Recent developments in the surface and catalytic chemistry of supported organoactinides

The adsorption of organoactinide complexes on dehydroxylated alumina (DA) yields coordinatively unsaturated, highly active catalysts for several demanding chemical transformations. Thus, in the case of Th(η³-allyl)₄ supported on dehydroxylated γ-alumina (DA), facile arene hydrogenation and alkane activation processes can be effected in slurry reactions at 90°C and P_H2 = 30-180 psi. Benzene reduction occurs at a turnover frequency of ≈ 25000 h^-1 per active site and cyclohexane CH exchange with D₂ at ≈ 1300 h^-1 per active site. Active site characterization using D₂O poisoning, hydrogenolysis, and CH₃Cl dosing indicates ≤ 8 ± 1 % of the Th surface sites are catalytically significant. EPR and XPS spectroscopy provide no evidence for Th oxidation states less than +4. The mechanisms for the above processes are discussed in terms of electrophilic "four-center" activation processes in which the active sites appear to bear sterically significant, nonhydridic ancillary ligation.