Electron-pair bases boron hydrides

The TEC model developed by Teo also has been successfully applied to rationalize the geometries of a large number of cluster compounds. The TEC model combines Lauher s rule with Euler s theorem and adds an adjustable parameter This parameter X is equal to the number of electron pairs present in excess of that predicted by the 18-electron rule. " X has also been interpreted in terms of the number of missing antibonding orbitals. Given a value for X, determined by the shape of the cluster, an equation predicts the electron count for a cluster. Theoretical justification of the parameter X is based largely upon the classical molecular orbital calculations performed by Hoffmann and Lipscomb via the extended Hiickel method on the corresponding polyhedral boron hydride clusters The values... 

Aluminum hydrides react violently with protic solvents and acids (path p.t.) to produce hydrogen gas and can be used only in aprotic media, like diethyl ether. The borohydrides, BH4 are weaker sources and react much more slowly with protic solvents than do the aluminum hydrides. After the first step, the trivalent aluminum or boron species is now electron deficient and can react with a lone pair donor to form a tetravalent Lewis acid-base salt (path An) that can donate hydride again. This repeats until all hydrogen-metal bonds have been used. 

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