Synthesis and Electrochemical Reactivity of Molybdenum Dicarbonyl Supported by a Redox-Active α‑Diimine Ligand

Low-valent molybdenum dicarbonyl
complexes with a diazabutadiene [mesDABR; [ArNC­(R)­C­(R)NAr];
Ar = 2,4,6-trimethylphenyl (mes), R = H or CH3] ligand
have been synthesized and fully characterized. The title complexes
exhibit elongated DAB C–N and shortened C–C bond lengths
over the free ligand and other zerovalent molybdenum complexes of
DAB. Compared to known examples theoretically described as iminato
π-radicals (L•–), the oxidation state
assignment fits a molybdenum­(II) description. However, Mo K-edge X-ray
absorption spectroscopy indicates that the complexes are best described
as molybdenum(0). This example demonstrates that caution should be
exercised in assigning the oxidation state based on structural parameters
alone. Cyclic voltammetry studies reveal an electrochemical–chemical
process that has been identified by in situ Fourier transform infrared
spectroelectrochemistry as cis-to-trans isomerization.