Catalytic aromatic C-H borylation via strained Si and Ge metallacycles.

Arenes bearing silyl and boryl, or germyl and boryl groups, represent a significant class of bifunctional molecules that have garnered considerable attention in organic synthesis due to their unique reactivity and versatility in undergoing diverse chemical transformations. Despite their importance, the synthesis of these mixed-metalloid compounds, particularly those with ortho-substituted aromatic frameworks, often involves complex, multi-step procedures. Herein, we present a highly efficient, single-step method for synthesizing ortho-boronated arylhydrosilanes and arylgermanes via catalytic C-H borylation reaction. The use of Si- and Ge-containing directing groups has been demonstrated to effectively suppress undesirable metathesis reactions, a side effect typically associated with their metallic nature. Our approach employs an iridium catalyst in combination with a ligand and an acetate base, which facilitates the formation of benzo-fused four-membered metallacycles within the catalytic cycle. The method's broad applicability and practicality are further underscored by its ability to generate a wide array of valuable intermediates that can be easily transformed into various functionalized molecules. Both experimental and computational studies provide profound insights into the reaction dynamics and the factors influencing the formation of these strained metallacycles.