Tuning Lanthanide Reactivity Towards Small Molecules with Electron-Rich Siloxide Ligands

• Published in: Angewandte Chemie International Edition 2014-09, Vol.53 (39), p.10448-10452
• Main Authors: Andrez, Julie, Pécaut, Jacques, Bayle, Pierre-Alain, Mazzanti, Marinella
• Format: Article
• Language: English
• Subjects: Anions; Carbon dioxide; carbon dioxide reduction; carbon disulfide reduction; Chemical Sciences; Cleavage; lanthanide complexes; Lanthanides; Ligands; Oxalates; Radicals; Reduction; siloxide ligands; small-molecule activation; Tuning
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201405031

The synthesis, structure, and reactivity of stable homoleptic heterometallic LnL4K2 complexes of divalent lanthanide ions with electron‐rich tris(tert‐butoxy)siloxide ligands are reported. The [Ln(OSi(OtBu)3)4K2] complexes (Ln=Eu, Yb) are stable at room temperature, but they promote the reduction of azobenzene to yield the KPhNNPh radical anion as well as the reductive cleavage of CS2 to yield CS32− as the major product. The EuIII complex of the radical anion PhNNPh is structurally characterized. Moreover, [Yb(OSi(OtBu)3)4K2] can reduce CO2 at room temperature. Release of the reduction products in D2O shows the quantitative formation of both oxalate and carbonate in a 1:2.2 ratio. The bulky siloxide ligands enforce the labile binding of the reduction products providing the opportunity to establish a closed synthetic cycle for the YbII‐mediated CO2 reduction. These studies show that the presence of four electron‐rich siloxide ligands renders their EuII and YbII complexes highly reactive. Yb and Eu can do it! The sterically demanding and electron‐rich coordination environment of EuII and YbII in homoleptic siloxide complexes leads to the reduction of azobenzene, carbon disulfide, and carbon dioxide, and the ready release of the reduction products.