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).