Intrinsic reactivity of [η-1,3-(MeSi)CH]U(η-CPh) in small molecule activation.

The uranium metallacyclocumulene, [η-1,3-(MeSi)CH]U(η-CPh) (3) was isolated from the reaction mixture containing [η-1,3-(MeSi)CH]UCl (1), potassium graphite (KC) 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 [η-1,3-(MeSi)CH]U(II) fragment in the presence of PhE (E = S, Se) and PhCN, 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 PhCS to 3 induces CS bond cleavage yielding the dithiolate complex [η-1,3-(MeSi)CH]U[S(CHPh)] (14). In contrast, the closely related, but sterically more encumbered uranium metallacyclocumulene [η-1,2,4-(MeSi)CH]U(η-CPh) (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.