Oxidative Addition to B—H Bonds

Early in the development of polyhedral borane and carborane chemistry the need arose to degrade these materials under protolytic conditions for analytical purposes. Such reactions, for example, 

The now well-known ortho-metalation reaction observed in certain low-valent transition metal complexes of arylphosphines (1, 79) provided a model for the observation of oxidative addition to terminal B—H bonds. 

The phosphine 1-(1,2-C2BxoHii)P(CHs)2 was prepared and reacted with an iridium (I) complex, as shown in Fig. 27. Spectroscopic evidence strongly supported the view that the complexed Ir(I) had inserted into a B—H bond with the formation of an iridium-boron bond and an iridium-hydride link (58). Specific deuterium labels attached to the carborane moiety of the phosphine clearly proved this point. Thus, the B-H vertices of the icosahedral carborane group that are nearest the carbon atom bearing phosphorus were shown to be involved, although a distinction could not be made between the 3,6 or 4,5 sets of BH groups. 

In another series of experiments (59), toluene solutions of 1-(1,2-C B,oHu)P(CH ) were reacted with deuterium gas in the presence of (Ph3P)3RuHCl. Mass spectral evidence proved that up to eight deuterium atoms had been introduced into the phosphine. Since only four BH exchange sites could possibly be involved in deuterium exchange which proceeded only through ortho-metalation intermediates, an intermolecular, reversible oxidative addition of catalyst to terminal B—H bonds was indicated. Indeed, further work proved that under the same conditions 1,2-, 1,7-, and 1,12-C2BioHi2 carboranes could be totally deuterated at boron 

With the foregoing results in hand the reactions of the 1,2-, 1,7-, and 1,12-C2BioHi2 carboranes were examined with Ir(I) compounds. In each case iridium was inserted into terminal B—H bonds to form stable cr-bonds between boron and iridium (GO)  

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