Uranium-Carbene-Imido Metalla-Allenes: Ancillary-Ligand-Controlled cis-/trans-Isomerisation and Assessment of trans Influence in the R2C=U-IV=NR' Unit (R=Ph2PNSiMe3; R'=CPh3)

摘要

Uranium(IV)-carbene-imido complexes [U(BIPMTMS)(NCPh3)(kappa(2)-N,N'-BIPY)] (2; BIPMTMS=C(PPh2NSiMe3)(2); BIPY=2,2-bipyridine) and [U(BIPMTMS)(NCPh3)(DMAP)(2)] (3; DMAP =4-dimethylaminopyridine) that contain unprecedented, discrete R2C=U=NR' units are reported. These complexes complete the family of E=U=E (E=CR2, NR, O) metalla-allenes with feasible first-row hetero-element combinations. Intriguingly, 2 and 3 contain cis-and trans-C=U=N units, respectively, representing rare examples of controllable cis/trans isomerisation in f-block chemistry. This work reveals a clear-cut example of the trans influence in a mid-valent uranium system, and thus a strong preference for the cis isomer, which is computed in a co-ligand-free truncated model-to isolate the electronic trans influence from steric contributions- to be more stable than the trans isomer by approximately 12 kJ mol(-1) with an isomerisation barrier of approximately 14 kJ mol(-1).