ansa-metallocene derivatives : IX. Electrochemical reactions of tetramethylethylene-bridged titanocene dichloride and dicarbonyl derivatives

In the reduction of tetramethylethylene-bridged (CH13)4C2(C5H4)2TiCl2 under argon, studied by cyclic voltammetry, a first reduction to the TiIII stage occurs at a potential of −0.92 V vs. SCE, close to that of (C5H5)2TiCl2, and a second reduction to the TiII stage at a potential of −2.53 V, about 0.3 V more negative than in the corresponding reduction of the unbridged analogue. Decay of the tetramethylethylene-bridged TiII product is considerably faster than that of its unbridged analogue. Changes induced by the presence of an N2 or H2 atmosphere indicate the occurrence of secondary reactions.In the presence of CO, reduction to (CH3)4C2(C5H4)2Ti(CO)2 occurs at −2.0 V. This tetramethylethylene-bridged titanocene dicarbonyl complex, which is also formed by reduction of (CH3)4C2(C5H4)2TiCl2 with Mg metal under CO, undergoes irreversible reduction and oxidation at −2.78 and −0.08 V, respectively. When the latter process is conducted in the presence of Cl−, the dichloride (CH3)4C2(C5H4)2TiCl2 is regenerated