PREPARATIONS, CRYSTAL-STRUCTURES, AND UNUSUAL PROTON NMR CHARACTERISTICS OF SOME PHTHALIMIDES

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 triethylenetetraamine, ethylene migration products N,N-bis(2-phthalimidoethyl)piperazine (2) and N,N',N''-(nitrilotriethylene)trisphthalimide (3) were obtained from room temperature and refluxing reaction mixtures, respectively. The crystal structures of 2, 3, and DPDAH-HP were determined and reveal a series of stabilizing complementary interactions for these favored products (i.e., offset pi-pi stacking and C-H...O and possibly C-H N hydrogen bonds (2), electrostatic interactions between the amine and pyrrolic functionalities (3), and offset pi-pi 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-phthalimide-hydrogen phthalate](n) motif and are linked in the a and c directions by N-H...O bonds. Solution H-1 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 behavior and then a singlet. As the temperature is further lowered, a complex second order spectrum reappears followed by a doublet of quartets. The phthalimide-amine interaction energy, determined from temperature dependent NMR studies, is ca. 20 kJ/mol. Solid state C-13 aromatic resonances are broadened by pi-pi interactions in 2 and DPDAH-HP while two sets of C-13 resonances are found for 3 as expected from the solid state structures. The hydrogen phthalate anion in DPDAH-HP exchanges rapidly with free phthalic acid (equilibrium constant, K similar or equal to 4 x 10(2) L/mol); this phthalate exchange exhibits almost temperature independent behavior indicating that it is predominantly entropy driven.