289-53-2Relevant articles and documents
Addition compounds of alkali-metal hydrides. 26. Facile reaction of borinic esters with lithium monoethoxyaluminohydride to form lithium dialkylborohydrides
Singaram, Bakthan,Cole, Thomas E.,Brown, Herbert C.
, p. 1520 - 1523 (2008/10/08)
Addition of 1 mol equiv of borinic esters to lithium monoethoxyaluminohydride in ethyl ether at 0°C results in a facile and rapid precipitation of the dialkoxyalane as a solid, producing the corresponding lithium dialkylborohydride in quantitative yield. The reaction is quite general, applicable to borinic esters of widely varied structural requirements. These derivatives are very stable and can be stored under nitrogen at 25 °C without hydride loss and either redistribution or isomerization of the alkyl groups. Methyl iodide or acids readily and quantitatively removes metal hydride from these dialkylborohydrides, generating the free dialkylboranes for further use. Thus the present study provides a simple method for preparing a wide variety of lithium dialkylborohydrides under mild conditions, valuable intermediates for storing dialkylboranes for extended periods of time, and a simple procedure for generating pure dialkylboranes as required for further application.
ORGANOBORANES. XXVIII. CONVENIENT PROCEDURES FOR THE SYNTHESIS OF BORINANE
Brown, Herbert C.,Pai, Ganesh G.
, p. 13 - 22 (2007/10/02)
Convenient syntheses of the six-ring boracyclane, borinane, have been developed.Hydroboration of 1,4-pentadiene with two molar equivalents of 9-borabicyclononane (9-BBN) in a suitable solvent, followed by reaction of the resulting trialkylborane with one molar equivalent of the borane-tatrahydrofuran complex (BH3*THF) or the borane-dimethyl sulfide complex (BH3*SMe2, BMS), leads to the cyclization of the pentadiene moiety, forming borinane with the regeneration of two molar equivalents of 9-BBN.Complete separation of the two dialkylboranes by fractional crystallization from solvents such as THF, 1,2-dimethoxyethane (DME), 1,3-dioxolane, n-hexane, n-pentane and hexane plus dioxolane was unsuccessful.Treating the reaction mixture in hexane with the requisite amount of triethylamine (Et3N) led to selective complexation with borinane.By cooling the reaction mixture to -78 deg C, it was now possible to crystallize out the uncomplexed 9-BBN almost quantitatively (98percent).Alternatively, borinane could be precipitated selectively from the hexane reaction mixture as its bis-adduct with either N,N,N',N'-tetramethylethylenediamine (TMED) or 1,4-diazabicyclooctane (DABCO).Free borinane was readily liberated from its amine adducts by treatment with boron trifluoride etherate (BF3*OEt2).Finally, the two dialkylboranes were readily separated by fractional distillation, using a specially designed reaction setup.Distillation at about 70-80 deg C and 0.01 mm pressure led to the clean distillation of borinane, leaving the 9-BBN, as a residue, readily recycled in subsequent preparations.Alternatively, once free borinane has been obtained, it can be used to hydroborate 1,4-pentadiene in place of 9-BBN.Treatment of the product with BH3*THF or BH3*SMe2 converts two moles of borinane into three, without the formation of a by-product.
