Boron-Hydrogen Compounds Boranes

The apparently bewildering variety of structures adopted by boron-hydrogen compounds (boranes) can be rationalized by recognizing some major families, illustrated by the series in Figure. 2. 

With this repertoire of bonding possibilities at our disposal, we car construct the molecular structures of various boron-hydrogen compounds, both neutral species and anions. The simplest is the tetrahydroborate126 or borohydride ion, BH. Although borane is unstable with respect to dimerization, the addition of a Lewis base, H , satisfies the fourth valency of boron and provides a stable entity. Other Lewis bases can coordinate as well. 

Boranes and borane ions are boron-hydrogen compounds that can also act as ligands. Carboranes are boranes in which some boron is replaced by carbon. Borane... 

Boron.—Boron-Hydrogen Compounds. Theoretical calculations have been made of likely sites for electrophilic and nucleophilic attack in a number of boranes and related anions. Electrophilic benzoylation of PioHjo " to form [2-BioH,COPh] follows simple second-order kinetics in acetonitrile. Reaction is inhibited by acid, and a kinetic analysis suggests that it is due to conversion of [BjoHioP" into the unreactive conjugate acid with K = 4.6moldm. The reaction of... 

Boron forms a remarkable series of binary compounds with hydrogen—the boranes. These compounds include diborane, B2H6, and more complex compounds such as decaborane, B10H14. Anionic versions of these compounds, the borohydrides, are known the most important is BH4 as sodium borohydride, NaBH4. 

Boron forms a class of binary compounds known as boron hydrides or boranes with hydrogen (Numbers in parentheses are the number of hydrogen atoms in each compound.) The names, CAS Numbers, and formulas of some of these compounds are ... 

The boranes are an extensive series of highly reactive electron-deficient binary compounds of boron and hydrogen. The boranes have three-center bonds. 

The electrophilic addition of hydrogen-bearing boranes to alkenes (hydroboration), now recognized as a vital component of organic synthesis, is covered in Chapter 1.7 of this volume. The boron compounds that do fall under the realm of this chapter are boron bromides. Suzuki and coworkers have demonstrated... 

Boron Compounds. Molecular hydrides of boron are called boranes. They are named by using a multiplying affix to designate the number of boron atoms and adding an Arabic numeral within parentheses as a suffix to denote the number of hydrogen atoms present. Examples are pentaborane(9) for B5H9 and pentaborane(ll) for B5Hn. 

First achievements. The founder of borane chemistry is rightfully held to be the German chemist A. Stock although the first boron and hydrogen compounds were obtained back in 1881. But, according to N. V. Sidgwick, All statements about the hydrides of boron earlier than 1912, when A. Stock began to work upon them, are untrue . 

Recently the addition of Boron or its compound with hydrogen, for example, ortho-boranc (Ci Hu Bio) was investigated by Pepekin, Makhov and Apin [87]. They examined mixtures of PETN and Cyclonite with boron or ortho-borane. The calorific value of Cyclonite-Boron reached a maximum (1890 kcal/kg) with ca. 16% B. PETN with ca. 22% reached a value of ca. 2050 kcal/kg. 

The compound borane-carbonyl occupies a special position in any discussion of molecules derived from boron hydrides with boron-carbon bonds. Carbon monoxide reacts with diborane (20 atm/room temperature) to give an adduct of the borane group which does not rearrange or lose hydrogen (39) The adduct OC BH3 does, however, dissociate into carbon monoxide and diborane at ordinary temperatures. No carbonyls of other Group III acceptor molecules have been prepared so far 133), and it has been suggested 27, 58) that borane-carbonyl owes its existence to the ability of the hydrogen atoms of borane to transfer electrons to a vacant p,-orbital in carbon monoxide. 

The compound BH3, which is analogous to BF3, is hi ily reactive until recently it was not even known to exist. H, unlike F, lacks the extra electrons needed for H—B ir bonding. The known compounds of boron and hydrogen, called boranes, thereibre exhibit ELECTRON DEFICIENCY. The simplest of these compounds is DIBORANE, BtH . A conventional structural formula for BiHb would require 7 bonds, and hence 14 electrons. But the total number of available electrons is only 12 (3 for each B and 1 for each H atom). The observed structure is ... 

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