Manipulation of organoactinide coordinative unsaturation and stereochemistry. Properties of chelating bis(polymethylcyclopentadienyl) hydrocarbyls and hydrides

The synthesis of the chelating polymethylcyclopentadienyl ligand (CH₃)₂Si[(CH₃)₄C₅] ₂^2- is reported. Reaction with ThCl₄ followed by alkylation yields the new, thermally stable thorium hydrocarbyls (CH₃)₂Si[(CH₃)₄C₅] ₂ThR₂, R = n-C₄H₉, CH₂C(CH₃)₃, CH₂Si(CH₃)₃, CH₂C₆H₅, and C₆H₅. The R = CH₂Si(CH₃)₃ complex has also been characterized by single-crystal X-ray diffraction. The most unusual feature of the molecular structure is the rather small (ring center of gravity)-Th-(ring center of gravity) angle of 118.4° and the rather large ring-ring dihedral angle of 105.4°. The hydrocarbyls undergo facile hydrogenolysis to yield the new thorium hydride {(CH₃)₂Si[(CH₃)₄C₅] ₂ThH₂}_x. The infrared spectrum of this hydride lacks terminal Th-H stretching transitions. The new hydride catalyzes olefin hydrogenation at turnover frequencies significantly in excess of those for {Th [(CH₃)₅C₅]₂H₂} ₂.