One-pot synthesis of 2,4,5-triarylimidazole and phenanthro[9,10-d]imidazole derivatives catalyzed by a new set of crystalline aluminium(III) complexes via CN bond formation

Abstract

A series of three new along with one existing hexacoordinated heteroleptic derivatives of aluminium(III) as [(C₆H₅COCHCOC₆H₅)Al(1a-1d)].H₂O {where 1a-1d are dianionic [ONO]-tridentate ancillary ligands} was synthesized quantitively by treating Al(OPrⁱ)₃ with Schiff bases (1a-1d) and dibenzoyl methane in a 1:1:1 ratio using anhydrous benzene as a solvent. As 2a was already reported by this research team only so the new derivatives (2b-2d) were characterized using appropriate analytical techniques such as FTIR, UV–Vis, NMR (¹H, ¹³C & DEPT-135) and HRMS. Specifically, SC-XRD authenticated the molecular structures of complexes of 2a, 2b and 2d. The developed crystals verified the hexacoordination around the central metal aluminium encircled with five oxygen atoms and one that of nitrogen. These trio crystals appeared as triclinic with a space group of P$\overline{1}$ and Z values 2, 4 and 4, respectively. Subsequently, computational investigation of the aluminium(III) derivatives was carried out using DFT/B3LYP/LanL2DZ method in Gaussian(09) software. Further, the optimized molecular structures were derived from B3LYP/6-311G(d,p) and the results were rationalized with the support of TD-DFT calculations. Afterwards, synthesis of a substituted five membered heterocyclic compounds were carried out in an ethanolic solution of benzil/9,10-phenanthrenequinone, substituted aldehydes and ammonium acetate (nitrogen source) as a substrate while employing aforementioned all four aluminium(III) complexes as catalyst. These organic compounds were characterized by spectral tools like NMR (¹H & ¹³C) and FTIR. Furthermore, nitro derivative 6c’ was validated by SC-XRD that appeared as monoclinic system with space group of P2₁/n. This study is the foremost approach to utilize aluminium(III) complexes as catalyst for the condensation reaction of 2,4,5-triarylimidazole and phenanthro[9,10-d]imidazole where obtained organic derivatives were synthesized in 83–95 % yields.