Relative reactivity of N,N-donor ligands in substitution reactions of cis-diaqua(2-aminomethylpiperidine)platinum(II): a detailed kinetic and mechanistic study

Abstract

The reactivity of cis- $$[\hbox {Pt}(\hbox {pipen})(\hbox {H}_{2}\hbox {O})_{2}]^{2+}$$ ( $$\hbox {pipen} = 2\hbox {-aminomethylpiperidine}$$ ) was investigated by studying the interaction with some didentate N,N-donor ligands, namely, dimethylglyoxime ( $$\hbox {L}_{1}\hbox {H}$$ ), 1,2-cyclohexanedionedioxime ( $$\hbox {L}_{2}\hbox {H}$$ ) and $$\upalpha $$ -furildioxime ( $$\hbox {L}_{3}\hbox {H}$$ ) in an aqueous medium. All the above substitution reactions have been monitored spectrophotometrically at 320, 308 and 290 nm, respectively, where the spectral difference between the reactants and the products are appreciable. The kinetic study has been substantiated by product isolation, UV, IR and ESI-MS spectroscopic analysis. The rate parameters have been evaluated under different reaction conditions. The reactions were found to occur in two consecutive steps. The mechanism of the substitution reactions appears associative in nature as supported by the large and negative values of $$\Delta \hbox {S}^{\ne }$$ . SYNOPSIS Kinetic and mechanistic studies on the substitution of aqua ligands from cis- $$[\hbox {Pt}(\underline{\hbox {pipen}})(\hbox {H}_{2}\hbox {O})_{2}]^{2+}$$ ion by vicinal-dioximes were carried out. The reactions were found to proceed via two distinct consecutive steps where the first is ligand-dependent and the second is ligand-independent. The modes of substitution reactions are associative. Pictogram