(532e) Investigating Imine-Based Porous Organic Cage Formation Mechanisms Using Time-Resolved Mass Spectrometry and Quantum Chemical Calculations

The synthesis of porous organic cages represents an important synthetic puzzle in self-sorting. Herein, we explored the formation of imine based porous organic cages using time-resolved electrospray ionization mass spectrometry, density functional theory and ab initio calculations. Specifically, the iminization reactions of triformylbenzene with (1R,2R)-1,2-diaminocyclohexane, and triformylbenzene with 1,5-pentanediamine were studied. We found that the typical [4+6] cycloimine cage between triformylbenzene and (1R,2R)-1,2-diaminocyclohexane, CC3-R, proceeds through a [2+3] intermediate, followed by rearrangement of the imine bonds towards the larger [4+6] cage. On the other hand, the iminization reaction between triformylbenzene and 1,5-pentanediamine first formed insoluble polymeric species that was later transformed to thermodynamically stable [2+3] cages. The presence of the low-energy small cage transition state in CC3-R synthesis is supported by theoretical calculations. The combination of DFT and ab initio calculations also indicated that common DFT methods could not capture the accurate energies of the electron-rich cage structures. Single point energy calculations at MP2 level is required for theoretical interpretation of the cycloimination reactions.