Divergent uranium- versus phosphorus-based reduction of Me3SiN3 with steric modification of phosphido ligands

Abstract

We describe an example of a two-electron metal- and ligand-based reduction of Me₃SiN₃ using uranium(IV) complexes with varying steric properties. Reaction of (C₅Me₅)₂U(CH₃)[P(SiMe₃)(Ph)] with Me₃SiN₃ produces the imidophosphorane complex, (C₅Me₅)₂U(CH₃)[NP(SiMe₃)₂(Ph)] through oxidation of phosphorus. However, a similar reaction with a more sterically encumbering phosphido ligand, (C₅Me₅)₂U(CH₃)[P(SiMe₃)(Mes)] forms the U(IV) complex, (C₅Me₅)₂U[κ²-(N,N)–N(SiMe₃)P(Mes)N(SiMe₃)]. In probing the mechanism of this reaction, a U(VI) bis(imido) complex, (C₅Me₅)₂U(NSiMe₃){N[P(SiMe₃)(Mes)]} was isolated. DFT calculations show an intramolecular reductive cycloaddition reaction leads to the formation of the U(IV) bis(amido)phosphane from the U(VI) bis(imido) complex. This is a rare example of the isolation of a reaction intermediate in f element chemistry.