Enzymes that use of molecular oxygen (O2) to promote challenging oxygen-atom transfer reactions often use a "monooxygenase" mechanism. This mechanism involves the use of a sacrificial reductant, such as NADH, to support reductive activation of O2: Sub + O2 + NADH + H+ → Sub=O + H2O + NAD+ (eqn. 1) Dioxygenases also exist; however, we are not aware of any enzyme in nature that promote oxygen-atom transfer to two independent equivalents of the same molecule, according to the following stoichiometry: 2 Sub + O2 →2 Sub=O (eqn. 2) This limitation, in part, reflects the kinetic barriers associated with O2 activation and oxygen-atom transfer at the active site of an enzyme. This presentation will show how electrochemical driving force may be used to overcome these kinetic barriers, enabling successful double oxygen-atom transfer, according to the stoichiometry in eqn. 2. A high valent M=O species is generated at the cathode via reductive activation of O2, while the same M=O species is generated at the anode via proton-coupled oxidation of a M-OH2 species. Both M=O species undergo O-atom transfer to organic sulfides to generate the corresponding sulfoxide. This electrochemical process involves no net consumption of electrons but uses electrochemical energy to overcome kinetic barriers intrinsic to O2 activation and H2O oxidation. Experimental and computational data provide valuable insights into the reaction mechanisms.

Metal-oxo mediated dioxygenase reactivity enabled by electrochemistry

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