Chloroborane bonds

B-Bromo and B-iodo-9-borabicyclo[3.3.1]nonane add similarly in a cis fashion to terminal triple bonds 471 They do not react, however, with alkenes and internal acetylenic bonds. In contrast to the results mentioned above, phenyl-substituted chloroboranes (PhBCl2, Ph2BCl) do not participate in haloboration. Instead, the C—B bond adds across the multiple bond to form phenylalkyl-(alkenyl) boranes.466,468... 

Intermolecular reactions of this type can be slow if either of the reaction partners has a bulky substituent. Reactions with chloroboranes R2BCI or RBCI2 go under much milder conditions. The stereochemistry of the carbon-boron bond is retained in the product for example, the borane (11) gave the amine (12 90%) on reaction with azidocyclohexane. 

Elements of Group III and the n-butyl analogue, have been obtained by treating the dialkoxy-chloroborane with hydrogen peroxide in diethyl ether.216 A mechanism for the thermal decomposition to boric acid and B(OR)3 is postulated in which the first stage is homolytic cleavage of the O—O bond. 

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