Catalytic Efficacy of Copper(II)– and Cobalt(III)–Schiff Base Complexes in Alkene Epoxidation

Abstract

A potentially hexadentate N2O4 donor Schiff base ligand N,N¤ -bis(5-bromo-3-methoxysalicylideneimino)-1,3- diaminopropane (H2L1 ) has been used to synthesize two mononuclear coordination complexes [Cu(L1 )]¢H2O (1) and [Co(L1 )(HL2 )]ClO4¢CH3CN (2). The cobalt complex is a unique mixed-ligand species comprising both the di- and monocondensed ligands; the latter (HL2 ) resulted from in situ hydrolytic cleavage of H2L1 . Ligand L1 assumes a planar arrangement in 1 and a folded β-cis configuration in 2, induced in this case by the chelating HL2 ligand. The complexes are characterized by elemental analyses, FT-IR, and UV­vis spectral methods, and their structures are established by single-crystal X-ray diffraction study. Both the complexes are proven to be efficient catalysts for the epoxidation of alkenes by H2O2 or PhIO. The efficiency of alkene epoxidation is however somewhat superior with PhIO, and in each case, 2 appears to be a slightly better catalyst than 1