Mononuclear and dinuclear salen type copper(II) Schiff base complexes: Synthesis, characterization, crystal structures and catalytic epoxidation of cyclooctene

A series of salen type Schiff base ligands and their mononuclear (CuLn, n = 1–4) or dinuclear Cu(II) complexes (Cu2(L5)2) were synthesized and characterized by 1H NMR, IR and UV–Vis spectroscopy as well as elemental analyses. The ligands were synthesized from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with various salicylaldehyde derivatives (x-salicylaldehyde for H2Ln, x = H (n = 1), 5-Br (n = 2), 5-Br-3-NO2 (n = 3), 3-OMe, (n = 5)) and 2′-hydroxyacetophenone (n = 4). Crystal structures of two complexes (CuL4 and Cu2(L5)2) were determined. Catalytic performance of the complexes was studied in the epoxidation of cyclooctene using tert-butylhydroperoxide (TBHP) as oxidant. Various factors including reaction temperature, solvent type, time, catalyst amount and substrate to oxidant ratio were optimized. High catalytic activity and epoxides selectivity was found. Solvent free epoxidation of cyclooctene was also studied and higher catalytic activity, epoxide selectivity and lower reaction times were observed.