Departamento de Química, Centro de Investigación y Estudios Avanzados del IPN, México DF 07360, México.
J Org Chem. 2009 Nov 20;74(22):8554-65. doi: 10.1021/jo901261j.
We describe in this paper the synthesis, crystallization, and solid-state NMR dynamics of molecules intended to emulate the structure and function of macroscopic compasses. The desired structures consist of polar pyridine (2) and pyridazine (3) groups as well as their corresponding N-oxides (2O and 3O), each linked axially to two bulky triphenyl methyl groups by 1,4-triple bonds. The structures are such that the central polar heterocycles may rotate about the dialkyne axle while being sterically shielded by the two trityl groups. In addition to the synthesis of samples with natural isotopic abundance, we describe the preparation of 2-d(2) and 3-d(30), one labeled with deuteria in the pyridine rotator and the other fully deuterated in the two trityl groups in the stator. Crystal structures of 2 and 3 revealed packing motifs analogous to those previously reported for samples prepared with substituted phenylene rotators. While solid-state NMR measurements by (13)C CPMAS NMR revealed insufficient chemical shift dispersion for a dynamic characterization of the rotation of compounds 2 and 3 (including 3-d(30)), the use of quadrupolar echo (2)H NMR methods with 2-d(2) revealed a rotational site exchange with a barrier of ca. 8.5 kcal/mol (35.5 kJ mol(-1)) for the pyridine group in 2.
本文描述了拟态宏观罗盘结构和功能的分子的合成、结晶和固态 NMR 动力学。期望的结构由极性吡啶（2）和哒嗪（3）基团以及它们相应的 N-氧化物（2O 和 3O）组成，每个基团通过 1,4-三键轴向连接到两个庞大的三苯甲基基团上。这些结构使得中央极性杂环可以在两个三苯甲基基团的空间位阻下绕二炔轴旋转。除了合成具有天然同位素丰度的样品外，我们还描述了 2-d(2) 和 3-d(30)的制备，其中一个在吡啶旋转体中标记氘，另一个在定子中的两个三苯甲基基团中完全氘代。2 和 3 的晶体结构揭示了与以前用取代的亚苯基旋转体制备的样品类似的堆积模式。虽然（13）C CPMAS NMR 的固态 NMR 测量没有为化合物 2 和 3（包括 3-d(30)）的旋转进行动态特征提供足够的化学位移分散，但使用 2-d(2)的四极子回波（2）H NMR 方法揭示了吡啶基团在 2 中的旋转位交换具有约 8.5 kcal/mol（35.5 kJ mol(-1))的势垒。
