TiCl₄(THF)₂ (L. E. Manzer, Inorg. Synth. 1982, 21, 135)
ⁿbutyllithium (2.5M in hexane, Acros Organics)
LiCp*
TiCl₄ (Aldrich)
THF (distilled from potassium)
conc. HCl (BDH)
chloroform (Fisher)

A 100 mL Rotaflo/Young's ampoule was charged with TiCl₄(THF)₂ (4.0 g, 11.9 mmol) and THF (25 mL) and cooled to -78^oC. Added dropwise, from a graduated ampoule, was ⁿBuLi (4.8 mL of a 2.5M solution in hexane, 11.9 mmol, 1 equivalent), with the immediate formation of a pale blue/green solid and a brown solution. The vessel was allowed to warm to room temperature, evacuated, refluxed for 1 hour and then allowed to cool. A separate vessel was charged with a slurry of LiCp* (3.36 g, 23.8 mmol) in THF (25 mL), which was added to the Ti(III) solution via wide-bore cannula. The reaction vessel was evacuated and heated to reflux for 2 days. A colour change to green is observed after an hour, after 18 hours (i.e. overnight) the suspension is purple. After the allotted reaction time, the reaction vessel was cooled to 0^oC and concentrated HCl was added (ca. 20 mL), resulting in the precipitation of a red solid. The contents of the reaction mixture were poured into chloroform (250 mL). The aqueous layer was discarded, and the organic phase dried over anhydrous sodium sulfate, which was removed by filtration and the solvent removed under reduced pressure to yield a waxy red solid in near quantitative yield (determined by NMR spectroscopy in CDCl₃ to be predominantly (C₅Me₅)₂TiCl₂, but containing some of the desired (C₅Me₅)TiCl₃; this is not problematic in view of the next step) The solid thus obtained was transferred to a 100 mL Rotaflo/Young's ampoule and dried under vacuum for 1 hour. Added via syringe was TiCl₄ (0.9 mL, 1 equivalent relative to the amount of titanocene dichloride present). The ampoule was evacuated and heated to 140^oC for 4 hours, after which time the solid was notably brighter red. Any residual TiCl₄ was removed under vacuum. The red solid was transferred to the glovebox and collected. Yield 4.85 g (16.7 mmol, 70% (over 2 steps) based on LiCp*). Whilst spectroscopically pure, the solid could be further purified by sublimation at 150-160^oC and 10^-3 Torr

There are other preps in the literature for this compound, however in my hands they are somewhat (and repeatedly) capricious. This procedure is an amalgamation of the two lead references shown below. The staple compounds LiCp* and TiCl₄(THF)₂ are relatively simple to prepare and the subsequent reactions straightforward for a well-trained organometallic chemist. The amount of half-sandwich compound prepared in the first reaction varies, but is not more than 30% at most. But remember; only use enough TiCl₄ for the amount of titanocene present, the Cp*TiCl₃ needs no further treatment. The sublimation is necessary for the removal of the product from any decomposition products in the final reaction.

For (C₅Me₅)₂TiCl₂ ¹H NMR (CDCl₃, 298 K): 2.01 ppm (s, 30H) For (C₅Me₅)TiCl₃ ¹H NMR (CDCl₃, 298 K): 2.38 ppm (s, 15H) (C₆D₆, 298 K): 1.87 ppm (s, 15H)

J. E. Bercaw, R. H. Marvich, L. G. Bell, H. H. Brintzinger, J. Am. Chem. Soc. 1972, 94, 1219-1238 and K. Mach, V. Varga, H. Antropiusova, J. Polacek, J. Organomet. Chem. 1987, 333, 205-215