Structural Variations within Group 1 (Li−Cs)+(2,2,6,6-Tetramethyl-1-piperidinyloxy)− Complexes Made via Metallic Reduction of the Nitroxyl Radical

详细信息    查看全文

• 作者：Liam Balloch ; Allison M. Drummond ; Pablo Garca-lvarez ; David V. Graham ; Alan R. Kennedy ; Jan Klett ; Robert E. Mulvey ; Charles T. O’ ; Hara ; Philip J. A. Rodger ; Iain D. Rushworth
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：July 20, 2009
• 年：2009
• 卷：48
• 期：14
• 页码：6934-6944
• 全文大小：999K
• 年卷期：v.48,no.14(July 20, 2009)
• ISSN：1520-510X

文摘

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·[Li⁺(TEMPO⁻)]₄ 1 crystallized from THF as a cyclic (Li₄O₄) molecule. Two Li centers are stabilized by coordination to a THF molecule; the others by intramolecular coordination to N_TEMPO atoms. [(THF)·Na⁺(TEMPO⁻)]₄ 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·Na⁺₃(TEMPO⁻)₂(OH)]₂ 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(μ₃-TEMPO⁻)₂(μ₂-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 μ₂-O and a N atom. The inner metal atoms are bound to three μ₃-O atoms and a N atom. [(THF)·K⁺(TEMPO⁻)]₄ 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)·Rb⁺₂(TEMPO⁻)₂]₂ 6 comprises a Rb₄O₄ 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 D₈-THF solution, and their NMR spectra are reported. The solution structures in donor solvent appear virtually identical.