Nickel-catalyzed dimerization of [5]cumulenes (hexapentaenes)
Nickel-catalyzed dimerization of [5]cumulenes (hexapentaenes)
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DOI：
10.1246/bcsj.78.2188
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发表时间：
2005-12
影响因子：
4
通讯作者：
Y. Kuwatani;G. Yamamoto;M. Oda;M. Iyoda
中科院分区：
文献类型：
--
作者：
Y. Kuwatani;G. Yamamoto;M. Oda;M. Iyoda
四芳基[5]累积多烯与低价镍络合物在第二个双键处反应以产生新颖的[4]放射烯衍生物，其是[5]累积多烯的头对头二聚体。头对头二聚体也通过逐步路线合成。另一方面，镍催化的具有大体积取代基的[4]累积多烯的二聚产生其他类型的扩展的[4]放射烯和[5]放射烯酮，这取决于末端烷基取代基的体积。因此，四叔丁基[5]枯烯和1，4-双（2，2，6，6-四甲基环亚己基）[3]枯烯在中心双键处反应得到相应的[4]radialene和[5]radialenone，而1，4-双（2，2，5，5-四甲基环亚戊基）[3]枯烯及其苯并稠合衍生物在第二个双键处以头-尾方式反应得到相应的扩展[4] radialene。采用甲基化脱水法将四叔丁基[5]radialenone转化为[5]radialene。扩展的[4]-和[5]radialenes和[5]radialenones已经通过光谱分析，X射线晶体学和/或独立的化学合成充分表征。详细研究了这些新的环外π电子体系的性质。芳基取代的[4]radialenes表现出轻松的键旋转与低能量障碍。[5]radialene和[5]radialenone通过加入酸性质子容易地形成相应的阳离子。在理论计算的基础上讨论了镍催化[5]累积多烯二聚反应的选择性。
Tetraaryl[5]cumulenes react with low-valent nickel complexes at the second double bond to produce novel [4]radialene derivatives that are head-to-head dimers of [5]cumulenes. The head-to-head dimers are also synthesized by a stepwise route. On the other hand, the nickel-catalyzed dimerization of ‖5]cumulenes with bulky substituents produces other types of extended [4]radialenes and [5]radialenones depending on the bulkiness of the terminal alkyl substituents. Thus, tetrakis-t-butyl[5]cumulene and l,4-bis(2,2,6,6-tetramethylcyclohexylidene)[3]cumulene react at the central double bond to give the corresponding [4]radialene and [5]radialenone, whereas 1,4-bis(2,2,5,5-tetramethylcyclopentylidene)[3]cumulene and its benzo-annelated derivative react at the second double bond in a head-to-tail manner to afford the corresponding extended [4]radialenes. Tetrakis-t-butyl[5]radialenone was converted into [5]radialene by using a methylation-dehydration procedure. The extended [4]- and [5]radialenes and [5]radialenones have been fully characterized by spectroscopic analyses, X-ray crystallography, and/or independent chemical synthesis. The properties of these novel exocyclic π-electron systems have been investigated in detail. The aryl-substituted [4]radialenes exhibit facile bond rotation with low energy barriers. The [5]radialene and [5]radialenone form the corresponding cations easily by the addition of an acidic proton. The selectivity of the nickel-catalyzed dimerization of [5]cumulenes is discussed on the basis of theoretical calculations.