Oxo Ligand Substitution in a Cationic Uranyl Complex: Synergistic Interaction of an Electrophile and a Reductant

Reaction
of [UVIO2(dppmo)2(OTf)]­[OTf] (dppmo
= Ph2P­(O)­CH2P­(O)­Ph2)
with 4 equiv of Ph3SiOTf and 2 equiv of Cp2Co
generates the U­(IV) complex UIV(OTf)4­(dppmo)2 (1), as a yellow-green crystalline solid in
83% yield, along with Ph3SiOSiPh3 and [Cp2Co]­[OTf]. This reaction proceeds via a U­(IV) silyloxide intermediate,
[UIV(OSiPh3)­(dppmo)2­(OTf)2]­[OTf] (2), which we have isolated and
structurally characterized. Similarly, reaction of [UVIO2­(TPPO)4]­[OTf]2 (TPPO
= Ph3PO) with 6 equiv of Me3SiOTf and 2 equiv
of Cp2Co generates the U­(IV) complex, [Cp2Co]­[UIV(OTf)5­(TPPO)2] (3), as a yellow-green crystalline solid in 76% yield, concomitant
with formation of Me3SiOSiMe3, [Ph3POSiMe3]­[OTf], and [Cp2Co]­[OTf].
Complexes 1 and 3 have been fully characterized,
including analysis by X-ray crystallography. The conversion of [UVIO2(dppmo)2­(OTf)]­[OTf] and
[UVIO2(TPPO)4]­[OTf]2 to complexes 1 and 3, respectively, represents
rare examples of well-defined uranyl oxo ligand substitution.