An Actinide Metallacyclopropene Complex: Synthesis, Structure, Reactivity, and Computational Studies

The synthesis, structure, and reactivity of an actinide metallacyclopropene were comprehensively studied. The reduction of [η<sup>5</sup>-1,2,4-(Me<sub>3</sub>C)<sub>3</sub>C<sub>5</sub>H<sub>2</sub>]<sub>2</sub>ThCl<sub>2</sub> (<b>1</b>) with potassium graphite (KC<sub>8</sub>) in the presence of diphenylacetylene (PhCCPh) yields the first stable actinide metallacyclopropene [η<sup>5</sup>-1,2,4-(Me<sub>3</sub>C)<sub>3</sub>C<sub>5</sub>H<sub>2</sub>]<sub>2</sub>Th­(η<sup>2</sup>-C<sub>2</sub>Ph<sub>2</sub>) (<b>2</b>). The magnetic susceptibility data show that <b>2</b> is indeed a diamagnetic Th­(IV) complex, and density functional theory (DFT) studies suggest that the 5f orbitals contribute to the bonding of the metallacyclopropene Th(η<sup>2</sup>-CC) moiety. Complex <b>2</b> shows no reactivity toward alkynes, but it reacts with a variety of heterounsaturated molecules such as aldehyde, ketone, carbodiimide, nitrile, organic azide, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, a comparison between Th and group 4 metals reveals that Th<sup>4+</sup> shows unique reactivity patterns.