Easy available click ligands enable iridium-catalysed aromatic C-H borylation with proximal selectivity: the critical role of solvent and B2pin2 in catalyst modification under operando conditions

Abstract

Transition metal-catalyzed C-H functionalization provides a powerful platform for the efficient synthesis of complex molecules, with iridium-catalyzed C-H borylation representing a cornerstone of this field. Fine-tuning N,N-chelating ligands effectively controls remote selectivity in aromatic substrates, whereas achieving proximal (ortho) selectivity typically requires preformed iridium complexes or highly sophisticated, air-sensitive ligands. Herein, we report a convenient and modular synthesis of sustainable ligands via cost-effective copper-catalyzed click chemistry. Although the resulting pyridyltriazolyl ligands are in principle designed for neutral N,N-chelation, they preferentially adopt an anionic N,C-chelating mode under catalytically relevant conditions. This behavior arises from triazolyl proton abstraction promoted by excess bis(pinacolato)diboron (B2pin2) and the use of polar, coordinating solvents. Control experiments, spectroscopic analysis, and kinetic studies support this mechanistic scenario. As a consequence, sterically demanding substrates, including phthalimides and related carbonyl-containing aromatics, undergo efficient proximal C-H borylation. Overall, this work underscores the importance of catalyst structural evolution under reaction conditions and highlights a general design principle that may apply to other transition metal-catalyzed atom-economy processes.