The kinetics and the mechanism of the substitution reactions of the complex [(TLtBu)PdCl]+, where TLtBu is 2,6-bis[(1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine, with nucleophiles (guanosine-5′-monophosphate (5′-GMP), L-Methionine (L-Met) and L-Histidine (L-His)) were studied using variable-temperature stopped-flow techniques in aqueous 0.1 M NaClO4 with 10 mM NaCl at 298 K. The order of reactivity is: L-Met > 5′-GMP > L-His. The formation equilibria of [(BLiPr)Pd(H2O)2]2+, where BLiPr is 1,2-bis(1,3diisopropyl-4,5-dimethylimidazolin-2-imino)ethane, and [(TLtBu)Pd(H2O)]2+ with some biologically relevant ligands (L-Met, 5′-GMP and L-His) were also studied. The stoichiometry and stability constants of the newly formed complexes are reported, and the concentration distribution of the various complex species has been evaluated as a function of pH. Comparing the values of logβ1,1,0 for 5′-GMP, L-His and L-Met complexes, the most stable complex is with 5′-GMP followed by L-His and L-Met for both complexes, [(BLiPr)Pd(H2O)2]2+ and [(TLtBu)Pd(H2O)]2+. The crystal structures of [(TLtBu)PdCl]ClO4 and [(BLiPr)PdCl2] were determined by X-ray diffraction. The coordination geometries around the palladium atoms are distorted square-planar, with the Pd–N1 distance to the central nitrogen atom of the TLtBu ligand, 1.944(2) Å, being shorter than those to the other two nitrogen atoms of TLtBu, viz. 2.034(3) and 2.038(2) Å. The BLiPr complex displays similar Pd–N distances of 2.031(2) and 2.047(2) Å.