Synthesis, structure, and reactivity of crystalline molecular complexes of the {[C(5)H(3)(SiMe(3))(2)](3)Th}(1–) anion containing thorium in the formal +2 oxidation state

Reduction of the Th(3+) complex Cp′′3Th, 1 [Cp′′ = C(5)H(3)(SiMe(3))(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 KC(8) in the presence of 18-crown-6 generates the analogous Th(2+) 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 6d(2) 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(C(8)H(8)), 4, and [K(18-crown-6)]Cp′′.