Stable in air for weeks as a solid and for days in solution, the blue-green pentaethynylcyclopentadienyl radical 1 is readily formed from ethynylated cyclopentadiene derivatives, which were prepared as potential precursors to decaethynyl metallocenes. The stability of 1 contrasts strikingly with that of previously described pentaaryl- and pentaisopropyl-cyclopentadienyl radicals, which, although stable at 25 °C, are highly sensitive to oxygen.
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Jux et al. (1996) studied this question.
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