Reversible chalcogen-atom transfer to a terminal uranium sulfide.

The reaction of elemental S or Se with [K(18-crown-6)][U(S)(NR2)3] (1) results in the formation of the new uranium(IV) dichalcogenides [K(18-crown-6)][U(η(2)-S2)(NR2)3] (2) and [K(18-crown-6)][U(η(2)-SSe)(NR2)3] (5). The further addition of elemental S to 2 results in the formation of [K(18-crown-6)][U(η(3)-S3)(NR2)3] (3). Complexes 2, 3, and 5 can be reconverted into 1 via the addition of R3P (R = Et, Ph), concomitant with the formation of R3P═E (E = S, Se).