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, ¹H NMR, ¹³C 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 CH₂Cl₂ 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).