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The formation reactions of the complexes of Pd(R4en)(H2O)2(super 2+), where R4en = N-substituted ethylenediamine and R = H, Me, Et, with ribose, adenosine, inosine and guanosine 5'-monophosphate were studied as a function of monophosphate concentration and temperature in the pH range of 4 to 5. The nucleotides reacted faster than the nucleosides, indicating the transition state stabilization effect by the monophosphate group. Furthermore, the complex formation rate constants of ribose monophosphate were smaller than those of inosine but larger than those of adenosine.

Complex formation between the diaqua palladium(II) complex of ethylenediamine and adenosine or inosine is a two-step process. The reaction rate depends on the nucleoside concentration and, in the case of adenosine, on the pH level. The adenosine complex is less stable than the inosine complex, probably due to exocyclic amine (6-NH2) group interference. Steric hindrance is more pronounced with the inosine complex, where N(1) is already coordinated to the metal center and only N(7) is available for the other moiety. The mechanism therefore involves more of an associative ligand substitution, as indicated by the activation parameters.