Iridium-Catalyzed Regioselective B(3)-Alkenylation/B(3,6)-Dialkenylation of o-Carboranes by Direct B-H Activation.

Iridium-catalyzed formal alkyne hydroboration with cage B-H of o-carborane has been achieved, leading to the controlled synthesis of a series of 3,6-[trans-(AlkCH=CH)]2 -o-carboranes (Alk=alkyl), 3-cis-(ArCH=CH)-o-carboranes (Ar=aryl), and 3-cis-(ArCH=CH)-6-trans-(AlkCH=CH)-o-carboranes in high yields with excellent regio- and very good cis-trans selectivity. The most electron-deficient B(3,6)-H vertices favor oxidative addition on electron-rich metal centers, which is responsible for the regioselectivity. On the other hand, the configuration of the resultant olefinic units is dominated by alkyne substituents. Alkyl groups lead to a trans-configuration whereas bulky aryl substitutions result in cis-configuration.