Reactions among Boron Hydrides

Although BHg has not been observed experimentally, the kinetics of the initial stages of several reactions of diborane IS, P) render the 

BHsD BaH( BsHiD BHj, where the last equation is rate determining. 

The last two reactions are then repeated starting with BgHjEt in place of BgHa to obtain B2H4Et2, which reacts with BHs to give BsHiEts. At this stage an autocatalytic reaction appears, 

SO that BgHe and C2H4 compete for these later products. The autocatalytic effect increases considerably as the final product BEts appears, and if 2(B2He) (C2H4), the reaction becomes explosive. 

The present literatiu e IS, 9, 60) on the polymerization to higher hydrides around 100°C may be summarized in the sequence of reactions 

---

In an attempt to prepare alkylamines by asymmetric reduction of imines with chiral hydride reagents, diphenylphosphinyl imines (38), prepared by reaction of ketoximes (39) with chlorodiphenylphosphine [(Cg 115)2 PCI], were reduced in the presence of a variety of chiral aluminum and boron hydride reagents43. Among the most promising reagents was BINAHL-H44 (40), a chiral hydride compound prepared by the modification of lithium... 

The first carboranes were discovered " ° 2 among the products of reactions between alkynes and boron hydrides. Such reactions remain the best routes to many dicarba species (Scheme 3.1, 3, route Derivatives... 

Diborane is not unique among the boron hydrides in its ability to form a carbonyl. High pressure reaction of either pentaborane-f / or tetra-borane-10 with carbon monoxide forms a substance which behaves like borane-carbonyl in its manner of decomposition. The formula of this polyborane-carbonyl has recently been established as OC B Hg (mp, — 114.5° bp, 59.6°) 41a). It reacts with trimethylamine without release of carbon monoxide. 

Among the most useful synthetic reactions of acetylenes are those initiated by addition of boron hydrides and aluminum hydrides to triple bonds. These reactions are discussed in Sections 4.9.4 and 4.9.5. 

One of the most promising applications of polyboron hydride chemistry is boron neutron capture therapy (BNCT) for the treatment of cancers (253). Boron-10 is unique among the light elements in that it possesses an unusually high neutron capture nuclear cross section (3.8 x 10-25 m2,0.02—0.05 eV neutron). The nuclear reaction between 10B and low energy thermal neutrons yields alpha particles and recoiling lithium-7 nuclei ... 

Chiral alkyldihaloboranes are among the most powerful chiral Lewis acids. In general, however, because alkyldihaloboranes readily decompose to alkanes or alkenes as a result of protonolysis or /3-hydride elimination, it is difficult to recover them quantitatively as alkylboronic acids. Aryldichloroborane is relatively more stable and can be reused as the corresponding boronic acid. We have developed chiral aryldichlorobor-anes 23 bearing binaphthyl skeletons with axial chirality as asymmetric catalysts for the Diels-Alder reaction of dienes and a,/3-unsaturated esters (see, e.g., Eq. 37) [36]. 

---