Synthesis and Characterization of New Schiff Base Metal Complexes and Their Use as Catalysts for Olefin Cyclopropanation

Abstract

New transition metal complexes of Co^II, Cu^II, Ni^II, and Fe^III of the ligands 2N,2-bis((7- hydroxy-5-methoxy-2-methyl-4-oxo-4H-chromen-6-yl)methylene)hydrazinecarbo-thioamide H₃L¹ and (E)-2-((7-hydroxy-5-methoxy-2-methyl-4-oxo-4H-chromen-6-yl)methylene)-N- phenylhydrazinecarbothioamide H₂L² have been prepared and characterized. Mass spectra and NMR assignments for the ligands, using COSY, NOESY homonuclear, and HMQC and HMBC heteronuclear correlation techniques were carried out. Electronic and magnetic moments of the complexes indicate that the geometries of the metal centers are either distorted square pyramidal or octahedral. The structures are consistent with the IR and UV-VIS, as well as conductivity and magnetic moments measurements. Cyclopropanation reactions of unactivated olefins by ethyldiazoacetate (EDA) in the presence of H₃L¹Cu₂.Cl₄.H₂O as catalyst proceed with excellent turn over numbers (TON: up to 12556).

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Keywords:

• Condensation reactions
• cyclopropanation reactions
• homogeneous catalysis
• metal complexes
• Schiff bases
• thiosemicarbazide