Amino Alcohol-Derived Reduced Schiff Base VIVO and VV Compounds as Catalysts for Asymmetric Sulfoxidation of Thioanisole with Hydrogen Peroxide

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• 作者：Pedro Ad茫o ; Maxim L. Kuznetsov ; S贸nia Barroso ; Ana M. Martins ; F. Avecilla ; Jo茫o Costa Pessoa
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：November 5, 2012
• 年：2012
• 卷：51
• 期：21
• 页码：11430-11449
• 全文大小：824K
• 年卷期：v.51,no.21(November 5, 2012)
• ISSN：1520-510X

文摘

We report the synthesis and characterization of several amino alcohol-derived reduced Schiff base ligands (AORSB) and the corresponding V^IVO and V^V complexes. Some of the related Schiff base variants (amino alcohol derived Schiff base = AOSB) were also prepared and characterized. With some exceptions, all compounds are formulated as dinuclear compounds {V^IVO(L)}₂ in the solid state. Suitable crystals for X-ray diffraction were obtained for two of the AORSB compounds, as well as a rare X-ray structure of a chiral V^IVO compound, which revealed a dinuclear {V^IVO(AOSB)}₂ structure with a rather short V鈥揤 distance of 3.053(9) 脜. Electron paramagnetic resonance (EPR), ⁵¹V NMR, and density functional theory (DFT) studies were carried out to identify the intervenient species prior to and during catalytic reactions. The quantum-chemical DFT calculations were important to determine the more stable isomers in solution, to explain the EPR data, and to assign the ⁵¹V NMR chemical shifts. The V(AORSB) and V(AOSB) complexes were tested as catalysts in the oxidation of thioanisole, with H₂O₂ as the oxidant in organic solvents. In general, high conversions of sulfoxide were obtained. The V(AOSB) systems exhibited greater activity and enantioselectivity than their V(AORSB) counterparts. Computational and spectroscopic studies were carried out to assist in the understanding of the mechanistic aspects and the reasons behind such marked differences in activity and enantioselectivity. The quantum-chemical calculations are consistent with experimental data in the assessment of the differences in catalytic activity between V(AOSB) and V(AORSB) peroxido variants because the V(AORSB) peroxido transition states correspond to ca. 22 kJ/mol higher energy activation barriers than their V(AOSB) counterparts.