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Strong Lewis Acids of Air‐Stable Metallocene Bis(perfluorooctanesulfonate)s as High‐Efficiency Catalysts for Carbonyl‐Group Transformation Reactions
Author(s) -
Qiu Renhua,
Xu Xinhua,
Peng Lifeng,
Zhao Yalei,
Li Ningbo,
Yin Shuangfeng
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201103874
Subject(s) - lewis acids and bases , chemistry , metallocene , organometallic chemistry , cationic polymerization , medicinal chemistry , dissociation (chemistry) , thermogravimetry , differential scanning calorimetry , inorganic chemistry , catalysis , nuclear chemistry , polymer chemistry , organic chemistry , polymerization , polymer , physics , thermodynamics
Strong Lewis acids of air‐stable metallocene bis(perfluorooctanesulfonate)s [M(Cp) 2 ][OSO 2 C 8 F 17 ] 2 ⋅ n H 2 O⋅THF (M=Zr ( 2 a ⋅3 H 2 O⋅THF), M=Ti ( 2 b ⋅2 H 2 O⋅THF)) were synthesized by the reaction of [M(Cp) 2 ]Cl 2 (M=Zr ( 1 a ), M=Ti ( 1 b )) with n BuLi and C 8 F 17 SO 3 H (2 equiv) or with C 8 F 17 SO 3 Ag (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 CH 3 CN solution. X‐ray analysis result confirmed 2 a ⋅3 H 2 O⋅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 Sc 3+ ( λ em =474 nm) and Fe 3+ ( λ em =478 nm). ESR spectra showed the Lewis acidity of 2 a (0.91 eV) was at the same level as that of Sc 3+ (1.00 eV) and Y 3+ (0.85 eV), while the Lewis acidity of 2 b (1.06 eV) was larger than that of Sc 3+ (1.00 eV) and Y 3+ (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.