Reduction of the Th3+ complex Cp′′3Th, 1 [Cp′′ = C5H3(SiMe3)2], with potassium graphite in THF in the presence of 2.2.2-cryptand generates [K(2.2.2-cryptand)][Cp′′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 Th2+ compound, [K(18-crown-6)(THF)2][Cp′′3Th], 3. Complexes 2 and 3 form dark green solutions in THF with ε = 23 000 M-1 cm-1, 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-(Cp′′ ring centroid) distances, respectively, equivalent to the 2.520 Å distance measured in 1. Density functional theory analysis of (Cp′′3Th)1- is consistent with a 6d2 ground state, the first example of this transition metal electron configuration. Complex 3 reacts as a two-electron reductant with cyclooctatetraene to make Cp′′2Th(C8H8), 4, and [K(18-crown-6)]Cp′′.
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© The Royal Society of Chemistry 2015.