The 85th Meeting of the Israel Chemical Society

Photoelectrochemical and electrochemical selective reduction of carbon dioxide catalyzed by rhenium complexes: Strategies for less negative potentials, CO2 binding and intramolecular proton transfer

Eynat Haviv 1 Linda J. W. Shimon 2 Dima Azaiza-Dabbah 1 Raanan Carmieli 2 Liat Avram 2 Jan M. L. Martin 1 Ronny Neumann 1
1Department of Organic Chemistry, Weizmann Institute of Science, Rehovot, Israel
2Department for Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel

The catalytic designs of new rhenium CO2 reduction catalysts will be presented and discussed that allow (1) reduction at less negative potentials and (2) higher turnover frequencies via CO2 binding and improved proton transfer needed for the reaction.

A dirhenium-polyoxometalate complex:1 The photochemical reduction of CO2 to CO requires two electrons and two protons. Towards the realization of a water splitting reaction as the source of electron and protons for CO2 reduction, we have found that a reduced acidic polyoxometalate, H5PWV2W10O40, is a photoactive electron and proton donor with visible light through excitation of the intervalence charge transfer band. Upon linking the polyoxometalate to a di-rhenium molecular catalyst a cascade of transformations occurs where the polyoxometalate is electrochemically reduced at a low negative potential of 1.3 V versus Ag/AgNO3 and visible light, a 60 W tungsten lamp, or a red LED is used to transfer electrons from the polyoxometalate to the di-rhenium catalyst active for the selective reduction of CO2 to CO. Overall, the reduction potential is reduced by 400mV.

Thiourea tether as a binding site for CO2 and a proton donor:2 The bipyridine ligand of a Re(I) catalyst was modified with a thiourea tether, known to form hydrogen bonds with carbonyl moieties. The resulting complex was an excellent electrocatalyst for CO2 reduction increasing the turnover frequency by an order of magnitude. Reaction intermediates were observed by NMR and EPR. Importantly, NMR experiments demonstrated the binding of CO2 to the thiourea tether thereby stabilizing carboxylic acid reaction intermediates. Furthermore, it was shown that the thiourea moiety is also a local proton source in a barrier-less proton transfer. Combined, these effects of the thiourea tether in the second coordination sphere explain the significantly higher activity.

  1. Eur. J. 2017, 23, 92.
  2. Am. Chem. Soc. 2018, 140, 12451.








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