Iron-Catalyzed Selective B–H Activation for 4/5-fold Methylation and Arylation of Carboranes
Peng Zhou, Yu Chen, Zuowei Xie
Abstract
Catalytic selective B–H functionalization of carboranes has recently attracted enormous research interest, resulting in the development of a series of methods for transition metal-catalyzed vertex-specific functionalization of carboranes. These established protocols require noble transition metal catalysts. Herein, we report a highly efficient iron-catalyzed silver-free 4/5-fold cage B–H methylation/arylation of carboranes using organoaluminum compounds as alkylation/arylation reagents, leading to a variety of B(3,4,5,6)-tetramethylated/tetraarylated o-carboranes and B(2,3,4,5,6)-pentamethylated/pentaphenylated m-carboranes in very good to excellent yields. The use of inexpensive diethyl oxalate as an oxidant makes this protocol practical, realizing easily the gram-scale synthesis of the products. The associated reaction mechanism is also proposed. This method represents an alternative strategy for the catalytic selective polyfunctionalization of carboranes via base metal catalysis.