Thorium(IV) and Uranium(IV) Ketimide Complexes Prepared by Nitrile Insertion into Actinide−Alkyl and −Aryl Bonds

Migratory insertion of benzonitrile into both An-C bonds of the bis(alkyl) and bis(aryl) complexes (C 5 Me 5 ) 2 AnR 2 yields the actinide ketimido complexes (C 5 Me 5 ) 2 An[-N=C(Ph)(R)] 2 (where An = Th, R = Ph, CH 2 Ph, CH 3 ;An = U, R = CH 2 Ph, CH 3 ) and provides a versatile method for the construction of electronically and sterically diverse ketimide ligands. The Th(IV) compounds represent the first examples of thorium ketimide complexes. The uranium complexes are surprisingly unreactive, and both the uranium and thorium bis(ketimido) complexes display unusual electronic structure properties. The combined chemical and physical properties of these complexes suggest a higher An-N bond order due to significant ligand-to-metal π-bonding in the actinide ketimido interactions and indicate that the f-electrons in mid-valent organouranium complexes might be far more involved in chemical bonding and reactivity than previously thought. We also report herein the structures of the known thorium and uranium complexes (C 5 Me 5 ) 2 Th(CH 2 Ph) 2 , (C 5 Me 5 ) 2 ThMe 2 , (C 5 Me 5 ) 2 U-(CH 2 Ph) 2 , and (C 5 Me 5 ) 2 UMe 2 .