Reactions of the Boranes and Their Derivatives

On the basis of known behavior most boron hydride reactions may be assigned to two main classes. The first class involves removal of a borane group from a boron hydride structure, while the second class involves nonsymmetrical cleavage of the hydrogen bridge bonds in a borane.2 

Removal of a borane group often occurs when a borane is treated with a nucleophilic reagent. The initial product of this type of reaction is an adduct of the borane group, but the nature of the donor part of the adduct controls the subsequent fate of the whole. For all such compounds there is a tendency, varying from complex to complex, to dissociate reversibly into donor and acceptor parts. Thus whereas (CH3)2S BH3 (49) is appreciably dissociated in the gas phase at 50°, the compound (CH3)3P BH3 (48) may be heated to 200° without appearance of significant amounts of borane decomposition products. 

Some borane adducts decompose irreversibly. Thus if the ligand atom has hydrogen bonded to it, elimination of molecular hydrogen from the complex occurs either as soon as it is formed [ ] or on heating for example, 

10 In this chapter, parenthesized numbers appearing to the right of chemical equations are reference numbers throughout. 

5 Since this article was submitted to the publisher, two papers concerned with classification of the reactions of the boranes in relation to their structures have appeared (83a, 86a). 

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