Lithium hydroalumination

Tetrahydrofuran is freshly distilled over lithium hydroaluminate. 

A commonly used synthetic method for these substituted phosphines involves the deprotonation of phosphine (or methylphosphine ) by a sodium-ammonia solution, followed by treatment with a methyl halide. More recently, methylphosphine has been produced by the reduction of methyldichloro-phosphine (unfortunately, not a readily available compound) by lithium hydroaluminate. The present method is essentially the deprotonation-methylation procedure, but instead of sodium-ammonia solutions, relatively easily handled KOH-dimethyl sulfoxide suspensions are used. 

Dimethylphosphine has been prepared by alkylation of phospho-nium iodide with methjd iodide and by reductive cleavage of phosphorus sulfides with methyImagnesium bromide. Diethyl-, dibutyl-, and dicyclohexylphosphines have been prepared by reduction of the corresponding tetraalkyldiphosphine disulfides with lithium hydroaluminate in ether. This latter method gives dialkylphosphines uncontaminated by mono- and trialkylphosphines. 

The distillation flask is charged udth 49.0 g. (0.26 mole) of tetramethyldiphosphine disulfide and 10.3 g. (0.27 mole) of lithium hydroaluminate, and the flask is flushed with nitrogen. Four hundred milliliters of anhydrous dioxane (distilled from sodium) is added all at once through the addition funnel. The distillation column is adjusted to provide total reflux of the dimethylphosphine, and the reaction mixture is stirred for 4 hours. Moderately rapid hydrogen evolution occurs, and the... 

Anhydrous diethyl ether, freshly obtained from a commercial supplier, is preferred for the reactions involving lithium hydro-aluminaie. The ether must be peroxide-free. Carbon dioxide must be rigorously excluded from these reaction systems. Explosions have been observed during evaporation of solutions of aluminum hydride and related compounds when carbon dioxide is present as an impurity.If it is necessary to concentrate ether solutions of lithium hydroaluminate by distillation, the following precautions must be observed. A large fluid volume must be maintained in the distillation flask such solutions should never be concentrated so far that very little ether remains in the reaction flask. Distillations must be effected in a protective atmosphere. Cyclic ethers, and especially tetrahydropyran solutions of lithium hydroaluminate, present a far greater explosion risk than diethyl ether solutions. 

A solution of fresh lump lithium hydroaluminate in diethyl ether is prepared by stirring 75 g. (1.98 moles, 25% excess) of... 

Silane, germane, and stannane can be synthesized by the reduction of a variety of silicon, germanium, or tin compounds with active metal hydrides. The general method described below, involving the lithium hydroaluminate (LiAlHi) reduction of silicon tetrachloride and tin (IV) chloride, is convenient for the eflficient preparation of 1-50 mmoles of silane and stannane. The method is easily adapted to the synthesis of the deuterio compounds, i.e., silane-d4, germane-dt, and stannane-d4, by... 

Hydroalumination of 1-chloro-l-alkynes. Lithium aluminum hydride adds to 1-chloro-l-alkynes (1) regio- and stereoselectively to form the a-chlorovinyl alanates 2, which are moderately stable at 0°C. On methanolysis they are converted into (E)-l-chloro-l-alkenes (3). They can also be converted into (Z)-l-bromo-l-chloro-l-alkenes (5) and into (Z)-l-chloro-l-iodo-l-alkenes (6). 

With the purpose of employing a more soluble form of complexed lithium hydride in such a process, Ziegler and Gellert heated ethylene in ether under pressure at 120-140 °C with LAH, which had been prepared for the first time by Schlesinger and coworkers. To Ziegler s gratification LAH was smoothly converted into lithium tetraethylaluminate (10), which could be isolated in high yield as a crystalline adduct. As proof of structure, the same adduct was also synthesized by the admixture of the lithium and aluminum ethyl derivatives in a 1 1 ratio (Scheme 2). This study represents the first authenticated instance of hydroalumination. 

Lithium trialkylaluminum hydrides, such as lithium diisobutyl(methyl)aluminum hydride (15), which can be readily prepared by the interaction of diisobutylaluminum hydride with methyllithium in DME, are useful for the anti hydroalumination of internal alkynes (equation 9). ... 

As a class alkynes are much more reactive in hydroalumination than are alkenes. Hence, both terminal and internal alkynes react at feasible rates with both dialkylaluminum hydrides in alkanes and lithium aluminum hydrides (LiAlRnH4-n) in ethers. Selected examples of such additions are presented in Table 2. With alkyl or aryl substituents, it should be noted that R2AIH adds in a kinetically syn manner, (5 equation 2) and (7 equation 3), and LAH yields the anti adduct (14 equation 6). 

This study opens up the possibility that hydroaluminations by LAH or LiAlBu 2MeH actually occur by the dissociation of such complex hydrides into AIH3 and R2AIH at higher temperatures. Steps of conventional syn hydroalumination, aluminum exchange and vinylic lithium isomerization could then lead to the anti adduct (Scheme 10). 

HYDROALUMINATION Dichlorobis-(cyclopentadienyl)titanium. Dichloro-bis(cyclopentadienyl)zirconium . Lithium aluminum hydride-Dichlorobis(cyclo-pentadienyl)zirconium. Borane-Di-methyl sulfide. 

Hydroalumination of enyne 15 with Dibal and conversion to the alanate with n-butyl lithium, followed by treatment with (7 )-propylene oxide afforded... 

Hydroalumination is a less often used reaction but the resulting organoalanes are more reactive than either organosilanes or boranes and less reactive than the traditional organometallic reagents derived from lithium or magnesium. Various aluminum hydrides are commercially available or readily prepared by reduction of aliuninum halides [10]. 

Hydroalumination of alkynes. The hydride reacts with alkynes in a hydrocarbon solvent by cis addition to yield a tran.t-vinylalane (1) from 1-alkynes and a cis-vinylalane from disubstituted alkynes. Treatment of the vinylalane with methyl-lithium in ether in a 1 1 ratio to give an ate complex (2) followed by carbonation... 

Other reducing agents proposed are tin (for the preparation of / -chloro-thiophenol,524 tin(n) chloride (for the preparation of 4,4 -biphenyldithiol),525 iron powder (for the preparation of o- and /7-thiocresol),526 and lithium tetra-hydroaluminate (for the preparation of 1-butanethiol).527... 

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