Synthesis, Spectroscopy, and Electrochemistry of (α-Diimine)M(CO)₃Br, M = Mn, Re, Complexes: Ligands Isoelectronic to Bipyridyl Show Differences in CO₂ Reduction

The synthesis and characterization of new Mn­(I)- and Re­(I)-centered organometallic complexes fashioned with 1,4-diazabutadiene (DAB) ligands is reported. Ten compounds of the type fac-(α-diimine)­M­(CO)₃Br (M = Mn, Re) were obtained in moderate to excellent yield (35–80%) and high purity from the coordination of the five ligands with M­(CO)₅Br in refluxing ethanol. Despite the electronic similarity of DAB to 2,2′-bipyridyl, the complexes described herein were poor mediators of electrochemical CO₂ conversion to CO, but provide insight into the role of redox-active ligands in catalysis. Additional characterization of the one-electron reduced rhenium compounds, relevant intermediates in CO₂ reduction, by EPR and single-crystal X-ray analysis is described.