Kinetics and mechanism of the reaction of tetrachloroplatinum(II) with propane-1,3-diamine

Abstract

The reaction of propane-1,3-diamine (pd) with [PtCl₄]^2– proceeds in two stages. The first stage, formation of [Pt(pd)Cl₂], is governed by the rate equation k_obs.,1=k_S,1+k_L,1[pd]_T. The rate constant k_S,l corresponds to the rate of hydrolysis of [PtCl₄]^2– and good agreement has been found with independent determinations of this rate constant. The hydrogen-ion dependence of k_L,1 is interpreted in terms of rate-determining attack on [PtCl₄]^2– by both unprotonated and monoprotonated forms of the ligand. Activation parameters for these paths have been determined. The second stage of the reaction, formation of [Pt(pd)₂]²⁺, is governed by the rate equation k_obs.,2=k_L,2[pd]_T, where the hydrogen-ion dependence of k_L,2% is similar to that of k_L,1. The kinetic data are discussed in the light of current views on the mechanism of substitution reactions at square-planar substrates, with special reference to the role of solvated intermediates.