Functional carbo-Butadienes: Nonaromatic Conjugation Effects through a 14-Carbon, 24-π-Electron Backbone

• Published in: Chemistry : a European journal 2014-01, Vol.20 (2), p.483-492
• Main Authors: Rives, Arnaud, Maraval, Valérie, Saffon-Merceron, Nathalie, Chauvin, Remi
• Format: Article
• Language: English
• Subjects: alkynes; Aromatic compounds; carbo-mers; chromophores; Conjugation; cumulenes; Design engineering; Embedded systems; Optical properties; Strategy; Wavelengths; X-rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201303169

A systematic study of carbo‐butadiene motifs not embedded in an aromatic carbo‐benzene ring is described. Dibutatrienylacetylene (DBA) targets R1C(R)CCC(Ph)C≡CC(Ph)CCC(R)R2 are devised, in which R is C≡CSiiPr3 and R1 and R2 are R, H, or 4‐X‐C6H4, with the latter including three known representatives (X: H, NMe2, or NH2). The synthesis method is based on the SnCl2‐mediated reduction of pentaynediols prepared by early or late divergent strategies; the latter allows access to a OMe–NO2 push–pull diaryl‐DBA. If R1 and R2 are H, an over‐reduced dialkynylbutatriene (DAB) with two allenyl caps was isolated instead of the unsubstituted DBA. If R1=R2=R, the tetraalkynyl‐DBA target was obtained, along with an over‐reduced DBA product with a 12‐membered 1,2‐alkylidene‐1H2,2H2‐carbo‐cyclobutadiene ring. X‐ray crystallography shows that all of the acyclic DBAs adopt a planar trans–transoid–trans configuration. The maximum UV/Vis absorption wavelength is found to vary consistently with the overall π‐conjugation extent and, more intriguingly, with the π‐donor character of the aryl X substituents, which varies consistently with the first (reversible) reduction potential and first (irreversible) oxidation peak, as determined by voltammetry. The more the merrier: A systematic study of carbo‐butadiene motifs not embedded in an aromatic ring is described (see scheme; E: electrophilic group). All of the acyclic dibutatrienylacetylene products adopt a planar trans–transoid–trans configuration. The results provide an experimental basis for the design of π‐extended organic molecules with promising optical or (opto)electronic properties.