Cerium(III) Iodide


[7790-87-6]  · CeI3  · Cerium(III) Iodide  · (MW 520.83)

(organocerium reagents prepared from cerium triiodide and organolithiums have reduced basicity and possess enhanced nucleophilicity toward the carbonyl group; promotes aldol reaction between a-halo ketones and aldehydes; in combination with LiAlH4 is a selective 1,2-reducing agent)

Alternate Name: cerium triiodide

Physical Data: mp 752 °C.

Solubility: sol water, acetone.

Form Supplied in: bright yellow solid.

Preparative Methods: pure CeI3 is prepared by the reaction of metallic cerium with iodine or mercury(II) iodide at high temperature.1,2 Another method is to dissolve CeO2 in aqueous HI solution, adding 12 moles of NH4I per mole of CeO2, and evaporating the mixture to dryness. The mixture is heated in vacuo at 300-350 °C to leave pure CeI3.3 CeI3 is prepared in situ by the reaction of powdered cerium with iodine in THF.4

Handling, Storage, and Precautions: extremely hygroscopic and turns brown when exposed to air owing to the liberation of iodine. This reagent should be stored under nitrogen and handled in a glove bag.

Organocerium Reagents.

Organocerium reagents are prepared by the reaction of CeI3 with organolithium compounds in THF.4 The reagents possess reduced basicity and react with various carbonyl compounds to give the corresponding addition products, even though the substrates are susceptible to enolization, metal-halogen exchange, or 1,4-addition (eqs 1-3) (see also Cerium(III) Chloride).4,5

Aldol Reaction.

Cerium triiodide is used for cross-aldol reaction between a-halo ketones and aldehydes including a,b-unsaturated aldehydes.6 The reaction proceeds in THF at room temperature to afford a,b-unsaturated ketones (eq 4); b-hydroxy ketones are not produced. Ketones, however, do not react under these conditions.

Selective Reductions.

a,b-Unsaturated carbonyl compounds are subject to selective 1,2-reduction by Lithium Aluminum Hydride in combination with CeI3 to give allylic alcohols.7 This method is applicable to a,b-unsaturated aldehydes (eq 5), esters, and lactones that do not undergo selective 1,2-reduction with NaBH4-CeCl3 (see also Cerium(III) Chloride).

1. Jantsch, G.; Grubitsch, H.; Hoffmann, F.; Alber, H. ZC 1929, 185, 49.
2. Asprey, L. B.; Keenan, T. K.; Kruse, F. H. IC 1964, 3, 1137.
3. Taylor, M. D. CRV 1962, 62, 503.
4. Imamoto, T.; Kusumoto, T.; Tawarayama, Y.; Sugiura, Y.; Mita, T.; Hatanaka, Y.; Yokoyama, M. JOC 1984, 49, 3904.
5. Mitchell, D.; Liebeskind, L. S. JACS 1990, 112, 291.
6. Fukuzawa, S.; Tsuruta, T.; Fujinami, T.; Sakai, S. JCS(P1) 1987, 1473.
7. Fukuzawa, S.; Fujinami, T.; Yamauchi, S.; Sakai, S. JCS(P1) 1986, 1929.

Tsuneo Imamoto

Chiba University, Japan

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.