School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
J Am Chem Soc. 2017 Jul 12;139(27):9376-9381. doi: 10.1021/jacs.7b04955. Epub 2017 Jul 3.
The "off" state for aminocatalysis by a switchable [2]rotaxane is shown to correspond to an "on" state for anion-binding catalysis. Conversely, the aminocatalysis "on" state of the dual-function rotaxane is inactive in anion-binding catalysis. Switching between the different states is achieved through the stimuli-induced change of position of the macrocycle on the rotaxane thread. The anion-binding catalysis results from a pair of triazolium groups that act together to CH-hydrogen-bond to halide anions when the macrocycle is located on an alternative (ammonium) binding site, stabilizing the in situ generation of benzhydryl cation and oxonium ion intermediates from activated alkyl halides. The aminocatalysis and anion-binding catalysis sites of the dual-function rotaxane catalyst can be sequentially concealed or revealed, enabling catalysis of both steps of a tandem reaction process.
通过一种可切换的[2]轮烷，展示了氨催化的“关闭”状态对应于阴离子结合催化的“开启”状态。相反，双功能轮烷的氨催化“开启”状态在阴离子结合催化中不起作用。通过大环在轮烷螺线上的位置受刺激诱导变化来实现不同状态之间的切换。阴离子结合催化是由一对三唑鎓基团共同作用产生的，当大环位于替代（铵）结合位点时，三唑鎓基团通过 CH-氢键与卤化物阴离子相互作用，稳定了从活化的烷基卤化物原位生成苄基阳离子和氧鎓离子中间体。双功能轮烷催化剂的氨催化和阴离子结合催化位点可以依次隐藏或揭示，从而能够催化串联反应过程的两个步骤。
