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2.10.6 Product Subclass 6: Bis- or Mono(η5-cyclopentadienyl)titanium(II) Complexes

DOI: 10.1055/sos-SD-002-00576

Mikami, K.; Matsumoto, Y.; Shiono, T.Science of Synthesis, (20032505.

In 1970, Brintzinger suggested the word titanocene to describe complex 98. It is, in fact, a titanium hydride complex, which may be formulated as [Ti(C5H4)CpH] (99) (Scheme 47).[‌224‌] It therefore appears that bis(η5-cyclopentadienyl)titanium(II) (98), if it does in fact exist as a reaction intermediate, exhibits a strong tendency to rearrange by ring-to-titanium α-hydrogen shift to a less reactive isomer. While the pentamethylcyclopentadienyl analogue, bis(η5-pentamethylcyclopentadienyl)titanium(II) (100), is sufficiently stable for the determination of its structure and chemical reactivity, the favored deactivation mechanism also appears to be hydrogen abstraction by the titanium center (Scheme 47), in close analogy to the deactivation mechanism of titanocene (98).[‌123‌] Direct evidence for the unique reactivity of titanocene is provided by the investigation of the metastable species tetrakis(η5-cyclopentadienyl)dititanium(II) (103). It is surprising that [Ti2(Cp)4] (103), a dimeric, yet highly reactive form of this compound, is fairly stable in solution at room temperature.[‌123‌]

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