Syntheses, structural characterizations, and catalytic activities of manganese(II)-aroylhydrazone complexes

Abstract

An aroylhydrazone, di-2-pyridyl ketone-4-methoxybenzhydrazone monohydrate (DKMBH·H2O), and its three Mn(II) complexes, [Mn(DKMB)2]·H2O (1), [Mn(DKMB)Cl] (2), and [Mn(DKMB)NO3] (3), were synthesized. The physicochemical properties of the aroylhydrazone and metal complexes were revealed using various methods, e.g., Fourier transform infrared (IR) spectroscopy, ultraviolet-visible spectroscopy, mass spectrometry, and 1H nuclear magnetic resonance (NMR) spectroscopy, in addition to analyses such as CHN elemental and thermal analyses and molar conductivity studies. The molecular structures of the aroylhydrazone and manganese complex, 1 were elucidated using single-crystal X-ray diffraction (XRD) analyses.IR spectroscopy, 1H NMR spectroscopy, and single-crystal XRD showed that the aroylhydrazone occurred in the amido form in the solid state. According to the results of XRD, the aroylhydrazone coordinated to the Mn(II) center via the pyridine and azomethine N atoms and iminolate O atom, with a distorted octahedral geometry, in bis-ligated complex, 1.The results of IR spectroscopy further supported the tridentate character of the aroylhydrazone. Furthermore, the Mn complexes displayed potential as catalysts in cyclooctene epoxidation. Among the three Mn complexes, the use of [Mn(DKMB)2]·H2O (1) resulted in a 92% conversion, with an epoxide selectivity of 95%.