Coordinative saturation and the chemistry of triscyclopentadienyl thorium (IV) alkyls and alkenyls

Air- and moisture-sensitive (C5H5)3Th(IV)R compounds (R = alkyl, alkenyl) were prepared by reacting (C5H5)3Th(IV)Cl with the corresponding Grignard or lithium reagent in toluene at -780. They were characterized by elemental analysis, molecular weight, and pmr, infrared, and Raman spectroscopy. The fluxional behavior in the nmr indicates a sigmatropic rearrangement with an activation energy of 8 to 9 kcal/mole. Alcoholysis is faster and more selective for alkane formation than in the analogous uranium system. In aromatic solvents the compounds exhibit first-order decomposition kinetics. Relative thermal stabilities are neopentyl > allyl > n-butyl > 2-cis-2-butenyl > 2-trans-2-butenyl > i-propyl. Respective half-lives of these compounds at 1670C are 7500, 566, 96, 39, 21, and 7 hr. Alkanes are the major product for R = alkyl. Retention of configuration is noted for R = cis- and trans-2-butenyl. k/sub H//k/sub D/ is 2.4 for R = n-butyl. The results are consistent with coordinative saturation about the Th center blocking β-elimination. The solid product was also crystallized, and x-ray diffraction results reveal a bridged dimer ((C5H5)2(C5H4)Th)2. To each Th are bound three rings in a pentahapto fashion and one ring, which is bound in a pentahapto fashion to the other Th center, in a monohapto fashion. These results suggest a short-lived intermediate, possibly an ylid, prior to dimerization. The photochemical decomposition of triscyclopentadienyl Th(IV) isopropyl leads to the formation of propene, propane, and an insoluble green solid. The solid analyzes as (C15 H15Th)2, has a temperature-independent paramagnetism of 18.45 x 10-4 cgs, and exhibits vibrational frequencies characteristic of pentahaptocyclopentadienyl ligands