Chemistry of boryllithium: synthesis, structure, and reactivity.
Chemistry of boryllithium: synthesis, structure, and reactivity.
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DOI：
10.1021/ja8057919
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发表时间：
2008-11
影响因子：
15
通讯作者：
Yasutomo Segawa;Yuta Suzuki;M. Yamashita;K. Nozaki
中科院分区：
文献类型：
--
作者：
Yasutomo Segawa;Yuta Suzuki;M. Yamashita;K. Nozaki
合成了一系列含硼阴离子的锂盐--硼硫锂，并用核磁共振光谱和晶体分析对其结构进行了表征。除了母体硼锂化合物35a外，通过在五元环上使用饱和的C-C和苯环化的C=C主链以及氮原子上的均三甲基团对硼锂进行结构修饰，也允许生成相应的硼锂。与氢化硼烷38a-c和优化的游离硼阴离子OPT-46a-c相比，硼锂的固态结构表明，在(35a X DME)(2)、35a x(THF)(2)、35b x(THF)(2)和35c x(THF)(2)中，硼原子都是阴离子，其中硼原子是极化的。分离的(35a X DME)(2)和35a x(THF)(2)单晶在THF-d(8)中的溶解表明，硼-锂键保留在溶液中，并观察到游离的DME或THF分子。在THF-d(8)或甲基环己烷-d(14)中观察到35a的~(11)B-核磁共振化学位移随温度的变化，表明硼中心附近的化学位移各向异性发生了变化。与苯基锂一样，OPT-35a x(THF)(2)的HOMO在硼原子上具有孤对特征，而氢化硼烷38a的HOMO对应于含硼五元杂环的pi轨道。AIM分析表明，B-Li键的极性与烷基锂相似。通过去质子化、S(N)2型取代、卤素-金属交换或电子转移、1，2-与羰基加成以及S(N)Ar反应，硼基锂35a和35b作为碱性或亲硼核试剂与有机亲电试剂反应。在与CO(2)反应的情况下，分子内环合，然后从硼羧酸盐阴离子中消除CO，然后质子化得到羟基硼烷64a和64b。用X-射线结晶学、红外光谱和~(13)C核磁共振谱研究了硼基取代物60a、60b、61、62和63a的羰基性质，结果表明，与碳取代的类似物相比，硼取代基削弱了C=O键。
A series of lithium salts of boryl anion, boryllithiums, were synthesized and characterized by NMR spectroscopy and crystallographic analysis. In addition to the parent boryllithium compound 35a, structural modification of boryllithium, using saturated C-C and benzannulated C=C backbones in the five-membered ring and mesityl groups on the nitrogen atoms, also allowed generation of the corresponding boryllithium. The solid state structures of boryllithium showed that the boron-lithium bond is polarized where the boron atom is anionic in all (35a x DME)(2), 35a x (THF)(2), 35b x (THF)(2), and 35c x (THF)(2) when compared to the structures of hydroborane 38a-c and optimized free boryl anion opt-46a-c. Dissolution of the isolated single crystals of (35a x DME)(2) and 35a x (THF)(2) in THF-d(8) showed that the boron-lithium bond remained in solution and free DME or THF molecules were observed. Temperature-dependent (11)B NMR chemical shift changes of 35a were observed in THF-d(8) or methylcyclohexane-d(14), suggesting a change of chemical shift anisotropy around the boron center. The HOMO of opt-35a x (THF)(2) had a lone pair character on the boron atom, as observed for phenyllithium, whereas the HOMO of hydroborane 38a corresponds to the pi-orbital of the boron-containing five-membered heterocycle. The polarity of the B-Li bond, estimated by AIM analysis, was similar to that of alkyllithium. Boryllithiums 35a and 35b behave as a base or a boron nucleophile in reaction with organic electrophiles via deprotonation, S(N)2-type substitution, halogen-metal exchange or electron-transfer, 1,2-addition to a carbonyl group, and S(N)Ar reaction. In the case of the reaction with CO(2), intramolecular cyclization followed by CO elimination from borylcarboxylate anion and subsequent protonation gave hydroxyboranes 64a and 64b. The characters of the carbonyl groups in the borylcarbonyl compounds 60a, 60b, 61, 62, and 63a, which were obtained from the reaction of boryllithiums 35a and 35b, were investigated by X-ray crystallography, IR, and (13)C NMR spectroscopy to show that the boryl substituent weakened the C=O bond when compared to carbon substituted analogues.