CYCLOMETALATED PT(II) SCHIFF BASE COMPLEXES: UNEXPECTED CIS/TRANS ISOMERY AND STRUCTURE-PROPERTY CORRELATIONS

Phosphorescent d6 and d8 metal complexes containing ?-conjugated ligands with N and/or C donor atoms have attracted widespread research interest due to their excellent emission properties and potential applications in fields such as optoelectronic devices, chemo-/biosensors, bioimaging and medicinal chemistry. Schiff base bidentate ligands are versatile and tunable structures, easy to prepare, and have been widely applied in the development of metal catalysts. On the contrary, transition-metal Schiff base complexes are less studied and developed in optoelectronics. In this communication we present the synthesis of two novel neutral square planar Pt(II) complexes, Pt-1 and Pt-2, characterized by the presence of an ancillary C^N (ppy or ppz) cyclometalated ligand and a O^N Schiff base ligand. This complexes have been synthesized as depicted in scheme 1 reacting the platinum chloro intermediate 1a,b with the O^N ligand. Reacting the intermediate 1a with NpOPh Shiff base ligand, we obtained a single compound whose structure is indicated as Pt 1 (Scheme 1).1 On the contrary, the reaction of 1b, carrying C^N = ppz ligand, with NpOPh ligand provided a mixture of two compounds which were easily isolated by chromatography and structurally characterized by HPLC-MS, NMR analysis and X-Ray diffraction. The two compounds proved to be the geometrical isomers cis-Pt 2 and trans-Pt 2 reported in scheme 1. To the best of our knowledge this is the first example of cis/trans isomer formation in neutral Pt(II) complexes carrying two different chelating ligands. Pt 1 and cis/trans-Pt 2 isomers were further investigated by means of UV-Vis spectroscopy, photoluminescence emission, cyclovoltammetry and IR techniques. The physical and electronic data are correlated to the structural parameters