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

Uranium(IV)-carbene-imido complexes [U(BIPMTMS)(NCPh3)(κ2- N, N′-BIPY)] ( 2; BIPMTMS=C(PPh2NSiMe3)2; BIPY=2,2-bipyridine) and [U(BIPMTMS)(NCPh3)(DMAP)2] ( 3; DMAP=4-dimethylamino-pyridine) 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. [ABSTRACT FROM AUTHOR]