Addition compounds of alkali metal hydrides. 15. Steric effects in the reaction of representative trialkylboranes with lithium and sodium hydrides to form the corresponding trialkylborohydrides
Addition compounds of alkali metal hydrides. 15. Steric effects in the reaction of representative trialkylboranes with lithium and sodium hydrides to form the corresponding trialkylborohydrides
复制标题
碱金属氢化物的加成化合物。
DOI：
10.1021/ja00479a016
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发表时间：
1978
影响因子：
15
通讯作者：
J. L. Hubbard
中科院分区：
文献类型：
--
作者：
H. Brown;S. Krishnamurthy;J. L. Hubbard
从速率、化学计量和产物等方面详细考察了氢化锂和氢化钠与具有代表性的三烷基硼烷反应的四氢呋喃反应。反应速度受三烷基硼烷的空间要求的影响很大。因此，氢化锂与一系列三烷基硼烷在25℃下的反应速度遵循如下顺序：Et3B>；n-Bu3B>；‘’-Bu3B？sec-Bu3B。即使在回流的四氢呋喃中，三叔丁基硼烷和其他受阻的有机硼烷与氢化锂的反应也缓慢且不完全。氢化钠在这些反应中表现出比氢化锂更大的反应性。氢化钠在回流四氢呋喃中与氢化钠反应迅速和定量，甚至在25℃时，氢化钠与几乎所有无阻碍的三烷基硼烷和一些受阻的三烷基硼烷反应。同样，反应速度随着硼上烷基取代基Et3B>；n-Bu3B>；三环戊基硼烷>；-Bu3B>；三环己基硼烷>；三-exo-2-降冰片基硼烷>；rec-Bu3B；高度受阻的有机硼烷如三硅戊基硼烷和三(rra？i-2-甲基环戊基)硼烷在65℃时对氢化锂和氢化钠基本上都是惰性的。碱金属氢化物与三烷基硼烷的反应按1：1的化学计量比进行，反应产物经氢化物分析、红外光谱和核磁共振表征。本反应为研究各种三烷基硼烷的空间要求提供了一种方便的手段。此外，它还提供了一条合成锂和三烷基硼氢化钠的简单路线。
The reactionin tetrahydrofuran of lithium and sodium hydrides with representative trialkylboranes of increasing ste-ric requirements was examined in detail with respect to rate, stoichiometry, and products. The rate of the reaction is strongly influenced by the steric requirements of the trialkylborane. Thus, the rates of reaction of lithium hydride with a series of trialk-ylboranes at 25 C follows the orderEt3B> n-Bu3B>¡'-Bu3B» sec-Bu3B. Even in refluxing tetrahydrofuran, tri-seobutyl-borane and other hindered organoboranes react with lithium hydride sluggishlyand incompletely. Sodium hydride exhibits greater reactivity than lithium hydride in these reactions. Sodium hydride reacts with essentially all of the unhindered trialkyl-boranes and with a number of hindered trialkylboranes even at 25 C. Other hindered trialkylboranes such as tri-rec-butylbor-ane, tricyclohexylborane, and tri-exo-2-norbornylborane react with sodium hydride in refluxing tetrahydrofuran rapidly and quantitatively. Here againthe rate of the reaction decreases drastically with increasing size of the alkyl substituent on boron: Et3B> n-Bu3B> tricyclopentylborane>¡-Bu3B> tricyclohexylborane> tri-exo-2-norbornylborane> rec-Bu3B. Highly hindered organoboranes such as trisiamylborane and tris (rra «i-2-methylcyclopentyl) borane are essentially inert toward both lithium hydride and sodium hydride at 65 C. The reaction of alkali metal hydrides with trialkylboranes proceeds in 1: 1 stoi-chiometry; the products of the reaction are alkali metal trialkylborohydrides characterizedby hydride analysis, IR, and nB NMR. The present reaction serves as a convenient means for studying the steric requirements of various trialkylboranes. In addition, it also provides a simple route to a number of lithium and sodium trialkylborohydrides.