(h6-Benzene)tricarbonylchromium

[12082-08-5]  · C9H6CrO3  · (h6-Benzene)tricarbonylchromium  · (MW 214.14)

(phenyl cation equivalent1)

Alternate Name: (benzene)chromium tricarbonyl.

Physical Data: mp 161.5-163 °C.

Solubility: sol THF, ether, benzene.

Form Supplied in: yellow crystals.

Preparative Method: for cases where large quantities are needed, it is easily prepared from the reaction of benzene with Hexacarbonylchromium.2

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

Handling, Storage, and Precautions: slightly air sensitive.

Nucleophilic Substitution.

Treatment of (benzene)tricarbonylchromium (1) with various nucleophiles at 25 °C, followed by Iodine oxidation, effects nucleophilic substitution of hydrogen.1 Nucleophiles derived from carbon acids having a pKa > ~22 lead to the arylated products (e.g. 3) in high yield (eq 1). Nucleophilic addition produces the pentadienylchromium complex (2) which converts to the substituted arene upon oxidation. Alternatively, treatment of complex (2) with Trifluoroacetic Acid leads to the cyclohexadiene derivatives (4-6) (eq 2).3 Alkyllithium reagents and Grignard reagents are not arylated under these conditions due to competing deprotonation and addition to the carbonyl ligands.

Nucleophilic Addition/Carbonylation.

Nucleophilic addition to (benzene)tricarbonylchromium, followed by treatment with alkyl iodides in the presence of carbon monoxide, leads to trans-5-acyl-6-substituted-1,3-cyclohexadiene derivatives (e.g. 7) (eq 3).4 Only very reactive carbanions such as 2-lithio-2-alkyl-1,3-dithiane derivatives will undergo this transformation. When less reactive carbanions are employed, the nucleophile undergoes direct alkylation by the alkyl iodide without incorporation of the benzene ring.

Lithiation.

Treatment of (benzene)tricarbonylchromium with n-Butyllithium produces the lithiated arene complex (8). Treatment of complex (8) with electrophiles produces the monosubstituted benzene complexes (e.g. 9) (eq 4),5,6 which are converted to the free arenes by treatment with iodine or Cerium(IV) Ammonium Nitrate. (Benzene)tricarbonylchromium thus appears to be substantially more acidic than benzene.

Hydrogenation Catalyst.

(Benzene)tricarbonylchromium catalyzes the hydrogenation of 1,3-dienes (eq 5).7 The major product is the (Z)-alkene resulting from 1,4-addition of hydrogen. Isolated double bonds are not hydrogenated using this catalyst.


1. (a) Semmelhack, M. F.; Hall, H. T. Jr.; Yoshifuji, M.; Clark, G. JACS 1975, 97, 1247. (b) For a review, see Semmelhack, M. F. COS 1991, 4, 517.
2. Mahaffey, C. A. L.; Pauson, P. L. Inorg. Synth. 1979, 19, 154.
3. Semmelhack, M. F.; Hall, H. T., Jr.; Yoshifuji, M.; Clark, G. JACS 1976, 98, 6387.
4. Kündig, E. P.; Simmons, D. P. CC 1983, 1320.
5. Semmelhack, M. F.; Bisaha, J.; Czarny, M. JACS 1979, 101, 768.
6. Card, R. J.; Trahanovsky, W. S. JOC 1980, 45, 2555.
7. Frankel, E. N.; Butterfield, R. O. JOC 1969, 34, 3930.

James W. Herndon

University of Maryland, College Park, MD, USA



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