Cyclopentadienyl halides and oxides

Many complexes in this class are found with the metals of Groups IV-VII in their hi er oxidation states. The jr-cyclopentadienyl ligand is versatile in that its complexes cover a wide range of formal oxidation states of the transition metals (cf. the CN ligand). 

The known halide complexes are shown in Table 16. Many of these may be prepared by direct reaction of a metal halide with an ionic cyclopenta-dienylating reagent (see p. 93). Other more specific routes are discussed incidentally below. 

Frequently the bis-Tt-cyclopentadienyl halides are thermally stable above 200°C and are stable to oxidation in dry air. They are rather less rapidly hydrolysed than the corresponding metal halides although partial hydrolysis or oxyhalide formation can occur. Thus contrast the rapid hydrolysis reactions of titanium and zirconium tetrachlorides with the reactions 

The mono-7t-cyclopentadienyl halides are usually more readily hydrolysed and are less stable to heat than the bis- r-cyclopentadienyl halides. 

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