Synthesis and characterization of chromium(III) complexes derived from tridentate ligands: Generation of phenoxyl radical and catalytic oxidation of olefins

The mononuclear chromium complexes [Cr(Phimp)2](ClO4) (1), [Cr(N–Phimp)2](ClO4) (2), and [Cr(Me–Phimp)2](ClO4) (3) (where PhimpH = (2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), N–PhimpH = (2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)napthalen-1-ol), Me–PhimpH = (2-(1-(2-phenyl-2-(pyridine-2-yl)hydrazono)ethyl)phenol) where H stands for dissociable proton) were synthesized and characterized spectroscopically. Electrochemical studies were investigated for the stabilization of Cr(III) complexes and electrochemically generation of phenoxyl radical complexes. Phenoxyl radical complexes were also generated by ceric ammonium nitrate (CAN) and characterized by UV–visible spectra. The complexes were evaluated for their activity as catalysts for the epoxidation of olefins. The chromium complexes catalyzed epoxidation of olefins, viz. styrene, cis-cyclooctene and trans-stilbene with hydrogen peroxide (H2O2) as terminal oxidant, to give corresponding epoxides and oxidative products at ambient temperature.