Procedures and Reagents Used in the McMurry Reactions

With a few exceptions, the active low-valent titanium spedes in McMurry reactions are obtained by reduction of TiCU or TiCls the choice of the reducing agent is of great importance. 

In some cases, the efficacy of the low-valent titanium species has been enhanced by ultrasonication. Under such conditions, reductive coupling of acetophenone with TiCU-Li was complete after 45 min at 30 °C in THF, as compared to 16 h at 65 °C without sonication however, the reaction stopped at the pinacol stage when performed in DME [206]. The synthesis of tetraferrocenylethylene 48 could only be achieved when the TiCls-Li reagent was ultrasonicated [66]. 

2 Effect of Additives on the TiCU- and TiCl3-Reducing Agent Systems 

The effects of a number of additives on the TiCU- and TiCls-reducing agent systems have been considered with a view to enhancing the formation of the alkene products of the coupling reaction or, on the contrary, to stop it at the pinacol stage. 

This tuning of the activity of the low-valent titanium species has been achieved by changing the ligand environment of the metal and/or by adding chemical redox agents. 

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