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Tert-Butylalumoxanes: Synthetic Analogs for Methylalumoxane (MAO) and New Catalytic Routes to Polyolefins and Polyketones
HARVARD UNIV CAMBRIDGE MA DEPT OF CHEMISTRY
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The hydrolysis of AltBu3 in toluene using the hydrated salt, A12SO43.14H20, results in the formation of the dimeric hydroxide TBu 2Almu-OH2 1 and Al4tBu7mu 3-02mu-OH2 as the major and minor products, respectively. Compound 1 may also be prepared by the addition of water to a refluxing toluene solution of A1tBu3. Compound 1 is remarkably stable to thermolysis and is converted slowly to a mixture of alumoxane species. Dissolution of compound 1 in MeCN or THF yields the hydrogen-bound trimeric complexes TBu2A1mu-OH3.nMeCN n 13, 2 and TBu2 Almu-OH3.2THF, respectively. The large scale synthesis of alumoxanes from the low temperature thermolysis of the trimeric hydroxide. TBu2A1mu-OH3, allows for the isolation of the penta-aluminum compound Al5tBu7mu-3-02mu-OH2 4 and the heptameric alumoxane TBuAlmu 3-O7 5. The structure of compound 4 is consistent with the condensation of TBu2 Almu-OH3 with TBu2Almu-OH2. Thermolysis of 4 yields an alumina gel. The structural relationship of 4 with respect to the structures reported for non-alkyl alumoxanes and alumina gels is discussed. Reaction of TBu2Gamu-OH3 with AltBu3 in toluene yields the octameric alumoxane GatBu3 and TBuA1mu3-08 6, as the major isolable products. Mass spectrometry indicates the incorporation of low levels of gallium 8 into samples of 6 made by this route. The molecular structures of compounds 2, 4 and 6 have been determined by X-ray crystallograhy.
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