The Ketimide Ligand is Not Just an Inert Spectator: Heteroallene Insertion Reactivity of an Actinide–Ketimide Linkage in a Thorium Carbene Amide Ketimide Complex**

The ketimide anion R(2)C—N(−) is an important class of chemically robust ligand that binds strongly to metal ions and is considered ideal for supporting reactive metal fragments due to its inert spectator nature; this contrasts with R(2)N(−) amides that exhibit a wide range of reactivities. Here, we report the synthesis and characterization of a rare example of an actinide ketimide complex [Th(BIPM(TMS)){N(SiMe(3))(2)}(N—CPh(2))] [2, BIPM(TMS)=C(PPh(2)NSiMe(3))(2)]. Complex 2 contains Th—C(carbene), Th—N(amide) and Th—N(ketimide) linkages, thereby presenting the opportunity to probe the preferential reactivity of these linkages. Importantly, reactivity studies of 2 with unsaturated substrates shows that insertion reactions occur preferentially at the Th—N(ketimide) bond rather than at the Th—C(carbene) or Th—N(amide) bonds. This overturns the established view that metal-ketimide linkages are purely inert spectators.