Indium chloride - aluminum

Lewis acids used for acylation of allylsilanes with acid chlorides include titanium and tin tetrachlorides, aluminum, gallium and indium trichlorides and zinc dichloride, and boron trifluoride for reactions with acid anhydrides. Although gallium and indium chlorides have been used successfully in catalytic (ca. 2 mol %) amounts, most frequently aluminum chloride has been used as catalyst, with titanium tetrachloride also commonly employed, both in molar quantities. With these catalysts, acylations can often be carried out at low temperatures, and with short reaction times. 

Fig. 2-15 [72] presents a chromatogram for analytical separation of radioactive zinc and indium chlorides (a) and indium and terbium chlorides (b) on an empty glass column (10 m x 1 mm). The separation was accomplished by using aluminum chloride vapors in a stream of helium as eluent. 

The regiochemistry of the reaction is strongly influenced by the identity of the Lewis acid catalyst employed as well as by the reaction temperature. For example, with indium chloride in place of aluminum chloride, compound 5 is obtained in higher selectivity (total yield 58%, 5 6 7=88 9 3). On increasing the temperature in the reaction with indium chloride, the product composition is changed and compound 6 is the predominant one (total yield 57%, 5 6 7=0 84 16). Quite similar results are achieved with iron trichloride, tin tetrachloride, and zinc chloride, while in the case of antimony pentachloride and titanium tetrachloride, compound 5 is the major product. 

Instead of using a stoichiometric amount of indium, the allylation of aldehydes and ketones can be carried out by using catalytic amounts of indium(III) chloride in combination with aluminum or zinc metals in a THF/water (5 2) mixture at room temperature. The reaction is much slower relative to the same reaction mediated by a stoichiometric amount of indium. When the reaction was carried out in anhydrous THE, the yield dropped considerably, while side reactions (such as reducing to alcohol) increased. The combinations of Al/InCh or Zn/InCh gave comparable results. The indium-mediated allylation carried out with allylstannanes in combination with indium chloride in aqueous medium was reported by Marshall and Hinkle. Allyl indium was proposed as the reaction intermediate. Various allylic compounds undergo palladium-catalyzed allylation of carbonyls via the transmetala-tion of r -allylpalladium(II) intermediates with indium in the presence of indium trichloride in aqueous media. °... 

In contrast to the non-trivial routes for the syntheses of pure aluminum(I) or gallium(I) subhalides, indium(I) chloride or bromide can simply be prepared by melting mixtures of elemental indium and indium trihalides [39]. When these in-dium(I) halides were treated with bulky alkyllithium compounds, deep violet orga-noelement indium dusters (13-18) were obtained [Eq. (3)] [40, 41]. 

One of the first published cluster compounds of the heavier group 13 elements was the closo-dodecaaluminate K2[Ali2iBui2] 54 (Figure 2.3-10) [79], which possesses an almost undistorted icosahedron of 12 aluminum atoms with short Al-Al distances (268-270 pm). Up until today, it remained the only homonuclear cluster compound of the elements aluminum to indium which, with respect to structure and cluster electron count, is completely analogous to any boronhydride (see Chapters 1.1.2, 1.1.3, 1.1.5.2, and 2.1.5.6) (in this case doso-[Bi2H12]2 ). Compound 54 was formed in small quantities by the reaction of di(isobutyl)aluminum chloride with potassium and was isolated as dark red crystals (Figure 2.3-10). 

In indium-mediated reactions, a catalytic use of expensive indium is desirable from an economical standpoint, and it has been achieved in combination with more electron-positive metals. Thus, allylation of aldehydes and ketones, as well as prenylation of 2-chlorobenzoquinone, has been performed by using metallic aluminum or zinc in combination with a catalytic amount of indium(m) chloride.63 Also, allylation of aldehydes and ketones with allyl bromide is carried out with a catalytic amount of indium powder (from 0.01 to 0.1 equiv.) in THF in the presence of manganese and chlorotrimethylsilane as the reducing and oxophilic agents, respectively (Scheme 2). 64,65... 

Hard Lewis acid chloroaluminate ionic liquids show intense catalytic activity in the Friedel-Crafts acylation reaction however, they suffer from the same issues as anhydrous aluminum chloride. i Of particular interest to these reactions, aluminum chloride may be replaced by indium trichloride to form chloroindate(III) ionic liquids. The advantage of using indium trichloride compared with aluminum chloride is represented by its hydrolytic stability and reduced oxophilicity. Chloroindate(III) ionic liquids are synthesized by mixing l-butyl-3-methylimidazolium chloride [C4mim]Cl with anhydrous indium trichloride at 80°C. In the benzoyla-tion of anisole with benzoic anhydride (BAN) at 80°C, the best yield of... 

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