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 kobs.,1=kS,1+kL,1[pd]T. The rate constant kS,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 kL,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 kobs.,2=kL,2[pd]T, where the hydrogen-ion dependence of kL,2% is similar to that of kL,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.