Group polyboranes

Today the chemistry of diborane and the polyboranes is well understood [2] and much of it is textbook knowledge. Therefore, after a brief survey, emphasis will focus on the development of polyhedral borane chemistry within recent decades, and even restricting discussions to homopolyboranes only certain areas can be dealt with. This incorporates synthetic procedures, the chemistry of some polyboranes and particularly polyborane anions. Other chapters of this book are devoted to heteropolyboranes such as the carbaboranes (see Chapter 3.1), azaboranes and related heteropolyboranes (see Chapter 3.3) of the main group elements. In these areas enormous progress has been achieved within the last two decades. 

Geometrically it is impossible for polyhedral boranes where two closo-polyboranes share two common boron atoms, i.e., a common edge, to exist, because the hydrogen atoms of the neighboring BH groups would interfere sterically. For instance, if two B12H12 units are joined by a common edge this would result in H-H distances of less than 1.5 A, well below the van der Waals contacts. However,... 

A metal atom cluster as defined by Cotton [1] is still a very broad term, because non-metal atoms can also be part of the cluster core. In this chapter mainly two types of metal atom clusters are presented the polyborane analogous polyhedral and the metalloid clusters E Rr of group 13 elements E. The structures and bonding of the polyhedral clusters with n < r are similar to those in the well-known polyboranes. 

The apparent Instability of homopolyatomic anions of elements to the left of group IV (and of polyatomic cations to the left of group V) Is thought to result from a deficiency of bonding electrons In species where the principal bonding Is considered to originate largely from p-type orbitals. The electron deficient polyboranes, with which these clusters have... 

Another method for preparing functional Ziegler-Natta polymers is to use an organoborane mediated synthesis. This method has been extensively studied and reviewed by Chung . The success of this technique results from these factors (a) trialkyl boranes are Lewis acids, which are stable to Z-N catalysts, (b) they are soluble in Z-N (hydrocarbon) solvents, (c) they are remarkably versatile synthons for a variety of functional groups. In this case, borane functional alpha olefin monomers (31) are polymerized to polyboranes which can be hydrolyzed to a variety of functional groups. 

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