[1291-32-3]  · C10H10Cl2Zr  · Dichlorobis(cyclopentadienyl)zirconium-Zinc-Dibromomethane  · (MW 292.32) (Zn)

[7440-66-6]  · Zn  · Dichlorobis(cyclopentadienyl)zirconium-Zinc-Dibromomethane  · (MW 65.37) (CH2Br2)

[74-95-3]  · CH2Br2  · Dichlorobis(cyclopentadienyl)zirconium-Zinc-Dibromomethane  · (MW 173.85)

(methylenating reagent for aldehydes, ketones, and enones1)

Physical Data: Cp2ZrCl2: mp 245 °C. Zn: mp 419.5 °C; d 7.14 g cm-3. CH2Br2: mp -52 °C; bp 96-98 °C; d 2.477 g cm-3.

Solubility: Cp2ZrCl2: sol THF, CH2Cl2, and CHCl3. Zn: insoluble in organic solvents. CH2Br2: miscible in common organic solvents.

Form Supplied in: Cp2ZrCl2: white crystalline powder; widely available. Zn: metallic gray granules or powder. CH2Br2: clear, colorless liquid.

Preparative Method: prepared in situ.

Handling, Storage, and Precautions: Cp2ZrCl2: store under N2. Zn: flammable solid. CH2Br2: harmful if inhaled or swallowed; may cause irritation.

The reagent is prepared in situ by the addition of Dibromomethane to a mixture of Zinc, Dichlorobis(cyclopentadienyl)zirconium, and the aldehyde or ketone in dry THF. Typical reaction time is 3 h at room temperature.1,3 The yield of methylenated products is good with enones, aldehydes, and ketones (Table 1), but the reagent will not methylenate lactones or esters.1

The reagent has also been used on readily enolizable ketones in the presence of hydroxyl and secondary amide protons (eq 1) where the Wittig reaction and Peterson alkenation were not successful.2

1. Tour, J. M.; Bedworth, P. V.; Wu, R. TL 1989, 30, 3927.
2. (a) Hartmann, M.; Zbiral, E. TL 1990, 31, 2875; (b) Hartmann, M.; Christian, R.; Zbiral, E. M 1991, 122, 111.
3. Beckwith, A. L. J.; Zimmermann, J. JOC 1991, 56, 5791.

James M. Tour & Peter V. Bedworth

The University of South Carolina, Columbia, SC, USA

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