Chiral oxovanadium(V) complexes with a 6-amino-6-deoxyglucopyranoside-based Schiff-base ligand: Catalytic asymmetric sulfoxidation and structural characterization

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• 作者：Ines Lippold ; Jana Becher ; Dieter Klemm ; Winfried Plass
• 关键词：Carbohydrates ; Chiral ligand ; Schiff-base ligand ; Sulfoxidation ; Vanadium ; X-ray diffraction
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2009
• 出版时间：18 February 2009
• 年：2009
• 卷：299
• 期：1-2
• 页码：12-17
• 全文大小：441 K

文摘

Two new chiral oxovanadium(V) complexes [VO(OMe)(L)] (1) and [VO(Osal)(L)] (2) derived from the Schiff-base ligand 6-N-[(3,5-di-tert-butyl-salicylidene)amino]-6-deoxy-1,2,3-tri-O-methyl-α-d-glucopyranose (H₂L) were synthesized via two different routes. The reaction of the Schiff-base ligand H₂L with ammonium metavanadate in hot methanol as well as with tris(isopropoxy)oxovanadium(V) in diethyl ether at room temperature leads to a mixture of complexes 1 and 2, which can be isolated by means of fractional crystallization. The complexes were characterized with elemental analysis, ⁵¹V, ¹H and ¹³C NMR, IR spectroscopy, MS and in case of 1 by X-ray diffraction. Complex 1 crystalizes in the orthorhombic space group P2₁2₁2₁ with a distorted trigonal bipyramidal geometry at the vanadium center (τ = 0.58). Under hydrolytic conditions 1 forms the cis-dioxovanadium(V) complex [VO₂(MeOH)(HL)] (3) which can be monitored by NMR spectroscopy. Complexes 1 and 2 were tested as catalysts for sulfoxidation of different sulfide substrates PhSR (R = Me, Bz) utilizing hydrogen peroxide or tert-butyl hydroperoxide (TBHPO) as oxidant in dichloromethane as solvent. The yield as well as the enantiomeric excess were found to strongly depend on the catalyst, substrate and oxidant used.