Redox Chemistry of Bis(pyrrolyl)pyridine Chromium and Molybdenum Complexes: An Experimental and Density Functional Theoretical Study

The three- and four-membered redox series [Cr(MePDP)2]z (z = 1–, 2–, 3−) and [Mo(MePDP)2]z (z = 0, 1–, 2–, 3−) were synthesized to study the redox properties of the pincer ligand MePDP2– (H2MePDP = 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine). The monoanionic complexes were characterized by X-ray crystallography, UV/vis/NIR spectroscopy, and magnetic susceptibility measurements. Experimental and density functional theory (DFT) studies are consistent with closed-shell MePDP2– ligands and +III oxidation states (d3, S = 3/2) for the central metal ions. Cyclic voltammetry established multiple reversible redox processes for [M(MePDP)2]1– (M = Cr, Mo), which were further investigated via chemical oxidation and reduction. For molybdenum, one-electron oxidation yielded Mo(MePDP)2 which was characterized by X-ray crystallography, UV/vis/NIR, and magnetic susceptibility measurements. The experimental and computational data indicate metal-centered oxidation to a MoIV complex (d2, S = 1) with two MePDP2– ligand...