Mild Generation of Highly Nucleophilic <i>N</i> ‐Heterocyclic Carbene Boryl Anion From Neutral sp ² –sp ³ Diboron Reagents and Its Applications in Nucleophilic Borylation

ABSTRACT Due to its high activity, the synthesis or generation of the N ‐heterocyclic carbene (NHC) boryl anion remains challenging, with only limited methods available. Traditional stabilization through bulky ligands or aromatic systems restricts its reactivity as a boron synthon. In this work, we present a straightforward strategy for the in situ generation of an NHC boryl anion at room temperature through the reaction of neutral sp 2 –sp 3 diboron reagent (NHC)BH 2 Bpin with KO t Bu. This less sterically hindered and strongly nucleophilic boryl anion demonstrates broad reactivity with diverse electrophiles, including those that are unreactive with other types of boryl anions or traditional diboron reagents. These nucleophilic borylation reactions enable the synthesis of a diverse array of four‐coordinate organoboron compounds. Detailed mechanistic studies and DFT calculations confirm the intermediacy of the NHC boryl anion and provide clear insights into the reaction pathways for the newly discovered reactivities.