Assessing the Electrocatalytic Properties of the {Cp*RhIII}2+‐Polyoxometalate Derivative [H2PW11O39{RhIIICp*(OH2)}]3– towards CO2 Reduction.

Storage of electricity produced intermittently by renewable energy sources is a societal issue. Besides the use of batteries and supercapacitors, conversion of excess electricity into chemical energy is also actively investigated. The conversion of CO2 to fuel or fuel precursors is an option that requires the use of a catalyst to overcome the high activation energy barrier. Of molecular catalysts, metal complexes with polypyridyl ligands are well represented, among which the [Cp*Rh(bpy)Cl]+ and [M(bpy)(CO)3X] (M = Re, Mn) complexes. As redox non‐innocent ligand, the bipyridine ligand is generally involved in the reduction mechanisms. It is thus tempting to replace it by other redox non‐innocent ligands such as vacant polyoxometalates (POMs). We have thus prepared [α‐H2PW11O39{RhIIICp*(OH2)}]3– which is closely related to [Cp*RhIII(bpy)Cl]+ by substitution of the monovacant [PW11O39]7– Keggin‐type POM for the bipyridine ligand. Its activity towards CO2 reduction has been assessed in acetonitrile in the presence of water. Compared to [Cp*Rh(bpy)Cl]+ that produces formate selectively over CO and H2, the POM derived catalyst favors proton reduction over CO2 reduction. [α‐H2PW11O39{RhIIICp*(OH2)}]3– was prepared by reaction between the monovacant Keggin‐type [α‐H2PW11O39]5– and [Cp*Rh(CH3CN)3]2+. It is closely related to the CO2 reduction electrocatalyst [Cp*RhIII(bpy)Cl]+ by changing the bpy ligand by the polyoxometalate, both acting as redox non‐innocent bidentate ligands. The selectivity of the CO2 reduction was altered from the production of formate to dihydrogen. [ABSTRACT FROM AUTHOR]