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Title

C3-Symmetric Trinuclear Molybdenum Cluster Sulfides: Configurational Stability, Supramolecular Stereocontrol, and Absolute Configuration Assignment

Authors
Guillamón, Eva
Llusar, Rosa
Polo, Victor
Vicent, Cristian
Published in Inorganic Chemistry. 2007, vol. 46, no. 25, p. 10717-10723
Abstract The chiral C3-symmetric [Mo3S4Cl3(dppe)3]+ cluster [dppe = 1,2-bis(diphenylphosphinoethane), P or M enantiomers] with incomplete cuboidal structure is shown to be configurationally stable at room temperature and configurationally labile at elevated temperature using enantiopure Delta- or Lambda-TRISPHAT [(tris(tetrachlorobenzenediolato)phosphate(V)] anions both as chiral NMR solvating and asymmetry-inducing reagents. It is evidenced that the enantiomers of this trinuclear cluster cation can equilibrate at higher temperature (typically 72 degrees C), and in the presence of the hexacoordinated phosphate anion, a moderate level of stereocontrol (1.2:1) can be achieved. It results in a diastereomeric enrichment of the solution in favor of the heterochiral ion pairs, e.g., M+ Delta- or P+ Lambda-. At higher temperature, a partial racemization of the TRISPHAT anion is also observed, and precipitation at room temperature of [rac-Mo3S4Cl3(dppe)3][rac-TRISPHAT] salts from the diastereomeric enriched solution improves the diastereomeric purity of the mother liquor to a 4:1 ratio. A low-energy pathway for the inverconversion between the [P-Mo3S4Cl3(dppe)3]+ and [M-Mo3S4Cl3(dppe)3]+ enantiomers has been found using combined quantum mechanics and molecular mechanics methodologies. This pathway involves two intermediates with three transition state regions, which result from the partial decoordination of the diphosphane coordinated at each metal center. Such decoordination creates a vacant position on the metal, producing a Lewis acidic site that presumably catalyzes the TRISPHAT epimerization.
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PMID: 17985875
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FRANTZ, Richard et al. C3-Symmetric Trinuclear Molybdenum Cluster Sulfides: Configurational Stability, Supramolecular Stereocontrol, and Absolute Configuration Assignment. In: Inorganic Chemistry, 2007, vol. 46, n° 25, p. 10717-10723. doi: 10.1021/ic701522p https://archive-ouverte.unige.ch/unige:6914

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Deposited on : 2010-06-18

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