Proton-coupled electron transfer (PCET) is ubiquitous in catalysis, allowing many chemical transformations to take place along energetically less demanding pathways. In water oxidation catalysis, PCET processes enable the buildup of redox equivalents in a narrower potential window in the “water oxidative activation” portion of the catalytic cycle. This provides access to high valent metal-oxo or metal-oxyl moieties such as RuV=O. PCET also plays a key role in the O-O bond formation step in the water nucleophilic attack (WNA) pathway where a proton transfer from the incoming water molecule to a nearby proton acceptor is required. In addition, PCET also plays an important role in oxidative activation steps following O-O bond formation and preceding the final O2 evolution step. In CO2 reduction catalysis, PCET processes provide access to one-electron reduced species at mild or moderate potentials compared to non-PCET single electron reductions. It also plays an important role in disproportionation reactions that result in doubly-reduced species incorporating two electrons and two protons (equivalent to a hydride and a proton) or two electrons and one proton (equivalent to a hydride). In this presentation, the role of PCET in the first three major steps of the water oxidation cycle as well as in CO2 reduction via hydride transfer will be discussed using specific examples.

Role of PCET in small molecule activation: Water oxidation and CO2 reduction

255th National Meeting (2018)

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