Linkage isomerism of (diamine)platinum(II) complexes of sulfur-containing ylidenemalonate ligands

A ¹H NMR study has been carried out on (diamine)platinum(II) complexes of 1,3-dithian-2-ylidenemalonate (DTAYM) and 1,3-dithiepane-2-ylidenemalonate (DTEYM) ligands as anionic leaving group in aqueous solution. Only the O,S-chelated isomer was observed in solution for all the DTAYM complexes regardless of the kind of carrier ligand amine as was in the solid state. However, both O,S- and S,S′-chelated isomers were observed in solution for DTEYM complexes, which show linkage isomerism from the O,S-chelate to the thermodynamically more stable S,S′-chelate. The rate of linkage isomerism of the DTEYM complexes was found to be dependent on their amine co-ligands. Molecular dynamics of the DTAYM complexes was also discussed based on their temperature-dependent NMR spectra. The crystal structure of the S,S′-isomer of (NH₃)₂Pt(DTEYM) · H₂O was determined whereas that of the O,S-isomer could not be obtained due to its poor crystallinity.