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

摘要

We describe an example of a two-electron metal- and ligand-based reduction of Me _(3) SiN _(3) using uranium( IV ) complexes with varying steric properties. Reaction of (C _(5) Me _(5) ) _(2) U(CH _(3) )[P(SiMe _(3) )(Ph)] with Me _(3) SiN _(3) produces the imidophosphorane complex, (C _(5) Me _(5) ) _(2) U(CH _(3) )[NP(SiMe _(3) ) _(2) (Ph)] through oxidation of phosphorus. However, a similar reaction with a more sterically encumbering phosphido ligand, (C _(5) Me _(5) ) _(2) U(CH _(3) )[P(SiMe _(3) )(Mes)] forms the U( IV ) complex, (C _(5) Me _(5) ) _(2) U[ κ ~(2) -( N , N )–N(SiMe _(3) )P(Mes)N(SiMe _(3) )]. In probing the mechanism of this reaction, a U( VI ) bis(imido) complex, (C _(5) Me _(5) ) _(2) U(NSiMe _(3) ){N[P(SiMe _(3) )(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.