Synthesis and properties of long [n]cumulenes (n ≥ 5)

• Published in: Chemical Society reviews 2014-05, Vol.43 (9), p.3184-323
• Main Authors: Januszewski, Johanna A, Tykwinski, Rik R
• Format: Article
• Language: English
• Subjects: Carbon; Carbyne; Derivatives; Historic; Mathematical models; Synthesis; Transformations; X-rays
• ISSN: 0306-0012; 1460-4744
• DOI: 10.1039/c4cs00022f

Molecules composed of a contiguous sequence of double bonds, the [ n ]cumulenes, share structural similarities to both of their conjugated relatives, the polyenes and polyynes. The synthesis and properties of [ n ]cumulenes are, however, quite different from those of either polyenes or polyynes. At an infinite length, [ n ]cumulenes would provide one structural form of the hypothetical sp-hybridized carbon allotrope carbyne, while shorter derivatives offer model compounds to help to predict the properties of carbyne. Finally, derivatization of the π-electron framework of [ n ]cumulenes provides a number of different synthetic transformations, with cycloaddition reactions being the most common. In this review, both historical and recent synthetic achievements toward long [ n ]cumulenes ( n ≥ 5) are discussed. This is followed by a description of our current understanding of the physical and electronic structure of [ n ]cumulenes based on UV/vis spectroscopy and X-ray crystallography. Finally, the reactivity of long [ n ]cumulenes is described. This review highlights the synthesis and reactivity of longer [ n ]cumulenes ( n ≥ 5) and summarizes their electronic and structural properties.