作者:Gorkem Gunbas、Nema Hafezi、William L. Sheppard、Marilyn M. Olmstead、Irini V. Stoyanova、Fook S. Tham、Matthew P. Meyer、Mark Mascal
DOI:10.1038/nchem.1502
日期:2012.12
Oxatriquinanes are fused, tricyclic oxonium ions that are known to have exceptional stability compared to simple alkyl oxonium salts. CâO bonds in ethers are generally â¼1.43Â Ã
in length, but oxatriquinane has been found to have CâO bond lengths of 1.54Â Ã
. A search of the Cambridge Structural Database turned up no bona fide CâO bond length exceeding this value. Computational modelling of oxatriquinane alongside other alkyl oxonium ions indicated that the electronic consequences of molecular strain were primarily responsible for the observed bond elongation. We also show that substitution of the oxatriquinane ring system with alkyl groups of increasing steric demand pushes the CâO bond to unheard of distances, culminating in a tert-butyl derivative at a predicted 1.60Â Ã
. Chemical synthesis and an X-ray crystallographic study of these compounds validated the results of the modelling work and, finally, an extraordinary 1.622Â Ã
CâO bond was observed in 1,4,7-tri-tert-butyloxatriquinane. Oxatriquinane is a remarkably stable alkyl oxonium ion, despite the fact that its carbonâoxygen bond lengths are 1.54 Ã
. The robust nature of this fused tricyclic molecule enabled the addition of increasing steric bulk to the system, culminating in a tri-tert-butyloxatriquinane with a record 1.62 Ã
CâO bond distance.
氧三奎烷是稠合的三环氧鎓离子,与简单的烷基氧鎓盐相比,已知其具有优异的稳定性。醚中的C–O键长度通常为±1.43±,但已发现氧三奎烷的C–O键长度为1.54±。对剑桥结构数据库的搜索发现,真正的 C–O 键长没有超过这个值。氧三奎烷与其他烷基氧鎓离子的计算模型表明,分子应变的电子效应是观察到的键伸长的主要原因。我们还表明,用烷基取代氧三奎烷环系统,增加空间需求,将 C–O 键推至闻所未闻的距离,最终形成预计为 1.60 × 的叔丁基衍生物。这些化合物的化学合成和 X 射线晶体学研究验证了建模工作的结果,最后,在 1,4,7-三叔丁基氧三奎烷中观察到了非凡的 1.622 × C−O 键。氧三奎烷是一种非常稳定的烷基氧鎓离子,尽管其碳-氧键长为 1.54 ×。这种稠合三环分子的坚固特性使得系统的空间体积增加,最终形成具有创纪录的 1.62 × C–O 键距的三叔丁基氧三奎烷。