Kinetic and Mechanistic Investigations on Some N,N-Chelated Pt(II) Oxalate Complexes with Some "S" Containing Biorelevant Ligands at Physiological Condition

Abstract

The substitution of the chelating oxalate group by a group of nucleophiles, viz. thiourea (L1), 2-thiouracil (L2), diethyldithiocarbamate (L3), dl-penicillamine (L4), and thiosemicarbazide (L5) was studied under pseudo-first-order conditions as a function of concentration and temperature using UV-vis spectrophotometry and stopped-flow technique. π-Accepting effects are often used to account for the unusual high lability of Pt(bipy) complexes. The complexes [Pt(dach)(oxalate)] (1) (dach = cis-1,2-diaminocyclohexane) and [Pt(bipy)(oxalate)] (2) (bipy = 2,2'-bipyridine) and substituted products were isolated and characterized by FTIR and ESI-MS spectroscopic analysis. The negative entropies of activation support a strong contribution from bond making in the transition state of the substitution processes.