Strong Lewis Acids of Air-Stable Metallocene Bis(perfluorooctanesulfonate)s as High-Efficiency Catalysts for Carbonyl-Group Transformation Reactions

Authors

  • Dr. Renhua Qiu,

    1. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
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  • Prof. Dr. Xinhua Xu,

    Corresponding author
    1. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
    2. State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjing, 300071 (P.R. China)
    • State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
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  • Dr. Lifeng Peng,

    1. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
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  • Dr. Yalei Zhao,

    1. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
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  • Dr. Ningbo Li,

    1. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
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  • Prof. Dr. Shuangfeng Yin

    Corresponding author
    1. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
    • State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (P.R. China), Fax: (+86) 731-88821310
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Abstract

Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s [M(Cp)2][OSO2C8F17]2nH2O⋅THF (M=Zr (2 a⋅3 H2O⋅THF), M=Ti (2 b⋅2 H2O⋅THF)) were synthesized by the reaction of [M(Cp)2]Cl2 (M=Zr (1 a), M=Ti (1 b)) with nBuLi and C8F17SO3H (2 equiv) or with C8F17SO3Ag (2 equiv). The hydrate numbers (n) of these complexes were variable, changing from 0 to 4 depending on conditions. In contrast to well-known metallocene triflates, these complexes suffered no change in open air for a year. thermogravimetry–differential scanning calorimetry (TG-DSC) analysis showed that 2 a and 2 b were thermally stable at 300 and 180 °C, respectively. These complexes exhibited unusually high solubility in polar organic solvents. Conductivity measurement showed that the complexes (2 a and 2 b) were ionic dissociation in CH3CN solution. X-ray analysis result confirmed 2 a⋅3 H2O⋅THF was a cationic organometallic Lewis acid. UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2 a. Fluorescence spectra showed that the Lewis acidity of 2 a fell between those of Sc3+ (λem=474 nm) and Fe3+ (λem=478 nm). ESR spectra showed the Lewis acidity of 2 a (0.91 eV) was at the same level as that of Sc3+ (1.00 eV) and Y3+ (0.85 eV), while the Lewis acidity of 2 b (1.06 eV) was larger than that of Sc3+ (1.00 eV) and Y3+ (0.85 eV). They showed high catalytic ability in carbonyl-compound transformation reactions, such as the Mannich reaction, the Mukaiyama aldol reaction, allylation of aldehydes, the Friedel–Crafts acylation of alkyl aromatic ethers, and cyclotrimerization of ketones. Moreover, the complexes possessed good reusability. On account of their excellent catalytic efficiency, stability, and reusability, the complexes will find broad catalytic applications in organic synthesis.

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