Synthesis, structure, and reactivity of crystalline molecular complexes of the {[C5H3(SiMe3)2]3Th}1– anion containing thorium in the formal +2 oxidation state† †Electronic supplementary information (ESI) available: Experimental and computational details; crystallographic data collection, structure solution, and refinement; and crystallographic data and complete bond distances and angles for compounds 1–4. CCDC 1018011–1018014. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4sc03033h Click here for additional data file. Click here for additional data file. Click here for additional data file.

Reduction of the Th complex Cp 00 3Th, 1 [Cp00 1⁄4 C5H3(SiMe3)2], with potassium graphite in THF in the presence of 2.2.2-cryptand generates [K(2.2.2-cryptand)][Cp 00 3Th], 2, a complex containing thorium in the formal +2 oxidation state. Reaction of 1 with KC8 in the presence of 18-crown-6 generates the analogous Th compound, [K(18-crown-6)(THF)2][Cp 00 3Th], 3. Complexes 2 and 3 form dark green solutions in THF with 3 1⁄4 23 000 M 1 cm , but crystallize as dichroic dark blue/red crystals. X-ray crystallography revealed that the anions in 2 and 3 have trigonal planar coordination geometries, with 2.521 and 2.525 Å Th–(Cp00 ring centroid) distances, respectively, equivalent to the 2.520 Å distance measured in 1. Density functional theory analysis of (Cp 00 3Th) 1 is consistent with a 6d ground state, the first example of this transition metal electron configuration. Complex 3 reacts as a two-electron reductant with cyclooctatetraene to make Cp 00 2Th(C8H8), 4, and [K(18-crown-6)]Cp00.