Preparation and structural investigations of new hexadentate Schiff base ligands and their bivalent metal complexes, and, catalytic applications of the complexes in allylic and benzylic C–H bond activation

Abstract

The reaction between 2-hydroxybenzaldehyde and piperazine-1,4-diylbis((2-aminophenyl)methanone) or N,N'-(ethane-1,2-diyl)bis(2-amino-N-methyl-benzamide) yields new hexadentate Schiff base ligands, (Z)-piperazine-1,4-diylbis((2-((Z)-(2-hydroxy-benzylidene)amino)phenyl)methanone) (PHMAPM) and 2-((2-hydroxybenzylidene)amino)-N-(2-(2-((E)-(2-hydroxybenzylidene)-amino)-N-methyl-benzimido)ethyl)-N-methylbenzamide (EHBAMB) respectively. PHMAPM crystallizes in the monoclinic space group <i style="mso-bidi-font-style:normal">P</i>2_{1/<i style="mso-bidi-font-style: normal">C</i>}. The Co(II), Ni(II) and Cu(II) complexes of these ligands have been prepared and characterized by elemental analyses, conductance, magnetic susceptibility and spectral investigations. The complexes are found to have the formula [M(PHMAPM)] and [M(EHBAMB)] respectively. The catalytic activity of these complexes in allylic and benzylic (C–H) activation has been investigated. The Cu(II) complexes are found to exhibit better activity in acetonitrile as compared to in other solvents.