Synthesis of benzimidazole derivatives via reaction between aromatic amines and aldehydes: Structure determination and theoretical insights

Abstract

The condensation reaction between primary amine and aromatic aldehyde or ketone ubiquitously synthesizes –C=N- function that appears in the Schiff bases. Presence of ortho –NH/NH2 group may form a cyclic product which is further oxidized to generate –C=N- function. Herein, two quinoline based cyclic benzimidazole compounds, namely, 2-[1-(Phenyl-pyridin-2-yl-methyl)-1H-benzoimidazol-2-yl]-quinoline (L5) and 2-[1-(Phenyl-pyridin-2-yl-methyl)-1H-benzoimidazol-2-yl]-quinolin-8-ol (L6) are synthesized from o-phenylenediamine derivative [N1-(phenyl(pyridin-2-yl)methyl)benzene-1,2-diamine] (L) via condensation followed by in-situ dehydrogenation. The structures of the products have been confirmed by the single crystal X-ray diffraction measurement and other physicochemical data. The intra- and intermolecular H-bonding, C–H … π interactions in the structures instigate supramolecular self-assembly. The DFT computation has been attempted to explain the formation of energy minimized cyclic product out of acyclic counterpart; the meticulous comparison of the present theoretical outcomes with that of previously reported o-phenylenediamine derivatives, further supports the formation of energy minimized products.