Tuning Reactivity of Platinum(II) Complexes

7.2.8 pKa Titrations of the Diaqua Complexes
For the pKa determination, the pH of each aqueous solution was measured using a
Jenway 4330 Conductivity/pH meter equipped with a Micro 4.5 diameter glass
electrode. This electrode was filled with 3M NaCl as the electrolyte to prevent
precipitation of KClO4, and was standardised at 25 °C using buffer solutions at pH 4.0,
7.0 and 10.0, purchased from Merck. In order to avoid absorbance corrections due to
dilution, a large volume (200ml) of the metal complex solution was used during the
titration. Adjustments in pH were made by stepwise additions of crushed solid NaOH
pellets in the pH range 2-3, micropipette dropwise addition of saturated, 1.0 and 0.1M
NaOH or conc. HClO4 (for reversibility of the pH) to the sample solution. After each
addition of base, aliquots of 2 mL of the solution were placed in small vials and the pH
monitored by UV–Vis spectroscopy. Afterwards, the aliquot samples were discarded to
avoid contamination by chloride ions leaching from the pH electrode.
7.2.6 Kinetic Measurements
All kinetic reactions of the complexes EnPt, PropPt, ButPt, HexPt, OctPt and DecPt
were monitored under pseudo first-order conditions with at least a twenty-fold excess of
the nucleophile. The reactions were started by the mixing of equal volumes of a solution
of the Pt (II) complex with a solution of the nucleophile directly in the stopped-flow
instrument or UV-Vis spectrophotometer at suitable wavelengths (Table S7.1). Observed
rate constants were calculated by a single exponential function or double exponential fit
to the kinetic traces. The reported pseudo first-order rate constants, kobs, are mean
values of at least five independent kinetic runs on the stopped-flow or duplicate
measurements on the UV-Vis spectrophotometer. Second-order rate constants, k2, were
obtained by a fit of a straight line to the plot of pseudo first-order rate constants kobs
versus concentration of nucleophile [NU], using a standard least-squares minimizing
routine by Origin 7.5 ®38 software package. Enthalpies and entropies of activation, ΔH ≠
and ΔS ≠ , were obtained by a fit of the natural logarithm of the second-order rate
constant, ln(k2/T) versus 1/T to the Eyring equation.
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