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

Herein, we report the synthesis and characterization of coinage metal complexes coordinated to a coumarin-functionalized (bis(4-(tert-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-beta-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 AuI 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 CuI, the new coinage metal complexes show low cytotoxicity and are useful for cell imaging.