LAUSR

The uranium metallacyclocumulene, [η5-1,3-(Me3Si)2C5H3]2U(η4-C4Ph2) (3) was isolated from the reaction mixture containing [η5-1,3-(Me3Si)2C5H3]2UCl2 (1), potassium graphite (KC8) and 1,4-diphenylbutadiyne (PhCC-CCPh) in good yield. The reactivity of 3 towards various small organic molecules was evaluated. For example, while complex 3 shows no reactivity towards alkynes and 2,2'-bipyridine, it may deliver the [η5-1,3-(Me3Si)2C5H3]2U(II) fragment in the presence of Ph2E2 (E = S, Se) and Ph3CN3, or react as a nucleophile in the presence of carbodiimides, isothiocyanates, aldehydes, ketones, and pyridine derivatives, forming five-, seven- or nine-membered heterometallacycles. On the contrary, addition of Ph2CS to 3 induces CS bond cleavage yielding the dithiolate complex [η5-1,3-(Me3Si)2C5H3]2U[S2(C12H5Ph5)] (14). In contrast, the closely related, but sterically more encumbered uranium metallacyclocumulene [η5-1,2,4-(Me3Si)3C5H2]2U(η4-C4Ph2) (4) features a more limited reactivity which is restricted to mono- and double insertions with small unsaturated organic molecules such as isothiocyanates, ketones and nitriles.