STABLE CARBOCATIONS .257. BRIDGEHEAD ADAMANTYL, DIAMANTYL, AND RELATED CATIONS AND DICATIONS
STABLE CARBOCATIONS .257. BRIDGEHEAD ADAMANTYL, DIAMANTYL, AND RELATED CATIONS AND DICATIONS
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DOI：
10.1021/ja00295a032
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发表时间：
1985-01-01
影响因子：
15
通讯作者：
SCHLEYER, PV
中科院分区：
文献类型：
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作者：
OLAH, GA;PRAKASH, GKS;SCHLEYER, PV
在超强酸介质中合成了金刚烷桥头1-阳离子3a和一系列甲基取代的金刚烷阳离子3b-d，并用~ 1H和~（13）C NMR进行了表征。桥头γ碳相对于β-亚甲基的相对去屏蔽已经被合理化为CC超共轭效应。由外-5，6-三亚甲基-2-辛基衍生物的电离产生的阳离子已被证明是平衡的2，3-三亚甲基-2-辛基阳离子12。12的~（13）C NMR谱研究表明，12的外2，3-氢简并位移能垒Δ G ~*= 7.2 kcal/mol. SO2 ClF溶液中的阳离子12即使在室温下也是稳定的;然而，在SO2溶液中，它平滑且不可逆地重排为桥头1-金刚烷基阳离子3a。另一方面，2-甲基-5，6-外三亚甲基-2-丙基阳离子17被发现相当稳定。还通过固态CPMAS 13 C NMR光谱研究了作为其分离的SbF 6-盐的1-金刚烷基阳离子。桥头1-和4-二金刚烷基阳离子4和27也制备和研究。还获得了3a和4的Fleteronuclear相关的2D NMR谱，并用于NMR位移的许多分配。阳离子27缓慢地不可逆地重排为4。阳离子4也是由3-二金刚烷衍生物电离产生的。上述重排到电子结构更稳定的离子4已经被合理化，因为分子间的氢位移比分子内的位移更容易。桥头二金刚烷基阳离子4和27的稳定性也来源于CC超共轭效应，类似于它们的金刚烷基类似物。与3-二金刚烷基仲阳离子的不稳定性相反，相应的3-甲基和3-苯基取代的类似物被发现是相当稳定的。还生成并研究了3，3 '-（1，1'-联金刚烷基）二价阳离子6和4，9-二金刚烷基二价阳离子5。CC超共轭稳定相互作用在所有的桥头阳离子包括双阳离子6中被发现是“有效的”，但在4，9-二金刚烷基双阳离子5中不存在。5中的电荷-电荷排斥似乎减少了这种CC超共轭相互作用。在过去的二十年中，已经进行了关于金刚烷、二金刚烷和其它所谓的金刚烷分子的化学的广泛研究。金刚烷（1）和二金刚烷（2）的独特结构特征也是系统研究其阳离子的理想选择，与结构和化学反应性有关。环己烷环的紧密互锁
The bridgehead 1-adamantyl cation 3a and a series of methyl-substituted adamantylcations 3b-d have been prepared in superacid medium and characterized by'H and 13C NMR spectroscopy. The relative deshielding of bridgehead y carbons with respect to/3-methylenes has been rationalized interms of a CC hyperconjugative effect. The cation generated from the ionization of exo-5, 6-trimethylene-2-norbornylderivatives has been shown to be the equilibrating 2, 3-trimethylene-2-norbornyl cation 12. The temperature-dependent 13C NMR spectroscopic studies on 12 indicate the barrier for the degenerate exo-2, 3-hydrogen shift, AG*= 7.2 kcal/mol. The cation 12 in a solution of S02C1F is stable even at room temperature; however, in a solution of S02, it smoothly and irreversibly rearranges to bridgehead 1-adamantyl cation 3a. On theother hand, 2-methyl-5, 6-exo-trimethylene-2-norbornyl cation 17 was found to be quite stable. The 1-adamantyl cation was also studied as its isolated SbF6" salt by solid-state CPMAS 13C NMR spectroscopy. The bridgehead 1-and 4-diamantyl cations 4 and 27 were also prepared and studied. Fleteronuclear-correlated 2D NMR spectra were also obtained for 3a and 4 and used in many assignments of the NMR shifts. Cation 27 slowly and irreversibly rearranges to 4. The cation 4 was also generated by the ionizationof 3-diamantyl derivatives. The above rearrangements to the thermodynamically more stable ion 4 has been rationalized in terms of facile intermolecular hydrogen shifts rather than intramolecular shifts. The bridgehead diamantyl cations 4 and 27 also derive theirstability from CC hyperconjugativeeffects similar to their adamantyl analogues. In contrast to the instability of secondary 3-diamantyl cation the corresponding 3-methyl-and 3-phenyl-substituted analogues were found to be rather stable. 3, 3'-(l, l'-Biadamantyl) dication 6 and 4, 9-diamantyl dication 5 were also generated and studied. The CC hyperconjugative stabilizing interaction which is found “operative” in all of the bridgehead cations including dication6 is absent in the 4, 9-diamantyl dication 5. Charge-charge repulsion in 5 seems to diminish such CC hyperconjugative interaction. All attempts to prepare the 1, 3-adamantyl dication 8 or theOver the past 2 decades, extensive research has been carried out pertaining to the chemistry of adamantane, diamantane, and other so-called diamondoid molecules. 2, 3 The unique structural features of adamantane (1) and diamantane (2) are also ideal for a systematic study of their cations, relating to both structure and chemical reactivity. The tight interlocking of cyclohexane rings