Diazoalkane Reduction for the Synthesis of Uranium Hydrazonido Complexes

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The reactivity of the uranium(III) alkyl Tp*2UCH2Ph (1) toward diazoalkanes is reported. Addition of 1 equiv. N2CPh2 produces 0.5 equiv. bibenzyl, along with Tp*2U(N2CPh2) (2). This species is dynamic in solution at room temperature and rapidly interconverts between the η1‐ and η2 isomers as determined by variable‐temperature 1H NMR spectroscopy. X‐ray crystallographic analysis at low temperature shows exclusively the η2 isomer, which features a short U–N multiple bond analogous to an imido species. The η1 isomer reacts quantitatively with aldehydes and ketones through multiple bond metathesis to produce Tp*2U(O) and the corresponding ketazine. Treatment of 1 with N2CHSiMe3 generates 0.5 equiv. bibenzyl and the η1 isomer Tp*2U(N2CHSiMe3) (3). This species is unstable over the course of hours, and there is no spectroscopic evidence for the η2 isomer. Tp*2U(η1‐N2CHSiMe3) can be trapped by addition of phenylacetylene by a [2+2] cycloaddition to afford the uranium(IV) metallacycle Tp*2U[(N‐N = CHSiMe3)CHCPh] (4). Crystallographic data for 4 are presented.