Ruthenium and rhenium complexes of fluorene-based bipyridine ligands: Synthesis, spectra, and electrochemistry

Bipyridine ligands featuring fluorene and ferrocene in the conjugation chai n were synthesized by Pd(II)/Cu(I)-catalyzed Sonogashira coupling reactions , and their complexation behavior was investigated. The octahedral complexe s formed by refluxing Ru(bpy)(2)Cl-2 and Re(CO)(5)Cl with the ligands in et hanol or benzene were characterized by NMR,electronic spectra, fluorescence spectra, mass spectra, elemental analyses, and electrochemical studies. Th e bipyridine ligands and the complexes except the ferrocene-containing comp ounds are luminescent at room temperature. The luminescence in the rutheniu m complexes is possibly from a MLCT state, and the fluorescence due to the ligand is completely quenched. When: compared to the Ru(bpy)(3)(2+), the ru thenium complexes studied in this work exhibit longer lifetimes, which prob ably stems from the delocalization of charge into the extended fluorene con jugation. The crystal structure of a ferrocenyl fluorene derivative is also reported.