title: Cation-triggered switchable asymmetric catalysis with chiral Aza-CrownPhos.
abstract: An aza-crown ether, modified phosphoramidite ligand, has been designed and synthesized. The ON/OFF reversible switch of catalytic activity for its rhodium catalyst was thoroughly investigated in the asymmetric hydrogenation of dehydroamino acid esters modulated by host-guest interactions. In the OFF state, the catalyst is almost inactive (less than 1% conversion) because of the formation of an intermolecular sandwich complex by two aza-crown ether moities and the cationic rhodium metal center. In using alkali-metal-cations as the trigger, the catalytic activity was turned ON and consequently resulted in full conversions and excellent enantioselectivities (up to 98% ee).
authors: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190 (P.R. China); Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072 (P.R. China).
authors: Guang-Hui
authors: GH
authors: Ouyang
authors: Yan-Mei
authors: YM
authors: He
authors: Yong
authors: Y
authors: Li
authors: Jun-Feng
authors: JF
authors: Xiang
authors: Qing-Hua
authors: QH
authors: Fan
keywords: asymmetric catalysis; cations; crown compounds; host-guest systems; hydrogenation