Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres
作者:Nick A. Giffin、Miller Makramalla、Arthur D. Hendsbee、Katherine N. Robertson、Cody Sherren、Cory C. Pye、Jason D. Masuda、Jason A. C. Clyburne
DOI:10.1039/c0ob00999g
日期:——
In this paper, we report a novel synthesis of anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-H). An X-ray crystal structure and full characterization of the compound are included. Compared to hydrated TEMPO-H, its anhydrous form exhibits improved stability and a differing chemical reactivity. The reactions of anhydrous TEMPO-H with a variety of low-valent carbon centres are described. For example, anhydrous TEMPO-H was reacted with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), an unsaturated NHC. Crystals of [CHNC6H2(CH3)3]2C⋯HO(NC5H6(CH3)4), IMes⋯TEMPO-H, were isolated and a crystal structure determined. The experimental structure is compared to the results of theoretical calculations on the hydrogen-bonded dimer. Anhydrous TEMPO-H was also reacted with the saturated NHC, 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr), giving the product [CH2Ni-Pr2C6H3]2CH⋯O(NC5H6(CH3)4). In contrast, the reaction of hydrated TEMPO-H with 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene gave small amounts of the hydrolysis product, N-(2,6-diisopropylphenyl)-N-[2-(2,6-diisopropylphenylamino)ethyl]formamide. Finally, anhydrous TEMPO-H was reacted with (triphenylphosphoranylidene)ketene to generate Ph3PC(H)C(O)O(NC5H6(CH3)4). A full characterization of the product, including an X-ray crystal structure, is described.
本文报道了一种新颖的无水1-羟基-2,2,6,6-四甲基哌啶(TEMPO-H)的合成方法,并包含了该化合物的X射线晶体结构及全面表征。与水合TEMPO-H相比,其无水形式表现出更高的稳定性和不同的化学反应性。描述了无水TEMPO-H与多种低价碳中心化合物的反应。例如,无水TEMPO-H与不饱和NHC,1,3-双(2,4,6-三甲基苯基)咪唑-2-亚基(IMes)反应。分离出了[CHNC6H2(CH3)3]2C⋯HO(NC5H6(CH3)4)(IMes⋯TEMPO-H)的晶体并测定了晶体结构。实验结构与氢键二聚体的理论计算结果进行了比较。无水TEMPO-H还与饱和NHC,1,3-双(2,6-二异丙基苯基)咪唑烷-2-亚基(SIPr)反应,得到了产物[CH2Ni-Pr2C6H3]2CH⋯O(NC5H6(CH3)4)。相比之下,水合TEMPO-H与1,3-双(2,6-二异丙基苯基)咪唑烷-2-亚基反应只得到了少量水解产物,N-(2,6-二异丙基苯基)-N-[2-(2,6-二异丙基苯基氨基)乙基]甲酰胺。最后,无水TEMPO-H与(三苯基膦亚基)乙烯酮反应生成了Ph3PC(H)C(O)O(NC5H6(CH3)4)。详细描述了该产物的全面表征,包括X射线晶体结构。