Molecular Structures of THF-Solvated Alkali-Metal 2,2,6,6-Tetramethylpiperidides Finally Revealed: X-ray Crystallographic, DFT, and NMR (including DOSY) Spectroscopic Studies
Molecular Structures of THF-Solvated Alkali-Metal 2,2,6,6-Tetramethylpiperidides Finally Revealed: X-ray Crystallographic, DFT, and NMR (including DOSY) Spectroscopic Studies
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DOI：
10.1002/chem.201100523
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发表时间：
2011-06-01
影响因子：
4.3
通讯作者：
Robertson, Stuart D.
中科院分区：
文献类型：
--
作者：
Armstrong, David R.;Garcia-Alvarez, Pablo;Robertson, Stuart D.
经常研究的实用碱金属酰胺2，2，6，6-四甲基哌啶锂和钠的THF溶剂化物显示以固态存在，作为含有中心M2 N2环和每个金属一个供体分子的不对称环状二聚体，以得到扭曲的三角平面金属配位。DFT研究支持这些结构，并确认环中的不对称性。在C6 D12溶液中，氨基锂显示出溶剂化和非溶剂化物种之间的浓度依赖性平衡，这已被证明由扩散有序NMR光谱（DOSY）是一个二聚体和较大的低聚物，分别。第三种物质，溶剂化单体，也以非常低的浓度存在，如通过用THF加标NMR样品所证明的。相比之下，氨基钠显示出更简单的C6 D12溶液化学，与固态二聚体排列一致，但具有不稳定的THF配体。
The often studied THF solvates of the utility alkali-metal amides lithium and sodium 2,2,6,6-tetramethylpiperidide are shown to exist in the solid state as asymmetric cyclic dimers containing a central M2N2 ring and one molecule of donor per metal to give a distorted trigonal planar metal coordination. DFT studies support these structures and confirm the asymmetry in the ring. In C6D12 solution, the lithium amide displays a concentration-dependent equilibrium between a solvated and unsolvated species which have been shown by diffusion-ordered NMR spectroscopy (DOSY) to be a dimer and larger oligomer, respectively. A third species, a solvated monomer, is also present in very low concentration, as proven by spiking the NMR sample with THF. In contrast, the sodium amide displays a far simpler C6D12 solution chemistry, consistent with the solid-state dimeric arrangement but with labile THF ligands.