Metal-mefenamato Complexes:Synthesis And Their Catalytic Property For Olefin Oxidation

The coordination of mefenamic acid to metal ions improves its pharmaceutical function, reduces its side effect as well as imposes some extra properties, such as catalytic, antimicrobial, anti-proliferative activities etc. In this work, the catalytic property of the metal-mefenamato complexes in olefin oxidation was explored. The coordination of mefenamic acid to transition metal ions (Mn2+, Co2+, Ni2+, Cu2+, Zn2+) in the presence of some heterocyclic ligands (2,2’-bipyridine or1,10-phenanthronine) leads to the formation of fifteen metal-mefenamato complexes. Among them,[Ni(mef)2(CH3OH)4],[Ni(mef)2(bipy)(CH3OH)2] and [Ni(mef)2(phen)] are reported for the first time. The complexes have been characterized by elemental analysis, UV-visible and IR spectroscopies and X-ray crystallography diffraction. The crystal structure of [Ni(mef)2(bipy)(CH3OH)2] has been determined. It is a mononuclear complex, the nickel atom is in six-coordinated mode and is surrounded by two mefenamato ligands, two methanol molecules and a bidentate2,2’-bipyridine ligand showing a distorted octahedral geometry.In order to explore the catalytic property of metal-mefenamato complexes for olefin oxidation, the oxidation of styrene using [Co(mef)2(phen)(CH3OH)2] as a model catalyst was systemically studied. The reaction solvent, temperature, time, pH were optimized. With the optimized reaction condition, the catalytic activity of the other as-synthesized complexes have also been examined. All of the metal complexes showed some extent of olefin oxidative catalytic activity except for zinc-mefenamato complexes.[Mn(mef)2(bipy)] and [Co(mef)2(phen)(CH3OH)2] exhibited higher catalytic activity than the other metal-mefenamato complexes at94℃in1,2-dichloroethane using tert-butyl hydroperoxide as oxidant for1h. The conversion of styrene to benzaldehyde can reach74.02%and63.39%, and selectivity of59.79%and59.68%, for these two complexes, respectively.