Synthesis, X-ray structures, Hirshfeld surface analysis, and redox behaviour of 2-substituted-1H-perimidine derivatives

Abstract

Peri-naptho fused pyrimidine derivatives, known as 1H-perimidines or 1H-benzo[d,e]quinazolines, have recently been studied for a diverse range of applications. A series of 2-substituted-1H-perimidine compounds (1A–1F) have been synthesized by the condensation reaction of 1,8-diaminonaphthalene with the appropriate aldehyde. The 2-substituted-1H-perimidinium iodide salts (1A+I––1F+I–) were obtained by methylating 1H-perimidine using methyl iodide in the presence of a mild base K2CO3. The perimidinium salts were reduced using NaBH4 in methanol to obtain 2-substituted-2,3-dihydro-1H-perimidine compounds (1AH–1FH). The compounds were characterized by 1H, 13C-NMR and UV–Vis absorption spectroscopy, elemental analysis, and in the case of compounds 1C, 1B+I–, 1C+I–, 1E+I–, 1F+I–, and 1BH–1EH, their molecular structures have been determined using single crystal X-ray analysis and compared to those of related 1H-perimidine derived species. The crystal packings from the solid-state structures of 1C, 1C+I–, and 1CH were compared and revealed further stability of the molecule 1C through intermolecular NH···N hydrogen bonding and π···π stacking interactions, while in the case of molecules 1C+I–, and 1CH through short interatomic CH···C contacts between two adjacent perimidine rings. To further quantify the intermolecular interactions and investigate their contributions to the crystal packing in each molecule, Hirshfeld surface analysis was performed. The redox properties of the perimidinium salts 1A+I––1F+I–, and the hydride reduced species 1AH–1FH were studied using cyclic voltammetry, and compared to that of N-DMBI-H ((4-(1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole-2-yl)phenyl)dimethylamine). The salts exhibit an irreversible reduction wave, like those of 2-substituted-1,3-dimethyl-1H-benzo[d]imidazolium salts, while the hydrides undergo a reversible oxidation process, with the peak ratio (Ipc/Ipa) > 0.5. This shows the chemical stability of the 1H•+ species at a scan rate of 100 mV s–1.