Mechanism of metal-free hydrogen transfer between amine-boranes and aminoboranes.
Mechanism of metal-free hydrogen transfer between amine-boranes and aminoboranes.
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胺硼烷和氨基硼烷之间的无金属氢转移机制。
DOI：
10.1021/ja307247g
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发表时间：
2012
影响因子：
15
通讯作者：
Leitao EM
中科院分区：
文献类型：
--
作者：
Leitao EM
详细研究了胺-硼烷Me_2NH·BH_3通过瞬时Me_2N-BH_2向氨基硼烷Pr2N-BH_2、产率Pr2NH·BH_3和环二硼氮烷[Me_2N-BH_2]_2的无金属氢转移的动力学，并通过同位素标记和密度泛函理论计算得到了进一步的信息。用11B{1H}核磁共振波谱在一系列溶剂中和在变温的四氢呋喃中从两个方向监测了该体系接近平衡的过程。根据一个简单的两阶段氢转移/二聚过程对所得到的时间浓度数据进行模拟，得到了满足两个平衡的速率常数和热力学参数。在室温下，双分子氢转移在正向略微放热(ΔG1°(2 95)=10±7kJ·m ol-1；ΔG1⧧(2 95)=91±5 kJ·m ol-1)，总的平衡是由随后的氨基硼烷Me2NBH 2(ΔG 2°(2 95)=−2 8±14 kJ·m o l-1)所驱动的。系统地对Me2NH·BH3和diPr2NBH中的NH和BH部分进行了氚标记，从而确定了参与氢转移的动力学同位素效应(KIE)。在硼原子上的小的反Kie(KH/Kd=0.9±0.2)和在氮原子上的大的正常Kie(KH/Kd=6.7±0.9)要么符合B-B氢转移的预平衡，要么是通过B-B氢转移高度推进的六元环过渡态的协同但非同步的氢转移。DFT计算与协调但不同步的过程完全一致。
The kinetics of the metal-free hydrogen transfer from amine–borane Me2NH·BH3to aminoboraneiPr2NBH2, yieldingiPr2NH·BH3and cyclodiborazane [Me2N-BH2]2via transient Me2NBH2, have been investigated in detail, with further information derived from isotopic labeling and DFT computations. The approach of the system toward equilibrium was monitored in both directions by11B{1H} NMR spectroscopy in a range of solvents and at variable temperatures in THF. Simulation of the resulting temporal–concentration data according to a simple two-stage hydrogen transfer/dimerization process yielded the rate constants and thermodynamic parameters attending both equilibria. At ambient temperature, the bimolecular hydrogen transfer is slightly endergonic in the forward direction (ΔG1°(295)= 10 ± 7 kJ·mol–1; ΔG1⧧(295)= 91 ± 5 kJ·mol–1), with the overall equilibrium being driven forward by the subsequent exergonic dimerization of the aminoborane Me2NBH2(ΔG2°(295)= −28 ± 14 kJ·mol–1). Systematic deuterium labeling of the NH and BH moieties in Me2NH·BH3andiPr2NBH2allowed the kinetic isotope effects (KIEs) attending the hydrogen transfer to be determined. A small inverse KIE at boron (kH/kD= 0.9 ± 0.2) and a large normal KIE at nitrogen (kH/kD= 6.7 ± 0.9) are consistent with either a pre-equilibrium involving a B-to-B hydrogen transfer or a concerted but asynchronous hydrogen transfer via a cyclic six-membered transition state in which the B-to-B hydrogen transfer is highly advanced. DFT calculations are fully consistent with a concerted but asynchronous process.
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影响因子：
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作者：
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作者：
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