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(eta3-allyl)4 supported on dehydroxylated gamma-alumina (DA), facile arene hydrogenation and alkane activation processes can be effected in slurry reactions at 90-degrees-C and P(H2) = 30-180 psi. Benzene reduction occurs at a turnover frequency of almost-equal-to 25000 h-1 per active site and cyclohexane C-H exchange with D2 at almost-equal-to 1300 h-1 per active site. Active site characterization using D2O poisoning, hydrogenolysis, and CH3Cl dosing indicates less-than-or-equal-to 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.