WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, UK.
Inorg Chem. 2009 Jul 20;48(14):6934-44. doi: 10.1021/ic900609e.
Treatment of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) with a group 1 metal (Li, Na, K, Rb, or Cs), resulted in the reduction of this important radical to the TEMPO(-) anion--the first examples of elemental-metal single electron reduction of the radical to its anionic form. The synthesis and characterization of seven alkali metal TEMPO(-) complexes are reported. A variety of structural motifs are encountered depending on the choice of metal and/or solvent. (THF)(2) x Li(+)(TEMPO(-)) 1 crystallized from THF as a cyclic (Li(4)O(4)) molecule. Two Li centers are stabilized by coordination to a THF molecule; the others by intramolecular coordination to N(TEMPO) atoms. (THF) x Na(+)(TEMPO(-)) 2 exists as a distorted cubane where each Na center is coordinated to a THF molecule. No appreciable Na-N(TEMPO) coordination is observed. (THF)(2) x Na(+)(3)(TEMPO(-))(2)(OH) 3 was serendipitously prepared and exists as a distorted bis(cubane). It is envisaged that 3 is formed from 2 by insertion of a (Na-OH)(2) double bridge into its framework. [Na(+)(4)(mu(3)-TEMPO(-))(2)(mu(2)-TEMPO(-))(2)(TMEDA)(2)] 4, adopts a four-runged ladder structure, whereby the two outer Na centers are coordinated to TMEDA, in addition to two mu(2)-O and a N atom. The inner metal atoms are bound to three mu(3)-O atoms and a N atom. (THF) x K(+)(TEMPO(-)) 5 resembles the motif found for 2; however, presumably because of the larger size of the metal, K-N(TEMPO) interactions are present in 5. The asymmetric unit of (TMEDA) x Rb(+)(2)(TEMPO(-))(2) 6 comprises a Rb(4)O(4) cubane with half a molecule of TMEDA coordinated to each metal. From a supramolecular perspective, 6 exists as a polymeric array of cubane units connected by TMEDA bridges. Completing the series, Cs(+)(TEMPO) 7 crystallizes from hexane to form a donor-free polymeric complex. Complexes 1, 2, and 4-7 are soluble in D(8)-THF solution, and their NMR spectra are reported. The solution structures in donor solvent appear virtually identical.
用碱金属（Li、Na、K、Rb 或 Cs）处理 2,2,6,6-四甲基-1-哌啶氧基（TEMPO），导致该重要自由基还原为 TEMPO(-)阴离子 - 这是自由基还原为其阴离子形式的首例元素金属单电子还原的例子。报告了七种碱金属 TEMPO(-)配合物的合成和表征。根据金属和/或溶剂的选择，遇到了各种结构基序。(THF)(2) x Li(+)(TEMPO(-)) 1 从 THF 中结晶为环状(Li(4)O(4))分子。两个 Li 中心通过与 THF 分子的配位稳定; 其他通过与 N(TEMPO)原子的分子内配位稳定。(THF) x Na(+)(TEMPO(-)) 2 作为扭曲的立方烷存在，其中每个 Na 中心与 THF 分子配位。没有观察到明显的 Na-N(TEMPO)配位。(THF)(2) x Na(+)(3)(TEMPO(-))(2)(OH) 3 是偶然制备的，作为扭曲的双立方烷存在。可以设想 3 是通过其骨架中插入(Na-OH)(2)双桥形成的。[Na(+)(4)(mu(3)-TEMPO(-))(2)(mu(2)-TEMPO(-))(2)(TMEDA)(2)] 4 采用四步梯结构，其中两个外 Na 中心除了两个 mu(2)-O 和一个 N 原子外，还与 TMEDA 配位。内部金属原子与三个 mu(3)-O 原子和一个 N 原子结合。(THF) x K(+)(TEMPO(-)) 5 类似于 2 中发现的图案; 然而，大概是因为金属的尺寸较大，在 5 中存在 K-N(TEMPO)相互作用。(TMEDA) x Rb(+)(2)(TEMPO(-))(2) 6 的不对称单元包括具有一半 TMEDA 配位到每个金属的 Rb(4)O(4)立方烷。从超分子的角度来看，6 存在为通过 TMEDA 桥连接的立方烷单元的聚合物阵列。完成该系列，Cs(+)(TEMPO) 7 从己烷中结晶形成无供体聚合物络合物。络合物 1、2 和 4-7 可溶于 D(8)-THF 溶液，报告了它们的 NMR 谱。在供体溶剂中的溶液结构几乎相同。
