Preparation of actinide phosphinidene complexes: Steric control of reactivity

We report herein that synthetic routes previously employed in the production of uranium organoimido complexes of the actinides have now been extended to the preparation of phosphinidene analogs.In summary, the first terminal phosphinidene complex of an f-elemen has been isolated. The structural features of the complex suggest a model of bonding which is similar to that proposed for some transition metal phosphinidine complexes,in which (while a metal-ligand multiple is clearly evident) a bent phosphinidene results when both ligand π-electron pairs are not strongly stabilized by interaction with metal-based orbitals. Evidence suggests that the base-free phosphinidene complexes are more reactive than their previously characterized imido analogs. Phosphinidene functional groups may be stabilized against further reaction, however, either by imposition of additional ligands at the metal center or by relaxation of the steric constraints introduced by the ancillary ligands so that dimerization is feasible.