Thorium methyl cation

There is a class of cationic bis(pentamethylcyclopen-tadienyl)thorium alkyls that deserve special mention. Marks and coworkers have discovered that treatment of Cp 2ThMe2 with protolytic reagents, in the form of sterically encumbered ammonium salts, provides an efi cient route to Cp 2ThMe+X complexes (equation 60). These complexes exhibit characteristic low-field thorium-methyl NMR signals that... 

The analysis of the extraction by CPo21 data reveals a 1 1 metal ion-to-ligand ratio for europium and thorium. The selectivity factors indicate a good selectivity toward these two cations with respect to Mn2+, Pb2, Cd2+, Fe2+, Ni2+, and Co2+, among which only cadmium is a weakly radioactive fission product.155 A synergistic extraction of almost three orders of magnitude was evidenced for the extraction of La3+, Nd3+, Eu3+, Ho3+, Lu3+ with 4-benzoyl-3-methyl-l-phenyl-5-pyrazolone and CPo21 however, it does not improve the separation factors between lanthanides.156... 

The molecular structure has been determined by X-ray diffraction, and the result is illustrated schematically in (25). Seven methyl groups surround the thorium atom in a distorted monocapped trigonal prismatic arrangement. Six of the methyl groups [Th-C = 2.667(8)-2.765(9)A ] are coordinated in a pair-wise manner to Li(TMEDA)+ cations, while the seventh [Th-C = 2.571(9) A] is not. 

Some support materials can be rendered Lewis acidic enough to ionize dialkyl metallocenes. Marks and co-workers have reported (33) that alnmina dried at very high temperatures can react at least to some small degree with both thorium-and zirconium-based metallocene dimethyl species to yield active catalysts for polyethylene. The resulting cationic metal center is believed to remain coordinated to the surface through an Al-O-M Lewis acid/base linkage, at least prior to exposure to ethylene. Hybrid surface/cocatalyst systems based on aluminum alkyl-treated clays have been developed (34) in which the solid substrate appears to play some role in promoting polymerization activity far beyond that expected for non-methyl aluminoxane- or trialkylaluminum-activated catalysts. 

Compared with the unit model and classical extractant, tri- -octylpho-sphine oxide (H5.26) showed remarkable selectivity for thorium(iv) and uranyl(vi) caions. The spacer length between the phosphine oxide moiety and the pillar[5]arene also affected the extraction efficiency. As the length of the spacer increased, the extraction efficiency of these cations increased, per-Methylated pillar[5]arene H5.2 did not extract these cations, therefore the 10 phosphine oxide moieties on the pillar[5]arene rim acted as an extractant. The efficiency was remarkably decreased in the unit model, indicating that the pillar[5]arene cavity is required to extract these cations efficiently. H5.26... 

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