Palladium(II) SeNSe Pincer Complex Mediated Regioselective Arylation of Thiophenes at Room Temperature

A SeNSe pincer ligand (L1) and its palladium(II) complex (C1) were synthesized and fully characterized by analytical and spectroscopic methods. Complex C1 displayed excellent catalytic efficiency for the regioselective C-4 arylation of thiophene derivatives, delivering the desired products in yields up to 91% under mild, room-temperature conditions. The method exhibits a broad substrate scope, including heteroarenes relevant to optoelectronic and pharmaceutical applications, and provides high regioselectivity while suppressing homocoupling and other side reactions. Under the standard conditions, unsubstituted thiophenes underwent selective C-3 arylation. A striking regioselectivity switch was observed in the arylation of benzothiophene, favoring C-3 arylation under milder, greener conditions compared to previously reported C-2 selective methods. Mercury-drop and triphenylphosphine poisoning tests confirmed homogeneous catalysis, while radical scavenger experiments excluded radical pathways. Control studies and high-resolution mass spectrometric analysis of reaction intermediates support the proposed catalytic cycle. These findings underscore the impact of ligand design and reaction parameters in directing site-selective C-H activation, establishing the SeNSe-Pd(II) pincer complex as a powerful catalyst for regioselective heteroarene functionalization.