Reactivity studies of trans-[PtClMe(SMe2)2] towards anionic and neutral ligand substitution processes

Reaction of trans-[PtClMe(SMe2)2] with the mono anionic ligands azide, bromide, cyanide, iodide and thiocyanate result in substitution of the chloro ligand as the first step. In contrast the neutral ligands pyridine, 4-Me-pyridine and thiourea substitute a SMe2 ligand in the first step as confirmed by 1H NMR spectroscopy and the kinetic data. Detailed kinetic studies were performed in methanol as solvent by use of conventional stopped-flow spectrophotometry. All processes follow the usual two-term rate law for square-planar substitutions, kobs = k1 + k2[Y] (where k1 = kMeOH[MeOH]), with k1 = 0.088 ± 0.004 s−1 and k2 = 1.18 ± 0.13, 3.8 ± 0.3, 17.8 ± 1.3, 34.9 ± 1.4, 75.3 ± 1.1 mol−1 dm3 s−1 for Y− = N3, Br, CN, I and SCN respectively at 298 K. The reactions with the neutral ligands proceed without an appreciable intercept with k2 = 5.1 ± 0.3, 15.3 ± 1.8 and 195 ± 3 mol−1 dm3 s−1 for Y = pyridine, 4-Me-pyridine and thiourea, respectively, at 298 K. Activation parameters for MeOH, N3-, Br−, CN−, I−, SCN−, and Tu are ΔH≠ = 47.1 ± 1.6, 49.8 ± 0.6, 39 ± 3, 32 ± 8, 39 ± 5, 34 ± 4 and 31 ± 3 kJ mol−1 and ΔS≠ = −107 ± 5, −77 ± 2, −104 ± 9,−113 ± 28, −85 ± 18, −94 ± 14 and −97 ± 10 J K−1 mol−1, respectively. Recalculation of k1 to second-order units gives the following sequence of nucleophilicity: MeOH

Graphical abstractThe substitution behaviour of trans-[PtClMe(SMe2)2] towards anionic and neutral ligands was investigated using stopped-flow spectrophotometry. The anionic ligands substitute the Cl− ligand while the neural ligands substitute a SMe2 ligand in the first step. All reactions follow an associative mode of activation as confirmed by large negative entropies of activation.Figure optionsDownload full-size imageDownload as PowerPoint slide