The mechanism of borane-amine dehydrocoupling with bifunctional ruthenium catalysts.
The mechanism of borane-amine dehydrocoupling with bifunctional ruthenium catalysts.
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DOI：
10.1021/ja311092c
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发表时间：
2013-09
影响因子：
15
通讯作者：
A. Marziale;A. Friedrich;I. Klopsch;M. Drees;V. R. Celinski;J. Schmedt auf der Günne;S. Schneider
中科院分区：
文献类型：
--
作者：
A. Marziale;A. Friedrich;I. Klopsch;M. Drees;V. R. Celinski;J. Schmedt auf der Günne;S. Schneider
硼烷-胺加合物作为化学储氢的载体和合成无机材料的前驱体，受到了广泛的关注。原则上，过渡金属催化氨-硼烷(H3N-BH3，AB)脱氢偶联提供了高速率大重量放氢和形成具有明确微结构的B-N聚合物的可能性。文献报道了几种不同的均相催化剂。目前的机理图表明，氨基硼烷(例如，镍卡宾和Shvo催化剂)的释放会导致生成2当量的氢气和1当量的氢气，而1当量的氢气和聚氨基硼烷也是与脱氢产物耦合的催化剂(例如，Ir和Rh双膦催化剂和钳形催化剂)。然而，与快速增长的催化剂数量相比，涉及机理细节的实验研究数量仍然有限。在本论文中，我们对高活性的Ru/Amido催化剂上AB脱氢偶联合成聚氨基硼烷的反应机理进行了全面的实验和理论研究。基于动力学、捕获实验、聚合物的(11)B MQMAS固体核磁共振表征、模型底物的光谱实验和密度泛函理论(DFT)计算，我们提出了胺催化剂[Ru(H)2PMe3{HN(CH2CH2PtBu2)2}]的两个机械连接的催化循环，这两个循环既可以解释金属介导的底物脱氢生成氨基硼烷，也可以解释通过将氨基硼烷插入H-NH_2BH_3键来催化聚合物包结。动力学结果和聚合物表征也表明，氨基催化剂[Ru(H)PMe3{N(CH2CH2PtBu2)2}]没有经历先前理论研究中提出的相同的反应机理。
Borane-amine adducts have received considerable attention, both as vectors for chemical hydrogen storage and as precursors for the synthesis of inorganic materials. Transition metal-catalyzed ammonia-borane (H3N-BH3, AB) dehydrocoupling offers, in principle, the possibility of large gravimetric hydrogen release at high rates and the formation of B-N polymers with well-defined microstructure. Several different homogeneous catalysts were reported in the literature. The current mechanistic picture implies that the release of aminoborane (e.g., Ni carbenes and Shvo's catalyst) results in formation of borazine and 2 equiv of H2, while 1 equiv of H2 and polyaminoborane are obtained with catalysts that also couple the dehydroproducts (e.g., Ir and Rh diphosphine and pincer catalysts). However, in comparison with the rapidly growing number of catalysts, the amount of experimental studies that deal with mechanistic details is still limited. Here, we present a comprehensive experimental and theoretical study about the mechanism of AB dehydrocoupling to polyaminoborane with ruthenium amine/amido catalysts, which exhibit particularly high activity. On the basis of kinetics, trapping experiments, polymer characterization by (11)B MQMAS solid-state NMR, spectroscopic experiments with model substrates, and density functional theory (DFT) calculations, we propose for the amine catalyst [Ru(H)2PMe3{HN(CH2CH2PtBu2)2}] two mechanistically connected catalytic cycles that account for both metal-mediated substrate dehydrogenation to aminoborane and catalyzed polymer enchainment by formal aminoborane insertion into a H-NH2BH3 bond. Kinetic results and polymer characterization also indicate that amido catalyst [Ru(H)PMe3{N(CH2CH2PtBu2)2}] does not undergo the same mechanism as was previously proposed in a theoretical study.