Development of a Class of Cyclopropenimine Based Compounds for Application in Catalysis
The present thesis outlines our latest findings in the pursuit of novel bis(diisopropylamino)cyclopropenimine (DAC) compounds. Particular focus was placed on the synthesis and investigation of DAC-substituted proton sponges, as well as their application in organo-catalysis. Herein, we report the synthesis of a non-symmetric DAC-functionalized proton sponge coined “Janus” sponge. Theoretical and experimental investigation of this sponge provided a monoprotonated salt, without a N-HN intramolecular hydrogen bond and a relatively low freebase strain. Instead, DFT calculations and X-ray crystallography revealed the presence of a hydrogen bond to the Cl- counter ion, leading to the unprecedented ¬in-out geometry of the molecule. Furthermore, the salt of the Janus sponge was found to be highly fluorescent both in the solid state and solution. Its experimentally measured pKa of 23.8 was found to be in good agreement with the calculated value of 23.9. The use of Janus, as well as the previously synthesized DACN (a naphthalene DAC derivative) sponge in phase transfer catalysis was also explored. The DACN proton sponge was found to be a highly efficient bifunctional phase-transfer catalyst, facilitating the movement of charged intermediates from the interface to the organic layer via favourable partitioning of hydrophilic/hydrophobic surface areas.