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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >The significance of secondary interactions during alkaline earth-promoted dehydrogenation of dialkylamine-boranes
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The significance of secondary interactions during alkaline earth-promoted dehydrogenation of dialkylamine-boranes

机译：碱土促进的二烷基胺-硼烷脱氢过程中次要相互作用的意义

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Reactions of anilidoimine magnesium n-butyl and calcium bis(trimethylsilyl) amide derivatives with Me2NH center dot BH3 at 25 degrees C resulted in the isolation of complexes containing [NMe2BH2NMe2BH3](-) and [NMe2BH3](-) anions respectively. Although onward reaction of the calcium species at 30 degrees C with a further equivalent of Me2NH center dot BH3 provided ca. 90% conversion of the coordinated dimethylamidoborane anion to [NMe2BH2NMe2BH3]-, this process also resulted in significant (ca. 25%) levels of competitive protonation of the anilidoimine spectator ligand. A similar reaction performed between a previously reported beta-diketiminato calcium dimethylamidoborane and Me2NH center dot BH3, however, provided clean conversion to a structurally characterised calcium [NMe2BH2NMe2BH3](-) complex. Reaction of a more sterically congested beta-diketiminato magnesium n-butyl reagent with Me2NH center dot BH3 has allowed the isolation of a magnesium derivative of the [NMe2BH3](-) anion. The thermal stability of these compounds as well as previously reported magnesium and calcium amidoborane species indicate, in partial agreement with a recent DFT study, that all of these compounds are resistant to the beta-and delta-hydride elimination reactions that have previously been implicated as the key B-N bond-forming and dehydrogenative steps in the group 2-catalysed dehydrocoupling of Me2NH center dot BH3. In contrast to these observations, addition of stoichiometric quantities of Me2NH center dot BH3 to the various isolated group 2 amidoborane species was found to result in facile elimination of the cyclic borazane [Me2N-BH2](2) which occurs with regeneration of the metallated amidoborane. On this basis, we suggest that the dehydrocoupling of Me2NH center dot BH3 at group 2 centres takes place as a sequence of concerted proton-assisted steps during which B-H and N-H bond breaking plays an equally prominent role, with the efficacy of boron hydride protonolysis dictated by the relative polarising influence of the B-H to Mg/Ca interactions. Furthermore, we propose a modified mechanism for group 2-mediated dimethylamine borane dehydrocoupling that is dependent on the intermediacy of key derivatives of the [NMe2 center dot BH3](-) and [NMe2BH2NMe2BH3](-) anions but does not require the formation of high energy alkaline earth hydride intermediates. Although these results are specifically focussed on the applications of alkaline earth species, this mechanistic insight may also be relevant to other redoxinactive main group element-based systems and to our understanding of hydrogen evolution from saline derivatives of ammonia borane.
机译：苯胺亚胺正丁基镁和双（三甲基甲硅烷基）钙酰胺衍生物与Me2NH中心点BH3在25℃下反应，分别分离出含有[NMe2BH2NMe2BH3]（-）和[NMe2BH3]（-）阴离子的配合物。尽管钙物质在30摄氏度下与另一当量的Me2NH中心点BH3进行进一步反应，大约可90％的配位二甲基氨基硼烷阴离子转化为[NMe2BH2NMe2BH3]-，此过程还导致苯胺亚胺旁观者配体的竞争性质子化水平很高（约25％）。在先前报道的β-二酮丁二酸钙二甲基酰胺基硼烷和Me2NH中心点BH3之间进行的类似反应，提供了向结构特征性钙[NMe2BH2NMe2BH3]（-）络合物的干净转化。在空间上更拥挤的β-二酮亚氨基乙酸正丁基镁与Me2NH中心点BH3的反应可以分离[NMe2BH3]（-）阴离子的镁衍生物。这些化合物以及先前报道的镁和氨基硼烷钙的热稳定性表明，与最近的DFT研究部分吻合的是，所有这些化合物均具有抗β-和δ-氢化物消除反应的能力，这些反应先前被认为是Me 2 NH中心点BH 3的2族催化脱氢偶联中关键的BN键形成和脱氢步骤。与这些观察结果相反，发现将化学计算量的Me2NH中心点BH3添加到各种孤立的第2组氨基硼烷物质中可轻松消除环状硼氮烷[Me2N-BH2]（2），这是由于金属化氨基硼烷的再生而产生的。在此基础上，我们认为第2组中心的Me2NH中心点BH3的脱氢偶联是通过一系列协调的质子辅助步骤进行的，在该过程中BH和NH键的断裂作用同样突出，氢化硼质子分解的效力决定了BH对Mg / Ca相互作用的相对极化影响。此外，我们提出了一种用于第2组介导的二甲胺硼烷脱氢偶联的修饰机理，该机理取决于[NMe2中心点BH3]（-）和[NMe2BH2NMe2BH3]（-）阴离子的关键衍生物的中间体，但不需要形成高能碱土金属氢化物的中间体。尽管这些结果特别集中在碱土类的应用上，但这种机理上的见解也可能与其他基于氧化还原活性主族元素的系统以及我们对氨硼烷盐类衍生物中氢的理解有关。

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