KINETICS OF THE REACTIONS OF ALLYLSILANES, ALLYLGERMANES, AND ALLYLSTANNANES WITH CARBENIUM IONS
KINETICS OF THE REACTIONS OF ALLYLSILANES, ALLYLGERMANES, AND ALLYLSTANNANES WITH CARBENIUM IONS
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DOI：
10.1021/ja00013a035
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发表时间：
1991-06-19
影响因子：
15
通讯作者：
MAYR, H
中科院分区：
文献类型：
--
作者：
HAGEN, G;MAYR, H
本文测定了对位取代二芳基碳正离子（ArAr'CH+ = 1）与烯丙基硅烷2、烯丙基锗烷3和烯丙基锡烷4在二氯甲烷溶液中于-70 ℃至-30 ℃反应的二级速率常数。通常，ArAr'CH+对烯丙基元素化合物2-4的CC双键的攻击是速率决定性的，并导致β-元素稳定的碳正离子5的形成，其随后与负抗衡离子反应以产生取代产物6或加成产物7。对于化合物H_2C = CHCH_2MPh_3，相对反应活性分别为1（M = Si）、5.6（M = Ge）和1600（M = Sn）。由化合物H_2C = CHCH_2X（X = H，SiBU_3，SnBU_3）的相对反应活性，导出了烯丙基三烷基甲硅烷基（5 × 10 ~（5））和三烷基甲锡烷基（3 × 10 ~（9））的活化效应。当Si或Sn上的烷基被感应吸走的取代基取代时，这种效应大大降低，烯丙基SiCl 3基团失活了300倍（比较异丁烯/2k）。烯烃和烯丙基元素化合物与碳正离子的反应之间的密切相似性被证明，并且不同的反应系列由表现良好的线性自由能关系连接。末端烯烃和烯丙基元素化合物的相对反应活性几乎不依赖于参比碳正离子的亲电性（恒定选择性关系），从而可以建立一个通用的亲核性标度。
Second-order rate constants for the reactions of para-substituted diarylcarbenium ions (ArAr'CH+ = 1) with allylsilanes 2, allylgermanes 3, and allylstannanes 4 have been determined in CH2Cl2 Solution at -70 to -30-degrees-C. Generally, the attack of ArAr'CH+ at the CC double bond of the allylelement compounds 2-4 is rate-determining and leads to the formation of the beta-element-stabilized carbenium ions 5, which subsequently react with the negative counterions to give the substitution products 6 or the addition products 7. For compounds H2C = CHCH2MPh3, the relative reactivities are 1 (M = Si), 5.6 (M = Ge), and 1600 (M = Sn). From thc relative reactivities of compounds H2C = CHCH2X (X = H, SiBU3, SnBU3), the activating effect of an allylic trialkylsilyl (5 x 10(5)) and trialkylstannyl group (3 x 10(9)) is derived. This effect is strongly reduced, when the alkyl groups at Si or Sn are replaced by inductively withdrawing substituents, and an allylic SiCl3 group deactivates by a factor of 300 (comparison isobutene/2k). A close analogy between the reactions of alkenes and allylelement compounds with carbenium ions is manifested, and the different reaction series are connected by well-behaved linear free energy relationships. The relative reactivities of terminal alkenes and allylelement compounds are almost independent of the electrophilicities of thc reference carbenium ions (constant selectivity relationship), thus allowing the construction of a general nucleophilicity scale for these compounds.