Ring-opening of a thorium cyclopropenyl complex generates a transient thorium-bound carbene.

The reaction of [Cp 3 ThCl] with in situ generated 1-lithium-3,3-diphenylcyclopropene results in the formation of [Cp 3 Th(3,3-diphenylcyclopropenyl)] (1), in good yields. Thermolysis of 1 results in isomerization to the ring-opened product, [Cp 3 Th(3-phenyl-1 H -inden-1-yl)] (3) via a hypothesized carbene intermediate. This transformation represents a new mode of reactivity of 3,3-diphenylcyclopropene with the actinides, improving our ability to use this reagent as a carbene source. A combined DFT and 13 C{ 1 H} NMR analysis of 1 shows a spin-orbit induced downfield shift at C α due to participation of the 5f orbitals in the Th-C bond.