Metathesis of a U(V) imido complex: a route to a terminal U(V) sulfide

Herein, we report the synthesis and characterisation of the first terminal uranium(v) sulfide and a related U(V) trithiocarbonate complex supported by sterically demanding tris(tert-butoxy)siloxide ligands. The reaction of the potassium-bound U(V) imido complex, [U(NAd){OSi(OtBu)(3)}(4)K] (4), with CS(2) led to the isolation of perthiodicarbonate [K(18c6)](2)[C(2)S(6)] (6), with concomitant formation of the U(IV) complex, [U{OSi(OtBu)(3)}(4)], and S[double bond, length as m-dash]C[double bond, length as m-dash]NAd. In contrast, the reaction of the U(V) imido complex, [K(2.2.2-cryptand)][U(NAd){OSi(OtBu)(3)}(4)] (5), with one or two equivalents of CS(2) afforded the trithiocarbonate complex, [K(2.2.2-cryptand)][U(CS(3)){OSi(OtBu)(3)}(4)] (7), which was isolated in 57% yield, with concomitant elimination of the admantyl thiocyanate product, S[double bond, length as m-dash]C[double bond, length as m-dash]NAd. Complex 7 is likely formed by fast nucleophilic addition of a U(V) terminal sulfide intermediate, resulting from the slow metathesis reaction of the imido complex with CS(2), to a second CS(2) molecule. The addition of a solution of H(2)S in thf (1.3 eq.) to 4 afforded the first isolable U(V) terminal sulfide complex, [K(2.2.2-cryptand)][US{OSi(OtBu)(3)}(4)] (8), in 41% yield. Based on DFT calculations, triple-bond character with a strong covalent interaction is suggested for the U–S bond in complex 7.