Synthesis, structure, and reactivity of crystalline molecular complexes of the {[C5H3(SiMe3)2]3Th}1- anion containing thorium in the formal+2 oxidation state

Reduction of the Th3+ complex Cp-3 '' Th, 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-3 '' Th], 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 '' Th-3], 3. Complexes 2 and 3 form dark green solutions in THF with epsilon = 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 angstrom Th-(Cp '' ring centroid) distances, respectively, equivalent to the 2.520 angstrom distance measured in 1. Density functional theory analysis of (Cp-3 '' Th)(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-2 '' Th(C8H8), 4, and [K(18-crown-6)]Cp ''.