Bonding boron family

Describe the bonding and structure of the boron family elements and the way in which they commonly react. 

Boron is similar to carbon in that it has a capacity to form stable covalently bonded molecular networks. Carbonates, metalloboranes, phosphacarboranes, and other families comprise thousands of compounds. 

Two other well defined carboranes 55g and 76 (vide infra, Section 3.2.7) are present in the reaction mixture containing 64c (vide infra, Scheme 3.2-35). Although pure 55g could not be isolated, its solution-state structure follows from a complete set of NMR spectra [71b], This unusual carborane is a spiro derivative without precedence and belongs to the family of 2,3,5-tricarba-mdo-hexaboranes(7). Ab initio MO calculations and NMR data indicate that the boron atom linked to the C3B3-framework by an endohedral C-B bond takes part in the cluster bonding [71b] (similar to an endohedral C-H bond in the other carboranes 55). 

Iminoboranes may be identified as a class of molecules with an imino group NR and a varying group X (e.g., F, RO, R2N, R3C) bonded to boron. Iminoboranes (XBNR) belong to the family of neutral two-coordinated boron species which may be arranged systematically in the following way ... 

Of all of the elements of the Periodic Table, only neighboring carbon and boron share the properties of self-bonding (catenation) and the support of electron-delocalized structures based upon these catenated frameworks. Carbon catenation, of course, leads to the immense field of organic chemistry. Boron catenation provides the nido-, arachno-, and /i p/io-boranes, which may be considered as the borane equivalents of aliphatic hydrocarbons, and the discrete families of c/oso-borane derivatives which bear a for nal resemblance to the aromatic hydrocarbons, heterocycles, and metallocenes. Aside from these analogies, boron and carbon chemistries are also important to each other through their extravagant ability to mix m ways not available to other element-pairs. Thus, the conflux of boron and carbon chemistries effectively provides an element-pair for exploitation in a variety of novel ways. 

K-bonding electrons to form the metal-carbon bonds their structures may be regarded as mixed metal-carbon clusters, the shapes of which clearly reflect the numbers of electrons available as do the mixed boron-carbon cluster shapes of carboranes. All are members of the same family of hypercarbon systems. 

Whereas the Lewis acid-base theory does not contradict Bronsted theory, as "bases" in Bronsted theory must have a pair of nonbonding electrons in order to accept a proton, it expands the family of compounds that can be called "acids" any compound that has one or more empty valence-shell orbital and provides an explanation for the instantaneous reaction of boron triflouride (BF3) with ammonia (NH3). The nonbonding electrons on the nitrogen in NH3 are donated into an empty orbital on the boron to form a new covalent bond, as shown in Eq. 13. 

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