The synthesis of a stable [6]cumulene

Le résumé fourni par la source

The synthetic evolution of even [n]cumulenes is presented, which culminates in the formation and study of the stable [6]cumulene [6]tBu. The instability of even [n]cumulenes is hypothesized to arise from the effects of the endgroups, in which bulky aryl endgroups are ineffective at protection, while bulky alkyl groups (tert-butyl) afford the ambiently stable [6]tBu. The lower molecular symmetry of [6]tBu, relative to the parent [6]cumulene ([6]H, H2C=(C4)=CH2], allows for experimental observation of the lowest excited singlet transition, which would otherwise be symmetry forbidden. X-ray crystallographic analysis reveals that [6]tBu has the lowest bondlength alternation of any [n]cumulene synthesized to date, making it an ideal starting point toward probing the properties of the unstable “cumulenic” carbyne, B-carbyne.

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