1277170-20-3Relevant academic research and scientific papers
Optically active tripodal dendritic polyoxometalates: Synthesis, characterization and their use in asymmetric sulfide oxidation with hydrogen peroxide
Jahier, Claire,Coustou, Marie-Flora,Cantuel, Martine,McClenaghan, Nathan D.,Buffeteau, Thierry,Cavagnat, Dominique,Carraro, Mauro,Nlate, Sylvain
experimental part, p. 727 - 738 (2011/04/26)
A series of structurally well-defined enantiopure tripodal allyl dendritic structures bearing three amine groups have been synthesized. The hydrogenation of the allyl groups in the presence of a Pd/C catalyst gave the corresponding enantiopure n-propyl counterparts. Treatment of these n-propyl amino dendrimers with heteropolyacid H3PW12O40 and excess H 2O2 gave the enantiopure n-propyl {PO 4[WO(O2)2]4}3- salts. Characterization of these dendritic POM hybrids in solution by NMR spectroscopy, elemental analysis, UV/Vis spectrophotometry, circular dichroism (CD), vibrational circular dichroism (VCD) and fluorimetry indicates the presence of POM-ligand interactions and confirms their optical and chiroptical properties. The hybrid compounds selectively oxidized sulfides to the corresponding chiral sulfoxides with up to 13% enantiomeric excess (ee), highlighting the transfer of chirality from the dendritic wedges to the inorganic cluster. The properties of the POM anion, especially its solubility and regio-and stereoselectivity, are sensitive to the structure of the cation. The catalyst was recovered by precipitation without any discernible loss in activity, selectivity or enantioselectivity over three catalytic cycles at-50 °C. Interestingly, a dendritic effect was noted in the enantioselectivity as the dendritic-POM hybrids are more selective than their non-dendritic counterparts. The ee resulting from chirality transfer to the anionic POM unit is comparable to that obtained in our previous work with monopodal dendritic polyoxometalates (14%) despite the polyvalency of the highly charged tripodal ligand, which is rationalized by different spectroscopic methods. Copyright
