Insight into substrate binding in Shibasaki's Li3(THF)n(BINOLate)3Ln complexes and implications in catalysis.
Insight into substrate binding in Shibasaki's Li3(THF)n(BINOLate)3Ln complexes and implications in catalysis.
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深入了解 Shibasaki 的 Li3(THF)n(BINOLate)3Ln 复合物中的底物结合及其催化意义。
DOI：
10.1021/ja7107933
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发表时间：
2008
影响因子：
15
通讯作者：
Walsh,PatrickJ
中科院分区：
文献类型：
--
作者：
Wooten,AlfredJ;Carroll,PatrickJ;Walsh,PatrickJ
杂双金属路易斯酸 M3(THF)n(BINOLate)3Ln [M = Li、Na、K； Ln = 镧系元素 (III)] 是非常有用的不对称催化剂，在多种反应中表现出高水平的对映选择性。尽管它们很突出，但关于催化剂-基质相互作用的性质以及催化剂运行机制的重要问题仍然存在。本文报道了 7 和 8 配位异双金属配合物 Li3(THF)4(BINOLate)3Ln(THF) [Ln = La、Pr 和 Eu]、Li3(py)5(BINOLate)3Ln(py) [Ln = Eu 和 Yb] 和 Li3(py)5(BINOLate)3La(py)2[py = 吡啶]。环己烯酮、DMF 和吡啶与 Li3(THF)n(BINOLate)3Ln [Ln = Eu、Pr 和 Yb] 和 Li3(DMEDA)3(BINOLate)3Ln [Ln = La 和 Eu] 的溶液结合研究； DMEDA =N,N'-二甲基乙二胺]证明了这些路易斯碱性底物类似物与镧系元素中心的结合。顺磁性铕、镱和镨络合物Li3(THF)n(BINOLate)3Ln在底物类似物上诱导相对较大的镧系元素诱导的位移，在1H NMR谱中范围为0.5至4.3ppm。 Li3(DMEDA)3(BINOLate)3Ln [Ln = Lu、Eu、La 和过渡金属类似物 Y] 的 X 射线结构分析和 NMR 研究揭示了 DMEDA 与锂中心的选择性结合。在 DMEDA 配位后，形成了六个新的立体氮中心，在固态下具有完美的非对映选择性，并且在溶液中仅观察到单一非对映异构体。在 NMR 时间尺度上，锂结合的 DMEDA 配体不会被环己烯酮、DMF 或 THF 取代。在三个催化不对称反应中使用 DMEDA 加合物 Li3(DMEDA)3(BINOLate)3La 产生与 Shibasaki 的 Li3(THF)n(BINOLate)3La 络合物相似的对映选择性。还报道了独特的二聚体 [Li6(en)7(BINOLate)6Eu2][μ-η1,η1-en] 结构 [en = 乙二胺]。基于这些研究，假设 Shibasaki 的 Li3(THF)n(BINOLate)3Ln 配合物中的镧系元素不能以螯合方式结合双齿底物。还提出了一个假设来解释为什么镧系催化剂 Li3(THF)n(BINOLate)3La 通常是 Li3(THF)n(BINOLate)3Ln 衍生物中最具对映选择性的。
Heterobimetallic Lewis acids M3(THF)n(BINOLate)3Ln [M = Li, Na, K; Ln = lanthanide(III)] are exceptionally useful asymmetric catalysts that exhibit high levels of enantioselectivity across a wide range of reactions. Despite their prominence, important questions remain regarding the nature of the catalyst−substrate interactions and, therefore, the mechanism of catalyst operation. Reported herein are the isolation and structural characterization of 7- and 8-coordinate heterobimetallic complexes Li3(THF)4(BINOLate)3Ln(THF) [Ln = La, Pr, and Eu], Li3(py)5(BINOLate)3Ln(py) [Ln = Eu and Yb], and Li3(py)5(BINOLate)3La(py)2[py = pyridine]. Solution binding studies of cyclohexenone, DMF, and pyridine with Li3(THF)n(BINOLate)3Ln [Ln = Eu, Pr, and Yb] and Li3(DMEDA)3(BINOLate)3Ln [Ln = La and Eu; DMEDA =N,N′-dimethylethylene diamine] demonstrate binding of these Lewis basic substrate analogues to the lanthanide center. The paramagnetic europium, ytterbium, and praseodymium complexes Li3(THF)n(BINOLate)3Ln induce relatively large lanthanide-induced shifts on substrate analogues that ranged from 0.5 to 4.3 ppm in the1H NMR spectrum. X-ray structure analysis and NMR studies of Li3(DMEDA)3(BINOLate)3Ln [Ln = Lu, Eu, La, and the transition metal analogue Y] reveal selective binding of DMEDA to the lithium centers. Upon coordination of DMEDA, six new stereogenic nitrogen centers are formed with perfect diastereoselectivity in the solid state, and only a single diastereomer is observed in solution. The lithium-bound DMEDA ligands are not displaced by cyclohexenone, DMF, or THF on the NMR time scale. Use of the DMEDA adduct Li3(DMEDA)3(BINOLate)3La in three catalytic asymmetric reactions led to enantioselectivities similar to those obtained with Shibasaki’s Li3(THF)n(BINOLate)3La complex. Also reported is a unique dimeric [Li6(en)7(BINOLate)6Eu2][μ-η1,η1-en] structure [en = ethylenediamine]. On the basis of these studies, it is hypothesized that the lanthanide in Shibasaki’s Li3(THF)n(BINOLate)3Ln complexes cannot bind bidentate substrates in a chelating fashion. A hypothesis is also presented to explain why the lanthanide catalyst, Li3(THF)n(BINOLate)3La, is often the most enantioselective of the Li3(THF)n(BINOLate)3Ln derivatives.