Crystal structures and catalytic performance of three new methoxy substituted salen type nickel(II) Schiff base complexes derived from meso-1,2-diphenyl-1,2-ethylenediamine

Catalytic epoxidation of cyclooctene was studied with three new structurally characterized salen type Ni(II) Schiff base complexes and enhanced catalytic activity and epoxide selectivity was achieved in solvent free conditions. [Display omitted] •Three new Ni(II) Schiff base complexes were synthesized.•Crystal structures of these complexes were determined.•Physico-chemical properties were correlated with position of substituents.•Epoxidation of cyclooctene with these catalysts was studied.•Solvent free conditions gave enhanced catalytic activity and epoxide selectivity. Three new nickel(II) complexes of a series of methoxy substituted salen type Schiff base ligands were synthesized and characterized by IR, UV–Vis and 1H NMR spectroscopy and elemental analysis. The ligands were synthesized from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with n-methoxysalicylaldehyde (n=3, 4 and 5). Crystal structures of these complexes were determined. Electrochemical behavior of the complexes was studied by means of cyclic voltammetry in DMSO solutions. Catalytic performance of the complexes was studied in the epoxidation of cyclooctene using tert-butylhydroperoxide (TBHP) as oxidant under various conditions to find the optimum operating parameters. Low catalytic activity with moderate epoxide selectivity was observed in in-solvent conditions but in the solvent-free conditions, enhanced catalytic activity with high epoxide selectivity was achieved.