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

complex of general formula I (CF DRAWING IN BOPI) wherein R1, R2 and R3, identical or different, independently represent a linear or branched alkyl radical from 1 to 5 carbon atoms, or together with the nitrogen atom to which they are linked 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 are identical or different, represent hydrogen, hydroxy, alkoxy, aryloxy, secondary or tertiary amine primary, or the group -alk-N + - (R1 R2 R3) wherein "alk", R1, R2 and R3 have the above meanings; M represents a transition metal such as Fe, Ru, or Os; X represents an anion and n is an integer corresponding to the number of positive charges of the complex.