Aluminum alkyls boron hydrides

Aluminum alkyls are stronger Lewis acids than the trialkyls of boron and galUum, and complex formation in the presence of Lewis bases is an important aspect of the reaction chemistry of organoaluminum compounds. The Lewis acidity of organoaluminum compounds accounts for the strong association of aluminum alkyls and hydrides by three-center two-electron bonds, as well as association of organoaluminum... 

The early developments in the chemistry of boron hydrides and aluminum alkyls quickly led to the realization that these species did not conform to the accepted theories of bonding, but required the development of new concepts that could account for the dimeric or polymeric nature of these derivatives. These concepts, were initially provided in a number of papers by Mulliken (88), Longuet-Higgins (70), Pitzer (93), Pitzer and Gutowsky (94), and Rundle (97, 98). Much of this work has been summarized recently in books by Wade (118), by Lipscomb (69),... 

Aluminum alkyls, aUcylaluminum halides, and alkylalu-minum hydrides strongly associate in solution and in the solid state." The association of trialkylaluminum compounds is in stark contrast to the monomeric nature of trialkylboron see Boron Organoboranes) and trialkylgaUium (see GalUum Organometallic Chemistry) compounds. 

Trivalent metals alkyl-aluminum and -boron compounds 1.33.7 Hydride Transferfr[Pg.79]

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],... 

The addition of metal and metalloid hydrides to carbon-carbon double bonds is not a new reaction, having been observed from time to time with silanes of the type R3SiH under free-radical conditions (4%, 85) and with boron hydrides (68). The versatility of such hydride-olefin interactions, nevertheless, first became evident with the recent researches of Ziegler with lithium and aluminum alkyls (139). The observation that attempted distillation of ethyllithium led to decomposition into lithium hydride, ethylene, and higher olefins prompted the following formulation of the reaction course (see 18) ... 

The tri-2-phenylpropylborane formed can be oxidized and hydrolyzed to 2-phenylpropanol-l, thus representing [as with aluminum alkyls (146)] an overall anti-Markownikoff hydration of a-olefins. Besides employing trialkylboranes as a source of boron hydrides, similar additions have been accomplished by heating olefins with boron hydride-amine complexes. As the latter are not as oxygen-sensitive, they are easier to handle (73) ... 

Alkyl and aryl groups on triorganoboranes are known to undergo ready exchange in the presence of catalytic amounts of boron hydrides at room temperature or below (S, 20). This reaction is also catalyzed by aluminum trialkyls (9). 

OrganometaUics and organometaHoids that yield peroxides in this manner include those in which Q is aluminum, antimony, arsenic, boron, cadmium, germanium, lead, phosphoms, siUcon, and tin and in which X is chlorine, bromine, alkoxy, acetoxy, cyano, oxide, hydride, hydroxyl, amino, alkyl, and boron tetrafluoride (28,33,44,60) (see Table 3). 

Secondary Alkyl Alcohols. Treatment of secondary alkyl alcohols with tri-fluoroacetic acid and organosilicon hydrides results only in the formation of the trifluoroacetate esters no reduction is reported to occur.1,2 Reduction of secondary alkyl alcohols does take place when very strong Lewis acids such as boron trifluoride126 129 or aluminum chloride136,146 are used. For example, treatment of a dichlo-romethane solution of 2-adamantanol and triethy lsilane (1.3 equivalents) with boron trifluoride gas at room temperature for 15 minutes gives upon workup a 98% yield of the hydrocarbon adamantane along with fluorotriethylsilane (Eq. 10).129... 

Neopentyl sulfides have been prepared by alkylation of sodium sulfide with neopentyl tosylate in high-boiling polar solvents,4,5 or in low yields by reduction of alkyl 2,2-dimethylpropanethioate with the combination of lithium aluminum hydride and a large excess of boron trifluoride-etherate. ... 

Reviews on stoichiometric asymmetric syntheses M. M. Midland, Reductions with Chiral Boron Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 2, Academic Press, New York, 1983 E. R. Grandbois, S. I. Howard, and J. D. Morrison, Reductions with Chiral Modifications of Lithium Aluminum Hydride, in J. D. Morrison, ed.. Asymmetric Synthesis, Vol. 2, Chap. 3, Academic Press, New York, 1983 Y. Inouye, J. Oda, and N. Baba, Reductions with Chiral Dihydropyridine Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 4, Academic Press, New York, 1983 T. Oishi and T. Nakata, Acc. Chem. Res., 17, 338 (1984) G. Solladie, Addition of Chiral Nucleophiles to Aldehydes and Ketones, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 6, Academic Press, New York, 1983 D. A. Evans, Stereoselective Alkylation Reactions of Chiral Metal Enolates, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 1, Academic Press, New York, 1984. C. H. Heathcock, The Aldol Addition Reaction, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 2, Academic Press, New York, 1984 K. A. Lutomski and A. I. Meyers, Asymmetric Synthesis via Chiral Oxazolines, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 

This new reagent is an active reducing agent and reduces cyclic and bicyclic ketones with supcrstcreoselectivity. Thus reduction of 2-mcthylcyclohexanone (I) gives rw-2-methylcyclohexanol in 99.3 (, purity. Note that reduction with lithium trimethoxy-aluminum hydride alone yields (2) in 69% yield. Thus increasing the size of the alkyl substituents on boron enhances the stereoselectivity of the borohydride anion. Even... 

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