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Molecules 2018, 23(7), 1595; https://doi.org/10.3390/molecules23071595

Molybdenum-Catalyzed Enantioselective Sulfoxidation Controlled by a Nonclassical Hydrogen Bond between Coordinated Chiral Imidazolium-Based Dicarboxylate and Peroxido Ligands

Departamento de Química Inorgánica, Universidad de Sevilla, Aptdo. 1203, 41071 Sevilla, Spain
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Received: 22 May 2018 / Revised: 25 June 2018 / Accepted: 28 June 2018 / Published: 30 June 2018
(This article belongs to the Special Issue Molybdenum-Catalyzed Oxidation Reactions)
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Abstract

Chiral alkyl aryl sulfoxides were obtained by molybdenum-catalyzed oxidation of alkyl aryl sulfides with hydrogen peroxide as oxidant in mild conditions with high yields and moderate enantioselectivities. The asymmetry is generated by the use of imidazolium-based dicarboxylic compounds, HLR. The in-situ-generated catalyst, a mixture of aqueous [Mo(O)(O2)2(H2O)n] with HLR as chirality inductors, in the presence of [PPh4]Br, was identified as the anionic binuclear complex [PPh4]{[Mo(O)(O2)2(H2O)]2(μ-LR)}, according to spectroscopic data and Density Functional Theory (DFT) calculations. A nonclassical hydrogen bond between one C–H bond of the alkyl R group of coordinated (LR) and one oxygen atom of the peroxido ligand was identified as the interaction responsible for the asymmetry in the process. Additionally, the step that governs the enantioselectivity was theoretically analyzed by locating the transition states of the oxido-transfer to PhMeS of model complexes [Mo(O)(O2)2(H2O)(κ1-O-LR)] (R = H, iPr). The ∆∆G is ca. 0 kcal∙mol−1 for R = H, racemic sulfoxide, meanwhile for chiral species the ∆∆G of ca. 2 kcal∙mol−1 favors the formation of (R)-sulfoxide. View Full-Text
Keywords: sulfoxidation; asymmetric catalysis; molybdenum; hydrogen peroxide; Density Functional Theory sulfoxidation; asymmetric catalysis; molybdenum; hydrogen peroxide; Density Functional Theory
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Carrasco, C.J.; Montilla, F.; Galindo, A. Molybdenum-Catalyzed Enantioselective Sulfoxidation Controlled by a Nonclassical Hydrogen Bond between Coordinated Chiral Imidazolium-Based Dicarboxylate and Peroxido Ligands. Molecules 2018, 23, 1595.

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