Electrochemically reduced titanocene dichloride as a catalyst of reductive dehalogenation of organic halides |
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Authors: | Tatiana V Magdesieva Magdalena Graczyk Oleg M Nikitin Kim P Butin |
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Affiliation: | a Department Chemistry, M.V. Lomonosov Moscow State University, Moscow 119992, Russia b LSEO-UMR 5188 CNRS, Université de Bourgogne, Dijon, France |
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Abstract: | We have studied a reaction between the reduced form of titanocene dichloride (Cp2TiCl2) and a group of organic halides: benzyl derivatives (4-X C6H4CH2Cl, X = H, NO2, CH3; 4-X C6H4CH2Br, X = H, NO2, PhC(O); 4-X C6H4CH2SCN, X = H, NO2) as well as three aryl halides (4-NO2C6H4Hal, Hal = Cl, Br; 4-CH3O-C6H4Cl). It has been shown that the electrochemical reduction of Cp2TiCl2 in the presence of these benzyl halides leads to a catalytic cycle resulting in the reductive dehalogenation of these organic substrates to yield mostly corresponding toluene derivatives as the main product. No dehalogenation has been observed for aryl derivatives. Based on electrochemical data and digital simulation, possible schemes of the catalytic process have been outlined. For non-substituted benzyl halides halogen atom abstraction is a key step. For the reaction of nitrobenzyl halides the complexation of Ti(III) species with the nitro group takes place, with the electron transfer from Ti(III) to this group (owing to its highest coefficient in LUMO of the nitro benzyl halide) followed by an intramolecular dissociative electron redistribution in the course of the heterolytic C Hal bond cleavage.The results for reduced titanocene dichloride centers immobilized inside a polymer film showed that the catalytic reductive dehalogenation of the p-nitrobenzyl chloride does occur but with a low efficiency because of the partial deactivation of the film due to the blocking of the electron charge transport between the electrode and catalytic centers. |
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Keywords: | AN acetonitrile Bn benzyl C6H5CH2 or els-cdn C6H4CH2" target="_blank">com/sd/entities/sbnd" class="glyphImg">C6H4CH2 Cp2TiCl2 titanocene dichloride p(Tc3Py) polymer obtained from Tc3Py TBAPF6 tetrabuthylammonium hexafluorophosphate Tc3Py [η5-3-(N-pyrrolyl)propylcyclopentadienyl)-η5-cyclopentadienyl titanium dichloride Cl2TiCpC5H4(CH2)3NC4H4 (titanocene-propyl-pyrrole) TEACl tetraethylammonium chloride THF tetrahydrofuran |
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