Reductive silylation of uranyl mediated by iminosemiquinone ligands

Abstract

Stoichiometric silylation of the uranyl species, (dippisq)2UO2THF, which features two reduced iminosemiquinone ligands, is reported. These ligand radicals facilitate the reduction of uranium 6+ to 4+, which is accompanied by silylation of the uranyl moiety with two equivalents of Me3SiBr and release of the oxidized ligand. The intermediate, (Me3SiO)2UBr2(OPPh3)2, is isolated prior to U–O bond cleavage by further addition of Me3SiBr, producing UBr4(OPPh3)2. U–O bond scission can also be performed in a one-pot reaction, by treating (dippisq)2UO2THF with Me2SiCl2, forming UCl4(OPPh3)2 and polymeric silyl products, (OSiMe2)n, with concomitant loss of oxidized ligand. In each case, isotopic 18O labeling experiments highlight the incorporation of the uranyl oxygen atoms into the resulting siloxanes released in the reactions.