The catalytic reduction of CO<sub>2</sub> to HCO<sub>2</sub><sup>-</sup>
requires a formal transfer of a hydride (two electrons, one proton). Synthetic
approaches for inorganic molecular catalysts have exclusively relied on classic
metal hydrides, where the proton and electrons originate from the metal (via heterolytic
cleavage of an M-H bond). An analysis of the scaling relationships that exist in
classic metal hydrides reveal that hydride donors sufficiently hydridic to
perform CO<sub>2</sub> reduction are only accessible at very reducing electrochemical
potentials, which is consistent with known synthetic electrocatalysts. By
comparison, the formate dehydrogenase enzymes operate at relatively mild
potentials. In contrast to reported synthetic catalysts, none of the major
mechanistic proposals for hydride transfer in formate dehydrogenase proceed
through a classic metal hydride. Instead, they invoke formal hydride transfer from
an orthogonal or bi-directional mechanism, where the proton and electron are
not co-located. We discuss the thermodynamic advantages of this approach for
favoring CO<sub>2</sub> reduction at mild potentials, along with guidelines for
replicating this strategy in synthetic systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.