] ²⁺ ([4] ²⁺ ). Complex dication [4] ²⁺ was exploited as a redox mediator between an anaerobic homogenous reaction solution of an enzyme system (sulfite/sulfite oxidase) and the electrode via participation of the low-energy π*-orbital of the disulfonato-substituted bridging ligand tape-(SO ₃ ) ₂ ^2- (E _red1 =-0.1 V versus Ag/AgCl/1 m KCl in water).
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