The influence of structural modification of Pd(II) pincer-type complexes on the kinetics of substitution reactions

Abstract

Abstract: This mini-review summarizes the kinetic data obtained for the substitution reactions of some palladium(II) complexes containing bis-pyrazolylpyridine derivatives as pincer-type ligands with biologically significant nitrogen- and sulfur-donor biomolecules as nucleophiles. Three structurally different palladium(II) complexes were selected: [Pd(L1)Cl]+ (Pd1), [Pd(L2)Cl]+ (Pd2) and [Pd(L3)Cl]+ (Pd3) (where L1 = bis(2- (1H-pyrazol-1-yl)ethyl)amine, L2 = 2,6-bis(5-(tert-butyl)-1H-pyrazol-3-yl)pyridine, and L3 = 2,6-bis(5-(tert-butyl)-1-methyl-1H-pyrazol-3-yl)pyridine, while for the entering nucleophiles thiourea (Tu), L-methionine (L-met), and guanosine-5’-monophosphate (5’- GMP) were used. Kinetic measurements were carried out for all systems as pseudo-first order reactions (at least 10 times the ligand in excess relative to the complex) under physiological conditions using a stopped-flow UV-Vis spectrophotometer. By comparing the published results for the second-order rate constant, the relationship between the structural properties of the complexes and their reactivity towards selected nucleophiles was established. This overview shows that by tuning the lability of the inert ligands through steric and electronic (σ-donor and π-acceptor) effects, the biological behavior of the complexes can be significantly changed.