Armstrong David R, Graham David V, Kennedy Alan R, Mulvey Robert E, O'Hara Charles T
WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, Scotland.
Chemistry. 2008;14(26):8025-34. doi: 10.1002/chem.200800158.
Two heavy alkali-metal salts of the sterically demanding amine, 2,2,6,6-tetramethylpiperidine (TMPH), have been prepared using different methodologies. Complex 1, [((tmeda)Na(tmp))2] (TMEDA=N,N, N',N'-tetramethylethylenediamine), can be synthesized by a deprotonative route. This is achieved by reacting butylsodium with TMPH in the presence of excess TMEDA in hexane. The potassium congener [((tmeda)K(tmp))2] (2), can be prepared by treating KTMP (made using a metathesis reaction between LiTMP and potassium tert-butoxide) with an excess of TMEDA in hexane. In the solid state, 1 and 2 are essentially isostructural. They are discretely dimeric and their framework consists of a four-membered M-N-M-N ring (M=Na or K, N=TMP). Due to the high steric demand of the TMP ligand, the TMEDA molecules bind to the metal centers in an asymmetric manner. In 2, each of the coordination spheres of the metals is completed by an agostic K...CH3(TMP) interaction. DFT calculations at the B3 LYP/6-311G** level give an insight into why 1 and 2 adopt dramatically different structures from their previously reported, "open-dimeric", lithium counterpart. The theoretical work also focuses on the TMEDA-free parent amide complexes and reveals that the energy difference for the formation of [(M(tmp))x] (in which, M=Li or Na, x=3 or 4; and M=K, x=2, 3 or 4) are small.
利用不同方法制备了位阻胺2,2,6,6-四甲基哌啶（TMPH）的两种重碱金属盐。配合物1，[((tmeda)Na(tmp))2]（TMEDA = N,N,N',N'-四甲基乙二胺），可通过去质子化途径合成。这是通过在己烷中过量TMEDA存在下，使丁基钠与TMPH反应来实现的。钾类似物[((tmeda)K(tmp))2]（2），可通过用过量的TMEDA在己烷中处理KTMP（由LiTMP与叔丁醇钾之间的复分解反应制得）来制备。在固态下，1和2基本同构。它们是离散二聚体，其骨架由一个四元M-N-M-N环组成（M = Na或K，N = TMP）。由于TMP配体的高空间需求，TMEDA分子以不对称方式与金属中心结合。在2中，金属的每个配位球通过一个agostic K...CH3(TMP)相互作用得以完整。在B3 LYP/6-311G**水平上的密度泛函理论（DFT）计算深入了解了为什么1和2与其先前报道的“开放二聚体”锂类似物具有显著不同的结构。理论研究还聚焦于无TMEDA的母体酰胺配合物，并揭示了形成[(M(tmp))x]（其中，M = Li或Na，x = 3或4；以及M = K，x = 2、3或4）的能量差异很小。
