Acid Catalyzed Dissociation of 4‐Aminopyridine Complex of Pentacyanoferrate (II)

Fe(CN)₅ampy^3? (ampy = 4‐aminopyridine) complex was unstable at pH ≤ 4 with respect to the dissociation due to the protonations of the complex. The first protonation on the 4‐aminopyridine ligand at pK_a = 3.2 resulted in a ? 150‐fold in crease in rate of dissociation as compared to that of the complex in the neutral solution. However, further protonation of the complex on the cyanide ligand at pK_a = 1.5 in creased the rate only slightly. The large in crease in the rate constant of dissociation for Fe(CN)₅ampyH^2? complex suggests that in the transition state the proton is likely shifted from the amino group and becomes coordinated to a pair of dπ electrons directed at the face of the coordinated octahedron.