Complexes of a transition metal with 2,2-bipyridine ligands substituted by at least one ammonium alkyl radical, process for their fabrication and their use as redox mediator

Complex of general formula I in which R1, R2 and R3, which may be identical or different, represent separately a linear or branched alkyl radical of 1 to 5 carbon atoms, or, together with the nitrogen atom to which they are attached, a heterocyclic radical having 5 to 7 carbon atoms; "alk" represents a linear or branched alkylene radical having 1 to 5 carbon atoms; R4 to R8, which may be identical or different, represent hydrogen, a hydroxyl, alkoxy or aryloxy group, a primary, secondary or tertiary amino group, or the group -alk-N