Aluminum hydrides, 155. reacting with

Sodium borohydride and lithium aluminum hydride react with carbonyl compounds in much the same way that Grignard reagents do except that they function as hydride donors rather than as carbanion sources Figure 15 2 outlines the general mechanism for the sodium borohydride reduction of an aldehyde or ketone (R2C=0) Two points are especially important about this process... 

Lithium aluminum hydride reacts with many inorganic and organic neutral ligands, forming coordinated alumina complexes associated with lithium ions ... 

When lithium aluminum hydride reacts with N-acylpyrazoles, the CN bond is hydrogenolyzed and aldehydes are produced in good yield. Ried even recommends this as a method of preparing otherwise inaccessible aldehydes.730,781 Certain labile a-amino aldehydes were... 

Lithium tetrakis[methyltelluro]aluminate, prepared from methanetellurol and lithium aluminum hydride, reacted with silyl, germyl, and stannyl halides at low temperatures to produce, for instance, methyl silyl tellurium derivatives1. 

Aluminum forms a number of borohydride anions with 3c-2e bonds, e.g., [AlH (BH4)4-n] (n = 0, 1, 2, 3). The anion [Al(i72-BH4)4] is a rare example of 8-coordinate Al111.22 Lithium aluminum hydride reacts with ammonium salts and amines to give Al amides 23... 

Studebaker identified the use of lithium aluminium hydride as a chemical probe.Under the right conditions it cleaves poly- and disulfide bonds, leaving the monosulfide intact. Lithium aluminum hydride reacts with polysulfides in an etheral solvent at moderate temperatures and then with a weak acid, the terminal groups are liberated as thiols and interior sulfur atoms are converted to hydrogen sulfide.Lithium... 

Finally, bis(dialkylamino)aluminum hydrides react with unsaturated carbon-carbon bonds. In the presence of catalytic amounts of (h -C5H5)2TiCl2 the reaction is complete within 10 min (93 % yieldf - ... 

Ziegler and Gellert (6) in 1949 showed that aluminum hydride reacts with ethylene at 60-80 °C to yield triethylaluminura. At 100-120 C reaction with additional ethylene leads to formation of higher alkyls of aluminum (Reaction 1). At temperatures above 120 C higher aluminum alkyls react with ethylene through a... 

Although the low-pressure polymerization of ethylene in the presence of a Ziegler catalyst is a catalytic process, the growth reaction of aluminum hydride or a corresponding alkylaluminum with ethylene occurs as an organometallic synthesis 29 at 60-80° aluminum hydride reacts with ethylene to yield tri-ethylaluminum ... 

Lithium aluminum hydride reacts with metal halides of silicon, germanium, tin, arsenic, and antimony to form hydrides, which are flammable and toxic ... 

Amides such as A/ AT-dimethylcyclohexanecarboxamide (23 see Chapter 20, Section 20.7) are also carboxylic acid derivatives. Sodium borohydride does not reduce an amide. Lithium aluminum hydride reacts with 23, but the product is an amine rather than an alcohol—specifically, l-(iV, Ar-dimeth-ylaminomethyl)cyclohexane, 24. Amine 24 is isolated in 88% yield. Although the mechanism will not be discussed here in a formal manner, delivery of hydride to the acyl carbon of the C=0 is followed by formation of an imine (C=N) that is further reduced to the amine. Nitriles such as octanenitrile (25) also react with LiAlH4 in one experiment, reduction of 25 gave amine 26 (1-aminopentane) in 92% isolated yield. This reduction also proceeds by delivery of hydride to the carbon of the nitrile, generating an imine that is further reduced to the amine. In general, NaBH4 does not reduce amides or nitriles. 

Consider the reaction of lithium aluminum hydride with an ester (Figure 15.34). The hydride will attack the carbonyl to give a tetrahedral intermediate, just as with aldehydes and ketones. However, this tetrahedral intermediate does not wait around to be protonated but loses ethoxide to give an aldehyde. We already know how lithium aluminum hydride reacts with aldehydes, and our final product, after work-up, is a primary alcohol. 

Lithium aluminum hydride reacts violently with water and alcohols, so it must be used in solvents such as anhydrous diethyl ether or tetrahydrofuran. Following reduction, a separate hydrolysis step is required to liberate the alcohol product ... 

The starting material is prepared by reacting 1-benzyl-4-piperidone with aniline, reducing the condensation product with lithium aluminum hydride, reacting the product thus obtained with propionic anhydride, than hydrogen. 

Alkylaluminum hydrides react with metal hydrides to eliminate RH, and if the metal fragment is bonded to a cyclopentadienyl ring, H2 may also be eliminated to produce a new aluminum-carbon bond, as illustrated in Equations (54)—(57).11,84,83 The hydride-bridged Al-Mo bond in 52 is considerably longer than the direct Al-Mo interaction (294.4(2) vs. 263.6(2) pm).83 A similar reaction with (C5H4R)Co(G2H4)2 yields a mixture of 5382... 

Lithium aluminum hydride reacts violently with water evolving hydrogen. About 2.36L H2 is evolved per 1 g of the compound at NTP. 

Lithium hydride reacts with aluminum hydride forming lithium aluminum hydride, a powerful reducing agent ... 

Lithium aluminum hydride reacts readily with pyridine to yield lithium tetrakis-(A/-dihydropyridyI)aluminate, LiAI(NR2)4 (structures 108 and 109).152 The NR2 groups represent 1,4-dihydro- and/or, 1,2-dihydropyridyl residues. The two diverse N-ligands may be part of the same molecule in association with the A1 metal. The structure of the adduct has been investigated by IR and NMR spectroscopy and by deuterium-labeling experiments. The latter approach has been used to determine the 1,2 to 1,4 ratio, which is found to be close to 1 2 when the reaction is carried out at room temperature. The N—A1 bond is assumed to be covalent, though of a markedly more ionic character as compared to the N—H bond in dihydropyridines.152... 

Lithium Aluminum Hydride. Reacts violently with trifluoroacetic acid.2 Dimethyl Sulfoxide. Reacts explosively with trifluoroacetic anhydride.3... 

On the basis of what we have already learned about the reactions of lithium aluminum hydride with aldehydes and ketones (Chapter 18) and the mechanisms presented so far in this chapter, we can readily predict the product that results when hydride reacts with a carboxylic acid derivative. Consider, for example, the reaction of ethyl benzoate with lithium aluminum hydride. As with all of the reactions in this chapter, this reaction begins with attack of the nucleophile, hydride ion, at the carbon of the carbonyl group, displacing the pi electrons onto the oxygen (see Figure 19.7). Next, these electrons help displace ethoxide from the tetrahedral intermediate. The product of this step is an aldehyde. But recall from Chapter 18 that aldehydes also react with lithium aluminum hydride. Therefore, the product, after workup with acid, is a primary alcohol. 

Although the hydrides having the general formula MH3 are known, only A1H3 is of much importance. Gallium hydride, GaH3, is so unstable that it decomposes at room temperature. Aluminum hydride reacts violently with water ... 

Lithium aluminum hydride reacts instantly with excess water or ethanol with liberation of 4 moles of hydrogen. Hochstein in a quantitative study of lithium... 

Aluminum hydrides react violently with protic solvents and acids (path p.t.) to produce hydrogen gas and can be used only in aprotic media, like diethyl ether. The borohydrides, BH4 are weaker sources and react much more slowly with protic solvents than do the aluminum hydrides. After the first step, the trivalent aluminum or boron species is now electron deficient and can react with a lone pair donor to form a tetravalent Lewis acid-base salt (path An) that can donate hydride again. This repeats until all hydrogen-metal bonds have been used. 

When organoaluminum hydrides react with acetylenes, a variety of products is formed not only mono- and di-addition to the triple bond, but also replacement of the ethynyl-hydrogen with removal of hydrogen, take place.254 The last of these reactions, which is a metallation, becomes the main reaction when a complex aluminum hydride MA1H4 (M = Li, Na, or K) reacts with an acetylene, so that complex acetylenylaluminates MA1(C =CR)4 can be obtained in this way.255... 

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