Transition Metal Chemistry

, Volume 39, Issue 4, pp 407–420 | Cite as

Detailed mechanistic study on ligand substitution reactions in dinuclear platinum(II) complexes: effect of alkanediamine linker

  • Peter O. Ongoma
  • Deogratius JaganyiEmail author


Substitution of the coordinated water ligands from the cis-[{Pt(NH3)2H2O}2-μ-NH2(CH2) n NH2]4+ (n = 2–4, 6, 8, 10) complexes: EnPt, PropPt, ButPt, HexPt, OctPt and DecPt with S-donor nucleophiles thiourea, N,N-dimethyl-2-thiourea and N,N,N,N-tetramethyl-2-thiourea was studied under pseudo-first-order conditions as a function of concentration and temperature, using stopped-flow and UV–Vis Spectrophotometric techniques. The substitution reaction proceeded in two steps: simultaneous substitution of the aqua ligands, followed by the displacement of the ammine ligands in the trans-position due to the strong trans-effect of the coordinated thiourea nucleophiles, with each of the steps being sensitive to steric and σ-electronic properties of the alkanediamine linker. A comparison of the second-order rate constants, k 2,1st and k 2,2nd, indicates that the rate constants of the first step are 1–2 orders larger than those of the second step in all cases. The large negative ΔS values support an associative mode of substitution mechanism for both reaction steps. 1H and 195Pt NMR spectroscopy established that the α,ω-alkanediamine linkers remained coordinated to the metal centres, possibly due to their cis geometry to the incoming thiourea nucleophiles.

Graphical Abstract

The lability of aqua ligands of cis-[{Pt(NH3)2H2O}2-μ-NH2(CH2) n NH2]4+ (n = 2–10) complexes decreased from EnPt to DecPt, due to lower electrophilicity of the platinum centre caused by σ-donor effect of the (CH2) n units and to steric constraints of coordinated thiourea ligands. The experimental results are supported by density function theory (DFT) at the B3LYP/LACVP** level.


Dinuclear Complex Density Function Theory Aqua Ligand TMTU Diaqua 
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The authors greatly acknowledge financial support from the National Research Foundation (NRF) Pretoria, South Africa, and the University of KwaZulu-Natal. P.O.O gratefully acknowledges continued support from Egerton University, Kenya. The authors kindly thank Craig Grimmer for the support with NMR measurements.

Supplementary material

11243_2014_9815_MOESM1_ESM.doc (3.8 mb)
Figures S1 to S3 show UV–Visible spectra for PropPt, ButPt and DecPt at different of pH values. Figures S4–S23, illustrate different concentration and temperature dependent studies for all nucleophiles and complexes. Table S1 shows a summary of the used wavelengths and Tables S2–S25 summarise all values of k obs determined for all reactions at different concentrations and temperatures for all nucleophiles. Included, are Figures S24 to S35 for IR, MS, 195Pt NMR spectra of the selected complexes and 13C NMR spectra for DecPt complex. (DOC 3872 kb)


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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  1. 1.School of Chemistry and PhysicsUniversity of KwaZulu-NatalPietermaritzburgSouth Africa

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