Endohedral Hydrogen Bonding Templates the Formation of a Highly Strained Covalent Organic Cage Compound. Issue 19 (3rd March 2021)

• Record Type: Journal Article
• Authors: Schäfer, Natalie; Bühler, Michael; Heyer, Lisa; Röhr, Merle I. S.; Beuerle, Florian
• Is Part Of: Chemistry. Volume 27:Issue 19(2021)
• Page Start: 6077
• Page End: 6085
• Publication Date: 2021-03-03
• Subjects: boronate esters -- cage compounds -- density functional calculations -- dynamic covalent chemistry -- hydrogen bonding; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202005276
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: A highly strained covalent organic cage compound was synthesized from hexahydroxy tribenzotriquinacene (TBTQ) and a meta ‐terphenyl‐based diboronic acid with an additional benzoic acid substituent in 2'‐position. Usually, a 120° bite angle in the unsubstituted ditopic linker favors the formation of a [4+6] cage assembly. Here, the introduction of the benzoic acid group is shown to lead to a perfectly preorganized circular hydrogen‐bonding array in the cavity of a trigonal‐bipyramidal [2+3] cage, which energetically overcompensates the additional strain energy caused by the larger mismatch in bite angles for the smaller assembly. The strained cage compound was analyzed by mass spectrometry and 1 H, 13 C and DOSY NMR spectroscopy. DFT calculations revealed the energetic contribution of the hydrogen‐bonding template to the cage stability. Furthermore, molecular dynamics simulations on early intermediates indicate an additional kinetic effect, as hydrogen bonding also preorganizes and rigidifies small oligomers to facilitate the exclusive formation of smaller and more strained macrocycles and cages. Abstract : Cages put under tension : Endohedral hydrogen bonding stabilizes a highly strained covalent organic cage compound. The introduction of carboxylic acid groups at the concave side of a curved diboronic acid linker switches cage geometry from tetrahedral [4+6] to trigonal‐bipyramidal [2+3] assembly. Thermodynamic stability and kinetic preorganization of early intermediates have been analyzed by DFT calculations.