Structure and reactions of a metallacyclic complex containing a remarkably long uranium–carbon bond

The intramolecular metalation of a β-silyl methyl group in [U{N(CH2CH2NSiMe2But)3}(CH2Ph)] occurs rapidly, despite the conformational demands of the triamidoamine ligand, to produce a highly strained metallacycle (U–C ca. 2.75 Å); this complex reacts cleanly with a range of carbon and other acids to give, for example, an alkynyl with a bent (156°) U–CC unit.