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The stabilization of long ncumulenes has traditionally been achieved by placing sterically bulky "protecting groups" at the termini, which shield the reactive carbon chain from unwanted reactions. Herein, we present an alternative strategy: stabilization through threading the sp-hybridized carbon chain through a phenanthroline-based macrocycle. The result is stable 9cumulene rotaxanes that enable the study of properties as a function of length for ncumulenes in unprecedented detail, including by quantitative UV/Vis spectroscopy, cyclic voltammetry, and differential scanning calorimetry. The experimental results are supported by DFT calculations.
Franz et al. (Mon,) studied this question.