Pentacoordinated copper–sparteine complexes with chelating nitrite or nitrate ligand: Synthesis and catalytic aspects

Copper(II)–sparteine complexes, [CuII{(-)Sp}(NO2)Cl] (1) and [CuII{(−)Sp}(NO3)Cl] (2) (Sp = sparteine) with chelating nitrite and nitrate ligands, respectively, have been synthesized and structurally characterized. The penta-coordinated 1 or 2 exhibits distorted square pyramidal geometry and shows characteristic EPR spectra with g||: 2.27 and g⊥: 2.06. 1 and 2 behave similarly towards the catalytic epoxidation of alkenes as well as oxidation of alcohols. Though the epoxidation of cyclohexene using 1 or 2 as a catalyst and tertiarybutyl hydroperoxide (TBHP) as an oxidant at 298 K in acetonitrile results in 100% cyclohexene oxide product, under identical reaction conditions styrene selectively transforms to benzaldehyde (∼90%) instead of any styrene oxide. However, at higher temperature (353 K) the selectivity of cyclohexene to corresponding epoxide formation decreases appreciably and additional products, cyclohexanol and cyclohexanone are formed. Furthermore, 1 or 2 effectively catalyzes the oxidation of benzyl alcohol to benzoic acid and cyclohexanol to cyclohexanone in presence of molecular oxygen (O2) as an oxidant at 353 K in acetonitrile.