Uranyl Oxo Silylation Promoted by Silsesquioxane Coordination

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Uranium Coordination Chemistry

Background:

• The coordination chemistry of uranium, particularly the uranyl ion (UO2^2+), is crucial for understanding actinide behavior in various environments.
• Silsesquioxanes are versatile silicon-oxygen cage compounds that can mimic mineral surfaces and act as ligands in coordination chemistry.
• Exploring the reactivity of uranium precursors with silsesquioxanes can lead to new structural motifs and reactivity patterns.

Purpose of the Study:

• To investigate the reaction between a uranium precursor, [UO2(N(SiMe3)2)2(THF)2], and a silsesquioxane ligand, Cy7Si7O9(OH)3.
• To characterize the products formed under different solvent conditions (THF vs. hexanes).
• To elucidate the reaction mechanism and explore the potential of silsesquioxanes as ligands in actinide coordination chemistry.

Main Methods:

• Reaction of [UO2(N(SiMe3)2)2(THF)2] with Cy7Si7O9(OH)3 in THF and hexanes.
• Isolation and characterization of products using X-ray crystallography and 29Si{1H} NMR spectroscopy.
• Independent synthesis of proposed intermediates and comparison with in situ NMR data.

Main Results:

• In THF, the reaction yielded [U(OSiMe3)3(Cy7Si7O12)] (1), a U(VI) silyloxide, and [U(Cy7Si7O12)2] (3), via silylation and ligand scrambling.
• In hexanes, the reaction produced the uranyl cluster [(UO2)3(Cy7Si7O12)2(Et2O)(MeCN)2] (2), featuring unsilylated uranyl fragments.
• The solvent significantly influences the reaction outcome, leading to distinct uranium coordination complexes.

Conclusions:

• The silsesquioxane ligand can induce unprecedented reactivity in uranyl complexes, leading to the formation of U(VI) silyloxides.
• The electron-donating ability of the silsesquioxane ligand plays a key role in promoting these transformations.
• Silsesquioxanes represent promising ligands for exploring novel actinide coordination chemistry and designing mineral surface mimics.