Reductive silylation of Cp*UO2(MesPDIMe) promoted by Lewis bases

Abstract

Functionalization of the uranyl moiety (UO₂²⁺) in Cp*UO₂(^MesPDI^Me) (1-PDI) (^MesPDI^Me = 2,6-((Mes)NCMe)₂C₅H₃N; Mes = 2,4,6-triphenylmethyl), which bears a reduced, monoanionic pyridine(diimine) ligand, is reported. Silylating reagents, R₃Si-X (R = Me, X = Cl, I, OTf, SPh; R = Ph, X = Cl), effectively add across the strong OUO bonds in the presence of the Lewis base, OPPh₃, generating products of the form (R₃SiO)₂UX₂(OPPh₃)₂ (R = Me, X = I (2-OPPh₃), Cl (3-OPPh₃), SPh (5-OPPh₃), OTf (6-OPPh₃); R = Ph, X = Cl (4-OPPh₃)). During this transformation, reduction to uranium(IV) occurs with loss of (Cp*)₂ and ^MesPDI^Me, each of which acts as a one-electron source. In the reaction, the Lewis base serves to activate the silyl halide, generating a more electrophilic silyl group, as determined by ²⁹Si NMR spectroscopy, that undergoes facile transfer to the oxo groups. Complete U–O bond scission was accomplished by treating the uranium(IV) disiloxide compounds with additional silylating reagent, forming the family (Ph₃PO)₂UX₄. All compounds were characterized by ¹H NMR, infrared, and electronic absorption spectroscopies. X-ray crystallographic characterization was used to elucidate the structures of 2-OPPh₃, 4-OPPh₃, 5-OPPh₃, and 6-OPPh₃.