The Importance of a Single Methyl Group in Determining the Reaction Chemistry of Pentamethylcyclopentadienyl Cyclooctatetraenyl Uranium Metallocenes

Authors

  • Dr. Michael K. Takase,

    1. Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025 (USA), Fax: (+1) 949-824-2210
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  • Dr. Joseph W. Ziller,

    1. Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025 (USA), Fax: (+1) 949-824-2210
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  • Prof. William J. Evans

    Corresponding author
    1. Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025 (USA), Fax: (+1) 949-824-2210
    • Department of Chemistry, University of California, Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025 (USA), Fax: (+1) 949-824-2210
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Abstract

The steric factors that allow trivalent [(C5Me5)3U] (1) to function as a three-electron reductant with C8H8 to form tetravalent [{(C5Me5)(C8H8)U}2(μ-C8H8)] (2) have been explored by examining the synthesis and reactivity of the intermediate, “[(C5Me5)2(C8H8)U]” (3), and the slightly less crowded analogues, [(C5Me5)(C5Me4H)(C8H8)U] and [(C5Me4H)2(C8H8)U], that have, successively one less methyl group. The reaction of [{(C5Me5)(C8H8)U(μ-OTf)}2] (4; OTf=OSO2CF3) with two equivalents of KC5Me5 in THF gave ring-opening to “[(C5Me5)(C8H8)U{O(CH2)4(C5Me5)}]” consistent with in situ formation of 3. Reaction of 4 with two and four equivalents of KC5Me4H generates two equivalents of [(C5Me5)(C5Me4H)(C8H8)U] (5) and [(C5Me4H)2(C8H8)U] (6), respectively, which in contrast to 3 were isolable. Tetravalent 5 reduces phenazine and PhEEPh (E=S, Se, and Te) to form the tetravalent uranium reduction products, [{(C5Me5)(C8H8)U}2(μ-C12H8N2)] (7), [{(C5Me5)(C8H8)U}2(μ-SPh)2] (8), [{(C5Me5)(C8H8)U}2(μ-SePh)2] (9), and [{(C5Me5)(C8H8)U}2(μ-TePh)2] (10), consistent with sterically induced reduction. In contrast, the less sterically crowded 6 does not react with these substrates.

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