In nature, the [NiFe] CO-dehydrogenase enzyme can reduce CO2 to CO selectively and reversibly through a catalytic process featuring a bifunctional activation of CO2 and an additional stabilization by hydrogen interactions between the active site and the functional groups in the secondary coordination sphere. To mimic this essential function and structural features, we developed a new type of rhenium and manganese bipyridine electrocatalysts M[bpyMe(Im-R)](CO)3Cl]+ (M= Re or Mn; R = Me, Me2 and Me4) featuring charged, redox-active imidazolium moieties in the secondary coordination sphere. Electronic structure calculations were performed to study the reaction mechanism for CO2-to-CO conversion in the presence of water as the proton source using this type of catalysts. For the first time, a solvation shell of water cluster (H2O)5 was applied explicitly to characterize the protonation steps and probe the role of secondary imidazolium moieties in catalytic activity. In addition, the energy span model was used to identify the TOF determining intermediate (TDI), and TOF determining transition state (TDTS) and calculate the turnover frequencies. The results show that the incorporation of imidazolium moieties in the secondary coordination sphere can not only shift the reduction potentials positively due to an electrostatic effect but also facilitate CO2 binding, proton transferring steps, and stabilize higher energy intermediates via intra- and inter-molecular interactions during catalysis. More importantly, when using different substituents in the imidazolium moiety, the relative activation energy barrier order in the rate-determining step strongly suggests that the C2-H functionality of the imidazolium moiety plays a crucial role on turnover frequency during catalysis.

Mechanistic study for the CO2 reduction reaction using M[bpyMe(Im-R)](CO)3Cl]+ complexes: Probing the role of the imidazolium moieties in the secondary coordination sphere

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.