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

Abstract

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; Φstd = 0.094).