Tris(η⁵-cyclopentadienyl)alkyl and -alkenyl Compounds of Thorium(IV)

The syntheses of a number of (η⁵-C₅H₅)₃ThR organometallics from (η-C₅H₅)₃ThCl and the corresponding RLi or RMgX reagents are reported. The new compounds have been characterized by chemical means, and by infrared, laser Raman, and proton NMR spectroscopy. The properties of these thorium organometallics are compared to those of the analogous (C₅H₅)₃UR compounds. With both elements the (C₅H₅₃M(allyl) species is a fluxional η¹-allyl; the barriers to sigmatropic rearrangement are comparable. The Th-C bond reacts more readily with protonic solvents. The (C₅H₅)₃ThR compounds are more thermally stable in solution. The thermolysis pathway is similar to uranium, with intramolecular extrusion of R-H taking place (H derived from a cyclopentadienyl ring) rather than olefin elimination. For thorium, the other product of thermolysis is (η⁵-C₅h₅)₂Th(η¹:η⁵-C₅H₅)₂Th(η⁵-C₅H₅)₂ which appears to arise via an intermediate η¹-C₅H₄ carbene complex-ylide. Coordinative saturation and 5f electron configuration play an important role in directing the course of certain types of reactions of organoactinides.