Microwave-Assisted Metal-Free C─N Coupling for The Synthesis of Common Ligand Precursors of Organometallic Complexes

Abstract

This study presents a microwave-assisted, metal-free approach for the fast and selective synthesis of pyridine-functionalized N-heterocyclic ligand precursors. Efficient synthetic methods are important in ligand development for fast and cost-effective synthesis of transition metal complexes commonly used as catalysts in various applications. Traditional methods for forming C–N and C–C bonds require long reaction times and harsh conditions, whereas microwave heating accelerates synthesis by significantly reducing time and temperature, under metal- and additive-free conditions. This has enabled the selective synthesis of mono- and di-substituted pyridine-based ligand synthons starting from 2,6-dibromopyridine as well as 2,6-dichloropyridine. The approach also applies to other pyridine-based substrates, delivering high-purity ligands in 5–15 min. Notably, this method provides an alternative approach to cross-coupling reactions, eliminating the requirement for copper catalysts, and provides a more sustainable and efficient alternative to conventional cross-coupling strategies. The ligand synthons prepared using the microwave-assisted approach reported here have been utilized to prepare some common ligands used in the preparation of organometallic complexes. © 2025 Wiley-VCH GmbH.