Phosphinoamine coinage metal complexes with a coumarin fluorophore: synthesis, characterization, and <i>in vitro</i> (photo)cytotoxicity

Herein, we report the synthesis and characterization of coinage metal complexes coordinated to a coumarin-functionalized (bis(4-(<i>tert</i>-butyl)phenyl)) phosphinoamine ligand (L1). Treatment of the ligand with CuCl led to the formation of an unexpected tetranuclear compound [L1CuCl]₄, while reaction with [Au(tht)₂SbF₆] or [Au(tht)Cl] (tht = tetrahydrothiophene) in an equimolar ratio resulted in [L1₂Au]SbF₆ or [L1AuCl]. Reaction of the latter compound with 1-thio-β-D-glucose tetraacetate (Glc) led to [L1Au(Glc)]. Owing to the presence of the fluorophore, the resulting metal complexes exhibited strong emissive properties, with the Au^I complexes demonstrating quantum yields exceeding 80%. The emission is mainly contributed by the coumarin moiety. As a result, we further investigated these compounds for their cytotoxicity, photocytotoxicity, and potential in cellular imaging applications. Despite the known general cytotoxicity of Cu^I, the new coinage metal complexes show low cytotoxicity and are useful for cell imaging.