.mu.-Hydrido-bridging in tricycloalkyl carbocations
.mu.-Hydrido-bridging in tricycloalkyl carbocations
复制标题
三环烷基碳阳离子中的μ-氢桥连
DOI：
10.1021/ja00178a043
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发表时间：
1990
影响因子：
15
通讯作者：
S. Whitworth
中科院分区：
文献类型：
--
作者：
T. S. Sorensen;S. Whitworth
以2-金刚烷酮为原料，经10步合成了一系列三环烯烃5（= 5-8）。类似的烯烃5（= 4）不能用同样的方法制备。在每种情况下，这些结构都被设计为具有一个向内金字塔化的桥头堡氢，其位置合适，以便在相反的桥头堡上形成阳离子中心，然后可能导致微氢化物桥接相互作用。羟基桥的性质被发现是非常依赖于结构的，人们可以将这种行为与三环烷烃框架中末端桥支撑碳（C—H-C+）之间的距离d联系起来。对于最短距离，可以形成完全对称的微桥，而较大的d则会导致向正常的叔碳正离子结构渐变。阳离子4（= 5）在pXa意义上是相当稳定的（pXa=-1），并且该阳离子与= 6情况之间的p/fa关系用半经验MO理论计算。计算得到的pKi为-5.3，与p/fa介于-3和-8之间的实验范围很好地吻合。有人还根据MO理论预测，未知阳离子4（= 4）的pXa=+ 10，即在中性水中稳定。
From 2-adamantanone, a series of tricyclic alkenes 5 (= 5-8) were synthesized in 10 steps. The analogous alkene 5 (= 4) could not be prepared by the same route. These structures, in each case, were designedto have an inwardly pyramidalized bridgehead hydrogen, which is suitably positioned so that the formation of a cationic center on the opposite bridgehead could then potentially lead to a µ-hydrido-bridging interaction. The nature of the hydrido bridge was found to be very structure-dependent, and one can correlate this behavior with the distance d between the terminal bridge-supporting carbons (C--H-C+) in the tricycloalkane framework. For the shortestdistances, one develops a fully symmetric µ-bridge, while larger d result in a gradation toward a normal tertiary carbocation structure. The cation 4 (= 5) is quite stable in a pXa sense (pXa=-1), and the p/fa relationship between this cation and the= 6 case was computed with semiempirical MO theory. The calculated pKi was-5.3, in good agreement with an experimental bracketing of the p/fa between-3 and-8. One also predicts from the MO theory that the unknown cation 4 (= 4) will have pXa=+ 10, ie, stable in neutral water.