Metal Halide Exchange in Benzylborane NHC‐Adducts: The Effect of Backbone Alkylation in the N ‐Heterocyclic Carbene

Among other main group elements, the chemistry of boron has been stimulated by N ‐heterocyclic carbenes (NHCs) as important ligands, the nature of which can significantly control the outcome of reactions. In four‐coordinate benzyl boranes of type (NHC)BH 2 CH 2 ( o ‐BrC 6 H 4 ), we demonstrate this effect at the example of a lithiation silylation procedure. For NHC=I i Pr lithiation of the arene ring by lithium‐bromide exchange with t BuLi ultimately leads to backbone substitution with proton rearrangement, as demonstrated by trapping with trimethylsilyl chloride. In contrast, such process is suppressed for NHC=I i Pr Me , which undergoes lithiation and subsequent trimethyl‐silylation at the arene moiety.