A Thorium(IV) metallacyclopropyne complex

Actinide metallacyclic chemistry has been of interest due to its involvement in various chemical processes. However, fundamental understanding on the key species, actinide metallacyclic complexes, is limited to metallacyclopropenes whereas little is known about the actinide metallacyclopropynes presumably due to their unusual high reactivity. Herein, we report the preparation of a thorium metallacyclopropyne complex (η²-C ≡ C)ThCl₃^- in the gas phase by using electrospray ionization mass spectrometry, and it is generated via a single-ligand strategy through sequential losses of CO₂ and HCl from the monopropynoate precursor (HC ≡ CCO₂)ThCl₄^- upon collision-induced dissociation. Alternatively, the dual-ligand strategy involving consecutive losses of two CO₂ and one C₂H₂ from the dipropynoate precursor (HC ≡ CCO₂)₂ThCl₃^- works as well. According to the reactivity experiments and theoretical calculations, (η²-C ≡ C)ThCl₃^- possesses a dianionic ligand C₂^2- coordinated to the Th(IV) center in a side-on fashion. Further bonding analysis demonstrates the presence of a triple bond between the two C atoms, and the Th 5 f orbitals are significantly involved in the Th-(C ≡ C) bonding. A Th metallacyclopropyne structure is thus established for (η²-C ≡ C)ThCl₃^-.