- Rehydrogenation of aminoboranes to amine-boranes using H2O: Reaction scope and mechanism
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Water has been successfully employed as a reagent with which to rehydrogenate aminoboranes (e.g., iPr2N=BH2, 2,2,6,6-Me4C5H6N=BH2, and also transient Me2N=BH2 derived from 1/2[Me2N-BH2]2) to amine-boranes (e.g., iPr2NH·BH3, 2,2,6,6-Me4C5H6NH·BH3, Me2NH·BH3) in approximately 30 yield. The conversion to amine-boranes from the corresponding aminoboranes using this method represents an example of a metal-free, single-step route for the hydrogenation of the B=N bond. Deuterium labeling studies indicated that the protic hydrogen (N-H) on the rehydrogenated amine-borane was derived from H2O, whereas the third hydridic hydrogen (B-H) on the amine-borane was generated from the formation of a postulated hydride-bridged intermediate H2B(μ-H)(μ-NR2)B(OH)H (R2 = Me2, iPr2, 2,2,6,6-Me4C5H6), which requires a second equivalent of the starting aminoborane, thus explaining the low yield. Formation of insoluble borates (BxOyHz) provides a driving force for the reaction. Significantly, the yield can be increased by adding a sacrificial source of BH3 (e.g., to ca. 53% for BH3·THF) or by adding a separate source of H- (e.g., to ca. 95% for LiBH4) to complement the H+ (from H2O) in a more atom-efficient reaction.
- Leitao, Erin M.,Manners, Ian
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p. 2199 - 2205
(2015/05/13)
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- Lithium aminoborohydrides 17. Palladium catalyzed borylation of aryl iodides, bromides, and triflates with diisopropylaminoborane prepared from lithium diisopropylaminoborohydride
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The Alcaraz-Vaultier borylation of aryl halides and triflates is reported utilizing diisopropylaminoborane (BH2N(iPr)2) prepared from the corresponding lithium aminoborohydride (LAB reagent). BH 2N(iPr)2, prepared by reacting lithium diisopropylaminoborohydride with trimethylsilyl chloride, provided the most consistent isolated yields from this reaction. Catalytic amounts of palladium dichloride produced the highest yields from aryl iodides, while catalytic tris(dibenzylideneacetone)dipalladium(chloroform) provided the best yields for aryl bromides and triflates. This route to boronic acids is mild enough to tolerate various functionalities and for the first time employs aryl triflates as substrates for the Alcaraz-Vaultier borylation. In addition, it was found that both boronic acid and ester compounds could be isolated from the reaction mixture utilizing simple work-up procedures. Treatment of the reaction intermediate with an acid/base work-up provided the corresponding boronic acid, while treating the same intermediate with a diol, such as neopentyl glycol, afforded the corresponding boronic ester.
- Haddenham, Dustin,Bailey, Christopher L.,Vu, Chau,Nepomuceno, Gabby,Eagon, Scott,Pasumansky, Lubov,Singaram, Bakthan
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scheme or table
p. 576 - 583
(2011/03/18)
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