Synthesis, structure and bonding of hexaphenyl thorium(IV): observation of a non-octahedral structure

We report herein the synthesis of the first structurally characterized homoleptic actinide aryl complexes, [Li(DME)3]2[Th(C6H5)6] (1) and [Li(THF)(12-crown-4)]2[Th(C6H5)6] (2), which feature an anion possessing a regular octahedral (1) or a severely distorted octahedral (2) geometry. The solid-state structure of 2 suggests the presence of pseudo-agostic ortho C-H···Th interactions, which arise from σ(C-H) → Th(5f) donation. The non-octahedral structure is also favoured in solution at low temperatures.