Theoretical and structural analysis of long C-C bonds in the adducts of polycyanoethylene and anthracene derivatives and their connection to the reversibility of Diels-Alder reactions.

Date publication

janvier 2014

Auteurs

Membres identifiés du Cancéropôle Est :
Pr LEHN Jean-Marie

Tous les auteurs :
Hirsch AK, Reutenauer P, Le Moignan M, Ulrich S, Boul PJ, Harrowfield JM, Jarowski PD, Lehn JM

Lien Pubmed

https://www.ncbi.nlm.nih.gov/pubmed/24339005

Résumé

X-ray structure determinations on four Diels-Alder adducts derived from the reactions of cyano- and ester-substituted alkenes with anthracene and 9,10-dimethylanthracene have shown the bonds formed in the adduction to be particularly long. Their lengths range from 1.58 to 1.62 A, some of the longest known for Diels-Alder adducts. Formation of the four adducts is detectably reversible at ambient temperature and is associated with free energies of reaction ranging from -2.5 to -40.6 kJ mol(-1). The solution equilibria have been experimentally characterised by NMR spectroscopy. Density-functional-theory calculations at the MPW1K/6-31+G(d,p) level with PCM solvation agree with experiment with average errors of 6 kJ mol(-1) in free energies of reaction and structural agreement in adduct bond lengths of 0.013 A. To understand more fully the cause of the reversibility and its relationship to the long adduct bond lengths, natural-bond-orbital (NBO) analysis was applied to quantify donor-acceptor interactions within the molecules. Both electron donation into the sigma*-anti-bonding orbital of the adduct bond and electron withdrawal from the sigma-bonding orbital are found to be responsible for this bond elongation.

Référence

Chemistry. 2014 Jan 20;20(4):1073-80