Synthesis and characterization of some transition metal complexes with a novel Schiff base ligand and their use as catalysts for olefin cyclopropanation

A novel ligand HL (1), N,2-bis(1-(2-oxo-2H-chromen-3-yl)ethylidene)hydrazinecarbothioamide was synthesized through the condensation of 3-acetyl-2H-chromen-2-one and hydrazinecarbothioamide. This ligand was used to prepare new transition metal complexes of Cu(II), Ni(II) and Co(II). Characterization of the HL (1) ligand and its complexes is also reported. Mass spectra and NMR assignments for the ligand, 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 octahedral, or square planar. The structures are consistent with the IR, UV–vis, ESR, as well as conductivity measurements. The catalytic activity of the copper complex, [HLCu2Cl3]Cl·H2O (2), in cyclopropanation reactions of unactivated olefins with ethyldiazoacetate (EDA) was studied. Cyclopropanes were obtained in high yield (up to 97%, TON up to 16,900) with moderate to good diastereoselectivities (50–91%).

Graphical abstractThe new ligand HL (1), N,2-bis(1-(2-oxo-2H-chromen-3-yl)ethylidene)hydrazinecarbothioamide was used to prepare new transition metal complexes. The catalytic activity of the copper complex, [HLCu2Cl3]Cl·H2O (2), in cyclopropanation reactions of unactivated olefins with ethyldiazoacetate (EDA) was studied. Cyclopropanes were obtained in high yield (up to 97%, TON up to 16,900).Figure optionsDownload full-size imageDownload as PowerPoint slide