C=O Activation in CO₂

Activation of the thermodynamically strong C=O bond in CO₂ is the first step to using CO₂ as a chemical feedstock. Uranium complexes have been explored as CO₂ activators due to their oxophilicity, Lewis acidity, and highly reducing nature.

Karsten Meyer and colleagues, University Erlangen−Nuremberg, Germany, have performed theoretical studies on the uranium complex, [((^MeArO)₃mes)U] (mes=2,4,6-trimethylphenyl) with CO₂. Reaction of [((^MeArO)₃mes)U] with toluene results in formation of the bridging carbonate complex [{((^MeArO)₃mes)U^IV}₂(μ-η²:η²-CO₃)].

Discrete Fourier transform (DFT) studies suggest a three step mechanism that forms the dinuclear CO₂ complex, releases CO to form the bridging μ-oxo species, then inserts a CO₂ molecule into the U–O bond generating the carbonate product. The authors note that the activation energy of this route to carbonate from CO₂ could be reduced through ligand modification.

• Carbonate Formation from CO₂ via Oxo versus Oxalate Pathway: Theoretical Investigations into the Mechanism of Uranium-Mediated Carbonate Formation
  L. Castro, O. P. Lam, S. C. Bart, K. Meyer, L. Maron,
  Organometallics 2010, 29.
  DOI: 10.1021/om100479r

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