Palladium-Catalyzed Regio- and Monoselective B(2)–H Alkylation of Zwitterionic nido-Carboranes at Room Temperature in Water

Abstract

The achievement of regio- and monoselective control is a fundamental challenge for the development of efficient B–H functionalization of polyhedral carboranes bearing multiple chemically similar B–H bonds. While exo-polyhedral B–H activation of zwitterionic nido-carboranes has witnessed remarkable progress, developing direct functionalization methods for the closed polyhedral B–H bonds remains a significant challenge. Herein, we report the development of a regioselective B(2)–H monoalkylation of nido-carboranes enabled by a novel pyridyl directing group containing a NH group that can form a favorable macrocyclic intramolecular H-bonding interaction with the alkyl substituent. A simple methyl substitution significantly enhances directing group efficacy, leading to unconventional B(2) selectivity. Exclusive monoselectivity was observed in the presence of three proximal B–H bonds, including a highly reactive exo-polyhedral B(11)–H site. Notably, the reaction proceeds in both water and organic solvents at room temperature.