Titanium divalent, chemistry

In this chapter we will review the synthesis, structural aspects, and basic chemical properties of formally divalent and trivalent titanium and zirconium metallocene complexes. We have restricted our coverage to the low-valent bis(rj-cyclopentadienyl) and related metallocenes metal halide complexes and organometallic mixed metal systems will not be discussed here. We have not attempted to present an exhaustive coverage of the field. Rather, our aim has been to describe critically and to evaluate the often confusing chemistry that has been reported for the reactive low-valent titanium and zirconium metallocenes. More general reviews (7) and a book (2) on the organometallic chemistry of titanium, zirconium, and hafnium have been published. 

This chapter reviews a range of recent calculations on several different problems involving titanium chemistry, performed primarily by this group. We begin, in Section 2, by considering the theoretical and computational methods that have been used. This is followed, in Section 3, by a discussion of unusual structures and associated potential energy surfaces that occur in titanium chemistry due in large part to the electron-deficient nature of this element. In Section 4, the potential use of divalent Ti as a catalyst is discussed. A summary and discussion of future topics is presented in Section 5. 

Compounds of divalent titanium are few, and Ti11 has no aqueous chemistry because of its oxidation by water, although it has been reported that ice-cold solutions of TiO in dilute HC1 contain Ti11 ions which persist for some time. The well-defined compounds are TiCl2, TiBr2, Til2 and TiO. The halides are best obtained by reduction of the tetrahalides with titanium ... 

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