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.