Blue-Green Luminescent Rhenium(I) Tricarbonyl Complexes with Pyridine-Functionalized N-Heterocyclic Carbene Ligands

Five rhenium(I) tricarbonyl chloride complexes with pyridine-functionalized N-heterocyclic carbenes, Re(CO) 3 (L)Cl (L = 3-methyl-1-(2-pyridyl)imidazol-2-ylidene ( 1 ), 3-methyl-1-(2-picolyl)imidazol-2-ylidene ( 2 ), 3-methyl-1-(2-pyridyl)benzimidazolin-2-ylidene ( 3 ), 3-methyl-1-(2-picoyl)benzimidazolin-2-ylidene ( 4 ), 1-methyl-4-(2-pyridyl)-1,2,4-triazoline-5-ylidene ( 5 )), have been synthesized by silver carbene transmetalation and characterized by elemental analysis, 1 H NMR, 13 C NMR, and IR spectra. The molecular structures of 3 – 5 have been determined by single-crystal X-ray diffraction. The electrochemical and photophysical properties of complexes 1, 3, and 5 have been studied. In both degassed CH 2 Cl 2 solution and the solid state at room temperature or 77 K, the emission wavelengths (465–511 nm) of complexes 1, 3, and 5 lie in the blue-green region, which are rare in contrast to the reported rhenium(I) tricarbonyl complexes. The photoluminescence lifetime decays of Re(I) complexes 1, 3, and 5 were measured, and the quantum yields were calculated by using the standard sample ([Ru(bpy) 3 ] 2+ (Cl – ) 2 in degassed acetonitrile solution; Φ std = 0.094).