老反应、新认识:不容小觑的乙硼烷与氨的反应  

Old Reaction,New Understanding:An Important Reaction of Diborane with Ammonia

作　　者：李慧珍 李运辉 庄惠芬 陈丽婷 梁瑛敏 易思远 Huizhen Li;Yunhui Li;Huifen Zhuang;Liting Chen;Yingmin Liang;Siyuan Yi(School of Chemistry and Chemical Engineering,Guangzhou University,Guangzhou 510006,China)

机构地区：[1]广州大学化学化工学院,广州510006

出　　处：《大学化学》2021年第8期43-55,共13页University Chemistry

基　　金：国家自然科学基金(21601051);广州大学大学生创新实验训练项目(XJ202011078038)。

摘　　要：看似简单实际却很复杂的乙硼烷(B_(2)H_(6),diborane)与氨(NH_(3))的反应已经困扰了硼化学家数十年。该反应在不同实验条件下可生成硼氢化二氢二氨合硼(III)([NH_(3)BH_(2)NH_(3)]BH_(4),diammoniate of diborane,DADB),氨硼烷(NH_(3)·BH_(3),ammonia borane,AB),氨基乙硼烷(NH_(2)B_(2)H_(5),aminodiborane,ADB)等化合物。从1923年起,化学家们对影响乙硼烷与路易斯碱反应的因素,如立体效应、诱导效应、溶剂效应、介电常数等进行研究,但一直无法根据上述影响因素准确预测产物。基于乙硼烷在THF中以THF·BH_(3)存在、路易斯碱与乙硼烷或THF·BH_(3)反应产物相同等实验事实,化学家们巧妙利用NH_(3)与THF·BH_(3)的反应,在温和的条件下研究了DADB、AB的生成机理,发现双氢键是控制反应的重要因素。利用AB与THF·BH_(3)的反应,实验和理论计算结果进一步揭示了基于双氢键的ADB的复杂形成机理。Although at first glance,the old reaction of B_(2)H_(6)(diborane)with NH_(3) seemed to be simple,it has been shown that the reaction was complex and had perplexed boron chemists for decades.The reaction was highly sensitive to the experimental conditions,and one or the mixture of the products,such as diammoniate of diborane(DADB,[NH_(3)BH_(2)NH_(3)][BH_(4)]),ammonia borane(AB,NH_(3)·BH_(3)),aminodiborane(ADB,NH_(2)B_(2)H_(5)),could be obtained.It was known that the asymmetrical cleavage of the double bridge bond of B_(2)H_(6) produced the ionic product DADB,whereas symmetrical cleavage afforded the covalent product,AB.The different cleavage patterns of B_(2)H_(6) under particular conditions attracted interest to study the key points of the selectivity including steric effect,inductive effect,solvent effect,and dielectric constant,but it is still not possible to predict the products of the reactions of B_(2)H_(6) with Lewis base.B_(2)H_(6) was present in THF as the THF·BH_(3) adduct,and the products of the reactions of Lewis bases with THF·BH_(3) or B_(2)H_(6) were of the same types.The formation mechanisms of AB and DADB were explored by an ingenious design using THF·BH_(3) as a proxy for more reactive B_(2)H_(6),and the reaction of THF·BH_(3) with NH_(3) could be carried out under mild conditions.It was found that dihydrogen bonds played a critical role in the competing formation of AB and DADB.Both experimental and computational results demonstrated that dihydrogen bond was the dominant factor in the complex formation mechanism of ADB.

关 键 词：硼氮氢化合物 乙硼烷 硼氢化二氢二氨合硼(III) 氨硼烷 氨基乙硼烷 双氢键 路易斯碱 

分 类 号：G64[文化科学—高等教育学] O6[文化科学—教育学]