NCS–Pincer NHC Palladium Complexes: Efficient Catalysts for Buchwald–Hartwig Amination of Chloroarenes and Heteroaromatics

ABSTRACT A series of N ‐pyridyl‐ N ′‐thioether‐functionalized imidazolium salts ( 2a – d ) were synthesized through quaternization of thioether‐substituted imidazole precursors ( 1a – d ). Subsequent metalation with PdCl 2 and following anion exchange reaction with CF 3 COOAg yielded the corresponding NCS–pincer N ‐heterocyclic carbene Pd complexes (NHC–Pd, 3a – d and 4a – d ). Comprehensive structural characterization was performed using NMR spectroscopy and high‐resolution mass spectrometry (HR‐MS), with the molecular structure of 3b unequivocally confirmed by single‐crystal X‐ray diffraction analysis. Catalytic evaluation revealed these complexes to be highly effective catalysts for Buchwald–Hartwig cross‐coupling reactions between chloroarenes and various cyclic secondary amines. Under optimized conditions, the NHC–Pd catalysts exhibited high catalytic efficiency at low loading (0.5 mol%), demonstrating excellent functional group tolerance (including both electron‐donating and electron‐withdrawing groups at o ‐position, m ‐position, and p ‐position), broad compatibility with heteroaromatic substrates, and practical utility in pharmaceutical synthesis. These well‐defined complexes, featuring straightforward synthesis and exceptional catalytic performance, represent promising candidates for C–N coupling applications.