Synthesis, Characterization And Catalytic Application Of Functional Organoantimony Complex

Antimony resources are very rich in our country, and antimony compounds have been widely used in petrochemical industry, polymer and bio-medicine. In the main group metal elements, antimony(Ⅲ) has special electrons with structural diversity, and often exhibits a highly coordination number with variable coordination geometry. In recent years, the research on organoantimony compounds have received much attention and was mainly focused on the synthesis and structural characterization of those complexes, while their applications were raroely studied. The main reasons include:(1) poor stability of Sb-C bonds in many organoantimony compounds and moisture (oxygen)-sensitive properties; (2) their catalytic applications in organic synthesis as Lewis acid is limited for the weak acid strength of organoantimony complexes; (3) the relationship between their structure and efficacy has not been disclosed clearly. Therefore, it can be envisaged that antimony compounds will find important scientific significance and potential applications with the development of organoantimony chemistry.Based on the above considerations, we have synthesized 4 tridentate ligand precursors bearing N, S atom as coordination atoms, and obtained 3 air-stable organoantimony chlorides.2 new organoantimony compounds with certain Lewis acidity were synthesized by the substitution of Cl with the strong electron withdrawing groups into organoantimony complexes. The component, structure and physicochemical properties of the compounds were characterized by single crystal X-ray diffraction, nuclear magnetic resonance (NMR), elemental analysis, thermogravimetric analysis (TG-DSC) etc. Their applications in catalysis such as carbon-carbon bond forming reactions and ring opening reactions of epoxides were investigated. Some main research results were obtained as follows:(1) Ligand precursors bearing N, S coordination atoms were synthesized in high yields using NBS and 1-bromo-2-methylbenzene as starting materials in the presence of the organic base triethylamine as a neutralizer through the optimization of reaction conditions. Then. organoantimony chlorides (C6H11N(C6H4CH2)2SbCl 3a, C6H5N(C6H4CH2)2SbCl 3b and C4H9N(C6H4CH2)2SbCl 3c) have been efficiently synthesized. The crystal structure analysis shows that organic groups connected with the nitrogen atom make some impacts on Sb-N bond length, the coordination bond length is 3a<3b≈3c. The Electron-donating ability of cyclohexyl is stronger than tert-butyl and phenyl, indicating that the Sb-N bond length becomes shorter by increasing electron-donating ability of nitrogen-containing organic groups.(2) Organoantimony trifluoromethylsulfonate C6H11N(C6H4CH2)2SbOSO2CF3 4 was synthesized by the reaction of C6H11N(C6H4CH2)2SbCl with AgOSO2CF3, and its catalytic application has been explored. The results show that compound 4 has certain Lewis acidity and good thermal stability. In the three-component Mannich reaction using water as the reaction medium,4 exhibits high activity and stereoselectivity under mild conditions. Moreover, the catalyst shows good reusability. It can be expected that the complex will find broad applications in organic synthesis.(3) Organoantimony fluoride C6H5N(C6H4CH2)2SbF 5 was synthesized by the reaction of C6H5N(C6H4CH2)2SbCl with AgBF4, and its catalytic application has been explored. The results show that Lewis acid strength of compound 5 is stronger than 4. It was found that 5 shows high catalytic efficiency towards ring opening reactions of epoxides, electronic and steric factors of the substrates made little impact on the reaction. The catalyst also shows good activity for the synthesis of (E)-α,β-unsaturated ketones by a condensation reaction between aldehydes and cyclohexanone in the presence of propylamine. In addition, it exhibits good stability and recyclability with good potential application.