Boron hydrides anionic

Lippard, S.J., Ucko, D.A. 1968. Transition metal borohydride complexes. II. Th reaction of copper(I) compounds with boron hydride anions. Inorg Chem 7 1051-1058. 

In the 1950 s and 1960 s a number of new boron hydrides and boron hydride anions were prepared. Although particular emphasis was placed upon stable higher borane entitles derived from BioHm, significant progress was made in the preparation of new, smaller boron hydrides. Unfortunately, at this period of time, most of these materials could be obtained only in small amounts. (A comprehensive treatment of all boron hydrides prepared through 1978 is given in references (51) and (52). 

The procedures are simple and give essentially stoichiometric reactions which can be carried out in the absence of a solvent. The systematic nature of these syntheses relates to the observation that hydride ion can be abstracted from certain boron hydride anions to give as one of the final products a neutral boron hydride which contains one more boron atom than the anionic starting material. These reactions are described below. 

The most versatile route to Ge—boron-containing species is from Ge halides and boron hydride anions, products embracing both oxidation states of Ge, inorganic and mono-, di-, and triorganogermyl derivatives, as well as borane and carborane substrates (Table 1) (cf. 5.3.7.3.2 for the analogous Si-based reactions). 

Table 1. Germanium Halides with Boron Hydride Anions ...

IV. Isoelectronic Compounds Boron Hydride Anions and Carboranes... 

Boron hydride anion (borane anion) A negatively charged ion containing only the elements boron and hydrogen. 

Bridge bond In boron hydrides, boron hydride anions, and their derivatives a three-center, two-electron bond in which a hydrogen atom links two boron or boron and another element located on the edge of the structure. 

We will consider two important groups of compounds that share the same kinds of geometries as boron hydrides, that is, can be viewed as polyhedra or polyhedral fragments. These are the boron hydride anions and carboranes. In many cases the boron hydrides and compounds in these groups are isoelectronic (same number of valence electrons), and in these cases the structures are isostructural with almost the same geometric arrangement of atoms. 

The are a number of boron hydride anions with more than one boron atom, and these follow the same bonding principles as the neutral boron hydrides discussed in previous sections. That is, their structures can again be viewed as polyhedra that may have one or more vertices removed. The numbers of the structural features, s, t, y, and X, will again depend on equations of balance, which need to be modified to account for the negative charge. For a boron hydride anion with the formula BpH + the equations will be... 

The known boron hydride anion with three boron atoms is B3Hg, for which the styx solutions are 2013 and 1104. Reasonable structures can be built using either of these solutions. X-ray diffraction studies show that the correct structure, at least in the solid phase, is 2013. 

Larger boron hydride anions can be evaluated as polyhedral fragments just as can the neutral boron hydrides... 

FIGURE 8 The structures and numbering conventions of the boron hydride anions, (left) and oh polyhedral... 

Because of their deficiency in the electrons necessary for the formation of all two-center bonds, reactions of boron hydrides with reducing agents would be expected to proceed easily. Reactive metals will contribute electrons to boron hydrides to produce boron hydride anions, for example. 

The closo boron hydride anions have been studied considerably more than the open ions, nido and arachno. The reactions of the open ions are quite varied, and we will consider only a few of these before proceeding to the reactions of the closo anions. 

Some boron hydride anions will add protons to produce neutral boron hydrides and thus provide a method of preparation for the neutral compounds, for example,... 

We have discussed certain boron hydride species such as the icosahedral carboranes and the closo boron hydride anions that are quite stable. A feature of these species compared to other stable boron compounds is that the fraction of their mass that is boron is very high. For example, 75% of the mass of the icosahedral carboranes (C2B10H12) is boron as is 69% of the disodium salt of the closo boron hydride anion B Hj In contrast, only 17% of the mass of boric acid is boron. Thus boron hydride species can deliver large concentrations of boron to situations where this is desired. 

M. J. S. Dewar and M. L. McKee, Inorg. Chem., 1978,17, 1569. Ground states of molecules 47. MNDO studies of boron hydrides and boron hydride anions. 

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