Intrinsic reactivity of [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(η 4 -C 4 Ph 2 ) in small molecule activation.

The uranium metallacyclocumulene, [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(η 4 -C 4 Ph 2 ) (3) was isolated from the reaction mixture containing [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 UCl 2 (1), potassium graphite (KC 8 ) 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 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U(II) fragment in the presence of Ph 2 E 2 (E = S, Se) and Ph 3 CN 3 , 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 Ph 2 CS to 3 induces CS bond cleavage yielding the dithiolate complex [η 5 -1,3-(Me 3 Si) 2 C 5 H 3 ] 2 U[S 2 (C 12 H 5 Ph 5 )] (14). In contrast, the closely related, but sterically more encumbered uranium metallacyclocumulene [η 5 -1,2,4-(Me 3 Si) 3 C 5 H 2 ] 2 U(η 4 -C 4 Ph 2 ) (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.