Supported Organoactinides. High-Resolution Solid-State ¹³C NMR Studies of Catalytically Active, Alumina-Bound (Pentamethylcyclopentadienyl)thorium Methyl and Hydride Complexes

This contribution reports a high-resolution solid-state ¹³C NMR study of the organoactinides Cp'₂Th(CH₃)₂, Cp'₂Th(¹³CH₃)₂, and [Cp'₂Th(μ-H)H]₂(Cp' = η5-(CH3)5C5) Adsorbed on partially dehydroxylated (PDA) or dehydroxylated (DA) 7-alumina. Cross-polarization (CP) combined with magic angle spinning (MAS) and high-power ¹H decoupling produces adsorbate ¹³C NMR spectra of sufficient resolution and sensitivity to obtain significant structural information. On the basis of the observed ¹³C chemical shifts, line widths, and field dependence thereof as well as comparison to a number of model systems and dipolar dephasing experiments, methyl transfer from Th to Al on the surface of the support is proposed for the reaction of Cp^/ ₂Th(¹³CH₃)₂with DA. Several types of experiments (Bloch decay, cessation of dipole decoupling, variable contact time) suggest that the adsorbed species are not highly mobile. On the other hand, adsorption of Cp'₂Th(¹³CH₃)₂on PDA results in protonolysis of the Th-CH₃units and the formation of surface Th-O-Al aluminoxy species. Useful correlations with the companion surface and catalysis study are presented. The utility of ¹³C CPMAS NMR spectroscopy in probing surface-bound metal alkyls (especially in proximity to quadrupolar support nuclei) is emphasized.