3 years ago

Carbon Dioxide Activation by a Uranium(III) Complex Derived from a Chelating Bis(aryloxide) Ligand

Carbon Dioxide Activation by a Uranium(III) Complex Derived from a Chelating Bis(aryloxide) Ligand
Alistair S. P. Frey, S. Mark Roe, Alexander F. R. Kilpatrick, F. Geoffrey N. Cloke, Christopher J. Inman
The new dianionic ligand C6H4{p-C(CH3)2C6H2Me2O}2 (=p-Me2bp), featuring two aryloxide donors and a central arene ring, has been synthesized and used to prepare the mixed-ligand U(III) compound [U(Cp*)(p-Me2bp)], which exhibits an η6 interaction with the uranium center. Reductive activation of CO2 was investigated using [U(Cp*)(p-Me2bp)] in supercritical CO2, which gave a dinuclear uranium carbonate complex, {U(Cp*)(p-Me2bp)}2(μ-η12-CO3), cleanly and selectively. Reactivity studies in conventional solvents using lower pressures of CO2 showed the formation of a rare U(IV) oxalate complex, {U(Cp*)(p-Me2bp)}2(μ-η22-C2O2), alongside {U(Cp*)(p-Me2bp)}2(μ-η12-CO3). The relative ratio of the last two products is temperature dependent: at low temperatures (−78 °C) oxalate formation is favored, while at room temperature the carbonate is the dominant product. The U(IV) iodide [U(Cp*)(p-Me2bp)I] was also synthesized and used as part of an electrochemical study, the results of which showed that [U(Cp*)(p-Me2bp)] has a UIV/UIII redox couple of −2.18 V vs FeCp2+/0 as well as a possible electrochemically accessible UIII/UII reduction process at −2.56 V vs FeCp2+/0.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00263

DOI: 10.1021/acs.organomet.7b00263

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