Synthesis,characterization And Asymmetric Catalytic Aryl Sulfide Oxidation Performance Of Transition Metal/rare Earth Complexes Containing Chiral Salen Ligands

Chiral sulfoxide compounds are widely used and have important applications in the field of drug synthesis.At the same time,the asymmetric oxidation of thioethers by metal catalysts is one of the most effective ways to obtain chiral sulfoxides.On the other hand,the synthesis method of sale ligand is simple and easy to combine with most metal ions,which leads to play an important role in the field of catalysis.Therefore,three chiral salen ligands were synthesized by reference to the literature method in this paper,which is(2E,2’E)-3,3’-(5,5’-(1E,1’E)-(1R,2R)-cyclohexane-1,2-diylbis(azan-1-yl-1ylidene)bis(methan-1-yl-1ylidene)bis(3-tertbutyl-4-hydroxy-5,1-phenylene))diacrylic acid(L1);5’,5’’-(1E,1’E)-(1R,2R)cyclohexane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(3’-tertbutyl-4’-hydroxybiphenyl-4-carboxylicacid)(L2);3,3’-((1E,1’E)-(((1R,2R)-cyclohexane-1,2diyl)bis(azaneylylidene))bis(methaneylylidene))bis(4-hydroxybenzoic acid)(L3).respectively.Secondly,the three ligands were reacted with Fe Cl3·6H2O,Mn(OAc)2·4H2O and Zn(OAc)2 and Ln(NO3)3·6H2O(Ln=Sm,Eu,Tb,Dy),respectively,acquiring 9 new transition metal salen complexes and 12 new rare earth salen complexes.36 new transition metal-salen-rare earth complexes were prepared by reacting the obtained transition metal salen complex with Ln(NO3)3·6H2O(Ln = Sm,Eu,Tb,Dy).The structure of the synthesized ligands and metal complexes was characterized by elemental analysis,infrared,nuclear magnetic,thermogravimetry,mass spectrometry and other testing methods.Combined with circular dichroism and UV-visible spectroscopy,it is known that the salen ligand and its corresponding metal complex have chirality.Besides,fluorescence spectroscopy indicated that the three chiral salen ligands L1~L3 could effectively sensitize the characteristic fluorescence emission of the corresponding rare earth ions.Finally,the asymmetric catalytic oxidation activity of thioanisole,4-methylthioanisole and 4-nitrothioanisole was investigated by using the synthesized series of salen complexes as catalysts and the influence of the structure,transition metal ions,rare earth ions and other factors on the performance of the asymmetric catalytic oxidation reaction was also explored.Among them,L2-Fe-Sm(26)complex has the best catalytic effect on 4-nitrothioanisole(conversion rate: ≥99%;selectivity: 100%;ee value: 63%),compared with corresponding literature about the catalytic activity of the similar complex(conversion: 64%;selectivity: 83%;ee value: 25%),it was high.