[12082-03-0]  · C9H5ClCrO3  · Tricarbonyl(h6-chlorobenzene)chromium  · (MW 248.59)

(phenyl cation equivalent1)

Alternate Name: (chlorobenzene)chromium tricarbonyl

Physical Data: mp 102-103 °C.

Solubility: sol THF, ether, benzene.

Form Supplied in: yellow crystals; not commercially available.

Preparative Method: prepared from the reaction of chlorobenzene with Hexacarbonylchromium in refluxing dioxane.2

Purification: recrystallized from ether/petroleum ether. Can also be purified by column chromatography on silica gel.

Handling, Storage, and Precautions: slightly air sensitive. Use in a fume hood.

Nucleophilic Substitution.

Treatment of tricarbonyl(chlorobenzene)chromium (1) with various nucleophiles at 25 °C effects nucleophilic substitution of chlorine.1,3 Nucleophiles derived from carbon acids having a pKa > ~20 lead to the arylated products in high yield (eq 1). Tricarbonyl(fluorobenzene)chromium is recommended for phenylation of less reactive nucleophiles. Nucleophilic addition produces the pentadienylchromium complex (2), which converts to the substituted arene complex (3). Oxidative removal of the metal with Iodine produces the free arene (4). Kinetically, nucleophiles attack the ortho and meta positions, and thus nucleophilic addition at low temperature followed by oxidation leads to chlorobenzene derivatives (5) and (6) (eq 2), in addition to (4).4


Treatment of the title reagent with n-Butyllithium produces the lithiated arene complex (7), which is stable at low temperature. Treatment of complex (7) with electrophiles produces the ortho-substituted chlorobenzene derivatives (e.g. 8) (eq 3).5 At temperatures higher that -78 °C, complex (7) undergoes decomposition through a benzyne mechanism.6

Related Reagents.

(h6-Benzene)tricarbonylchromium; Dibenzenechromium; Hexacarbonylchromium.

1. (a) Semmelhack, M. F.; Hall, H. T. JACS 1974, 96, 7091. (b) For a review, see: Semmelhack, M. F. COS 1991, 4, 517.
2. Mahaffy, C. A. L.; Pauson, P. L. Inorg. Synth. 1979, 19, 154.
3. Nicholls, B.; Whiting, M. C. JCS 1959, 551.
4. Semmelhack, M. F.; Hall, H. T. JACS 1974, 96, 7092.
5. Semmelhack, M. F.; Bisaha, J.; Czarny, M. JACS 1979, 101, 768.
6. Semmelhack, M. F.; Ullenius, C. JOM 1982, 235, C10.

James W. Herndon

University of Maryland, College Park, MA, USA

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