Synthesis of 4<i>H</i>-pyrimido[2,1-<i>b</i>]benzimidazoles catalyzed by a Schiff base cobalt(<scp>ii</scp>) complex supported on cobalt ferrite magnetite nanoparticles

Nano-[CoFe₂O₄@SiO₂/propyl-1-(<i>o</i>-vanillinaldimine)][CoCl₂] was designed and reported with the Schiff base cobalt(ii) complex anchored onto cobalt ferrite magnetite nanoparticles. The resulting nanomagnetite Schiff base cobalt(ii) complex was employed as a recoverable catalyst for the condensation reaction of aryl aldehyde, 2-aminobenzimidazole and ethyl acetoacetate at 90 °C to synthesize 4<i>H</i>-pyrimido[2,1-<i>b</i>]benzimidazoles under solvent-free condition. According to the proposed mechanism, the cobalt complex can accelerate the reaction <i>via</i> a structural rearrangement from a tetrahedral to a square planar geometry.