A Chiral [2+3] Covalent Organic Cage Based on 1,1’‐Bi‐2‐naphthol (BINOL) Units

A chiral cage formed with three 2,2’-BINOL units was prepared through a dynamic covalent chemistry approach. This architecture contains six OH functions pointing inside the cavity. Host-guest studies demonstrated enantiopreference of the cage for a chiral ammonium cation.

Abstract

A [2+3] chiral covalent organic cage is produced through a dynamic covalent chemistry approach by mixing two readily available building units, viz. an enantiopure 3,3’-diformyl 2,2’-BINOL compound (A) with a triamino spacer (B). The two enantiomeric (R,R,R) and (S,S,S) forms of the cage C are formed nearly quantitatively thanks to the reversibility of the imine linkage. The X-ray diffraction analysis of cage (S,S,S)-C highlights that the six OH functions of the BINOL fragments are positioned inside the cage cavity. Upon reduction of the imine bonds of cage C, the amine cage D is obtained. The ability of the cage D to host the 1-phenylethylammonium cation (EH⁺) as a guest is evaluated through UV, CD and DOSY NMR studies. A higher binding constant for (R)-EH⁺ cation (Ka=1.7 10⁶±10 % M⁻¹) related to (S)-EH⁺ (Ka=0.9 10⁶±10 % M⁻¹) is determined in the presence of the (R,R,R)-D cage. This enantiopreference is in close agreement with molecular dynamics simulation.

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