Stable Alkanes Containing Very Long Carbon-Carbon Bonds
Stable Alkanes Containing Very Long Carbon-Carbon Bonds
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DOI：
10.1021/ja302258q
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发表时间：
2012-08-22
影响因子：
15
通讯作者：
Schreiner, Peter R.
中科院分区：
文献类型：
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作者：
Fokin, Andrey A.;Chernish, Lesya V.;Schreiner, Peter R.
在2-(1-乙二胺基)[121]正十四烷中，金属诱导的叔烷类溴化物的偶联反应得到了空间高度密集的碳氢(杂)二聚体，其中心C-C键非常长，最大可达1.71埃。然而，这些二聚体即使在200摄氏度以上的温度下也非常稳定，这与常见的C-C键长与键强度的相关性不一致。我们认为，这种特殊的稳定性来自于相邻的类钻石表面之间存在大量的分子内范德华引力。用变温H-1和C-13核磁共振谱研究了1-(1-金刚烷基)二烷基、1-(1-金刚烷基)二烷基、2-(1-金刚烷基)金刚烷、2-(1-金刚烷基)金刚烷和2-(1-二烷基)[121]十四烷的C-C键转动动力学。内向(Endo)CH表面的形状决定了动力学行为，将中心C-C键的旋转势垒从7千卡摩尔(-1)改变到33千卡摩尔(-1)。我们用6-31G(d，p)和cc-pVDZ基组探讨了常用的密度泛函(DFT)方法(包括BLYP、B3LYP、B98、B3LYP-Dn、B97D、B3PW91、BHandHLYP、B3P86、PBE1PBE、wB97XD和M06-2X)对这种异常成键情况的描述能力。只有考虑色散的泛函能够再现实验几何形状，而大多数DFT泛函由于误差抵消而能够再现实验旋转势垒。对较大的钻石形体的计算表明，CH表面的形状和大小之间的相互作用甚至可以制备开壳的烷基自由基二聚体(可能还有聚合物)，它们完全通过分散力强烈地结合在一起。
The metal-induced coupling of tertiary diamondoid bromides gave highly sterically congested hydrocarbon (hetero)dimers with exceptionally long central C-C bonds of up to 1.71 angstrom in 2-(1-diamantyl)[121]tetramantane. Yet, these dimers are thermally very stable even at temperatures above 200 degrees C, which is not in line with common C-C bond length versus bond strengths correlations. We suggest that the extraordinary stabilization arises from numerous intramolecular van der Waals attractions between the neighboring H-terminated diamond-like surfaces. The C-C bond rotational dynamics of 1-(1-adamantyl)diamantane, 1-(1-diamantyl)diamantane, 2-(1-adamantyl)triamantane, 2-(1-diamantyl)triamantane, and 2-(1-diamantyl)[121]tetramantane were studied through variable-temperature H-1- and C-13 NMR spectroscopies. The shapes of the inward (endo) CH surfaces determine the dynamic behavior, changing the central C-C bond rotation barriers from 7 to 33 kcal mol(-1). We probe the ability of popular density functional theory (DFT) approaches (including BLYP, B3LYP, B98, B3LYP-Dn, B97D, B3PW91, BHandHLYP, B3P86, PBE1PBE, wB97XD, and M06-2X) with 6-31G(d,p) and cc-pVDZ basis sets to describe such an unusual bonding situation. Only functionals accounting for dispersion are able to reproduce the experimental geometries, while most DFT functionals are able to reproduce the experimental rotational barriers due to error cancellations. Computations on larger diamondoids reveal that the interplay between the shapes and the sizes of the CH surfaces may even allow the preparation of open-shell alkyl radical dimers (and possibly polymers) that are strongly held together exclusively by dispersion forces.