Thorium butadiene

Scheme 22 Reactivity of P4 and AS4 towards thorium butadiene complex [282,283]...

Actinide diene complexes (Smith et al. 1986) can be prepared from Cp MCl (M = U, Th) and the appropriate Grignard reagent. The X-ray structure of the Cp2Th(r)" -C4H6) compound shows a bent sandwich CpJTh moiety coordinated to the butadiene ligand in s-cis conformation with an tj" bonding mode. Thermochemical studies of the thorium-butadiene bond disruption enthalpy do not indicate particular Th-butadiene stabilization, it is comparable to that for Th to carbon o-bonds. The compound adopts the familiar bent sandwich structure. 

A claim has been made in patents issued to Auzies (374) that nicotine can be prepared on an industrial scale from ammonia and butadiene. This process is reported to involve the production of pyrrole by the catalytic interaction of ammonia and butadiene, the methylation and hydrogenation of pyrrole, the conversion of ZV-methylpyrrolidine to 8-chloropyridine by heating over a thorium catalyst with chloroform, and the interaction of /8-chloropyridine with A-methylpyrrolidine over the same catalyst. The process, however, does not seem to have been put into practice and the reactions described have never been confirmed by a precise chemical investigation. 

The crystal structure supports the ri -haptidty of the butadiene ligand. The average Th-C distance to the terminal carbon atoms of the butadiene ligand (2.57(3) A) is only slightly smaller than that to the internal carbon atoms (2.74(2) A), and are comparable to those found in other thorium alkyl complexes. The C(l)-C(2) and C(3)-C(4) average distances (average of four independent molecules in the unit cell) is 1.46(5) A, which is compared to the average C(2)-C(3) distance of 1.44(3) A. 

Thorium oxide is one of the catalysts active for hydrogenation by anionic intermediates. 1,3-Butadiene and 2-methyl-l,3-butadiene undergo hydrogenation by 1,4 addition of H atoms to form trarw-2-butene and 2-methyl-2-butene, respectively. The formation of alkanes is negligibly small even after complete consumption of the reactants. The intermediates are allylic carbanions, and the skeletal structures of carbon are retained during the reaction. Detailed mechanisms are described in section 4.15. 

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