Indium(I) iodide

[13966-94-4]  · (MW 241.72)

Physical Data: mp 365 °C; bp 715 °C; d 5.32 g cm-3.

Solubility: sparingly soluble in common organic solvents.

Form Supplied in: red plates or beads.

Preparative Methods: heating of stoichiometric amounts of indium metal and iodine at 400 °C for 24 h,1 reaction of activated indium metal with iodine in refluxing xylene,2 from In + InI33 or from In[InI4] in diethyl ether.4

Handling, Storage, and Precautions: store in the dark under nitrogen.

Allylations

The oxidative addition of InI to alkyl halides provides a convenient route to alkylindium dihalides.1,3 Allyl iodide provides allylindium diiodide, which couples with various carbonyl compounds to give the corresponding homoallylic alcohols.5 The yields are generally high, even for carbonyl compounds bearing an active hydrogen such as ethyl acetoacetate and salicylaldehyde (1). With a,b-unsaturated carbonyl compounds, 1,2-addition products are obtained. In contrast to the case with metallic indium, the InI-mediated crotylation of aldehydes generally yields a mixture of a- and g-coupling products in a 55:45 ratio. Crotyl bromide and cinnamyl bromide also give the a- and g-coupling products. The reactions with allylic bromides are slower than with allylic iodides and require refluxing in THF, THF being the solvent of choice since DMF gives less satisfactory yields. It has been reported that InI reacts with diallylmercury in water to give allylindium(I), which couples with 2-methylcyclohexanone to give the corresponding homoallylic alcohol in 99% yield with the ratio of 84:16 in favor of the trans isomer (2).6

Reformatsky-type Reactions

Indium(I) iodide is effective for Reformatsky-type reactions.5 Various carbonyl compounds give the corresponding b-hydroxy esters by reaction of ethyl iodoacetate and InI in THF; no reaction occurs with ethyl bromoacetate. a,b-Unsaturated compounds undergo exclusive 1,2-addition and a hydroxyl group in the substrate is compatible with the reaction conditions (3).

Palladium-catalyzed Allylations

Allyl acetate and InI react with benzaldehyde in the presence of a catalytic amount (5 mol %) of Pd(PPh3)4 to give the corresponding homoallylic alcohol in high yield (4).7 The reaction proceeds via a p-allylpalladium(II) complex followed by a reductive transmetalation with InI to give an allylindium compound. The reaction can be carried out in a variety of solvents including THF, 1,3-dimethyl-2-imidazolidinone (DMI), and dichloromethane. Protic solvents such as water, methanol, and ethanol can also be used, though somewhat longer reaction times are needed for the alcoholic solvents. Non-polar solvents, such as diethyl ether, benzene, and hexane, give poor yields of the product. A variety of allylic substrates, such as allyl chloride, vinyloxirane, and acrolein acetal, can be employed. However, g,g-disubstituted allylic acetate is not converted to the corresponding allylic indium reagent. Intramolecular cyclization of the acetate to the macrocyclic syn,trans-alcohol has been achieved highly stereoselectively (5).8

Indium(I) iodide-palladium(0)-mediated allylations of aldehydes with N-activated vinylaziridines, as well as allylic acetates, proceed with regio- and stereoselectivity irrespective of the chirality of the allylic carbon bearing a vinyl group to provide syn,syn-2-vinyl-1,3-amino alcohols possessing three contiguous chiral centers in good yields (6).9

Palladium-catalyzed Propargylation

Transmetalation of an allenylpalladium intermediate with InI proceeds stereoselectively. Propargyl mesylate (R)-1 (ee >95%) reacts with cyclohexanecarbaldehyde in the presence of InI to give racemic adducts in 66% yield as a 96:4 mixture of anti/ syn isomers via an allenylindium intermediate.10 An adduct of 95% ee (anti/syn 95:5) is obtained in 76% yield from (R)-1 and InI in the presence of 5 mol % Pd(dppf)Cl2 as the catalyst precursor (7). The addition is most efficient in 3:1 THF-HMPA or 1:1 THF-DMPU. Pd(OAc)2·PPh3 also serves as an efficient catalyst precursor. Anti/syn ratios are excellent with a-branched aldehydes, but only modest with unbranched and conjugated aldehydes. Addition to PhCHO affords a nearly 1:1 mixture of the anti/syn adducts. The reaction of a matched combination of 1 with chiral a-oxgenated aldehyde (2) proceeds with high stereoselectivity, giving the anti,anti-adduct, whereas a mismatched combination affords a mixture of diastereoisomers (8).11

Allenylindium reagents bearing a protected amino group are effectively formed by treatment of 2-ethynylaziridines with InI, H2O, and catalytic Pd(0). Subsequent reaction of the indium reagents with aldehydes affords 2-ethynyl-1,3-amino alcohols stereoselectively (9).12

Preparation of gem-diindium species

The reaction of InI and InCl3 in a dichloromethane/toluene/N,N,N,N-tetramethylethanediamine (TMEDA) mixture yields the bis(TMEDA) adduct of ClIInCH2InCl2 as a yellow precipitate (10).13

Related Reagents.

InCl3.


1. Gynane, M. J. S.; Waterworth, L. G.; Worrall, I. J., J. Organomet. Chem. 1972, 43, 257.
2. Chao, L.-C.; Rieke, R. D., J. Organomet. Chem. 1974, 67, C64.
3. Poland, J. S.; Tuck, D. G., J. Organomet. Chem. 1972, 42, 315.
4. Freeland, B. H; Tuck, D. G., Inorg. Chem. 1976, 15, 475.
5. Araki, S.; Ito, H.; Katsumura, N.; Butsugan, Y., J. Organomet. Chem. 1989, 369, 291.
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7. Araki, S.; Kamei, T.; Hirashita, T.; Yamamura, H.; Kawai, M., Org. Lett. 2000, 2, 847.
8. Marshall, J. A.; McNulty, L. M.; Zou, D., J. Org. Chem. 1999, 64, 5193.
9. Takemoto, Y.; Anzai, M.; Yanada, R.; Fujii, N.; Ohno, H.; Ibuka, T., Tetrahedron Lett. 2001, 42, 1725.
10. (a) Marshall, J. A.; Grant, C. M., J. Org. Chem. 1999, 64, 696. (b) Marshall, J. A.; Grant, C. M., J. Org. Chem. 1999, 64, 8214.
11. Marshall, J. A.; Chobanian, H. R., J. Org. Chem. 2000, 65, 8357.
12. (a) Ohno, H.; Hanaguchi, H.; Tanaka, T., Org. Lett. 2000, 2, 2161. (b) Ohno, H.; Hamaguchi, H.; Tanaka, T., J. Org. Chem. 2001, 66, 1867.
13. Khan, M. A.; Peppe, C.; Tuck, D. G., Organometallics 1986, 5, 525.

Shuki Araki & Tsunehisa Hirashita

Nagoya Institute of Technology, Nagoya, Japan



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