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 sev eral demanding chemical transformations. Thus, in the case of Th(eta3- allyl)4 supported on dehydroxylated gamma-alumina (DA), facile arene h ydrogenation and alkane activation processes can be effected in slurry reactions at 90-degrees-C and P(H2) = 30-180 psi. Benzene reduction o ccurs 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, hyd rogenolysis, and CH3Cl dosing indicates less-than-or-equal-to 8 +/- 1 % of the Th surface sites are catalytically significant. EPR and XPS s pectroscopy provide no evidence for Th oxidation states less than +4. The mechanisms for the above processes are discussed in terms of elect rophilic ''four-center'' activation processes in which the active site s appear to bear sterically significant, nonhydridic ancillary ligatio n.