Boranes Boron Hydrides

Over 50 neutral boranes, B H , and an even larger number of borane anions have 

Hydrides of Boron and Silicon, Cornell University Press, Ithaca, New York, 1933, 250 pp. 

Examples of these various series are listed below and illustrated in the accompanying stmctural diagrams. Their interrelations are further discussed in connection with carborane stmctures 51-81. 

B H +4, e.g. B2H6 (8), B5H9 (9), BeHio (10), BioHi4(11) BgHi2 also has this formula but has a rather more open stmc-ture (12) which can be visualized as being formed from B10H14 by removal of B(9) and B(10). 

B H +3 formed by removal of 1 bridge proton from B H 4,4, e.g. BsHg , B10H13 other anions in this series such as B4H7 and B H are known though the parent boranes have proved too 

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Wade electron counting rules borane-like cluster nomenclature. On initially studying compounds such as boranes (boron hydrides) and carboranes (or carbaboranes boron—carbon hydrides), Wade (1976) proposed a number of rules which have then been extended to several compounds and which relate the number of skeletal electrons with the structure of deltahedral clusters. A polyhedron which has only A-shaped, that is triangular, faces is also called a deltahedron. 

This chapter provides an overview of the structural and electronic properhes of polyhedral heteroborane clusters and their potenhal use as building blocks in nanotechnology. These clusters comprise polyhedral boranes (boron hydrides),... 

Localized Bonds. Because boron hydrides have more valence orbitals than valence electrons, they have often been called electron-deficient molecules. This electron deficiency is partiy responsible for the great interest surrounding borane chemistry and molecular stmcture. The stmcture of even the simplest boron hydride, diborane(6) [19287-45-7] 2 6 sufficientiy challenging that it was debated for years before finally being resolved (57) in favor of the hydrogen bridged stmcture shown. 

The possible number of valence stmctures for a given boron hydride has been defined exacdy using three general equations of balance. For a borane... 

Despite the fact that many boron hydride compounds possess unique chemical and physical properties, very few of these compounds have yet undergone significant commercial exploitation. This is largely owing to the extremely high cost of most boron hydride materials, which has discouraged development of all but the most exotic appHcations. Nevertheless, considerable commercial potential is foreseen for boron hydride materials if and when economical and rehable sources become available. Only the simplest of boron hydride compounds, most notably sodium tetrahydroborate, NajBHJ, diborane(6), B2H, and some of the borane adducts, eg, amine boranes, are now produced in significant commercial quantities. 

Diborane(6), B2H. This spontaneously flammable gas is consumed primarily by the electronics industry as a dopant in the production of siHcon wafers for use in semiconductors. It is also used to produce amine boranes and the higher boron hydrides. Gallery Chemical Co., a division of Mine Safety AppHances Co., and Voltaix, Inc., are the main U.S. producers of this substance. Several hundred thousand pounds were manufactured worldwide in 1990. 

Sodium borobydride reacts with Lewis acids in nonprotic solvents to yield diborane [19287-45-7] 2 6 which can then be used to generate other useful organoboranes such as amine boranes, alkyl boranes, and boron hydride clusters. 

As a result of the systematic application of coordination-chemistry principles, dozens of previously unsuspected stnicture types have been synthesized in which polyhedral boranes or their anions can be considered to act as ligands which donate electron density to metal centres, thereby forming novel metallaboranc elusters, ". Some 40 metals have been found to act as acceptors in this way (see also p. 178). The ideas have been particularly helpful m emphasizing the close interconnection between several previously separated branches of chemistry, notably boron hydride clu.ster chemistry, metallaboranc and metallacarbaborane chemistry (pp. 189-95). organometallic chemistry and metal-metal cluster chemistry. All are now seen to be parts of a coherent whole. 

It is also noteworthy that Alfred Stock, who is universally acclaimed as the discoverer of the boron hydrides (1912). " was also the first to propose the use of the term "ligand (in a lecture in Berlin on 27 November 1916). Both events essentially predate the formulation by G. N. Lewis of the electronic theory of valency (1916). It is therefore felicitous that, albeit some 20 years after Stock s death in 1946, two such apparently disparate aspects of his work should be connected in the emerging concept of boranes as ligands . 

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