Kinetics and mechanism of the substitution behaviour of Pd(II) piperazine complexes with different biologically relevant nucleophiles

The interaction of the palladium(II) complex [Pd(Pip)(H₂O)₂]²⁺, where Pip is piperazine, with a series of biologically relevant nucleophiles including guanosine-5′-monophosphate, L-methionine and thiourea was studied under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV-Vis spectrophotometric and stopped-flow techniques. The reactions were found to occur in two subsequent steps. For the sulfur donor containing nucleophiles thiourea and L-methionine, a third reaction step, the displacement of the labilized amine, as a result of the strong trans-effect of S-donor ligands, was observed. The activation parameters for all reactions studied suggest an associative substitution mechanism.