Science of Synthesis

Mikami, K.; Matsumoto, Y.; Shiono, T., Science of Synthesis, (2003) 2, 476.

Steric considerations introduce some limitations to the preparation of bis(η5-cyclopentadienyl)titanium complexes. One preferred method for the synthesis of bulky cyclopentadienyl complexes is the reaction of titanium(III) halides with the cyclopentadienyl moiety, followed by oxidation with hydrochloric acid. This method gives higher yields (up to 40%) of dichlorobis(η5-pentamethylcyclopentadienyl)titanium(IV) (‌104‌) than are obtained by the reaction of titanium(IV) chloride with sodium pentamethylcyclopentadienide (14%).[‌123‌] Titanium(III) chloride is also used for the synthesis of bis[(diphenylphosphino)tetramethylcyclopentadienyl] complex ‌57‌ (‌Scheme 21‌).[‌124‌] Many ansa-titanocene derivatives, for example, the ethylene-bridged ansa-titanocene complex ‌58‌ (‌Scheme 21‌), reported by Brintzinger,[‌125‌] have also been synthesized by this method. Complex ‌58‌ is readily reduced by sodium sand in toluene to the corresponding titanium(III) complex. The 3-alkyl[‌126‌] and 2,4-dialkyl[‌127‌] derivatives of the ethylene-bridged complex are obtained as mixtures of rac- and meso-compounds. The permethylated complex dichloro[ethylenebis(1-η5-2,3,4,5-tetramethylcyclopentadienyl)]titanium(IV) is prepared as dark red crystals in a 15% yield.[‌128‌]

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References

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• 8.Meeeee-Meee, (8888) M 88-8, 888.