Diazoalkane Reduction for the Synthesis of Uranium Hydrazonido Complexes

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