Formation Mechanisms and Defect Engineering of Imine-Based Porous Organic Cages

Abstract

Syntheses of porous organic cages (POCs) represent an important synthetic puzzle in dynamic covalent chemistry-based self-sorting. Improved understanding of the formation mechanisms of POCs can lead to control and rational design of cages with desired functionality. Herein, we explore the formation mechanisms of imine-based POCs using time-resolved electrospray mass spectrometry and electronic structure calculations at the density functional theory and correlated molecular orbital theory levels. We found that the synthesis of the [4 + 6] cycloimine cage CC3-R and the [2 + 3] cycloimine cage CC-pentane both proceed through similar intermediates via a series of consecutive reactions. The proposed reaction mechanisms are supported by electronic structure calculations. On the basis of our observations from both experiments and calculations, we propose a comprehensive method for designing and predicting new POC species. In addition, the observation of stable incomplete cages during CC3-R synthesis inspired us to design intentionally defective cages. These missing-linker-type molecular defects were installed into CC3-R via nonsolvent induced crystallization. The defective CC3-R materials were found to have enhanced CO2 interaction and improved CO2 uptake capacity due to the additional functional groups present within the CC3 crystals.

Inducing Social Self‐Sorting in Organic Cages To Tune The Shape of The Internal Cavity

“…[41,[57][58][59] Comparing the thermodynamic stabilities of potential cage products can be ag ood guide to selectivity,b ut the reaction outcome can also be affected by factors,s uch as reaction kinetics, [39,[60][61][62][63][64] solvent effects, [65][66][67][68] and the solubilities of the species involved in the equilibrium. [33,40,47] In parallel with the synthetic efforts,w eu sed computational techniques to predict the stability of the different homo-and heteroleptic structures originating from aldehydes B1-B2 and L1-L4.T he experimentally observed outcomes agreed with the relative gas-phase formation energies of the possible Tet 3 Di 6 products,s howing the predictive power of the simple model for the self-sorting behaviour of imine-based organic cages.…”

“…[22,30,31] Reducing the symmetry of the host may induce anisotropy in the solid state,i mprove the binding of low-symmetry guests, or enable more controlled and directional post-synthetic modification. [32][33][34][35] Forexample,fine-tuning of the cavity of an organic cage has been shown to afford precise control over the selectivity of the resultant solid-state material. [7] Stepwise syntheses exploiting orthogonal reactivities can afford lowsymmetry organic cages, [6,36,37] but this limits the scalability of the resulting materials.Alternatively,low-symmetry architectures may be obtained by purification of complex mixtures, but this is al aborious process and may be unachievable on ap reparative scale due to reconfiguration of the desired products.…”

Organic Cage Dumbbells

“…We were also interested as to why there was consistent formation of a mixture of both cage and dumbbell, and so we turned to computational modelling to explore this. We showed previously that it is possible to predict the most likely cage topology formed from two precursors by calculating and comparing the formation energies per imine bond for different molecular assemblies . These calculations are performed on isolated molecules in the gas phase, which does not consider solvent effects, and hence large energetic differences are needed to predict solution‐phase structures with confidence.…”

Organic Cage Dumbbells

“…We showedp reviously that it is possible to predict the most likely cage topology formed from two precursors by calculating and comparing the formation energies per imine bond for different molecular assemblies. [22,23,24] These calculations are performed on isolated molecules in the gas phase, which does not consider solvente ffects, and hence large energetic differences are neededt op redicts olution-phase structures with confidence. This process becomesm ore difficult for complex precursor mixtures, as the number of potentiala ssemblies that might form increases.…”