BINOL-based chiral cages formed by a dynamic covalent bond approach through imine linkages

Abstract

Enantiopure [2 + 3] covalent organic cages deriving from the 3,3’-diformyl-2,2’-BINOL building block are produced through a dynamic covalent chemistry approach. These architectures are formed with different triamino caps, 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene (2a), 1,3,5-tris(aminomethyl)-2,4,6-trimethylbenzene (2b), and 2,7,14-triaminotriptycene (3). For the synthesis of the cage 6b containing 3, a less direct synthetic route regarding the formation of the amine cages (4a and 4b) generated from the spacers 2a and 2b was followed. Instead of being directly synthesized from 3,3’-diformyl-2,2’-BINOL, the targeted compound 6b required a protected BINOL derivative. The ability of the three cages to host the 1-phenylethylammonium cation (8⁺) as a guest was evaluated through UV–vis titration, CD, and DOSY NMR studies. while the formation of the supramolecular complex 8⁺ with cage 6b was not possible, cages 4a and 4b were able to bind 8⁺ with the same enantiopreference, higher association constants being obtained for cage 4a. The association constants determined for the host–guest complexes are discussed in relation with the cavity size calculated for the host cages.