Thorium hydride complex reaction with

Actinide Hydrides. Thorium and other actinides form complex systems with non-stoichiomelric and stoichiometric phases. Uranium hydride is of some importance chemically as it is often more suitable for the preparation of uranium compounds than is the massive metal. Uranium reacts rapidly and exothermically with hydrogen at 250-300° to give a pyrophoric black powder. The reaction is reversible ... 

On the basis of the kinetic and thermodynamic data, a plausible mechanism for the Tishchenko reaction is presented in Scheme 15. In the first step of the reaction, the precatalyst 1 reacts with two equivalents of the aldehyde to give exothermically the alkoxo complex 42 (Step i in Scheme 15 AHcaic = —68 kcal/mol). A second insertion of an aldehyde into the thorium-alkoxide bond yields complex 43 (step ii in Scheme 15). The concomitant hydride transfer from complex 43 to an additional aldehyde releases the ester 44 and produces the active catalytic species 45 (step iii in Scheme 15). The insertion of an aldehyde into complex 45 (step iv, AHcaic = —25 kcal/mol) gives complex 46, and its hydride transfer reaction (step v, rate determining step, AHcaic = —22 kcal/mol) with an additional aldehyde via a plausible six-centered chair-like transition state (47) produces the ester 38 and regenerates the active complex 45. 

It has recently been reported83 that di-n-cyclooctatetraene complexes of uranium, thorium, and plutonium can be prepared by the direct reaction of the finely divided metals with cyclooctatetraene. The finely divided metals were prepared by a procedure described by Seaborg and Katz.84 Several cycles of formation and descomposition of the hydride gave a finely divided reactive metal. However, treatment of the pyrophoric uranium with cyclopentadiene under the same conditions used to form uranocene failed to produce any detectable amounts of the known compounds U(CsH5)3 or U(C5H5)4. 

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