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Chiral Discrimination of Diamines by a Binaphthalene-Bridged Porphyrin Dimer

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journal contribution
posted on 23.06.2017, 21:19 by Wenxin Lu, Huifang Yang, Xinyao Li, Chiming Wang, Xiaopeng Zhan, Dongdong Qi, Yongzhong Bian, Jianzhuang Jiang
A pair of 1,1′-binaphthalene-bridged bisporphyrins, (R)- and (S)-H1, were designed to examine their chiral discrimination abilities toward a range of model diamines by using UV–vis absorption, CD, and 1H NMR spectroscopy with the assistance of DFT molecular modeling. The spectroscopic titrations revealed that (R)-/(S)-H1 could encapsulate (R)-/(S)-DACH and (R)-/(S)-PPDA in the chiral bisporphyrin cavities, leading to the selective formation of sandwich-type 1:1 complexes via dual Zn–N coordination interactions. In particular, the chiral recognition energy (ΔΔG°) toward (R)-/(S)-DACH was evaluated to be −4.02 kJ mol–1. The binding processes afforded sensitive CD spectral changes in response to the stereostructure of chiral diamines. Remarkable enantiodiscrimination effects were also detected in the NMR titrations of (R)-/(S)-H1, in which the nonequivalent chemical shift (ΔΔδ) can reach up to 0.57 ppm for (R)-/(S)-DACH. However, due to the large steric effect, another chiral diamine ((R)-/(S)-DPEA) could not be sandwiched in the chiral bisporphyrin cavity; therefore, (R)-/(S)-DPEA could hardly be discriminated by (R)-/(S)-H1. The present results demonstrate a chiral bisporphyrin host with integrated CD and NMR chiral sensing functions and also highlight the binding-mode-dependent character of its enantiodiscrimination performance for different chiral guests.