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

Abstract

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(<i>tert</i>-butoxy)siloxide ligands. The reaction of the potassium-bound U^V imido complex, [U(NAd){OSi(O<i>t</i>Bu)₃}₄K] (<b>4</b>), with CS₂ led to the isolation of perthiodicarbonate [K(18c6)]₂[C₂S₆] (<b>6</b>), with concomitant formation of the U^IV complex, [U{OSi(O<i>t</i>Bu)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(O<i>t</i>Bu)₃}₄] (<b>5</b>), with one or two equivalents of CS₂ afforded the trithiocarbonate complex, [K(2.2.2-cryptand)][U(CS₃){OSi(O<i>t</i>Bu)₃}₄] (<b>7</b>), 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 <b>7</b> 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 CS₂, to a second CS₂ molecule. The addition of a solution of H₂S in thf (1.3 eq.) to <b>4</b> afforded the first isolable U^V terminal sulfide complex, [K(2.2.2-cryptand)][US{OSi(O<i>t</i>Bu)₃}₄] (<b>8</b>), in 41% yield. Based on DFT calculations, triple-bond character with a strong covalent interaction is suggested for the U-S bond in complex <b>7</b>.