Toward a four-toothed molecular bevel gear with C2-symmetrical rotors.
Toward a four-toothed molecular bevel gear with C2-symmetrical rotors.
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具有 C2 对称转子的四齿分子锥齿轮。
DOI：
10.1021/jo2009017
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Jye‐Shane Yang
中科院分区：
文献类型：
--
作者：
C. Kao;Y. Hsu;Hsiu;I. Chao;Shou‐Ling Huang;Ying;Wei;Jye‐Shane Yang
报道了戊二烯基分子齿轮PP(2)X的设计、合成、构象分析和变温核磁共振研究，其中PP是未标记的(1H)或甲氧基标记的(1OM)戊二烯转子，X是含有邻位桥联乙炔轴的苯基定子。用具有C(2)对称性的四齿定形转子构造四齿分子齿轮的方法是前所未有的。此外，还展示了第一个手性戊二烯支架对映体拆分的例子。这些PP(2)X系统的密度泛函理论(DFT)和AM1计算表明，可能存在两种相互关联的扭转运动，即齿轮摇摆和四齿齿轮转动，它们与不相关的齿轮滑移竞争。由密度泛函推导出的摆动、四齿旋转和齿轮打滑在1H内的扭转势垒分别约为2.9、5.5和4.7千卡摩尔(-1)。这些扭转运动的低能垒是由于弯曲乙炔轴的低能量成本造成的。比较了1OM在立体异构体混合物(1OM-MIX)和对映体形式(1OM-OP)中的核磁共振谱，证实了在这些PP(2)X体系中存在快速的齿轮滑移。还讨论了甲氧基标记对转动势能面和转子间动力学的影响。
The design, synthesis, conformational analysis, and variable-temperature NMR studies of pentiptycene-based molecular gears Pp(2)X, where Pp is the unlabeled (in 1H) or methoxy groups-labeled (in 1OM) pentiptycene rotor and X is the phenylene stator containing ortho-bridged ethynylene axles, are reported. The approach of using shape-persistent rotors of four teeth but C(2) symmetry for constructing four-toothed molecular gears is unprecedented. In addition, the first example of enantioresolution of chiral pentiptycene scaffolds is demonstrated. Density functional theory (DFT) and AM1 calculations on these Pp(2)X systems suggest two possible correlated torsional motions, geared rocking and four-toothed geared rotations, which compete with the uncorrelated gear slippage. The DFT-derived torsional barriers in 1H for rocking, four-toothed rotation, and gear slippage are approximately 2.9, 5.5, and 4.7 kcal mol(-1), respectively. The low energy barriers for these torsional motions result from the low energy cost of bending the ethynylene axles. Comparison of the NMR spectra of 1OM in a mixture of stereoisomers (1OM-mix) and in an enantiopure form (1OM-op) confirms a fast gear slippage in these Pp(2)X systems. The effect of the methoxy labels on rotational potential energy surface and inter-rotor dynamics is also discussed.