Ligand substitution reactions of some sterically hindered Pt(II) complexes. The crystal structures of [TLtBuH2](ClO4)2·0.5H2O

Substitution reactions of the complexes [(TLtBu)PtCl]+ and [Pt(tpdm)Cl]+, where TLtBu = 2,6-bis[(1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine and tpdm = terpyridinedimethane, with nucleophiles: thiourea, I−, Br−, NO2−, pyridine and dimethyl-sulfoxide (DMSO) were studied in 0.1 M NaClO4 aqueous solution in the presence of 10 mM NaCl. The reactions were carried out at three different temperatures (288, 298 and 308 K) using variable-temperature UV–VIS spectrophotometer. The substitutions were followed under the pseudo-first-order conditions with a large excess of nucleophiles. The slightly higher reactivity of complex with tpdm ligand can be attributed to the influence of the bulkiness of tert-butyl-groups from [(TLtBu)PtCl]+ complex. The order of reactivity of studied ligands is: thiourea > I− > Br− > NO2− > pyridine > DMSO. The negative values reported for entropy of activation confirmed the associative substitution mode. These results are discussed in order to find the connection between structure and reactivity of the complexes with tridentate sterically hindered ligands. The crystal structure of [TLtBuH2](ClO4)2·0.5H2O was determined by X-ray diffraction.

Substitution reactions of two sterically hindered Pt(II) complexes with different nucleophiles were investigated. Linear Free Energy Relationship (LFER) was used for determination the affinity of the complex towards the studied nucleophiles.Figure optionsDownload as PowerPoint slideHighlights
► The substitution reactions of sterically hindered Pt(II) complexes were investigated.
► The order of reactivity of ligands is: thiourea > I− > Br− > NO2− > pyridine > DMSO. LFER indicate that the substitution occurs via the same mechanism.
► The mechanism of the substitution reactions is associative supported by the negative values of ΔS≠.