Uranyl Oxo Silylation Promoted by Silsesquioxane Coordination

The reaction of [UO2(N(SiMe3)(2))(2)(THF)(2)] with 1 equiv of Cy7Si7O9(OH)(3) in THE affords [U-(OSiMe3)(3)(Cy7Si7O12)] (1) as orange plates in 24% isolated yield. Its X-ray crystal structure reveals three silylated O-yl ligands, confirming the unprecedented conversion of the uranyl ion to a U(VI) silyloxide. We propose that the formation of 1 proceeds through a transient uranyl silsesquioxide intermediate, [{Cy7Si7O11(OH)}UO2], which undergoes rapid oxo silylation by HN(SiMe3)(2), followed by silyloxy ligand scrambling, to form 1 and the U(VI) bis(silsesquioxane) complex, [U(Cy7Si7O12)(2)] (3), among other products. The formation of 3 was confirmed by its independent synthesis and comparison of its Si-29{H-1} NMR spectrum with that of the in situ reaction mixture. In contrast to the reaction in THF, the reaction of [UO2(N(SiMe3)(2))(2)(THF)(2)] with Cy7Si7O9(OH)(3) in hexanes, followed by recrystallization from Et2O/MeCN, results in the formation of the uranyl cluster, [(UO2)(3)(Cy7Si7O12)(2)(Et2O)(MeCN)(2)] (2), as yellow rods in 42% isolated yield. Complex 2 features two O-yl center dot center dot center dot U dative interactions, but in contrast to 1, none of its three uranyl fragments are silylated. Overall, the conversion of [UO2(N(SiMe3)(2))(2)(THF)(2)] to 1 and 3 is likely promoted by the strong electron donor ability of the silsesquioxane ligand and suggests that the actinide coordination chemistry of mineral surface mimics, such as silsesquioxane, is a fruitful arena for the discovery of new reactivity.