Synthesis, characterization, and reactivity of molybdenum-quinoid complexes supported by a redox and acid/base non-innocent ligand

The propensity for earth-abundant transition metals to preferentially access single-electron chem. remains one of the more prominent obstacles in their utilization to facilitate efficient multi-proton, multi-electron activation of small mols. such as dioxygen or carbon dioxide. Incorporation of redox non-innocent ligands as well as pendant acid/base moieties has proven effective as a method for altering the reactivity of transition metal complexes. A series of low-valent molybdenum-quionoid complexes supported by a redox and acid/base non-innocent ligand have been synthesized and characterized demonstrating both hydrogen atom and proton and electron transfer chem. spanning a total of four electrons and two protons. Five different protonation/oxidn. state combinations were isolated from Mo(0)-catechol to Mo(II)-quinone. Substrate-based multi-proton, multi-electron reactivity was demonstrated through redn. of dioxygen to water, and mechanistic insight gained via substituting the protons for other Lewis-acidic moieties will also be presented.