Actinide Metallocene Hydride Chemistry: C–H Activation in Tetramethylcyclopentadienyl Ligands to Form [μ‑η⁵‑C₅Me₃H(CH₂)-<i>κC</i>]^2– Tuck-over Ligands in a Tetrathorium Octahydride Complex

Hydrogenolysis of the dimethyl actinide metallocenes (C₅Me₄SiMe₃)₂UMe₂ and (C₅Me₄H)₂AnMe₂ (An = Th, U) was examined for comparison with the hydrogenolysis of (C₅Me₅)₂AnMe₂ that forms the hydrides [(C₅Me₅)₂ThH₂]₂, [(C₅Me₅)₂UH₂]₂, and [(C₅Me₅)₂UH]₂. Parallel reactivity is not found with the (C₅Me₄SiMe₃)⁻ and (C₅Me₄H)⁻ complexes. Instead, this study led to the first example of a “tuck-over” [μ-η⁵-C₅Me₃H­(CH₂)-<i>κC</i>]^2– dianion derived from (C₅Me₄H)⁻ ligands by C–H bond activation and rare examples of a polymetallic thorium polyhydride compound and an organometallic Th³⁺ complex. (C₅Me₄SiMe₃)₂UMe₂ reacts with H₂ to form the bis­(tethered alkyl) complex (η⁵-C₅Me₄SiMe₂CH₂-<i>κC</i>)₂U, a product of C–H bond activation of the silylmethyl groups. The only identifiable product of hydrogenolysis of (C₅Me₄H)₂UMe₂ is (C₅Me₄H)₃U. The first thorium complex of (C₅Me₄H)⁻ was synthesized by reaction of 2 equiv of (C₅Me₄H)­MgCl­(THF) with ThBr₄(THF)₄ to produce (C₅Me₄H)₂ThBr₂. This complex reacts with MeLi to make (C₅Me₄H)₂ThMe₂. The latter complex reacts with H₂ to form the ligand redistribution product (C₅Me₄H)₃ThMe and the tetrametallic octahydride tuck-over complex (C₅Me₄H)₄[μ-η⁵-C₅Me₃H­(CH₂)-<i>κC</i>]₂Th₄(μ-H)₄(μ₃-H)₄. For comparison with the (C₅Me₄H)₃U product, the thorium analogue, (C₅Me₄H)₃Th, was synthesized by potassium reduction of a [(C₅Me₄H)₃Th]­[BPh₄] intermediate obtained in situ from (C₅Me₄H)₃ThMe and [HNEt₃]­[BPh₄]. (C₅Me₄H)₃Th can also be prepared from KC₈ and (C₅Me₄H)₃ThBr, obtained from KC₅Me₄H and ThBr₄(THF)<sub>4