[HTICL(THF) (SIMILAR-TO-0.5)](X) - A HIGHLY REACTIVE TITANIUM HYDRIDE AND AN ACTIVE SPECIES IN THE MCMURRY REACTION

The complex [TiCl3(THF)3] reacts with catalytically-prepared solid magnesium hydride (MgH2*) or dissolved magnesium hydride (MgH2') with evolution of hydrogen to give a highly reactive titanium hydride, [HTiCl(THF) approximately 0.5]x (1). The well-known low valent titanium species, obtained by reduction of TiCl3 with LiAlH4, utilized in the McMurry reaction, has been shown to be 1. An X-ray absorption spectroscopy study (EXAFS) of 1 reveals that the Ti absorber is surrounded by 0 (from THF) and Cl atoms plus two types of Ti neighbors. Possible structural models for 1 compatible with the EXAFS results are proposed. Complex 1 is an active reagent for the coupling reaction of benzophenone to give tetraphenylethene. During the reaction hydrogen is liberated and the inorganic side product has been shown to be titanium(III) oxychloride; thus the McMurry reaction employing 1 as the reagent can be described by [GRAPHICS] On the basis of these results, a new interpretation of the mechanism for the McMurry reaction is presented. Complex 1 also undergoes a number of carbenoid type reactions, which may proceed via a ''titanium carbenoid'' intermediate 9a-c.