Chiral-at-Metal Phosphorescent Square-Planar Pt(II)-Complexes from an Achiral Organometallic Ligand

The synthesis and characterization of a new kind of cis- and trans-cyclometalated square-planar platinum(II) complexes is reported. Uncharged organometallic compounds carrying one or two of the C(∧)N-donor ligand L(CN) were prepared. Due to the heterobidentate coordination of the achiral chelate ligand, the formed [PtL(CN)Cl(SEt2)], cis- and trans-[PtL(CN)2] complexes are chiral with the metal serving as the stereo center. The enantiomers of complex trans-[PtL(CN)2] could be separated and their absolute configuration was determined by anomalous X-ray diffraction, in accordance with CD spectroscopic results and TD-DFT calculations. All compounds were fully characterized by NMR spectroscopy, mass spectrometry and X-ray structure determination. The photophysical properties of trans-[PtL(CN)2] have been investigated showing phosphorescence in solution and in the solid state with a moderate quantum yield. For the enantiomers, strong circular dichroism (CD) and circularly polarized luminescence (CPL) effects were observed, rendering this new structural motif suitable for application in chiroptical and luminescent materials.