Two‐step Conformational Control of a Dibenzo Diazacyclooctane Derivative by Stepwise Protonation

Abstract

The conformational control of a dibenzo-1,5diazacyclooctane (DACO) derivative with tertiary and secondary amino groups by stepwise protonation is investigated by single crystal X-ray diffraction analysis, computational simulation, and variable temperature NMR measurements. The DACO derivative undergoes two-step protonation, to afford bent-shape monoprotonated and diprotonated species, whose conformations are different from each other. The monoprotonated form is characterized by a Tröger'sbase-like proton-bridged pseudo bicyclic structure, while the diprotonated form features a deformed boat-shape eight membered ring structure. The degree of bending and conformational rigidity of the DACO skeleton become higher as the degree of the protonation is increased. Such a multistep conformational control of the DACO derivative would be useful for developing new stimuli-responsive supramolecular systems that exhibit a multistep change in properties.

Deciphering the Role of Noncovalent Interactions in the Conformations of Dibenzo‐1,5‐dichalcogenocines

“…More recently, Ishiwari and co-workers showed that 1,5-diaza analogues adopt straight-shape twisted conformation with a transannular NH HB, but change to more or less bent boat-type structures upon mono-or di-protonation. [12] The involvement of a putative intramolecular HB was also reported between Se and H of the methylene groups in the selenated analog of 1, namely dibenzo-1,5-selenocine 2-Se [13] (Figure 1). In this work, the authors noticed shorter distances in (calculated) 2-SeB than in 2-SeC, which "may indicate a stronger CÀ H…Se nonbonded interaction in 2-SeB than in 2-SeC".…”

“…Interestingly, the B/C interchange temperature could be raised from −60 to 60 °C by finely tuning the position and NCI properties of the substituents. More recently, Ishiwari and co‐workers showed that 1,5‐diaza analogues adopt straight‐shape twisted conformation with a transannular NH HB, but change to more or less bent boat‐type structures upon mono‐ or di‐protonation [12] …”

Cover Feature: Deciphering the Role of Noncovalent Interactions in the Conformations of Dibenzo‐1,5‐dichalcogenocines (ChemPlusChem 4/2022)

“…More recently, Ishiwari and coworkers showed that 1,5-diaza analogues adopt straight-shape twisted conformation with a transannular NH HB, but change to more or less bent boat-type structures upon mono-or diprotonation. [12] The involvement of a putative intramolecular HB was also reported between Se and H of the methylene groups in the selenated analog of 1, namely dibenzo-1,5-selenocine 2-Se [13] (Figure 1). In this work, the authors noticed shorter distances in (calculated) 2-SeB than in 2-SeC, which "may indicate a stronger C-H---Se nonbonded interaction in 2-SeB than in 2-SeC".…”