Inorganic Seminar Series

Seminar series
Inorganic Chemistry
Wed, May 22 4:30pm
3440 Mol Sci
Speaker Professor Andrew Bocarsly
Princeton University
Department of Chemistry

Electrocatalytic and Photoinduced Reduction of CO2Using the [XMn(CO)3bpy] System:Two is Better Than One When it Comes to Manganese

Abstract:   The complex [BrMn(bpy)(CO)3] is an established electrocatalyst affecting the reduction of CO2 to CO in the presence of a proton source. We have used this complex as a “testbed” to study the interactions of protons and electrons during the conversion of CO2 to CO. To that end, we have dangled a phenolic moiety from various bipyridine ring positions in order to probe the role (or lack thereof) of hydrogen bonding in this process. These studies have indicated the need for a key hydrogen bond that appears to facilitate the oxygen transfer portion of the transformation. H vs. D isotope studies indicate a complex set of equilibria associated with this proton coupled electron transfer reaction (PCET).

A major experimental challenge associated with the study of this and related complexes is the that they undergo facile photochemical decomposition under typical room light conditions. We have demonstrated several modifications of this complex that help to mitigate this decomposition route. However, these variations have not provided a sufficient degree of stability to produce a pragmatic electrocatalyst. We now report that the cyanide bridged dimer shown in the Figure, {[Mn(bpy)(CO)3]2(μ-CN)}+, eliminates this deleterious photochemistry. Further, this cyanide bridged dimer is not only a viable electrocatalyst, but is effective as a photocatalyst for the reduction of CO2 to CO when irradiated at wavelengths that absorb into the metal to bpy charge transfer band. In this photochemical reaction, the initial photodissociation of a CO ligand provides a site for CO2 binding. Follow up photochemically induced electron transfers lead to the reduction of the bound CO2 ligand. Mechanistically, the photochemical reduction of CO2 appears to follow the electrochemical reduction of CO2 using this complex.