Higher boron hydrides

The concepts discussed above, permit proposals to be made concerning the structure of other boron hydrides which have not been subjected to such an extensive experimental investigation as has diborane. The proposed formulae fall into two groups, that favouring the resonance of structures analogous to those represented schematically for diborane in IV to VIII (Syrkin and Dyatkina ) and that employing the concept of the protonated double bond (Pitzer ).  

As pointed out above, it is doubtful whether resonance alone would be able to link the two outer boron atoms to the central group, although the ready dissociation of this molecule is explained by the looseness of this bond. A more fundamental objection is the small value of the B B H and B+B H angles in the central group of atoms. The protonated double bond structure is H H 

The main objection to these formulae would appear to be the full negative charge existing on each boron atom. 

BgHjo — For this molecule the following structures have been proposed  

B4H10— This molecule is represented by Syrkin and Dyatkina4 as a resonance hybrid of the following structures  

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Only H2, BeH2, and Be(BH 2 have higher heats of combustion. When diborane is pyroly2ed above 100°C ia a sealed tube, it is decomposed to higher boron hydrides and hydrogen gas ia a complex sequence of reactions. This reaction has been investigated ia considerable detail (65). 

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. 

Boron Hydrides" under "Boron Compounds" in ECT 1st ed., Vol. 2, pp. 593—600, by S. H. Bauer, Cornell University "Boron Hydrides and Related Compounds" under "Boron Compounds," Suppl. 1, pp. 103—130, by S. H. Bauer, Cornell University "Diborane and Higher Boron Hydrides" under "Boron Compounds," Suppl. 2, pp. 109—113, by W. J. Shepherd and E. B. Ayres, Gallery Chemical Company "Boron Hydrides" under "Boron Compounds" in ECT 2nd ed., Vol. 3, pp. 684—706, by G. W. Campbell, Jr., U.S. Borax Research Corporation "Boron Hydrides and their MetaHo Derivatives" under "Boron Compounds," in ECT 3rd ed., Vol. 4, pp. 135—183, by R. W. Rudolph, The University of Michigan. 

Boron Compounds (Boron Hydrides)" in ECT 1st ed., Vol. 2, pp. 593—600, "Boron Compounds (Boron Hydride and Related Compounds)" Suppl. 1, pp. 103—130, by S. H. Bauer, Cornell University "Boron Compounds (Diborane and Higher Boron Hydrides)" Suppl. 2, pp. 109—113, byj. W. Shepherd and... 

Little kinetic data are available on the decomposition of higher boron hydrides, though a study of the conversion of B4H10 to B5Hn through the process... 

As a result of the hydridic nature of the hydrogen attached to boron, amine-boranes are interesting and useful reducing agents and have been employed in the reduction of numerous organic carbonyl compounds. They have been utilized in studying the kinetics and mechanism of hydride reactions and are precursors for the synthesis of substituted boranes, borazines, boronium ions, higher boron hydrides, and carboranes. 

C10H20B2D4 B2D4 + C10H10 B2D4 -> B2DJ + D2 + higher boron hydrides... 

Dunbar 44,152,203) has studied the ion-molecule reactions of several boron hydrides BaHa, B4H10, BsHg, B5H11, and BeHio and the gas-phase reactions of diborane with the same higher boron hydrides and with... 

Stock continued these studies between 1912 and 1936 and succeeded in isolating diborane (B2Hg). Tbe formulas of diborane and the higher boron hydrides do not fit the comfortable Lewis-Langmuir electron pair structures. For example, BH3 (the monomer of diborane) has a total of only 6 valence shell electrons. Diborane is electron deficient by two electrons with no nice Lewis structure. It would be some decades... 

Exchange reactions of alkylated diboranes with higher boron hydrides are discussed in Sections II,B>1 and II,D. 

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