Electronic and Photophysical Properties of ReI(CO)3Br Complexes Modulated by Pyrazolyl–Pyridazine Ligands

The direct reaction of a series of substituted (1H-pyrazol-1-yl)pyridazine (LI: 6-(1H-pyrazolyl)pyridazine; LII: 3-chloro-6-(1H-pyrazole-1-yl)-pyridazine; LIII: 6-(1H-3,5-dimethylpyrazolyl)pyridazine-3-carboxylic acid; LIV: 3,6-bis-N-pyrazolyl-pyridazine; and LV: 3,6-bis-N-3-methylpyrazolyl-pyridazine) with the bromotricarbonyl(tetrahydrofuran)-rhenium(I) dimer leads to the monometallic complexes [(LX)Re(CO)3Br] (I–V), which displays a nonregular octahedral geometry around the ReI center and a fac-isomerism for the carbonyl groups, whereas pyridazine and pyrazolyl rings remain highly coplanar after coordination to rhenium. Cyclic voltammetry shows one irreversible oxidation and one irreversible reduction for each compound as measured in N,N-dimethylformamide. Oxidation ranges from 0.94 V for III to 1.04 V for I and have been attributed to the ReI/ReII couple. In contrast, the reductions are ligand centered, ranging from −1.64 V for II to −1.90 V for III and V. Density functional theory calculations on the...