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; Φstd = 0.094).