Barrett-Adams, Dawn M.Y.,; Kahwa, Ishenkumba A.; Mague, Joel T.; McPherson, Gary L.
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Preparation, crystal structure and unusual proton NMR characteristics of some phthalimides
Journal of Organic Chemistry
Date of Publication
Protection of NH2 groups as phthalimides using a mixture of acetic acid, phthalic anhydride, and the relevant polyamine can take unusual routes. For diethylenetriamine the major product is diphthalimidodiethylammonium-hydrogen phthalate (DPDAH-HP). For triethylemetetraamine, ethylene migration products N, N-bis(2-phthalimidoethyl)piperazine (2) and N,N'N'-(nitrilotri-ethylene) trisphthalimide (3) were obtained from room temperature and refluxing reaction mixtures, respectively. The crystal structures of 2, 3, and DPDAH-HP were determined and revealed a series of stabilizing complementary interactions for these favoured products (i.e., offset p-p stacking and C-H...O and possibly C-H...N hydrogen bonds (2), electrostatic interactions between the amine and pyrrolic functionalities (3), and offset p-p stacking and N-H...O hydrogen bonding (DPDAH-HP)). the DPDAH-HP units stack along a screw axis parallel to the b-direction to yield a striking [phthalimide-phtalimide-hydrogen phthalate]n motif and are linked in the a and c directions by N-H...O bonds. Solution1H NMR studies of 3 reveal unusual temperature (178-420 K) evolution of sharp aromatic proton resonances in various solvents. Typically, the spectra exhibit a spectacular temperature evolution from a sharp doublet of quartets at high temperature to complex second order behaviour and then singlet. As the temperature is further lowered, a complex second order spectrum appears followed by a doublet of quartets. The phthalimide-amine interaction energy, determined from temperature dependent NMR studies, is ca. 20 kJ/mol. Solid state 13C aromatic resonances are broadened by p-p interactions in 2 and DPDAH-HP while two sets of 13C resonances are found for 3 as expected from the solid state structures. The hyrdogen phthalate anion in DPDAH-HP exchanges exhibits almost termperature independent behaviour indicating that it is predominantly etropy driven....