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RESEARCH PRODUCT

In situ spectroelectrochemical study of the reductive coupling of benzaldehyde catalyzed by Ti(III) complexes in the presence of Mg(II)

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Abstract The UV–vis spectroelectrochemical technique has been used to visualize for the first time, the formation of a trimetallic intermediate Ti(III)Mg(II)Ti(III) during the reductive coupling of benzaldehyde in the presence of electrogenerated Ti(III) and MgCl 2 . This intermediate is supposed to induce the high diastereoselectivity of the reaction. We have built a special thin layer cell adapted from the scheme proposed by A. Neudeck and L. Dunsch [‘J. Electroanal. Chem. 370 (1994) 17; J. Electroanal. Chem. 386 (1995) 135’] which allows the simultaneous recording of the cyclic voltammogram and of a great quantity of UV–vis spectra at a frequency of 1 spectrum per second by means of a UV–vis diode array spectrometer. The intermediate complex has been characterized by its UV–vis spectrum ( λ max =287, 321 and 370 nm). Its formation needs the simultaneous presence of electrogenerated Ti(III), MgCl 2 and benzaldehyde in the spectroelectrochemical cell. The global chemical reaction rate constant of Cp 2 TiCl 2 with ArCHO in the presence of MgCl 2 has been determined by cyclic voltammetry and spectroelectrochemistry. Both techniques are in good agreement and provide the same value, k =410±127 M −3/2 s −1