The rate of substitution by ethylenediamine, of Cl - , in the substrates [Pd(R 2 N(CH 2 ) 2 NR 2 )Cl 2 ] and of 2,2 -bipyridine (bpy), in the complexes [Pd(bpy)(R 2 N(CH 2 ) 2 NR 2 )](ClO 4 ) 2 (R = H, methyl, ethyl or phenyl) have been studied, at 25°C, respectively in dimethylformamide and in water. In both processes the rate of reaction depends on the nature of the substituent R at nitrogen. While the kinetic data for neural complexes can be accounted for simply in terms of electronic and steric properties of the ligands, the trend of the kinetic constants seem to be related to the capacity of the various complexes to form hydrogen bonding with water.