Braunschweig Adam B, Dichtel William R, Miljanić Ognjen S, Olson Mark A, Spruell Jason M, Khan Saeed I, Heath James R, Stoddart J Fraser
The California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095, USA.
Chem Asian J. 2007 May 4;2(5):634-47. doi: 10.1002/asia.200700035.
A series of donor-acceptor [2]-, [3]-, and [4]rotaxanes and self-complexes ([1]rotaxanes) have been synthesized by a threading-followed-by-stoppering approach, in which the precursor pseudorotaxanes are fixed by using Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition to attach the required stoppers. This alternative approach to forming rotaxanes of the donor-acceptor type, in which the donor is a 1,5-dioxynaphthalene unit and the acceptor is the tetracationic cyclophane cyclobis(paraquat-p-phenylene), proceeds with enhanced yields relative to the tried and tested synthetic strategies, which involve the clipping of the cyclophane around a preformed dumbbell containing pi-electron-donating recognition sites. The new synthetic approach is amenable to application to highly convergent sequences. To extend the scope of this reaction, we constructed [2]rotaxanes in which one of the phenylene rings of the tetracationic cyclophane is perfluorinated, a feature which significantly weakens its association with pi-electron-rich guests. The activation barrier for the shuttling of the cyclophane over a spacer containing two triazole rings was determined to be (15.5+/-0.1) kcal mol(-1) for a degenerate two-station [2]rotaxane, a value similar to that previously measured for analogous degenerate compounds containing aromatic or ethylene glycol spacers. The triazole rings do not seem to perturb the shuttling process significantly; this property bodes well for their future incorporation into bistable molecular switches.
通过“先穿线后封端”的方法合成了一系列供体-受体型[2]轮烷、[3]轮烷和[4]轮烷以及自络合物（[1]轮烷），其中前体准轮烷通过铜（I）催化的惠斯根1,3-偶极环加成反应固定，以连接所需的封端基团。这种形成供体-受体型轮烷的替代方法，其中供体是1,5-二氧萘单元，受体是四阳离子环番环双（对苯二酚-对亚苯基），相对于经过试验和测试的合成策略，产率有所提高，后者涉及在预先形成的含有π电子供体识别位点的哑铃周围夹上环番。这种新的合成方法适用于高度收敛的序列。为了扩展该反应的范围，我们构建了[2]轮烷，其中四阳离子环番的一个亚苯基环被全氟化，这一特征显著削弱了其与富π电子客体的缔合。对于简并双位点[2]轮烷，环番在含有两个三唑环的间隔基上穿梭的活化能垒测定为（15.5±0.1）kcal mol-1，该值与先前测量的含有芳族或乙二醇间隔基的类似简并化合物的值相似。三唑环似乎不会对穿梭过程产生显著干扰；这一特性预示着它们未来有望被纳入双稳态分子开关。
