[95936-00-8]  · C16H28P2Ti  · (330.21)

(used as a source of ‘Cp2Ti’)

Physical Data: mp (105°C decomposes); black needles.

Solubility: soluble in most organic solvents.

Preparative Methods: bis(h5-2,4-cyclopentadienyl)bis(trimethylphosphine)titanium is prepared by the reduction of Cp2TiCl2 by magnesium in the presence of trimethylphosphine.1 It may also be generated in situ from Cp2TiCl2, butyllithium and trimethylphosphine.

Handling, Storage, and Precautions: Cp2Ti(PMe3)2 is pyrophoric and must be handled and stored in an argon filled glove-box.

Reductive Cyclization

One of the most important features of bis(h5-2,4-cyclopentadienyl)bis(trimethylphosphine)titanium [Cp2Ti(PMe3)2] is the ease of dissociation of both of the PMe3 ligands to yield a complex with two open coordination sites. Treatment of enynes with a catalytic amount of Cp2Ti(PMe3)2 in the presence of trialkylsilyl cyanides, followed by hydrolysis produces bicyclic cyclopentenones (eq 1).2 Although a variety of metal complexes promote cyclopentenone formation, most require a stoichiometric amount of metal complex.

Cp2Ti(PMe3)2 also catalyzes the reductive cyclization of 1,6-enones3 and 1,6-enals4 to cyclopentanols. These reactions proceed with good diastereoselectivity to produce predominately the syn diastereomer (eq 2).

Imines also form the titanocycles, but do not cleave to form cyclopentylamines. When a stoichiometric amount of Cp2Ti(PMe3)2 is used in the presence of enones, followed by CO, the CO inserts into the resulting metallacycle and, after thermal reductive elimination, produces g-butyrolactones (eq 3).5

A catalytic version of this reaction which uses trialkylsilylcyanides as the CO equivalent, is also an effective method for generating lactones. However, generation of ‘Cp2Ti’ is carried out in situ using 2 equiv of ethylmagnesium bromide or butyllithium.6

Related Reagents.

Cp2TiCl2 Cp2ZrCl2.

1. Kool, L. B.; Raush, M. D.; Alt, H. G.; Herberhold, M.; Honold, B.; Thewalt, U., J. Organomet. Chem. 1987, 32, 37.
2. Berk, S. C.; Grossman, R. B.; Buchwald, S. L., J. Am. Chem. Soc. 1994, 116, 8593.
3. Kablaoui, N. M.; Buchwald, S. L., J. Am. Chem. Soc. 1995, 117, 6785.
4. Crowe, W. E.; Rachita, M. J., J. Am. Chem. Soc. 1995, 117, 6787.
5. Kablaoui, N. M.; Hicks, F. A.; Buchwald, S. L., J. Am. Chem. Soc. 1996, 118, 5818.
6. Hicks, F. A.; Berk, S. C.; Buchwald, S. L., J. Org. Chem. 1996, 61, 2713.

Erik Kuester

Wayne State University, Detroit, MI, USA

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