Hydrides of aluminum

The chemistry has also been extended to related formamidinato metal hydrides of aluminum and gallium. In the case of aluminum, LiAlH4 and AlH3(NMe3) served as metal hydride precursors. Scheme 39 summarizes the synthetic routes. The complexes thus formed are thermally very stable. °... 

Boron differs from aluminum in showing almost no metallic properties and its resemblance to silicon is greater. Both boron and silicon form volatile, very reactive hydrides the hydride of aluminum is a polymeric solid. The halides (except BF3) hydrolyze to form boric acid and silicic acid. The oxygen chemistry of the borutes and silicates also has certain resemblances. 

Similarly, reactions of metallic hydrides of aluminum or boron, in which hydride is transferred to the carbon [Eq. (3) [6] or (4) [7,8]], are also considered reductions [8] ... 

The induction period can also be shortened or even eliminated by the addition of reducing agents either to the catalyst or to the reactor. Particularly effective are the alkyls or hydrides of aluminum, boron, zinc, lithium, magnesium, etc. When added in ppm quantities, they can eliminate the induction time of Cr(VI)/silica and also raise the steady-state polymerization rate. Some metal alkyls can remove poisons and redox byproducts. All metal alkyls no doubt help reduce the Cr(VI), perhaps to Cr(IV). And some may even help alkylate the chromium, similar to the chemistry of Ziegler catalysts. Figure 16 shows how triethylaluminum cocatalyst can be used to shorten the induction time [52],... 

Aluminum hydride, AIH3, seems to be the unique binary hydride of aluminum. This is indeed a dramatic contrast to the extensive hydride chemistry of boron. In fact, this example is remarkably recent as a well-defined compound because solvents useful in its preparation tend to remain bound in the crystals. The hydride ean form at least six crystalline modifications. The most stable form, the a form, has a saltlike structure, with aluminum oc-... 

Matrix isolation methods have been used to prepare the binary aluminum hydride AI2H6 [7]. Prior to this work, the only known hydride of aluminum was the polymeric (A1H3) solid. The dimer was formed following the reaction of laser-ablated A1 atoms with pure H2 during co-deposition at 3.5 K, followed by radiation with ultraviolet light and heating to 6.5 K. AI2H6 was identified by seven new infrared absorptions that were accurately predicted by quantum mechanical simulations. Many other examples can be found in [8]. 

Preparation. Commercial manufacture of LiAlH uses the original synthetic method (44), ie, addition of a diethyl ether solution of aluminum chloride to a slurry of lithium hydride (Fig. 2). 

Reactions of HCl and nitrides, borides, silicides, germanides, carbides, and sulfides take place at significant rates only at elevated (>650° C) temperatures. The products are the metal chlorides and the corresponding hydrides. The reactions most studied are those involving nitrides of aluminum, magnesium, calcium, and titanium, where ammonia (qv) is formed along with the corresponding metal chloride. 

Oxygen-containing azoles are readily reduced, usually with ring scission. Only acyclic products have been reported from the reductions with complex metal hydrides of oxazoles (e.g. 209 210), isoxazoles (e.g. 211 212), benzoxazoles (e.g. 213 214) and benzoxazolinones (e.g. 215, 216->214). Reductions of 1,2,4-oxadiazoles always involve ring scission. Lithium aluminum hydride breaks the C—O bond in the ring Scheme 19) 76AHC(20)65>. 

Johnson and Whitehead have further shown that the reductive elimination of the pyrrolidine group from the pyrrolidine enamine of 2,4-dimethyl-cyclohexanone (16), which involved treating it with a mixture of lithium aluminum hydride and aluminum chloride (9), gave the trans isomer of 3,5-dimethyl-/l -cyclohexene (17) which on subsequent hydrogenation on a platinum catalyst led to the // onr-3,5-dimethylcyclohexane (18). 

R" = CH20H). The use of sodium borohydride in place of lithium aluminum hydride did not lead to ring closure but to 3-[j8-(A-l,2,3,4-tetrahydroisoquinolyl)ethyl]indole derivatives (53). Reductive cyclization by means of lithium aluminum hydride of the j8-(3-indolyl)ethyl-l-isoquinoline (52) to the pentacyclic tetrahydro-j8-carboline 49 (R = R = R" = H) has been reported. Strong acid alone sufficed to convert 52 into 54, the 0x0 derivative of 49. ... 

In a 500-ml three-necked flask, equipped with a mechanical stirrer, a dropping funnel, and a reflux condenser (drying tube), is placed 6.7 g (0.05 mole) of anhydrous aluminum chloride. The flask is cooled in an ice bath, 50 ml of dry ether is slowly added from the dropping funnel, and the mixture is stirred briefly. Powdered lithium aluminum hydride (0.6 g) is placed in a 100-ml flask fitted with a condenser, and 20 ml of dry ether is added slowly from the top of the condenser while the flask is cooled in an ice bath. The mixture is refluxed for 30 minutes then cooled, and the resulting slurry is transferred to the dropping funnel on the 500-ml flask. The slurry is added to the stirred ethereal solution of aluminum chloride over 10 minutes, and the reaction mixture is stirred for an additional 30 minutes without cooling to complete the formation of the mixed hydride . 

The Mecrwein-Ponndoi f-Verlev reaction involves reduction of a ketone by treatment with an excess of aluminum triisopropoxide. The mechanism of the process is closely related to the Cannizzaro reaction in that a hydride ion acts as a leaving group. Propose a mechanism. 

Butyl alcohol in synthesis of phenyl 1-butyl ether, 46, 89 1-Butyl azidoacetate, 46, 47 hydrogenation of, 46, 47 1-Butyl chloroacetate, reaction with sodium azide, 46, 47 lre l-4-i-BUTYLCYCLOHEXANOL, 47,16 4-(-Butylcyclohexanonc, reduction with lithium aluminum hydride and aluminum chloride, 47, 17 1-Butyl hypochlorite, reaction with cy-clohexylamine, 46,17 l-Butylthiourea, 46, 72... 

The synthesis of the right-wing sector, compound 4, commences with the prochiral diol 26 (see Scheme 4). The latter substance is known and can be conveniently prepared in two steps from diethyl malonate via C-allylation, followed by reduction of the two ethoxy-carbonyl functions. Exposure of 26 to benzaldehyde and a catalytic amount of camphorsulfonic acid (CSA) under dehydrating conditions accomplishes the simultaneous protection of both hydroxyl groups in the form of a benzylidene acetal (see intermediate 32, Scheme 4). Interestingly, when benzylidene acetal 32 is treated with lithium aluminum hydride and aluminum trichloride (1 4) in ether at 25 °C, a Lewis acid induced reduction takes place to give... 

To achieve higher energy in solid proplnts the most notable advances were achieved with the addition of aluminum and beryllium to both double-base and composite proplnts. Energy in this case is commonly equated to high specific impulse. Later developments added aluminum hydride and beryllium hydride to this list. In Table 16, the specific impulse performance of proplnts using AP with various metals and hydrides is compared to those systems without these additives (Ref 43)... 

To mitigate the problem, a diffusion barrier is incorporated between the aluminum and the silicon (see Sec. 5 below). It is also possible to replace aluminum by alloys of aluminum and copper or aluminum and silicon, which have less tendency to electromigration. These alloys are usually deposited by bias sputtering. However, they offer only a temporary solution as electromigration will still occur as greater densities of circuit elements are introduced. It was recently determined that improvements in the deposition of aluminum by MOCVD at low temperature with a dimethyl aluminum hydride precursor may reduce the problem.bl... 

Another study (200) presented IR data for a number of hydride and deuteride species. Using matrix-isolation spectroscopy in conjunction with a hollow-cathode, sputtering source (the apparatus for which is shown in Fig. 36), the IR-active vibrations of the diatomic hydrides and deuterides of aluminum, copper, and nickel were observed. The vibra-... 

In 1968, Eisch and Foxton showed that nickel(II) salts enhance the rate of BU2AIH addition to internal alkynes by a factor of ca. 1000 compared to the process in the absence of a catalyst [26]. Similar catalytic activity of nickel compounds was found for the addihon of aluminum hydrides to alkenes. 

Derivatives of aluminum hydrides in which one or more of the hydrides is replaced by an alkoxide ion can be prepared by addition of the calculated amount of the appropriate alcohol. 

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